Unit 4Chemical Bonding

ICPMr. Patel

SWHS

Topic Outline

• Valence electrons• Cations/Anions – The Octet Rule• Metallic Bonding• Ionic Bonding• Covalent Bonding• Nomenclature

A Look Back…

• So far we have covered (and mastered):– Evolution of the Atomic Model• Democritus, Thomson, Rutherford, Bohr, QM

– Bohr Model and Bohr Diagram– Quantum Mechanical Model and Orbitals– Rules of Electron Configuration– Writing Electron Configurations

Electrons

• Chemical reactions are the breaking and forming of bonds

• There are two types of bonds: covalent and ionic (and metallic)

• Bonding involves the movement of electrons

Valence Electrons

• Valence Electron: electrons in the highest occupied level

• These are the electrons that participate in bonding!!!

Valence Electrons

• You do not have to draw a Bohr Model every time you need to determine the VE’s

• The valence electrons (valency) for an atom is the same as the group number

• Note: In general, transition metals have two valence electrons.

Determine the valence electrons for:

1. Ca2. Be3. O4. Si5. H6. Ne7. Ar

1. 22. 23. 64. 45. 16. 107. 10

Lewis Dot Structures

• Show bonding electrons

• These structures show only valence electrons.

• How to draw:– Write Symbol for element– Determine group number– Place that many (group number)

dots around symbol

N

B

Lewis Dot Structures

1 2 3 4 5 6 7 8

Lewis Structures

Draw the Lewis Dot Structure for:

Cs Al

Ge Br

Practice Time!!!

The Octet Rule

• Remember that Noble Gases were very stable– They all have 8 valence electrons (2 for He)– FULL outer shell of electrons

• Every element will try to become like a noble gas

• The Octet Rule – atoms will try to have a full outer shell (= 8 electrons) when bonding

Cations

• Metals tend to lose electrons to have a full outer shell

• Cation – positively charge ion– Results from metals losing electrons

• Naming: element name + ion– Ex: Na = Sodium but Na1+ = sodium ion

Anions

• Nonmetals/Metalloids tend to gain electrons to have a full outer shell

• Cation – positively charge ion– Results from nonmetals gaining electrons

• Naming: element name with –ide ending + ion– Ex: Br = Bromine but Br1- = bromide ion

Cations/Anions

• To determine the charge of an element’s ion, look at the group/column that it is in– Group 1: 1+– Group 2: 2+– Group 3: 3+– Group 4: 0– Group 5: 3-– Group 6: 2-– Group 7: 1-

Lewis Dot Structures for Ions

• Draw the normal Lewis Dot structure for the neutral element

• Add electrons if gained or remove electrons if lost

• Place the appropriate charge

N NNitrogen: Nitride ion:

3-

1. Draw the Lewis Dot Structure for Phosphorus.

2. Will this element for a cation or anion?3. What charge will it have?4. What will be the name of the ion?5. What noble gas is it similar to?6. Draw the Lewis Dot Structure for the ion.

1. Draw the Lewis Dot Structure for Barium.

2. Will this element for a cation or anion?3. What charge will it have?4. What will be the name of the ion?5. What noble gas is it similar to?6. Draw the Lewis Dot Structure for the ion.