Science 10 Chapter 4 Atomic Theory Explains the Formation of Compounds

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1 What is a pure substance? -contains only 1 kind of matter What are the 2 categories of pure substances? -elements -compounds What is an element? -a pure substance that cannot be broken down into simpler substances What is a compound? -a pure substance that is composed of 2 or more atoms combined in a specific way What is an atom? -the smallest particle of any element that retains the properties of the element How can atoms be seen? -too small to be seen with regular light -can be seen with a femtosecond laser How does a femtosecond laser detect atoms? -The energy from the pulse of laser light is used to position atoms and detect chemical changes What are chemical changes? -changes in the ways the atoms and molecules in a pure substance are arranged and interconnected What are sub-atomic particles? -particles that make up an atom -3 kinds: protons, neutrons, and electrons What are protons? -Subatomic particles that have a positive (1+) electric charge ( p for positive) What are neutrons? -subatomic particles that do not have any electric charge ( n for neutral) What are electrons? -subatomic particles that have a negative (1-) electric charge Where is the nucleus of the atom? -in the center of the atom -it occupies a very tiny region of the atom What particles are found in the nucleus? -protons and neutrons Where are the electrons? -found around the nucleus in regular patterns called shells -electrons occupy most of the volume of an atom: it is huge in comparison to the space occupied by the nucleus What are neutral atoms? -Have an equal number of protons and electrons Why are very heavy atoms unstable? -The repulsion between the protons is so high What do neutrons do? - Help to make the nucleus stable by keeping the protons as far apart from each other as possible What is a stable nucleus? -nucleus not likely to break apart Why would a nucleus break apart? - the protons repulse each other due to their positive charge What is the nuclear charge? -term given to the electric charge on the nucleus -always positive from the protons -found by counting the number of protons The same as the atomic number What does the atomic number =? -the number of protons = the number of electrons of a neutral atom = the atomic number 1

2 What does the atomic number identify? Which 2 subatomic particles have nearly equal mass? Describe the organization of the periodic table? What do elements from the same groups or family have? The Alkali metal family are: -the element to which the atom belongs: i.e. all atoms with atomic number of 8 are oxygen because all oxygen atoms have 8 protons -protons and neutrons -listed according to its atomic number -each row is called a period -each column is called a group or family -metals are on the left and middle -non- metals are in the upper right corner -similar chemical properties -group 1 excluding hydrogen -very reactive metals (i.e. sodium) The alkaline earth metal family are: -group 2 -somewhat reactive metals (i.e. calcium) The Halogens are: -group 17 ( 2 nd last column) -very reactive non-metals (i.e. chlorine) The noble gases are: --group 18 (last column) -very un-reactive gaseous non-metals What are the transition metals? -the block of elements from group 3 through to 12 What are ions? What are cations? What does multivalent mean? What are anions? Bohr Diagram: What is the maximum number of electrons in the first shell? What is the maximum number of electrons in the 2 through shells? What is a stable octet? What is the valence shell? What are valence electrons? -(i.e. iron nickel, copper, silver and gold -electrically charged particles -formed when atoms gain or lose electrons Positively charged ions formed when electrons are lost -metals form cations when they lose electrons -( i.e. cats are positive!) -metals that can form ions in more than one way depending on the chemical reaction -have more than one combining capacity -negatively charged ions -formed when electrons are gained -non metals usually form anions -shows how many electron are in each shell around the nucleus 2 8 -Complete set of eight electrons in the outermost shell -outermost shell that contains electrons -the electrons in the valence shell 2

3 What happens when 2 atoms move close together? What determines the stability of an ion, atom or compound? How is low energy achieved? What are the 3 ways that a compound can acquire a stable octet? What 2 types of compounds are there What are ionic compounds? What is ionic bonding? What is covalent bonding? What is a covalent molecule? What is the bonding pair? What is a lone pair? What is a Lewis diagram? What are the differences between a Bohr diagram and a Lewis diagram? How do Lewis diagrams show ions? What does a line represent in a Lewis diagram? What are diatomic molecules? -their valence electrons interact -a chemical bond may form if the new arrangement of atoms and electrons is stable -the lower the energy level the more stable it is Having a valence shell like that of the closest noble gas ( outer valence has a full, stable octet) -metal atoms may lose electrons to other atoms -non metals may gain electrons from other atoms -atoms may share electrons Covalent and ionic Contain a positive ion (usually a metal ) and a negative ion (usually a non-metal) -one or more electron transfer from each atom of the metal to each atom of the non-metal -atoms overlap slightly and they one unpaired electron from each atom will pair together -both atoms are attracted to each pair forming a covalent bond -group of atoms bound together by sharing one or more pairs of electrons -pair of electrons involved in a covalent bond -pair of electrons in the valence shell not used in bonding -diagram that illustrates chemical bonding by showing only the valence electrons and the chemical symbol -used primarily to show covalent bonding -Bohr diagram shows : 1)the nucleus with the number of protons and neutrons 2)all the electrons arranged in all the valence shells -Lewis diagram shows: 1) element symbol and the outer valence electron arrangement 1) square brackets and a positive or negative symbol on the top right i.e. [Na]+ [:Cl:] (There would be two more dots at the top and at the bottom of the Cl) The pair of electrons shared by the atoms A pair of atoms that are joined by covalent bonds 3

4 Why do diatomic elements form this way? What are the diatomic elements? What are ionic compounds? What are the rules for naming ionic compounds? Describe the chemical formula of an ionic compound Define multivalent Why are Roman numerals used with multivalent metals? What are polyatomic ions? What can t polyatomic ions exist on their own? How does the use of subscripts differ in covalent compounds from ionic compounds What do binary covalent compounds contain? What do prefixes indicate with covalent compounds? Define chemical change and what are some examples The 2 atom molecule is more stable than the individual atoms -oxygen O₂, hydrogen H₂, fluorine Fl ₂, chlorine Cl₂, bromine Br₂ and iodine I₂ and nitrogen N₂ - Compounds composed of positive and negative ions The metal part (positive ion)is always named first -negative non metal ion is always named second using the ending ide -contains a symbol to identify each ion and may have subscripts (small number to the right of the symbol) showing the number of ions of each element -shows the smallest whole number ratio of ions -metals which can form ions in more than one way -to indicate the charge formed from multivalent metals -ions composed of more than one type of atom joined by covalent bonds -because they carry an electric charge -in covalent the subscript shows the exact number of atoms of each element (H is hydrogen peroxide and is not reduced to H0) -in ionic the subscript shows the smallest whole number ratio (ie Pb 4+ combining with S 2- is written as PbS 2 NOT Pb 2 S 4) -2 non metal elements joined together with covalent bonds -they combine chemically by sharing electons -can contain many atoms C 25 H 52 (candle wax) or only 2 atoms such as CO (carbon monoxide) -number of atoms of each element (if the first element has only one atom no prefix is used.(co is carbon monoxide NOT monocarbon monoxide) -change in the arrangement and connections between ions -involves reactants (starting elements and compounds) and products (new elements and compounds with different properties than the reactants) -some chemical changes produce electricity ( in a battery), some produce heat (in a fire) some produce light ( in a glow stick) or may use energy (cooking food) 4

5 What are chemical reactions? How are chemical changes represented? - One or more chemical changes that occur at the same time -using a chemical equation which may be in words or with symbols -reactants are listed to the left of the arrow and the products are listed on the right Word equation example: What are the 2 types of symbolic equations: Balanced Symbolic equation example: Coefficients: Nitrogen Monoxide + oxygen Nitrogen dioxide -provides only limited information about a reaction (doesn t show the amounts of reactants and products) -skeleton NO + O 2 NO 2 -balanced chemical equation : 2NO + O 2 2NO 2 2NO + O 2 2NO 2 recipe for the chemical reaction Gives the specific amounts of each reactant and product so that all atoms are accounted for (Law of Conservation of Mass) -integers placed in from of the formula or a chemical symbol for an element. -show the ratios between the various compounds ( how much of each) State of Matter: Letters which indicate whether it is gas (g), liquid (l), solid (s) or dissolved in water (aq) What is the Law of Conservation of Mass? -mass is conserved in a chemical reaction -the total mass of the products is always equal to the mass of the reactants -atoms are conserved (neither made or destroyed) in al chemical reactions What do the symbols + and mean in equations? -On the left side + means reacts or combines with -On the right side + means plus or and ( means produces ) CH 4 +O 2 H 2 o+co 2 (CH 4 reacts with O 2 and produces H 2 o plus CO 2) 5

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