1. Ionic and Covalent Bonding Ionic CompoundsCovalent Compounds transfer electronsshare electrons (can form single, double or triple bonds) form ions that combine in formula units atoms share electrons to form molecules hard, crystal latticeusually softer high melting pointslower melting points good conductors of electricity when liquid poor conductors metal plus nonmetaltwo or more nonmetals

2. Why do atoms form bonds at all?

3. Ionic & covalent bonds are formed for the same reason.

4. Ionic compounds transfer electrons.

5. Ionic compounds transfer electrons from a metal to a nonmetal in order to have full outer energy levels. This forms ions with opposite charges. These ions then attract each other to form formula units that arrange themselves into a crystal lattice. The shape of the lattice depends on the compound formed. Table salt, NaCl forms a cube-shaped crystal.

6. Sapphire (Al & O) forms a hexagonal crystal like the one shown here. The actual arrangement of the ions is shown here. A crystal ‘standing up’ is shown on the left. On the right is a view of the crystal from the end, just like the real one above.

7. The atoms in covalent compounds share electrons to form molecules with very strong bonds.

8. Covalent compounds share electrons so that each atom can have a full outer energy level. Most of the substances you use everyday are covalent compounds, including you & the food you eat.

9. Covalent compounds can form single, double or triple bonds. Ionic compounds cannot do this. In a double covalent bond, two pairs of electrons are shared. In a single covalent bond, one pair of electrons is shared.

10. In a triple covalent bond, _______ pairs of electrons are shared. Three different covalent compounds are shown below. How do they show single, double and triple bonds?

11. Covalent compounds do not always share their electrons equally. If one atom has a higher electronegativity than the other, then the electrons will spend more time closer to the atom with higher electronegativity. These types of covalent compounds are called polar covalent compounds. Water is an example of a polar covalent compound. The shared electrons spend more time closer to oxygen than the hydrogen. Notice the partial positive & negative charges on the molecule. The symbol δ is used to denote a partial charge. No ions are formed.

12. Covalent compounds that do share their electrons equally are called nonpolar covalent compounds. Hydrogen gas, oxygen gas and methane (the gas used for our Bunsen burners) are examples of nonpolar covalent compounds. δ+ δ-

13. Since there is a little bit of charge on parts of a polar covalent molecule, the opposite charges can attract each other. This is what happens between water molecules. Hydrogen bonding between two water molecules (above) & how lots of water molecules would arrange themselves in liquid water (right).

14. Water expands when it freezes because each molecule is arranged in a lattice due to hydrogen bonding, so there is more empty space between the molecules when frozen in place.

15. To name an ionic compound always write & name the metal first. Then name the nonmetal but add and ide ending to its name. For example; sodium chloride, calcium oxide, potassium iodide When transition metals that can form more than one type of ion are involved, then we must indicate which ion is in the compound. This is done with Roman numerals. The Fe 3+ ion is called iron (III), Cu 1+ is called copper (I). What would Cu 2+ be called? _______________________ What would the name of Cu 2 O be?

16. Name these ionic compounds: a)KBr b)BaO c)Fe 2 O 3 d)CuO e)Al 2 O 3 f)LiF g)MgS h)NaI

17. What does a chemical formula tell us? Fe 2 O 3 1. What elements are in this compound? 2. How many atoms of each element are in this compound? 3. Will the ratio of each atom always be the same for this compound?

18. What is the correct way to write a chemical formula? H 2 SO 4 The 2 and 4 are written as subscripts. The symbol for each element must have correct upper and lowercase letters. CO is not the same as Co

19. You must be able to write the correct formula for any ionic compound. Remember an ionic compound is always a metal and nonmetal. Each atom must be ‘happy’ in the end with a full set of valance electrons. Always write the metal first and then the nonmetal. How would Na and Cl combine? How many valence electrons does Na have? _____ And Cl has ______ valence electrons. What will happen to these electrons? Why? Make a drawing of how these two elements will combine showing the electrons in each energy level. Remember each atom must end up with a full set of valence electrons-a full outer energy level.

20. Sodium will give its one valence electron to chlorine. Each atom now has a full outer energy level. Each ‘atom’ now has a charge so it is called an ion. Why do the atoms now have charges?

21. 1. How will K and Br combine? 2. How will Ca and O combine? 3. How will Al and O combine?

22. Do you always have to draw a picture to figure out how two elements will combine? Fortunately the answer is no. There is a short-cut method called the ‘criss-cross’ method to figure out what the formula should be. Write the metal first with its ionic charge. Write the nonmetal next with its ionic charge. Now cross the charge numbers down across to the other element. Al 3+ O 2- Al 2 O 3

23. Write the correct formula for these ionic compounds. a)Li & Br b)Be & O c)B & O d)Zn (2+) & I

24. Polyatomic ions are several elements covalently bonded that act as if they were one element. They always go around together as buddies. The whole group has a charge and it acts as an ion. Examples include sulfate ion; SO 4 2-, carbonate ion; CO 3 2-, hydroxide ion; OH -. You will need to memorize some of these since they are important in ionic bonding. Most of the polyatomic ions act like nonmetals and form ionic bonds with metals. Examples include CaCO 3, KNO 3, K 2 SO 4, NaOH. When polyatomic ions are in an ionic compound their names are not changed when naming the compound. Calcium carbonate and potassium nitrate are the names of the first two compounds above. What are the names of the other two? _______________________________

25. Write the correct name and formula for the following ionic compounds that include polyatomic ions. a)K & SO 4 2- b)NH 4 + & SO 4 2- c)Al & CO 3 2- d)Mg & NO 3 1-

26. Naming covalent compounds is different from naming ionic compounds. Since covalent compounds can form single, double and triple bonds the same two elements can form several different compounds together. For example both carbon monoxide and carbon dioxide are just carbon and oxygen combined. So we must add prefixes to tell us how many atoms of each element there are in the compound. The prefixes were used to name carbon monoxide and carbon dioxide. The prefixes are listed in your textbook in this chapter. Some rules: if there is only one atom of the first element then it does not receive a prefix. All other elements always receive a prefix. The ide ending is still added. Name these covalent compounds. a)SO 2 b) N 2 O 2 c) SiOd) P 2 O 3

27. How is metallic bonding different from ionic and covalent bonding? ( see next slide) Why are metals malleable while ionic compounds are not? Why are metals such good conductors of electricity? What is an alloy? Why are they used? Bronze is an alloy of tin and _____________ Brass is an alloy of copper and _____________ The main component in steel alloys is ____________

29. What is the correct way to write a chemical reaction? When substances react chemically, the elements combine or recombine to form new compounds with all new properties. However, no atoms or elements ever disappear, or appear from nowhere, so all of them must show up at both the beginning and end of any chemical reaction. 2H 2 + O 2  2H 2 O There are two reactants in this equation, H 2 and O 2. There is one product, water. Notice that an arrow is used to indicate that the reactants go to form the product.