Drawing Lewis Structures “valence dot diagrams”

The valence shell holds up to 8 electrons.

0. Determine the number of valence electrons.

1. Write the element’s symbol.2. Add one electron to each

side.3. Then double up the electrons

as necessary.4. Any single electrons are

available for bonding.

How many unpaired electrons?

Practicing Lewis StructuresDraw:Chlorine, Chlorine Ion

Sodium, Sodium ion

Oxygen, Oxygen ion

Neon

Draw Lewis dot diagrams for

Oxygen and Sodium (determine valence electrons, distribute dots

appropriately)

Covalent compounds are also known as:

Molecular Compounds

CH 6 Covalent Compounds

Molecular Compounds

Ch 5 Chemical Names and Formulas5

Consist of two or more non-metals 1.2.

Naming Covalent Compounds(molecular compounds)

Ch 5 Chemical Names and Formulas6

Ionic charge does NOT dictate ratio of atoms.

The name of the compound must indicate the number of each element .

Compounds of Carbon and Oxygen

Ch 5 Chemical Names and Formulas7

Both are non-metalsCombine in multiple

ratios“carbon oxide” does not provide enough

information to give the correct ratio of “C” and “O”.

Carbon and Oxygen combine to form the following molecular compounds:

COCO2

Use of Numeric Prefixes1st element: if more than 1

2nd element: always

Ch 5 Chemical Names and Formulas8

COCO2

Read “Naming Covalent Compounds” Pgs. 206-207

Then complete the following chart:

Formula Ionic or Covalent?

Name

CO

CO2

N2O

KCl

PCl5

MgCl2

P4O6

Number Prefixes 1-10

Ch 5 Chemical Names and Formulas10

MonoDiTriTetraPentaHexaHeptaOctaNonaDeca

BF3

N2O

Covalent Bonding

The more civilized way to form a relationship

Comparing Ionic to CovalentIonicElectrons are “stolen” or

move to another atom to complete octets

A net charge is created.The ions are attracted to

opposite charge forming an electrically neutral “salt”

Usually a metal and non-metal like Sodium and Chlorine…NaCl

CovalentAtomic Orbitals [valence]

overlap and hybridize to form molecular orbitals.

Electrons are “shared” to complete octets.

2 non-metals like Carbon and Oxygen….CO2

Shared Electrons…Sharing occurs to form a

stable gas configuration (full octet)

It takes two electrons to form a bond

These bonding electrons are called a “shared pair”

The pair counts toward a full octet for each atom. Draw out the valence

dot diagrams for Fluorine and Chlorine

How many electrons do each need for a full octet?

1e- needed 1e- neededWhy not share a pair??

The line represents a bond, consisting of 2 electrons. This shared pair counts for both Cl and F

Shared pairs vs. unshared pairs.

Bonding TendenciesFamily Number of

valence electrons

Electrons needed to make an

octet

Number of bonds formed

Halogens 7 1 1

Oxygen

Nitrogen

Carbon

Hydrogen 1For H and He, an “octet” is

only 2 electrons

Drawing “Lewis Structures”Valence Dot Diagrams

1. Count the total number of valence electrons.2. Connect each atom using single bonds.

The first atom is usually central to the structure

Halogens are usually terminal (end atoms) Hydrogen is always terminal.

3. Add lone pairs to each atom in order to get a full octet.

CCl4 H2O NH3

Multiple bonds: double, tripleIf there are not enough

electrons to make every atom single bonded, you will need to use double or triple bonds.

For every 2 electrons you are “short”, you will need one more bond.

H2CO

Double and Triple bondsDouble bonds use 2

shared pairsTriple bonds use 3

shared pairs

Carbon Dioxide CO2

Nitrogen (gas) N2

Draw Lewis structures for:

Oxygen gas

NI3

Lewis structures…resonanceResonance helps explain

the true structure when 2 or more equally valid structures can be drawn for a molecule.

Resonance structures have identical arrangements of atoms, they differ in distribution of electrons.

Draw 03 (ozone)

What type of bonds does ozone have?

The bond length shows that there the ozone bonds are neither the single nor the double bond length.

The length is in-between single and double

This tells us that it is a hybrid, “1 ½ bond”

Drawing resonance structures is the chemists way to show this.

Type of bond Length in picometers

O-O oxygen-oxygen single bond 148

O=O oxygen-oxygen double bond

121

Oxygen-Oxygen bond in OZONE 128

Resonance explained

Draw Lewis Structures for:

Carbonate ion, CO3

2-

1. Count up available electrons.

2. Identify the central atom, then single bond everything.

3. Assign lone pairs so all atoms have 8 electrons

4. Compare amount used to amount available.

5. If you used 2 many, retry with multiple bonds.

6. Determine if resonance is necessary.

Covalent Bonds…shared electronsNon-polar covalent, (Pure covalent)

Electronegativity values

Polar Covalent

Polar Covalent2 different atoms are

covalently bonded.The bond is a Polar Bond

The more electronegative atom pulls the shared electrons closer to it’s nucleus.

H and Cl

H and C

F and Cl

Find the electronegativity differences in the following pairs of atoms. Check pg 194 Figure 6

WaterFind the

Electronegativity difference for H and O

Draw Water

Label the partial – and partial + charge

The polar molecules cause special properties

Dipole interactions:A molecule that is polar is said

to be a polar molecule…DIPOLE

Hydrogen Bonding:Occurs w/ water. The partial positive H is

attracted to the lone pairs of oxygen.Use : δ+ (delta)

Molecular ShapesIdeal Geometries of molecules

with a Central Atom.

1. Determine the number of bonds to the central atom.

2. Determine the number of lone pairs around the central atom.

Put this information into the “AXE” formula to help categorize the molecule.

A = Represents the Central Atom

X# = Bonded atoms to central atom

E# = Lone pairs around central atom

X + E = 4

AXE formula Shape Example AX4 Methane

CH4

AX3E Ammonia NH3

AX4 WaterH2O

VSEPR Valence Shell Electron Pair Repulsion Theory

Bonding Angles for a tetrahedral are ______°

Example: Methane , CH4 [AX4]

Draw Ammonia, NH3

AXE:

Bond anglesMethane:Ammonia:

Draw Water (lewis dot)

What effect do unshared pairs have?

X + E < 4AXE formula Shape Example

AX2 CO2

AX2E GeF2

AX3 BeF3

Molecules with 2 atoms are linear

Warm UPWhat are the bond angles for the following molecules:

MethaneAmmoniaWaterCarbon Dioxide

Exceptions to the octet rule: Odd # of electrons

If the total number of valence electrons is odd you end up with a free radical. This unpaired electron is extremely reactive.

Examples: NO NO2