COVALENT BONDING DAY 1

Ionic Bonding vs Covalent BondingWhile we have been writing Ionic bonds as single formulas (ex. NaCl), there is no such thing as a single molecule of NaCl

Ionic bonds keep repeatingto form a crystal, with thecation and anion repeatingagain and again.

Ionic Bonding vs Covalent BondingThe big difference between ionic and covalent is that covalent molecules are individual molecules

Covalent Bonds

Covalent bonds are formed when two or more atoms (usually non-metals) SHARE electrons

Atoms share electrons instead of giving or taking because there is a small difference (or no difference) in electronegativity

Lewis Structures

• Shows the arrangement of valence electrons in a bond

• Electrons are not transferred using arrows, but drawn in-between two atoms to show that they are shared

IONIC COVALENT

Steps for Drawing Lewis Structures1. Add up the total number of valence electrons from

the formula.2. Arrange the atoms so there is a central atom with

the rest surrounding it.3. Draw in single bonds between the atoms using 2

electrons per bond. 4. Now figure out how many electrons are left over.

Fill in leftover electrons around each atom to give them each 8 electrons.• Having 8 Electrons is known as having a “full octet”• Hydrogen can only have 2 electrons- is still full

Example: CH4

Step 1: Add up the total number of valence electrons from the formula.CH4 = 1 C and 4 H’s

C = 4 electronsH = 1 electron x 4 = 4 electronsTotal = 8 Valence Electrons

Example: CH4

Step 2: Arrange the atoms so there is a central atom with the rest surrounding it.• This is usually the first atom in the formula• Hydrogen is NEVER a central atom

H

H C H

H

Example: CH4

Step 3: Draw in single bonds between the atoms using 2 electrons per bond.

Example: CH4

Step 4: Figure out how many electrons are left over. Fill in leftover electrons around each atom to give them a full octet.

Started with 8 Electrons to work withUsed 8 Electrons for initial bonds = 0 Electrons left

Don’t need to fill in any leftover electronsCarbon has 8 electrons around itHydrogen has 2 electrons around it

Lewis Structures

If you have enough electrons to create all of the bonds and give every atom a full octet (2 for Hydrogen, 8 for the rest) with no electrons left over then you have the right structure.• Too few electrons– you will need a double or

triple bond• Too many electrons– double check your math!

Practice

CF4 NH3 H2O

CCl4 CH2F2 HF PBr3

C2H6 H2 SiCl4 H2S

COVALENT BONDS DAY 2

Write the Lewis Structure for SO2

What’s the problem?

What if we don’t have enough?

•If you do not have enough electrons, you need to add double bond(s) and/or triple bond(s)•Don’t go too fast – try ONE double bond first, and if that doesn’t work try another double bond or try a triple bond instead.

Let’s try SO2 again…

General InformationAlways try a formula with single bonds first and count how many electrons you used…•If you have enough for all single bonds and dots you are fine•If you used 2 more electrons than you had available you need a double bond•If you used 4 more electrons then you had available you need 2 double bonds OR a triple bond

Hydrogen can only have 1 single bond, it will NEVER have a double bond or triple bond

Few more practice problems

GeO SiO2 C2H2Cl2

Polyatomic Ions• Still draw lewis structures the same way for polyatomic ions• The charge on the polyatomic ion gets added or subtracted to

the total number of valence electrons you have to work with!

• Polyatomic Ions with a negative charge: Add that many electrons to the total at the beginning• Add because negative charge means it has extra electrons

Example: SO42- Total Valence Electrons = 30

Valence Electrons: (add charge) +2S = 6 New Total = 32O = 6 x 4 = 24

Polyatomic Ions• Polyatomic Ions with a positive charge: Subtract electrons

from the beginning total.• Subtract because positive charge means it has lost electrons

Example: NH4+1 Total Valence Electrons = 9

Valence Electrons: (subtract charge) -1N = 5 New Total = 8H = 1 x 4 = 4

Draw the lewis structure for…SO3

2-

Valence Electrons:S = O =