1. Ionic Bonding + 

2. Valence Electrons
An atom can have many electrons. How many of them take part in chemical bonding?
The number can vary, but in all cases the same principle is in effect:
The electrons in the highest occupied energy level of an element’s atoms are the ones involved in bonding.
These electrons are called valence electrons.

3. Determining Valence Electrons
The number of valence electrons of an atom is usually obvious from examining the electron configuration of the element.
The valence electrons determine the chemical properties of the element.

4. The Group Number and Valence
For representative elements (s and p blocks) the number of valence electrons is equal to the last digit of the group number:
Group 1 = 1
Group 2 = 2
Group 13 =3
Group 14 = 4
Group 15 = 5
Group 16 = 6
Group 17 = 7
Group 18 has no valence electrons, because they are not generally available for making chemical bonds

6. Electron Dot Structures
Valence electrons are often represented as dots surrounding the element’s symbol.
For example, going across period 2,
All of the elements of a given group (except He) have the same number of electron dots in their structures.

7. The Octet Rule
In 1916, Gilbert Lewis (UC Berkeley) came up with a simple principle to explain why atoms form many kinds of ions and molecules – the octet rule.
The octet rule – atoms in compounds tend to have the electron configuration of a noble gas.

8. How the Octet Rule Works
Remember, each noble gas (except He) has the electron configuration ns2 np6 in its highest energy level.
Metallic elements obey the octet rule by losing electrons.
The loss of valence electrons produces a positive ion – a cation.
Non-metallic elements obey the octet rule by gaining electrons to become negative ions – anions
Non-metals can also share electrons with another non-metals to satisfy the octet rule, making covalent bonds.

9. Some Examples of the Octet Rule in Action
Al and Br2  AlBr3
Na and Cl2  NaCl
In both cases, the metal donates electrons to the non-metal.
The metal forms a positive ion (cation) to form an octet
The non-metal forms a negative ion (anion) to form an octet

10. Ionic Bonding Worksheet
Complete the following table by providing the electron configurations for the outermost energy level, the number of valence electrons, and the electron dot diagrams for each of the elements given.

11. Electron Configuration
Electron Dot Diagrams
Element
Electron Configuration
Valence e-
Electron Dot
Lithium
Nitrogen
Silicon
Bromine

12. Electron Configuration
Write the formula and the complete electron configuration for each of the following:
Formula
Electron Configuration
Sodium ion
Fluoride ion
Potassium ion
Strontium ion
Sulfide ion

13. Atom Ion Na, Na ion Cl, Cl ion P, P ion Ca, Ca ion
Write the electron dot structures for each of the following atom-ion pairs.
Atom
Ion
Na, Na ion
Cl, Cl ion
P, P ion
Ca, Ca ion

14. Representing Ionic Compounds with Lewis Diagrams
Lewis structures are useful tools to keep track of the valence electrons in elements and compounds.
In sodium fluoride, we can represent it in a number of ways: - +
Brackets are often used;
The octet from the lower energy level of the metal is often left out
[Na]+[ ]-

15. Write the electron dot formula for each ion in the ionic compound:
Chemical Formula
Na, F
Mg, Cl
Ca, S

16. K, O
Al, Br
Rb, N
Al, O

17. Properties of Ionic Compounds
Solids at room temperature
Very high melting points (>> 300◦C)
Do not conduct electricity in solid state
Many are highly soluble in water
Solutions of ionic compounds are electrolytes – they conduct electricity

18. Ionic compounds do NOT form molecules!
NaCl – formula unit water – H2O – molecular formula
Chemical structure of ionic compounds are known as formula units – the simplest whole number ratio of the ions.

19. The Octet Rule in Action
sodium, (2-8-1) or 1s2 2s2 2p6 3s1
when it loses its electron, it has an octet in its highest (2nd) energy level.
3s  loss of valence electron
2p         
2s   
1s    +

20. Electron Configurations of Anions
When non-metal atoms gain valence electrons, they become negative ions - anions.
For fluorine (and all group 17 elements) form halide ions:
1s2 2s2 2p5 + e-  1s2 2s2 2p6 an octet in n=2!
e-  2-8
2p      
2s  + e-  
1s   -

21. Models of Ionic Compounds