Unit 2 Notes: Chemistry

Drawing Lewis Structures and predicting formulas of covalent compounds

Atoms bonds to form molecules◦ Hydrogen and Oxygen bond to form water

We learned that all atoms have electrons but only electrons in their outtermost orbital determine how a bond takes place.◦ These are called valence electrons

For Practice 1: Lewis diagram for single atoms (Book chapter 12 p. 413)

The group number determines how many valence electrons an atom has.◦ Group 1A = 1 valence electrons◦ Group 2A = 2 valence electrons…◦ Group 8A = 8 valence electrons

Only exception is helium which only has 2 valence electrons. ◦ This makes sense since helium only has 2

electrons

For Practice 1: Lewis diagram for single atoms (Book chapter 12 p. 413)

Lewis Structures for first 10 compounds

All bonds between atoms is due to the sharing or paring of 2 electrons between 2 different atoms◦ Example H:O The hydrogen and oxygen bond by

2 electrons. Octet rule: All atoms want to the Lewis

structure of a noble gas, which have 8 valence electrons

Duet rule: Hydrogen on wants 2 electrons to be like helium

For Practice 2: Lewis diagram for single bonded molecules (Book chapter 12 p. 416)

How to draw a structure for a compound. Example: H2O◦ Count total amount of valence electrons

H=1x2, O=6X1, 2+6 = 8

◦ Write the center atom (the first non hydrogen element

O

◦ Using 2 electrons, bond the remaining atoms to the center atom(s)

H:O:H

◦ Using remainder valence electrons, complete the octet rule/duet rules

For Practice 2: Lewis diagram for single bonded molecules (Book chapter 12 p. 416)

Hence Lewis structure of water

Double bond = the sharing of 4 electrons between atoms◦ C::C

Triple bond = sharing of 6 electrons between atoms◦ C:::C

Lone pair electrons: Two electrons that are on an atom but not bonding that atom to another one.

For Practice 3: Lewis diagram for double and troiuple bonded molecules (Book chapter 12 p. 416)

All compounds need to follow the octet rule. Lone pair electrons can become double and triple bonds to follow this octet rule.

For Practice 3: Lewis diagram for double and triple bonded molecules (Book chapter 12 p. 416)

Draw the Lewis structure of CO2

◦ Total valence electrons = 4 + 2X6 = 16◦ Center atom carbon with 2 oxygen's attached

O:C:O 16-4 = 12 electrons remain

◦ Complete the octet rule for the outer atoms

◦ Now no electrons left so lone pairs need to be shares between bonds

For Practice 3: Lewis diagram for double and troiuple bonded molecules (Book chapter 12 p. 416)

Lewis Structure of CO2

HCN Total valence = 10 Carbon center atom Connect outside atoms to center atom

◦ H:C:N◦ 10-4=6

After putting the remaining 6 electrons around Nitrogen, I need to make a triple bond to complete with octete rule with Carbon

H:C:::N

Triple Bonds Same Thing

For polyatomics (multiple atoms) ions, drawing the Lewis structure is the same thing only you add electrons when the charge is negative and subtract electrons when charge is positive.

Polyatomic Ions

Polyatomic Ions

Polyatomic Ions