Focus on Valence Electrons:

1
Focus on Valence Electrons

• Draw valence for Na and Cl

What will happen when the two elements are
combined?
Na1
Cl-1
This is one molecule of NaCl
Na
Cl
Now, both atoms have full valence!
Na will transfer 1 electron to Cl
To write compound 1 atom of Na needed for every
1 atom of Cl. So, compound formula NaCl
Opposite charges attract and ionic bond forms
between Na Cl
2
What happens when Na and Ca combine together?

• Write the ions for Na and Ca
• Na1 and Ca2
• So, both ions are positive and so would repel
  each other
• Both atoms are trying to lose electrons.

3

• What is the easiest way for potassium (K) to
  follow the Octet Rule?
• Lose 1 electron
• What is potassiums oxidation number?
• 1
• What is the easiest way for nitrogen (N) to
  follow the Octet Rule?
• Add 3 electrons
• What is nitrogens oxidation number?
• -3

4
Draw the valence of 3 K and 3 N atoms
What will happen when you combine these two
elements?
How do you determine the compound formula?
K loses 1 electron to N
This K atom has a full valence
How many atoms are left with full valence ?
These are the atoms in one molecule
This K atom has a full valence
K
N
N
K
But, this N atom does NOT have a full valence
K
N
So, another K atom will lose an electron to N
Always write POSITIVE ion first!
Compound Formula K3N