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 NaCl The arrow means “produces” or “yields”.

Making compounds using Lewis structures:

Sodium has one valence electron, chlorine has seven.

Na + Cl ------> Na ClSodium 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.

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 Na2O. The subscript 2 means there are two sodiums.

The same rules hold true for sodium phosphide.

3Na + P ------> Na P

The formula for sodium phosphide is Na3P.(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