Focus on Valence Electrons:

Draw valence for Na and Cl:

Na Cl

What will happen when the two elements are combined?

Na will transfer1 electron to Cl

Now, both atoms have full valence!

Na+1 Cl-1

Opposite charges attract and ionic

bond forms between Na & Cl

To write compound:

1 atom of Na needed for every 1 atom of Cl.

So, compound formula = NaCl

This is onemolecule of NaCl

What happens when Na and Ca combine together?

Write the ions for Na and Ca:

Na+1 and Ca+2

So, both ions are positive and so would repel each other

Both atoms are trying to lose electrons.

• What is the easiest way for potassium (K) to follow the Octet Rule?

Lose 1 electron

• What is potassium’s oxidation number?

+1

• What is the easiest way for nitrogen (N) to follow the Octet Rule?

Add 3 electrons

• What is nitrogen’s oxidation number?

-3

Draw the valence of 3 K and 3 N atoms:

K

K

K

N

N

N

What will happen when you combine these two elements?

K loses1 electron

to N

This K atom has a full valence

But, this N atom does NOT have a

full valence

So, another Katom will lose

an electron to N

This K atom has a full valence

How do you determine the compound formula?

How many atomsare left with full

valence Theseare the atoms in

one molecule

Always write POSITIVE ion

first!Compound Formula = K3N