1. Notes – Combining Atoms to Make Compounds Compound – a combination of two or more elements whose atoms are bonded together to form a new substance. Example: Sodium + chlorine produces sodium chloride. Na + Cl  NaClThe arrow means “produces” or “yields”. Making compounds using Lewis structures: Sodium has one valence electron, chlorine has seven. Na +Cl------>Na Cl Sodium donates its one valence electron to chlorine to form a bond. The new substance is called sodium chloride, a compound. Now, the valence orbitals of both atoms (now ions) are full.

2. Many compounds are made of different atoms in different combinations. For example, sodium chloride has one atom each of sodium & chlorine. But some compounds the ratio is not 1:1. Example: Sodium and oxygen Na + O ------> Na O We still need one more electron to fill the valence orbitals, so let’s add another sodium. Na + Na O ------>Na ONa Notice how we rearranged the electrons to accommodate the second sodium on the opposite side of the oxygen. The formula for this compound is Na 2 O. The subscript 2 means there are two sodiums.

3. The same rules hold true for sodium phosphide. 3Na + P ------> Na P The formula for sodium phosphide is Na 3 P. (Actually the electrons are all the same; the colors are for keeping track.) Assignment: For Period 2 on the periodic table, make compounds from the following. Show the recations as in the above examples. Write their Lewis structures, formulas and names. Note: in the compound, the name for the negative ion assumes the “–ide” ending. Group one + group 17 Group one + group 16 Group one + group 15 Group one + group 14 (assume group 14 element forms a negative ion) Group 13 + group 17 Group 13 + group 15 Group two + group 17 Group two + group 16 Group two + group 14