School of Elements SCHOOL SECTION 1

. School of Elements SCHOOL SECTION

SCIENCE & TECHNOLOGY MT EDUCARE LTD. Q.I (A) Fill in the blanks :. The horizontal rows in the periodic table are..... From left to right, the atomic size of an atom.... 3. There are... periods in the periodic table.. 4. An element is placed in group II A, so the number of valence electrons is.... 5. An element is placed in nd period, so it has... shells. 6. Noble gases have valency as.... 7. Metals have a tendency to... electrons... Valency across a period.... 9. Valency down the group.... 0. Elements of group I A and II A are..... An atom is said to be a non-metal if it... electrons..... is the only element in duplet state. 3. The electronic configuration of Neon is.... 4. Sodium is a.... 5. Silicon and antimony are.... 6. Group A is called.... 7. Group II A is called as..... Group VII A is called as.... 9. The chemical properties down the group.... 0. First period contains... elements.. Moseley arranged elements according to..... The non-metals are present in.... 3. The number of shells down the group.... 4. The transition character of elements is from... to.... *5. The formula of chloride of metal is MCl, the metal M belongs to... group. *6.... group contains all gases at room temperature. *7. The arrangement of elements in a group of three is called.... *. The law used by Newlands to arrange elements is called.... *9. Elements showing properties of both metals and non-metals are called as.... *30. The element eka-aluminium is called as.... Answers :. periods. decreases 3. 7 4. 5. 6. 0 7. donate. varies gradually 9. ramains the same 0. metals. gains or shares. Helium 3., 4. metal 5. metalloids 6. alkali metals 7. alkaline earth metals. halogens 9. remain the same 0.. Atomic number. upper right hand corner 3. increases 4. metallic to Non-metallic 5. II A 6. or zero 7. triad. Newlands Law of octaves 9. metalloids 30. gallium. SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY Q.I (B) Match the following :. Column I Column II (i) Mendeleev (a) Octaves (ii) Dobereiner (b) Periodic law (iii) Newlands (c) Triads Ans. (i - b), (ii - c), (iii - a).. Column I Column II (i) Alkali metals (a) II A group (ii) Alkaline earth metals (b) I A group (iii) Halogens (c) zero group (iv) Noble gases (d) VII A group Ans. (i - b), (ii - a), (iii - d), (iv - c). 3. Column I Column II (i) Helium (a) Halogen (ii) Chlorine (b) Alkaline earth metal (iii) Hydrogen (c) H (iv) Magnesium (d) Noble gas Ans. (i - d), (ii - a), (iii - c), (iv - b). 4. Column I Column II *(i) Sodium (a) Non-metal (ii) Sulphur (b) Lanthanide (iii) Manganese (c) Metal (iv) Cerium (d) Transition metal Ans. (i - c), (ii - a), (iii - d), (iv - b). 5. Column I Column II (i) Mendeleev (a) Russian scientist (ii) Dobereiner (b) German scientist (iii) Newlands (c) Englishman Ans. (i - a), (ii - b), (iii - c). Q.I (C) State whether the following statements are true or false. If false write the corrected statement :. Atomic number is the number of protons or electrons in the nucleus. Ans. True.. Fourth and fifth periods are longest periods. Ans. False. Fourth and fifth periods are long periods, 6 th period is the longest period 3. Newlands arranged elements based on their atomic number. Ans. False. Newlands arranged elements based on their atomic mass. 4. Mendeleev was the first scientist to create a periodic table for the elements. Ans. True. 5. Mendeleev arranged 63 elements in the periodic table. Ans. True. 6. Eka boron is known as Germanium. Ans. False. Eka boron is known as Scandium SCHOOL SECTION 3

SCIENCE & TECHNOLOGY MT EDUCARE LTD. 7. Tellurium, Polonium are metalloids. Ans. True.. Isotopes have same atomic masses. Ans. False. Isotopes are atoms of the same element having same atomic number but different atomic masses. 9. Isotopes have similar chemical properties. Ans. True. 0. La stands for Lutetium. Ans. False. La stands for Lanthanum.. s-block includes I A, II A and hydrogen. Ans. True.. d-block elements are called normal elements. Ans. False. d-block elements are called transition elements. 3. f-block elements are metalloids. Ans. False. f-block elements are metals. 4. Metalloids are also called as semi-metals. Ans. True. 5. Bordering the zig-zag line are elements called as metalloids. Ans. True. 6. In an atom of an element, extra-nuclear electrons take part in the chemical. reaction. Ans. True. 7. The number of shells increases down the group. Ans. True.. Helium is the only element in octet state. Ans. False. Helium is the only element in duplet state. Q.I (D) Find the odd man out :. Carbon, Nitrogen, Oxygen, Sulphur. Ans. Sulphur. It is in third period while the rest are in second period.. Hydrogen, Helium, Neon, Argon. Ans. Hydrogen. The rest are noble gases. 3. Lithium, Sodium, Iodine, Potassium. Ans. Iodine as a halogen and rest belong to group A. MEMORISE : Fluorine and Chlorine are gases, bromine is a liquid, iodine and astatine are solids. Extra Information. 4. Boron, Silicon, Arsenic, Sodium. Ans. Sodium belongs to group IA and rest are metalloids. *5. Li, Sr, K, Na. Ans. Sr is an element of a different triad whereas Li, Na, K are elements of same triad. 6. B and Al, O and S, Be and Mg, N and S. Ans. N and S. It does not show similarities in properties according to Newlands law of octaves whereas the others show similarities. 7. Electrons, protons, neutrons, lanthanides. Ans. Lanthanides. It is a series and rest all make up an atom. MEMORISE : Electrons, Protons and neutrons are called as sub-atomic or elementary particles. Extra Information. 4 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY Q.I (E) Write the correlated terms :. Newlands : Octaves ::... : Triads. Ans. Dobereiner.. Ca, Sr, Ba : Triad II ::... Triad I. Ans. Li, Na, K. 3. Fluorine :... :: Chlorine : Third period. Ans. Second period. 4. Neon : Inert element :: Bromine :.... Ans. Halogen/normal element. 5. Fifth period : elements :: Sixth period :.... Ans. 3 elements. 6. Alkali metals : Monovalent :: Alkaline earth metal :.... Ans. Divalent. 7. Tellurium :... :: Radium : Metal. Ans. Metalloid. Q.I (F) Complete the following table : Element Symbol Group Molecular formula of Valency compound with chlorine Sodium... IA NaCl... Lithium... IA... Fluorine... VII A ClF... Barium... II A BaCl Calcium... II A CaCl Ans. Element Symbol Group Molecular formula of Valency compound with chlorine Sodium Na IA NaCl Lithium Li IA LiCl Fluorine F VII A ClF Barium Ba II A BaCl Calcium Ca II A CaCl MEMORISE : To get the molecular formula of a compound: Eg: Sodium chloride Symbol Na Cl Valency Criss cross Na Cl i.e. NaCl Extra Information. Q.I (G) Give two names of the following :. Member of st period : Hydrogen, Helium. Member of nd period : Carbon, Nitrogen. 3. Alkali metals : Lithium, Sodium 4. Alkaline earth metals : Magnesium, Calcium 5. Member of 3 rd period : Phosphorus, Sulphur 6. Elements of zero group : Neon, Argon 7. Elements of halogen family : Fluorine, Chlorine. Metalloid : Silicon, Antimony SCHOOL SECTION 5

SCIENCE & TECHNOLOGY MT EDUCARE LTD. Q.II (A) State the following :. Dobereiner s triads law. Ans. He arranged chemically similar elements in the increasing order of their atomic weights in a group of three which is known as Dobereiner s triads. In a Triad, atomic mass of the middle element is approximately equal to the mean of atomic masses of other two elements in that triad.. Newlands law of octaves. Ans. When the elements are arranged in increasing order of their atomic masses, the properties of every eighth element are similar to the first, as in the octave of music. 3. Mendeleev s periodic law. Ans. The physical and chemical properties of elements are periodic function of their atomic masses. 4. Modern periodic law. Ans. The physical and chemical properties of elements are periodic function of their atomic numbers. Q.II (B) Define the following :. Groups. Ans. Vertical column of elements in a periodic table are called as a groups.. Periods. Ans. Horizontal row of elements in a periodic table are called as a periods. 3. Inert gas elements. Ans. The elements in which all the shells including the outermost shell is completely filled are called as inert gas elements. 4. Normal elements. Ans. The elements in which only the last shell is incompletely filled are called as normal elements. 5. Transition elements. Ans. The elements in which last two shells are incompletely filled are called transition elements. 6. Inner transition elements. Ans. The elements in which last three shells are incompletely filled are called inner transition elements. 7. Metalloids. Ans. Elements showing properties of both metals and non-metals are called as metalloids. Lanthanides. Ans. 4 elements (post lanthanum) with atomic numbers 5 to 7 (Ce to Lu) are called lanthanides. 9. Actinides. Ans. 4 elements (post actinium) with atomic numbers 90 to 03 (Th to Lr) are called actinides. Q.III (A) Give scientific reasons :. Group VII A elements are strong non-metals and group I A elements are strong metals. Ans.. Non-metals are electron acceptors and metals are electron donors. The elements of group VII A have seven electrons in their outermost shell. So, they have a strong tendency to accept one electron and form a negatively charged ion (anion) with octet state.. The elements of group I A have one electron in their outermost shell. So, they have a strong tendency to donate one electron and form positively charged ion (cation) with octet state or duplet state. 6 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY MEMORISE : Electropositivity is the property of an atom to donate electrons when combined in a compound. Electronegativity is the property of an atom to accept electrons when combined in a compound. Extra Information.. Metallic character decreases across a period. Ans.. Metals have a tendency to lose electrons and are said to be electro positive.. As we move across a period, the atomic number and the nuclear charge increases. So, the atomic size decreases. 3. As a result, electrons are more tightly bound to the nucleus and more amount of energy is needed to remove an electron from the outermost shell. So, metallic character decreases across the period. MEMORISE : Nuclear charge is the positive charge on the nucleus of an atom. Extra Information. 3. Non-metallic character increases across a period. Ans.. Non-metals have a tendency to gain electrons.. As we move across a period, the atomic number and the nuclear charge increases. So, the atomic size decreases. 3. As a result, the electron that is gained is pulled more strongly. So, non-metallic character increases across the period. 4. Atomic size decreases across a period. Ans.. Atomic size is defined as the distance between the centre of the nucleus of an atom to its outermost shell.. Across a period, the nuclear charge increases. Nuclear charge is the positive charge on the nucleus of an atom. Also, across the period electrons are added to the same shell. So, electrons experience greater pull from the nucleus. 3. Therefore, atomic size decreases across a period. 5. Atomic size increases down the group. Ans.. Atomic size is defined as the distance between the centre of the nucleus of an atom to its outermost shell.. As we go down the group, the number of shells increases and so the nuclear distance from valence electrons increases. 3. The nuclear charge also increases but increase in number of shells dominates over increase in nuclear charge. So, atomic size increases down the group. 6. Valency varies gradually across a period. Ans.. In the modern periodic table, the elements are arranged in increasing order of atomic number (Z).. Atomic number is related to the electronic configuration. 3. As the atomic number increases, the number of valence electrons increases. The first element has one electron in its outermost shell while the last element in a period has either completed duplet or octet. 4. So, valency varies gradually across a period. 7. Elements in a particular group have similar chemical properties. OR Elements in the same group show same valency Ans.. Position of an element in the periodic table is related to its electronic configuration. The elements of a particular group have the same number of electrons in the outermost shell (i.e. valence electrons).. Chemical properties of an element depends on the number of electrons in the valence shell. Eg, Chemical properties of sodium and potassium in group I A are similar. 3. Hence, elements in a particular group have similar chemical properties. SCHOOL SECTION 7

SCIENCE & TECHNOLOGY MT EDUCARE LTD.. The family of noble gases is called as zero group. Ans.. Zero group or group is a family of inert gases also called as noble gases or rare gases.. In their atoms, all the electronic shells including the outermost shell are completely filled. They have stable electronic configuration with complete duplet (Helium) or complete octet (Neon, Argon etc). 3. So, atoms do not gain, lose or share electrons and hence have zero valency. 4. Hence, the family of noble gases is called as zero group. MEMORISE : Noble gases have a stable electronic configuration, they are in duplet or octet state. So, they don't lose, gain, share electrons. So, inert gases exist in their free atomic state. Extra Information. 9. Chlorine is placed in VII A group in the modern periodic table. Ans.. Number of valence electrons is equal to the group number.. Chlorine has atomic number 7 and hence its electronic configuration is,, 7. 3. There are 7 electrons in the valence shell. 4. Hence, Chlorine is placed in VII A group in the modern periodic table. Q.III (B) Answer the following questions in short :. From the list of elements given below, make three triads and name the family of each triad. List : Cl, Li, Ca, Br, Na, Sr, I, K, Ba. Ans. Alkali metal triad : Li Na K. Alkaline earth metal : Ca, Sr, Ba. Halogens triad : Cl, Br, I.. The elements A and B obey the law of octaves. How many elements are there between A and B? Ans. There are 6 elements between A and B. 3. What was the basis of classification of elements in Mendeleev's periodic table? Ans. Basis of Mendeleev's periodic table :. Similarities in the chemical properties of the elements.. Increasing order of atomic mass of the elements. 4. What are transition elements? Which amongst the following are transition elements? K, Mn, Ca, Cr, Cu, Cs, Fe Ans.. The elements in which last two shells are incompletely filled are called transition elements.. The elements Mn, Cr, Cu, Fe are transition elements. 5. Name alkali metals, to which group do they belong? Ans.. The alkali metals are Lithium, Sodium, Potassium, Rubidium, Cesium, Francium.. These elements belong to group I A. 6. Name alkaline earth metals, to which group do they belong? Ans.. The alkaline earth metals are Beryllium, Magnesium, Calcium, Strontium, Barium, Radium.. These elements belong to group II A. SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY 7. Name halogens, to which group do they belong? Ans.. The halogens are Fluorine, Chlorine, Bromine, Iodine, Astatine.. These elements belong to group VII A.. Oxygen (Z = ) and sulphur (Z = 6) belong to the same group of the periodic table. On the basis of electronic configuration, name the group and period to which they belong. Ans.. Group number indicates number of valence electrons.. Period number indicates no of shells. 3. The electronic configuration of oxygen is, 6. So, it belongs to Group VI A and nd period. 4. The electronic configuration of sulphur is,, 6. So, it belongs to Group VI A and 3 rd period. 9. Name the noble gases, to which group do they belong? Ans.. The noble gases are Helium, Neon, Argon, Krypton, Xenon, Radon. These elements belong to group. 0. What are the names of the periods and how many elements do they have? Ans. First period is the shortest period with elements.. Second, Third period are short periods with elements. 3. Fourth, Fifth period are long periods with elements. 4. Sixth period is the longest period with 3 elements. 5. Seventh period is the incomplete period with 30 elements.. An element is in the second period and group VI A of the periodic table.. Is it metal or non-metal. Ans. Non-metal.. Number of valence electrons. Ans. 6. 3. Electronic configuration. Ans., 6. 4. Name of the element. Ans. Oxygen. 5. Formula of compound with sodium. Ans. Na O.. Label each of the following as either metal, metalloid or a non-metal : K, Ni, As, Br, S, Al. Ans. Metals : K, Ni, Al Non-metals : Br, S Metalloid : As. 3. Which are the three elements having single electron in the outermost shell? Ans. Lithium, Sodium, Potassium. 4. Which are the three elements with filled outermost shell? Ans. Helium, Neon, Argon. 5. Which are the three elements having seven electrons in the valence shell? Ans. Chlorine, Bromine, Iodine. SCHOOL SECTION 9

SCIENCE & TECHNOLOGY MT EDUCARE LTD. Q.IV Distinguish between :. Periods and Groups. Ans. Periods. Modern periodic table has 7 horizontal rows called as periods.. The number of shells present in the atom of an element determines the period number. 3. Elements show gradual variation in chemical properties along a period. Neighbouring elements show some similarities but nonneighbouring elements show appreciable dissimilarity in their properties.. Alkali metals and Alkaline earth metals. Ans. Alkali metals. In the modern periodic table, IA group elements including lithium, sodium, potassium, rubidium, caesium and radioactive francium are alkali metals.. Atoms of these elements have one electron in the valence shell. 3. They are monovalent. 4. Their oxides and hydroxides dissolve readily in water. Groups. Modern periodic table has vertical columns of elements called groups.. The number of electrons present in the outermost shell of an atom of the element determines the group number. 3. Elements belonging to a particular group show strong resemblance in their chemical properties like valency, formulae of compounds and chemical reactions. Alkaline earth metals. In the modern periodic table, IIA group elements including beryllium, magnesium, calcium, strontium, barium, radioactive radium are alkaline earth metals.. Atoms of these elements have two electrons in their valence shell. 3. They are divalent. 4. Their oxides and hydroxides dissolve slightly in water. Q.V Answer the following in detail :. Explain Dobereiner s law of triads giving examples. Ans.. He arranged chemically similar elements in the increasing order of their atomic masses in a group of three which is known as Dobereiner s Triads. In a triad atomic mass of middle element is approximately equal to the mean of atomic masses of other two elements in that Triad. Eg.: Lithium (Li), Sodium (Na), Potassium (K) form a triad as they show similar chemical properties. The atomic weights are 6.9, 3, 39 respectively.. According to Dobereiner s law of triads, 6.9 39 = 45.9 =.95 ~ 3 = Atomic weight of sodium. Thus, the atomic weight of sodium (3) is the average of the atomic weights of lithium (7) and potassium (39). The other examples are: Elements Atomic Mass Calcium (Ca) 40. Strontium (Sr) 7.6 Barium (Ba) 37.3 0 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY Elements Atomic Mass Chlorine (Cl) 35.5 Bromine (Br) 79.9 Iodine (I) 6.9 Elements Atomic Mass Sulphur (S) 3 Selenium (Se) 79 Tellurium (Te). Explain the limitations of Dobereiner's law of triads. Ans.. All the elements known at that time could not be classified as triads (i.e. law was applicable to a few elements only.. It does not take into account the isotopes of elements. 3. It cannot be applied to other chemically similar elements. Eg. : Triads III IV Elements Cu Ag Au Zn Cd Hg Atomic weights 63.5 0 97 65.5 00 Mean of atomic weights 30.5 3.5 The above set of triads do not obey Dobereiner's law. 3. Explain Newlands law of octaves giving examples. Ans. Newlands Law : When the elements are arranged in increasing order of their atomic masses, the properties of the eighth element are similar to that of the first. Examples :. The eight element from lithium is sodium. Similarly, eight element from sodium is potassium. Lithium, sodium, potassium have similar chemical properties.. The eighth element from fluorine is chlorine. Fluorine and chlorine have similar chemical properties. 4. Explain the limitations of Newlands law of octaves. Ans.. Newlands law was applicable to elements with low atomic masses only. He could arrange elements only upto calcium out of total 56 elements known.. The law fails to explain similarities in properties of elements with higher atomic weights. After calcium, every eighth element did not possess properties similar to the first. 3. Newlands thought only 56 elements existed, but later several elements were discovered. 4. In order to fit the existing elements, Newlands adjusted two elements in the same position which differed in their properties. 5. This periodic table did not include inert gases as they were not discovered. Eg. : Sa (Do) Re (Re) Ga (Mi) Ma (Fa) Pa (So) Da (La) Ni(Ti) H Li Be B C N O F Na Mg Al Si P S Cl K Ca Ti Cr Mn F e SCHOOL SECTION

SCIENCE & TECHNOLOGY MT EDUCARE LTD. In the above table, Ti is the eighth element with respect to Al, but does not show similar properties. Similarly, Cr is different from Si. The elements Ti, Cr, Mn, Fe and Co, Ni do not show similarities as per Newlands law. 5. Explain the merits of Mendeleevs periodic table. Ans.. Mendeleev was the first who successfully classified all known elements.. Mendeleev kept some blank places in his periodic table. These vacant spaces were for elements that were yet to be discovered. He also predicted properties of these elements even before they were discovered. Later they were found to be correct. 3. In the periodic table, some gaps were left by Mendeleev for unknown elements that could be found in the future. Three such unknown elements were named as Eka-Boron, Eka-Aluminium and Eka-Silicon. Even the properties of these unknown elements were predicted and these were found to accurate. Predicted element Eka-boron Eka-Aluminium Eka-Silicon Actual element discovered after Scandium Gallium Germanium Comparison of properties of eka-aluminium and gallium. Eka-Aluminium Gallium Atomic weight About 6 69.7 Density of solid 6.0g/cm3 5.9g/cm 3 Melting point Low 9.7 Valency 3 3 Method of discovery Probably from its spectrum Spectroscopically Oxide Ea O 3 Ga O 3 Density = 5.5 g/cm 3 Density = 5. g/cm 3 Soluble in acids and bases Soluble in acids and bases 4. When noble gases were discovered later, they were placed in Mendeleev s periodic table without disturbing the positions of other elements. MEMORISE : Spectrum : A vacuumised cylindrical discharge tube is taken and filled with hydrogen gas (whose spectrum is to be obtained). Electric current is passed through it. Hydrogen (Z=), so Total number of protons = total number of electrons = The electron present in the first shell absorbs electrical energy and goes in an excited state, i.e jumps to the next shell. As a result, the atom becomes unstable. To gain stability, the electron emits the same amount of energy that was absorbed and comes back to its ground state. This energy emitted is in the form of light. This light when passed through a prism, gets dispersed to give coloured bands. This is spectrum. This similar to dispersion of white light when passed through the prism. The spectrum of each element is unique as fingerprints vary from person to person. This method of obtaining the spectrum is spectroscopy. Extra Information. SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY *6. Explain the demerits of Mendeleevs periodic table. Ans.. Hydrogen resembles alkali metals as well as halogens. Therefore, no fixed position could be given to hydrogen in the periodic table.. Isotopes of same elements have different atomic masses; therefore each one of them should be given different position. On the other hand as isotopes are chemically similar, they had to be given same position. 3. At certain places, an element of higher atomic mass has been placed before an element of lower atomic mass. For eg, cobalt (Co = 5.93) is placed before nickel (Ni = 5.7) 4. Some elements placed in the same sub-group had different properties. Eg. Manganese (Mn) is placed with halogens which totally differs in the properties. 7. Explain the modern periodic table. Ans.. In 93, Henry Moseley, an English physicist found that it was atomic number (Z) and not atomic mass which was the fundamental property of an element. Thus atomic number is useful for arrangement of elements in the periodic table.. The modern periodic table is also called as long form of periodic table. 3. In the modern periodic table, elements are arranged in the increasing order of atomic number (Z). 4. The modern periodic table contains 7 horizontal rows called as periods and vertical columns called as groups. 5. Apart from the seven rows, there are two additional rows called lanthanide series and actinide series placed at the bottom of the periodic table. 6. Based on electronic configuration, the modern periodic table is divided into four blocks namely, s-block, p-block, d-block and f-block. 7. The blocks gives rise to 4 types of elements namely normal elements, zero group elements, transition elements and inner-transition elements.. Elements belonging to a particular group show strong resemblance in their chemical properties like valency, formulae of compound and chemical reactions. 9. Elements show gradual variation in chemical properties along a period. 0. Neighbouring elements within a period show some similarities but nonneighbours show appreciable dissimilarity in their chemical properties. *. Explain the merits of modern periodic table. OR How could the modern periodic table remove various anomalies of Mendeleev's table? Ans.. The modern periodic table was classified based on atomic number. All isotopes of the same elements have different masses but same atomic number. Therefore, they occupy the same position in the modern periodic table.. When elements are arranged according to their atomic numbers, the anomaly regarding certain pairs of elements in Mendeleev's periodic table disappears eg.atomic number of cobalt and nickel are 7 and respectively. Therefore, cobalt will come first and then nickel although its atomic mass is greater. 3. Elements are classified according to their electronic configuration into different blocks. 9. Explain the four blocks of periodic table Ans. Based on electronic configuration, the modern periodic table is divided into four blocks namely, s-block, p-block, d-block, f-block. SCHOOL SECTION 3

SCIENCE & TECHNOLOGY MT EDUCARE LTD. s-block p-block d-block f-block No. of shells incomplete/ valence electrons Outermost shell incomplete ( or valence electrons). Outermost shell incomplete except zero group elements that have completely filled shells (3 to valence electrons). Last two shells incomplete. Last three shells incomplete. Position I A, II A and hydrogen. III A to VII A and zero group. Group IIIB to II B along with group VIII. Lanthanides and actinides placed separately at the bottom of the periodic table. Includes All metals except hydrogen. Metals, non-metals, metalloids, zero group elements. Metals. Metals. Types of elements Normal elements. Normal and inert elements. Transition elements. Innertransition elements. MEMORISE : Position of hydrogen : Hydrogen is at the head of table A and it has one valence electron much like the other members of group. However hydrogen is not considered as part of group A because chemically it is a non-metal whereas all other members of group are strong alkali metals. In fact position of hydrogen in periodic table is unresolved. Extra Information. 0. Explain the zig-zag line in the periodic table. Ans.. On the basis of electronic configuration of elements, the periodic table is divided into four blocks namely, s-block, p-block, d-block and f-block.. The elements of s-block (except hydrogen), d-block and f-block are all metals. 3. In the p-block, all the three types of elements, i.e metals, non-metals and metalloids are present. 4. A zig-zag line separates the metals on the left side form the non-metals on the right side of the periodic table. 5. The bordering elements along the zig-zag line are the metalloids. These are Antimony ( Sb), Germanium ( Ge), Boron ( B), Silicon (Si), Arsenic (As), Tellurium (Te), Polonium (Po). They show intermediate properties and are called as metalloids or semi-metals. MEMORISE : The zigzag line on the periodic table, sometimes referred to as the Hays-McDaniel line, distinguishes between the metals and non metals. It is also called as stair case. Extra Information.. Explain the term periodic properties and explain the following trends of the periodic table with respect to :. Valency. Metallic character *3. Atomic size. Ans.. Valency : (a) In the modern periodic table, the elements are arranged in increasing order of atomic number (Z). Atomic number is related to the electronic configuration. 4 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY (b) (c) As the atomic number increases, the number of valence electrons increases. The first element has one electron in the outermost shell while the last element in a period has either completed duplet or completed octet. So, valency varies gradually across a period. The group number indicates number of valence electrons. So, elements in a group have the same number of valence electrons. Therefore, down the group, valency remains the same. MEMORISE : Valency is the combining power of an atom or it is the number of electrons donated or accepted or shared to attain the nearest inert gas configuration. Extra Information.. Metallic character : The tendency of an element to lose electrons and form positively charged ions (cations) is called as metallic character. Non-metallic character : The tendency of an element to gain electrons and form negatively charged ions (anions) is called as non-metallic character. As we go down a group, the atomic size increases. So, the nuclear attraction on the outermost electron decreases and electrons can be lost more easily. So, down the group, metallic character increases and non-metallic character decreases. Across a period, the nuclear charge increases. Consequently, the attraction on the valence electrons increases and so more energy is required to lose the electron. So, across a period, metallic character decreases and non-metallic character increases. MEMORISE : Factors affecting metallic and non-metallic character:. Atomic size : The greater the atomic size, the electron can be lost more easily.. The energy required to remove the electron is also less. So, lower the energy, more is the metallic nature of element. The energy required to remove a loosely bound electron from the outermost shell of an isolated gaseous atom is called as ionization potential. Extra Information. 3. Atomic size is defined as the distance from the centre of the nucleus to the outermost shell of an atom. Across a period, the number of shells remain the same. So, as nuclear charge increases due to increase in atomic number, the attraction to the outermost electron increases and pulls the electrons inwards. So, atomic size decreases across a period. Li Be B C N O F Down the group, the number of shells increases. So, although the nuclear charge increases, the attraction to the outermost electron decreases. So, down the group, the atomic size increases. F Cl Br I SCHOOL SECTION 5

SCIENCE & TECHNOLOGY MT EDUCARE LTD.. What are the causes of the periodicity of elements? Ans. Periodicity in properties of elements are seen because. In the modern periodic table, the elements are arranged according to their increasing atomic numbers.. The physical and chemical properties of elements largely depends upon the outermost electronic configuration, that is the valence electrons. 3. Hence the outermost electronic configuration for each group remain the same. 4. Since periodicity in properties of elements are seen due to same outermost electronic configuration. 3. State Dobereiners law of triads. P, Q, R are elements of a Dobereiner's triad. If atomic mass of P is 35.5 and R is 7, what would be the atomic mass of Q? Ans. Dobereiner's law of triads : He arranged chemically similar elements in the increasing order of their atomic masses in a group of three which is known as "Dobereiner's Triads". In a Triad, atomic mass of middle element is approximately equal to the mean of atomic masses of other two elements in that Triad. Atomic weight of P Atomic weightof R Atomic weight of Q = 35.5 7 = = 6.5 =.5. 4. Why is atomic number said to be a fundamental property? Ans.. Atomic number (Z) is defined as the number of protons or electrons in an atom.. It is more important than atomic mass because atomic number tells us about the chemical properties of an element. 3. It tell us about the number of valance electrons and valance electrons decide the chemical properties. It tell us about the nature of an element and its electronic configuration. 5. Explain the features of Mendeleev's periodic table. Ans. Main features of Mendeleev s periodic table are as follows :. The horizontal rows in the periodic table are called periods. There are seven periods. These are numbered from to 7.. Properties of elements in a particular period show regular gradation from left to right. 3. Vertical columns in the periodic table are called groups. There are eight groups numbered from I to VIII. Groups I to VII are further divided into A and B subgroups. *6. Among the first twenty elements, which are metals, non-metals and metalloids? Ans. Metals : Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, Calcium. Non-metals : Hydrogen, Helium (zero group), Carbon, Nitrogen, Oxygen, Fluorine, Neon(zero group), Phosphorus, Sulphur, Chlorine, Argon (Zero group). Metalloids : Boron, Silicon. 6 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY ACTIVITY BASED QUESTIONS ACTIVITY :.3 Q. Consider isotopes of oxygen 6 O and O. Would you able to place them in Mendeleev s periodic table? Ans. No, we cannot place 6 O and O in Mendeleev s periodic table. Q. Find resemblance between hydrogen and alkali metals by writing compounds of both with chlorine, sulphur and oxygen. Ans. Alkali metals are : Li, Na, K, Rb, Cs, Fr. H O Na O H S Na S HCl NaCl Hydrogen and alkali metals form similar formulae with, oxygen, sulphur and chlorine. Q. Find out a pair of elements from the periodic table where higher mass element is placed before lower mass element. Ans. Co Ni ; Te I (5.9) (5.7) (.) (.7) ACTIVITY :.4 Q. How are isotopes of different elements placed in the Modern Periodic Table? Ans. Isotopes have same atomic number, but different atomic mass. In modern periodic table the elements are arranged in increasing order of atomic numbers. So, all isotopes of an element can be given the same position. Q. What should be the position of Hydrogen in the Modern Periodic Table? Why? Ans. In modern periodic table, elements are arranged in the increasing order of their atomic number, so a Hydrogen must be the first element in modern periodic table, because it has the least atomic number. Q. Write the name, symbol and electronic configuration of first ten elements. Ans. Elements Symbol Atomic number E.C. Hydrogen H () Helium H e () Lithium Li 3 (,) Beryllium Be 4 (,) Boron B 5 (,3) Carbon C 6 (,4) Nitrogen N 7 (,5) Oxygen O (,6) Flurorine F 9 (,7) Neon Ne 0 (, ) SCHOOL SECTION 7

SCIENCE & TECHNOLOGY MT EDUCARE LTD. ACTIVITY :.5 Q. Write the electronic configuration of elements from atomic number to. Ans. Elements Symbol Atomic No. E.C. Sodium Na (,, ) Magnesium Mg (,, ) Aluminium Al 3 (,, 3) Silicon Si 4 (,, 4) Phosphorous P 5 (,, 5) Sulphur S 6 (,, 6) Chlorine Cl 7 (,, 7) Argon Ar (,, ) Q. What similarities do you find in their electronic configuration? Ans. They all have three shells in their atoms. Q. How many valence electrons are present in sodium, aluminium and chlorine? Ans. Elements No. of valence electrons Sodium Aluminium 3 Chlorine 7 Q. Write the electronic configuration of. Mg and Ca.. F and Cl. Ans. Elements Atomic number Electronic configuration Magnesium (,, ) Calcium 0 (,,, ) Flurine 9 (, 7) Chlorine 7 (,, 7) Q. Do these elements contain same number of valence electrons? Ans. Yes, they contain same number of valence electrons. Q. Write the electronic configuration of B, O, Na, Al, S and K. Ans. Symbol Atomic number Electronic configuration B 3 (, ) O (, 6) Na (,, ) Al 3 (,, 3) S 6 (,, 6) K 9 (,,, ) SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY ACTIVITY :.6 Q. Classify elements from atomic number to as metals or non metals depending on the electrons present in the outermost shell. Ans. Symbol Atomic number Electronic configuration Na (,, ) Mg (,, ) Metals Al 3 (,, 3) Si 4 (,, 4) P 5 (,, 5) S 6 (,, 6) Non metals Cl 7 (,, 7) Ar (,, ) ACTIVITY :. Q. How do you calculate valency of an element from its electronic configuration? Ans. Electronic configuration tells about the valence electrons. If the number of valence electrons are, or 3, then such elements will donate, or 3 electrons their valency is also, or 3 respectively. If an element has 4 valence electrons, it shares all 4 electrons, so the valency is 4. If the number of valence electrons are 5, 6 or 7 electrons, then such elements accept 3, or electrons respectively. Thus their valency is 3, or. When the valence electrons are (for only one shell) or then it is a stable electronic configuration. Thus, the valency is zero. Q. What is the valency of elements with atomic number, 4, 7 and 0? Ans. Atomic number Electronic configuration Valency (, 6) 4 (,, 4) 4 7 (,, 7) 0 (,,, ) ACTIVITY :.9 Q. Atomic radii of elements of third period are given below. Ans. Period 3 elements S Na Cl P Mg Si Al Atomic radius (pm) 7 90 99 60 3 43. Arrange them in the decreasing order of their atomic radii. Ans. Na Mg Al Si P S Cl Ans. Ans. 90 60 43 3 7 99. Are they arranged as in the periodic table? Yes. 3. Which are the atoms of highest and lowest atomic radii? Highest atomic radius = Na (90 pm) Lowest atomic radius = Cl (99 pm) SCHOOL SECTION 9

SCIENCE & TECHNOLOGY MT EDUCARE LTD. 4. What trend is observed in the atomic radii in a period from left to right? Ans. Atomic radii decreases from left to right in a period. Q. Atomic radii of group 7 are given below : Ans. Group 7 elements I F Cl Br Atomic radius (pm) 33 7 99 4. Arrange them in the increasing order of thier atomic radii. Ans. F (7) Cl (99) Br (4) I (33). Are they arranged as in the periodic table? Ans. Yes. 3. Which are the atoms of highest and lowest atomic radii? Ans. Highest atomic radii = Iodine (33). Lowest atomic radii = Fluorine (7). 4. What trend is observed in the atomic radii down the group? Ans. Atomic radii increases down the group. Atomic Elements Symbol Electronic Valence Valency number configuration electrons electrons Hydrogen H Helium H e 0 3 Lithium Li, 4 Beryllium Be, 5 Boron B, 3 3 3 6 Carbon C, 4 4 4 7 Nitrogen N, 5 5 3 Oxygen O, 6 6 9 Flurine F, 7 7 0 Neon Ne, 0 Sodium Na,, Magmesium Mg,, 3 Aluminium Al,, 3 3 3 4 Silicon Si,, 4 4 4 5 Phosphorus P,, 5 5 3 6 Sulphur S,, 6 6 7 Chlorine Cl,, 7 7 Argon Ar,, 0 9 Potassium K,,, 0 Calcium Ca,,, 0 SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY 3 4 5 6 7 H Hydrogen.00794 3 Li Lithium 6.94 Na Sodium.99769 H Hydrogen.00794 37 Rb Rubidium 5.47 55 Cs Caesium 3.905459 7 Fr Francium (3) 3 4 5 6 7 9 0 3 4 5 6 7 3 4 Be Beryllium 9.0 Mg Magnesium 4.3050 0 Ca Calcium 40.07 3 Sr Strontium 7.6 56 Ba Barium 37.37 Ra Radium () 3 Sc Scandium 44.9559 39 Y Yttrium.9055 C Hg H Rf 57 7 9 9 03 Ti Titanium 47.67 40 9 Zr Zirconium 9.4 7 Hf Hafnium 7.49 04 Rf (6) 3 0 V Vanadium 50.945 4 0 Nb Niobium 3 0 9.9063 73 Ta Tantalum 0.947 3 3 05 Db 0 Dubnium (6) 4 Cr Chromium 4 5.996 Mo Molybdenum 95.96 74 3 W Tungsten 3 3 3.4 06 Sg Seaborgium (66) 5 Mn Manganese 54.93045 43 3 Tc Technetium (97.909) 3 75 Re Rhenium 7.49 3 3 07 Bh Bohrium (64) 6 3 Fe Iron 55.45 44 4 Ru Ruthenium 0.07 3 0 76 Os Osmium 90.3 0 3 3 Hs Hassium (77) 7 4 Co Cobalt 3 5.93395 45 5 Rh Rhodium 77 4 0.90550 Ir Iridium 9.7 3 3 09 Mt 4 Meitnerium (6) 5 Ni Nickel 5.6934 46 6 Pd Palladium 06.4 3 5 7 Pt Platinum 95.04 0 3 3 Ds 5 (7) 9 6 Cu Copper 3 63.546 47 0 Ag Silver 79 7 07.6 Au Gold 96.966569 3 3 7 Rg (7) 3 3 3 30 Zn Copper 65.3 4 Cd Cadmium.4 0 Hg Mercury 00.59 3 3 (5) 5 B Boron 0. 3 Al Aluminium 6.9536 3 Ga Gallium 69.73 49 In Indium 4. Tl Thallium 04.333 3 3 3 3 3 3 3 3 3 (4) 3 6 C Carbon.007 4 Si Silicon.055 3 Ge Germanium 7.64 50 Sn Tin.70 Pb Lead 07. 4 4 4 4 3 4 4 3 3 (9) 4 7 N Nitrogen 4.0067 5 P Phosphorus 30.97376 33 As Arsenic 74.960 5 Sb Antimony.760 3 Bi Bismuth 0.9040 5 5 5 3 5 5 3 3 () 5 5 O Oxygen 5.9994 6 S Sulfur 3.065 34 Se Selenium 7.96 5 Te Tellunium 7.60 4 Po Polonium (0.94) 6 6 3 6 6 3 3 (9) 6 6 6 9 F Fluorine.99403 7 Cl Chlorine 35.453 35 Br Bromine 79.904 53 I Iodine 6.90447 5 At Astatine (09.97) 7 7 7 7 3 7 7 30 Zn Copper 63.546 0 Ne Neon 0.797 Ar Argon 39.94 36 Kr Krypton 3.79 54 Xe Xenon 3.93 6 Rn Radon (.076) 3 3 3 (94) 57 9 3.90547 9 Actinium (7) 3 9 5 Cerium 40.6 90 Thorium 3.0306 9 9 3 0 59 40.90765 9 3 0 9 3.035 60 44.4 9 Uranium 3.09 3 9 6 3 (45) 93 Neptunium (37) 3 9 6 Samarium 50.36 94 Plutonium (44) 4 3 4 63 5 5.964 95 Americium (43) 3 5 64 5 9 57.5 96 Curium (47) 3 59 65 Terbium 5.9535 97 Berkelium (47) 7 3 7 66 6.500 9 3 (5) 67 Holmium 64.9303 9 99 3 9 (5) 6 Erbium 67.59 00 Fermium (57) 30 3 30 69 Thulium 6.934 3 0 3 3 (5) 70 Ytterbium 73.054 0 Nobelium (59) 3 3 3 Ununoctium (94) 3 3 03 3 39 (6) SCHOOL SECTION

SCIENCE & TECHNOLOGY MT EDUCARE LTD. HOTS QUESTIONS & ANSWERS. X, Y, Z are the elements of Dobereiner s triad. If the atomic mass of X is 7 and that of Z is 39. What should be the atomic mass of y? Ans. In the triads, the atomic mass of the middle element is approximately the mean of the atomic masses of the other two elements. Hence, Y = 7 39 = 46 = 3 Atomic mass of Y = 3.. Read the following descriptions and decide whether the element belongs to metal or non-metal. Justify your answer. (a) Element X has atomic number. (b) Element Y has atomic number 6. Ans. (a) Element X is a metal. Its electronic configuration is (,, ). The element has a tendency to loose one electron making it metallic in nature. (b) Element Y is a non-metal. Its configuration is (,, 6). Therefore there is a tendency to accept the electrons rather than to loose, making it non-metallic in nature. 3. The atomic number of an element X is 7. Predict : (a) Its valency. (b) Whether it is a metal or non-metal. (c) Its relatively atomic size with respect to other members in the group. Ans. (a) Valency is (Electronic configuration,, 7). (b) It is a non-metal. (Tendency to accept electron as the outermost orbit has 7 electrons.) (c) Atomic size is relatively smaller with respect to the other members in a group. (Electrons in the outer shell are not released easily.) 4. Inert gases are neutral because.... (a) they do not combine with other elements under normal circumstances. (b) the number of electrons in their outer shell is. (c) they do react with other elements, but the process remains incomplete. Ans. The number of electrons in their outer shell is. 5. Identify the main characteristic of the elements given below from their description. (a) Element P is in O group element. (b) Element Q is in group with atomic number 9. (c) Element R is a d-block element and its two outermost shells are incomplete. (d) Element S is f-block element. (e) Element T has two different atomic masses. Ans. (a) It is an inert gas. (b) It is a metal with one electron in the outer shell. (c) It is called a transition element and is metallic in nature. (d) They are either lanthanides or actinides with three incomplete outermost shells and metallic in nature. (e) They are isotopes of element T. SCHOOL SECTION

MT EDUCARE LTD. SCIENCE & TECHNOLOGY GLOSSARY Alkali metals : Elements of group IA are most reactive. They are called alkali metals as they form alkali on reaction with water. Alkali : Soluble bases which produce OH ions in water. Alkaline earth metal : Elements belonging to group II A. They form alkali on reaction with water and their oxides are found in earth. So, they are called alkaline earth metals. Atomic number : Number of protons (in nucleus) or extra nuclear electrons. Atomic mass number : the total number of protons and neutrons in the nucleus of an atom. Electronic configuration : Distribution of electrons shell wise. Electrostatic force of : A strong force of attraction between particles of attraction opposite charges. Element : A substance that cannot be divided further into simpler substances. Isotopes : They are different atoms of same element having same atomic number but different mass number Halogens : Elements belonging to group VII A. The elements of this group form salts and are called as salt formers. Noble gases : Elements of group also called as rare gases/ noble gases. Metals : Electron donors, hence electro-positive. Non-metals : Electron acceptors, hence electro-negative. Metalloids : Elements showing properties of both metals and non-metals. Valency : Combining power of an atom or number of electrons donated/accepted/shared to attain the nearest inert gas configuration. Periodicity : A phenomenon occurring at regular intervals. Cations : Positively charged ions. Anions : Negatively charged ions. Nuclear charge : The positive charge on the nucleus of an atom. Ionisation potential : The energy required to remove a loosely bound electron from the outermost shell of an isolated gaseous atom is called as ionization potential. AMAZING FACTS The noble gas Xenon lasers can cut through materials that are so tough even diamond tipped blades will not cut. Astatine is the rarest element on Earth (approx g in the Earth's entire crust.) SCHOOL SECTION 3