1. BONDING

2. Types of Bonding Covalent Bonding Ionic Bonding Metallic Bonding
Nonmetal with nonmetal
Ionic Bonding
Metal with nonmetal
Metallic Bonding
Metal with metal

3. Covalent Bonds Why do covalent bonds occur?
The electrons occupy a larger ‘cloud’ in the covalent bond than in the individual atomic orbitals. This larger cloud is more stable than the smaller clouds.

4. Covalent Bonds
Covalent bonds result when electrons in atomic orbitals are combined into a bonding orbital.
Each bonding orbital can contain two electrons.
Each atom has a stable ‘octet’ of electrons.

5. Lewis Dot Structures
A simple method of accounting for electrons in compounds. Only valence electrons are shown. Dots are added as orbitals are filled.
Valence electrons are represented using dots ( • )
Example 1: Lewis dot structure of a nitrogen atom
Nitrogen has 5 valence electrons: N
Example 2: Lewis dot structure of a chloride anion
Chloride anion has 8 valence electrons: Cl • • • • • – • • •

6. Lewis Electron Dot (cont)
Step Step Step Step 4
Step Step Step Step 8

7. Lewis Dot Structures

8. Problems Write Lewis dot structures for the following atoms:
beryllium b) neon
strontium d) aluminum

9. Lewis Dot Structures
The Lewis Dot picture can help one understand the formation of ionic compounds.
Consider potassium bromide (KBr):
element dot structure ion dot structure fate
K K K+ K loses electron
Br Br Br- Br- gains electron • • • • • • • • • • •
K Br  K+ Br- • • • • • • •

10. Covalent Bonds
Examples: combine hydrogen atoms with oxygen, nitrogen, or carbon atoms to form stable molecules

11. Steps to Write a Lewis Dot Structure
Sum up all valence electrons of all atoms.
Choose a central atom (all compounds exhibit symmetry)
Place electrons(dots) around central atom to obey octet rule.
Place remaining electrons around outer atoms to obey octet rule (remember exceptions to the octet rule!)

12. PRACTICE!!
Water
Ammonia
Methane

13. Exceptions to the Octet Rule
Elements on the 3rd row or beyond often violate the octet rule.
These elements have empty d-orbitals that can participate in bonding.
Boron molecules often have empty atomic orbitals, and do not have a stable octet of electrons.
Now, use the boards to draw the LDS!

14. + Multiple Covalent Bonds O = O
In some cases, stable molecules are formed by sharing more than two electrons between two atoms.
Consider the oxygen molecule (O2) , which we all breathe in and depend on for life:
double bond
lone pairs
• •
• • +
O = O
• •
• •
The molecule O2 contains a double bond that is represented with two lines connecting the atoms. Each bond contains two electrons, so a total of four electrons are counted in this bond.
Each oxygen atom has a stable octet of electrons.

15. Multiple Covalent Bonds
Ethylene (C2H4):
two carbon atoms, each contribute four valence electrons = 8
four hydrogen atoms, each contribute one valence electron= 4
12 e- total

16. Chemical Formulas • • • • H H
A molecular formula indicates the atoms and numbers of each atom that contribute to form the molecule.
The molecular formula does not provide information about the connectivity of the atoms in the molecule.
Structural formulas show how atoms are connected in the molecule.
H2O vs O
* A molecular formula differs from a formula unit (for ionic compounds) since it is not the simplest ratio of atoms that make up the substance
• •
• • H H
Ex: The molecule ethylene contains two carbon atoms and four hydrogen atoms in each molecule. Its molecular formula is C2H4, not CH2

17. Lewis Dot Structure Practice
trichlorophosphide, PCl3
ozone, O3 (be careful)

18. Lewis Dot Structure Practice
carbon dioxide, CO2
nitrate ion, NO3-