COVALENT COMPOUNDS

COVALENT COMPOUNDS1. Usually soft and squishy

2. Not soluble in water

3. Does not conduct electricity

4. Low melting points

5. Low boiling points

TWO TYPES OF BONDS Ionic: Electrons are transferred

Covalent: Electrons are shared Non-polar covalent: equally shared

Polar Covalent: unevenly shared

NAMING COVALENT COMPOUNDS

NAMING COMPOUNDSNonmetal – Nonmetal

USE PREFIXES!

1. Change the ending of the second word to -ide

2. No mono on the first word

3. Drop any double vowels

COVALENT PREFIXESNumber of Atoms Prefix

1 Mono-2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-

10 Deca-

THE PREFIX TELLS YOU HOW MANY ATOMS YOU

HAVE!NO CRISS CROSS!!!!

EXAMPLES

1. CO

2. CO2

3. SO2

4. SO3

5. N2H4

6. N2O3

1. Carbon Monoxide

2. Carbon Dioxide

3. Sulfur Dioxide

4. Sulfur Trioxide

5. Dinitrogen Tetrahydride

6. Dinitrogen Trioxide

EXAMPLES

1. disilicon hexafluoride

2. tricarbon octachloride

3. phosphorus pentabromide

4. nitrogen monoxide

5. selenium difluoride

6. dihydrogen monoxide

1. Si2F6

2. C2Cl8

3. PBr5

4. NO

5. SeF2

6. H2O

EMPIRICAL AND MOLECULAR FORMULAS

Define Empirical Formula:A chemical formula that gives the simplest whole-number ratio of the elements in the formula.

Which of the following is an empirical formula? CO2 C2O4

Fe2Cl6 FeCl3

Define Molecular Formula:A chemical formula that gives the actual number of the elements in the molecular compound. For the following molecular formulas, write the empirical formula:

Molecular: Empirical: C2H4 C6H12O6

C9H21O6N3

LEWIS STRUCTURES

F F

LEWIS STRUCTURES FOR COMPOUNDS The pair of dots between two symbols

represents the shared pair. How many shared pairs does each fluorine have

below?

An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom.

F F

LEWIS STRUCTURES The shared pair of electrons is often

replaced by a long dash.

Each dash represents TWO electrons

F F+

7e- 7e-

F F

8e- 8e-

F F

F F

Lewis structure of F2

lone pairslone pairs

lone pairslone pairs

single covalent bond

single covalent bond

WHY SHOULD TWO ATOMS SHARE ELECTRONS?To get a valence of 8 electrons!

HC

HCH

H

MULTIPLE COVALENT BONDS double bond:

covalent bond in which two pairs of electrons are shared between two atoms

shown by two side-by-side pairs of dots or by two parallel dashes

MULTIPLE COVALENT BONDS triple bond:

covalent bond in which three pairs of electrons are shared between two atoms

shown by three side-by-side pairs of dots or by three parallel dashes

STEPS FOR DRAWING LEWIS STRUCTURES1. Draw the Lewis Dot diagram for each individual

atom

2. Count up the number of valence electrons

3. Connect the atoms together to pair up the electrons (put atoms that can make the most connections in the center)

4. Once all electrons are paired, recount electrons to double check total valence

PRACTICEDraw the Lewis Structure for HBr

1. H Br2. 1 + 7 = 8

3. H — Br

4. 2 + 6 = 8

BOND POLARITY

Which element is the most electronegative?

H F

Fluorine- Has 7 valence e- and wants 8

ability of an atom to attract electrons

REVIEW:WHAT IS ELECTRONEGATIVITY?

H F FH

electron richregion

electron poorregion

e- riche- poor

d+ d-

POLAR BOND :covalent bond with greater electron density around one of the two atoms

1

2

3 4 5 6 7 8 9 10 11 12

13 14 15 16 17

18

NonpolarCovalentshare e-

Polar Covalentpartial transfer of e-

Ionictransfer e-

Increasing difference in electronegativity

Electronegativity Difference Bond Type

0 to 0.3 Nonpolar Covalent

0.4 to 1.6 Polar Covalent

1.7 Ionic

WHAT TYPE OF BOND IS IT?

Classify the following bonds as ionic, polar covalent,or covalent:

Cs – 0.7 Cl – 3.0 3.0 – 0.7 = 2.3 Ionic

H – 2.1 S – 2.5 2.5 – 2.1 = 0.4 Polar Covalent

Cl – 3.0 N – 3.0 3.0 – 3.0 = 0 Nonpolar Covalent

Cs to Cl

H to S

Cl to N

INTERMOLECULAR FORCES

Intermolecular forces: attractive forces between molecules.

Intramolecular forces: attractive forces within a molecule (the bonds)

intramolecular forces are much stronger than intermolecular forces

Intramolecular Forces

Intramolecular Forces

Intermolecular Forces

DIPOLES What is a dipole?

A polar molecule Uneven sharing of electrons so

there is a separation of charge

DIPOLE-DIPOLE FORCES

Attraction between two polar molecules

— + — +

HYDROGEN BONDING Special type of Dipole – Dipole

Attraction between:Hydrogen and Nitrogen/Oxygen/Fluorine

DIPOLE – INDUCED DIPOLE Attraction between one polar and one

nonpolar molecule

— +

— + — +

Electrons shift toward

positive end of dipole

LONDON DISPERSION FORCES Attraction between two nonpolar molecules

— + — +

Electrons become

uneven and form a dipole

STRENGTH OF IMF Hydrogen Bond Dipole – Dipole Dipole – Induced Dipole London Dispersion Forces

strongest

weakest

WHAT DOES IMF EFFECT? Viscosity Surface Tension Cohesion/Adhesion Boiling Point

Stronger IMF Higher Viscosity

VISCOSITY Measures a fluid’s resistance to flow

Stronger IMF Higher Surface Tension

SURFACE TENSION result of an imbalance of forces at the

surface of a liquid.

Adhesion

Cohesion

ADHESION AND COHESION Cohesion:

intermolecular attraction between like molecules Adhesion:

intermolecular attraction between unlike molecules

BOILING POINT Point at which liquid particles escape the

surface of the liquid into the gas phase

Stronger IMF Higher Boiling Point