Chapter 9: Elements are the Building blocks of Life

Transcription

1 Chapter 9: Elements are the Building blocks of Life

2 Section 9.1- Elements and the Periodic Table Keep Scale in mind Animation:

3 I. ELEMENTS All matter is made up of one or more elements or a mixture of elements An element is a pure substance made out of any one kind of atom. ex. gold is made up of gold atoms only ex. carbon monoxide is made up of carbon atoms and oxygen atoms and so is NOT an element

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5 At room temperature (25 0 C), elements may be in solid, liquid, or gas state Only 92 occur naturally! There are over 115 types of elements. Each element has a specific number of electrons and protons. ex. carbon has 6 electrons/protons ex. oxygen has 8 electrons/protons ex. hydrogen has 1 electron/proton

6 II. CHEMICAL SYMBOLS Each element is represented by one or two letters taken from its Latin name or Greek name. The first letter is always capitalized. The second letter (if there is one), is always lower case. This is called the chemical symbol and it is used by scientists in all languages. ex. H stands for hydrogen ex. Hg stands for mercury (from latin word hydrargyrum, meaning liquid silver)

7 Symbols can also be used to show the proportion of each element in a compound ex. H 2 O = two parts hydrogen and one part oxygen

8 9.2- The PT and Chemical Properties I. PERIODIC TABLE All known elements are listed in a giant table called the periodic table. The periodic table lists each element name, symbol, atomic number, atomic mass, and ion charge(s)

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10 Did You Know? Most of your body s mass is made up of: 65% oxygen 18% carbon 10% hydrogen 3% nitrogen 2 % calcium trace other elements

11 ATOMIC NUMBER: the number of protons in the nucleus of an element. always a whole number. the number of protons equals the number of electrons, unless the atom is an ion, or charged. there are no ions in the periodic table- everything is shown in its neutral state.

12 ATOMIC MASS/MASS NUMBER: the mass of an average atom of an element. measures the number of protons and neutrons. is written in a decimal form and uses the atomic mass unit (amu). the number of neutrons can vary from atom to atom, so atomic mass may not be a whole number as it represents the average.

13 You Try. Write the chemical symbol for Madeitupium: 7 protons 8 neutrons 7 electrons A= Chemical Symbol: B= Atomic number: C= Atomic weight/mass: D=

14 Here is an example of hydrogen and three possible scenarios. Hydrogen can have no neutrons, one neutron, or two neutrons. An isotope is an atom that has the same number of electrons and protons but a different number of neutrons.

15 How many neutrons in Carbon? Atomic weight (mass)= (= p + n) Atomic number = 6 (=p only) # of neutrons = 12-6 = 6 neutrons

16 Ion Charge: this is an electric charge that forms on an atom when it gains or loses electrons. A charged atom is called an ion. If an atom.gains electrons, it becomes negatively charged àhas more electrons than protons.loses electrons, it becomes positively charged àhas more protons than electrons An ion is designated with a charge in the top right region of the symbol. Ex. O 2-

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18 IV. CLASSIFICATION of ELEMENTS Properties of any element are specific to that element Properties are used to group similar elements together Three major classification groups are: 1. METALS 2. NON-METALS 3. METALLOIDS (semi-metals)

19 Metalloids are elements that share some properties of metals and some of non-metals. Malleability: ability to beat into sheets Ductility: ability to be drawn into wires

20 All metals appear on the left side of the periodic table All non-metals appear on the right side of the periodic table The metalloids form a diagonal line between metals and non-metals, often called the staircase What about hydrogen????

21 Note that in chemical reactions, metals tend to form positive ions, or cations, while non-metals tend to form negative ions, or anions.

22 III. PERIODS AND FAMILIES Period = horizontal row, numbered 1-7 Family or Group = vertical columns, #1-18 The period tells you how many shells (rings) there are in the Bohr model Ex. Lithium (Li) is in the 2 nd period and so has 2 rings Ex. Magnesium (Mg) is in the 3 rd period and so has 3 rings

23 The chemical family indicates the number of electrons in the outer shell Ex. Lithium (Li) is in the 1 st family, so it has 1 electron in the outer shell Ex. Magnesium (Mg) is in the 2 nd family, so it has 2 electrons in the outer shell

24 Some families you should know 1. ALKALI METALS- family #1- HIGHLY reactive, soft, react with oxygen and water, low melting points. Members include: Li, Na, K, Rb, Ca, Fr 2. ALKALINE EARTH METALS- family #2- less reactive than alkali metals, burn if heated and used in fireworks Members include: Be, Mg, Ca, Sr, Ba, Ra

25 3. HALOGENS- family #17- highly reactive nonmetals Members include: F, Cl, Br, I, At 4. NOBLE GASES- family #18- VERY, VERY STABLE Members include: He, Ne, Ar, Kr, Xe, Rn

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27 General trends 1. The atomic number increases one by one through the period table, left from right, top to bottom. 2. The atomic mass tends to increase along with the atomic number but there are some exceptions (e.g. cobalt and nickel)

28 3. Elements on the left side of the table generally form positive ions. Elements on the right side, except for the last column, tend to form negative ions. Elements in the same column often form ions with the same charge as other elements in that column.

29 9.3 The PT and Atomic Theory I. Patterns in the Periodic Table The patterns we have seen in the periodic table are not a just coincidence! The properties of elements are determined by the electrons in the outer shells. Elements with similar properties line up in columns because all those elements have the same number of electrons in the outer shell

30 II. Drawing Bohr Models The BOHR MODEL is a diagram that we use to show the electrons in each shell Each electron shell (layer) has a maximum number of electrons it can hold 1 st shell à up to 2 electrons 2 nd shell à up to 8 electrons 3 rd shell à up to 8 electrons 4 th shell à up to 18 electrons This pattern of electrons is followed by all atoms, although not all atoms have that many electrons.

31 Electrons are usually drawn in pairs, if possible. Also, electrons must fill up the entire inner shell before moving to the outer shell. There are various ways to write a Bohr diagram, but for science 8 you should include: chemical symbol Number of protons Show where the electrons are in the shells

32 You are expected to be able to draw Bohr Models.

33 III. Valence Shells the electrons in the outermost shell are called valence electrons. These electrons have the greatest influence on the properties of an atom. -the shell that contains valence electrons is called the valence shell. same family à same # of valence electrons same period à SAME # of shells that have electrons

34 Try This: Sketch a Bohr Model for. a) Helium b) oxygen c) Boron

35 Why are the noble gases so stable? Their outer shell is full of electrons! In order for atoms to react with other atoms, they must give/take/share electrons. Noble gases DO NOT do this. Atoms always want to be stable. They will take/give electrons from other atoms to fill up their outer shell.

36 Recall Metals tend to lose electrons (à + ion) Did you know? Metal Ions burn different colours

37 Non-metals tend to gain electrons (à - ion) Once an atom has gained/lost electrons, it becomes charged (= ion)

38 Ions are written by giving the symbol of the element followed by a superscript showing the charge Ex. Li loses an electron to become positive (3 protons, 2 electrons) Li + Mg loses two electrons to become positive (12 protons, 10 electrons) Cl gains one electron to become negative (17 protons, 18 electrons) Mg 2- Cl -

39 Section 9.4 Elements Combine to Form Compounds

40 Section 9.4 Compounds COMPOUND: a pure substance made up of more than one kind of element in which the elements are joined together (= chemical bonds) CHEMICAL BONDS: link between two or more - atoms that hold the atoms together There are two types of compounds: covalent compounds ionic compounds

41 I. Covalent Compounds Always between two non-metals Atoms combine by sharing electrons and make molecules Examples: H 2 0

42 Covalent Compounds Share! You will not need to know anything beyond this for Science 8!

43 II. Ionic Compounds Between metal and non-metal Atoms give or take electrons and make ions Example: table salt (NaCl) Na + Cl à NaCl

44 Ionic compounds exist as a solid in the form of an ionic lattice (a repeating pattern of positive and negative ions). This is because all the positive ions attract all the negative ions and repel other positive ions.

45 Ionic Compounds Give and Take!

46 In summary: