Chapter 8 – Covalent Bonding

Review of Chapter 7

In Chapter 7, we learned about electrons being transferred (“given up” or “stolen away”)

This type of bond between a METAL and NONMETAL is called an IONIC BOND

http://ed.ted.com/lessons/how-atoms-bond-george-zaidan-and-charles-morton

Chapter 8.1 – Molecular Compounds

In this chapter, you will learn about another type of bond in which electrons are shared

Covalent Bonds are atoms held together by SHARING electrons between NONMETALS

Covalent MoleculesA group of atoms joined together by

a covalent bond is called a MOLECULE

Properties of Molecular Compounds

Lower Melting Points than Ionic Compounds

(which means that they are weaker than ionic)

Liquids or gases at room temperature

Molecular FormulasThe Molecular Formula is the formula of a molecular compound

It shows how many atoms of each element a molecule contains

H2O contains 3 atoms (2 atoms of H, 1 atom of O) C2H6 contains 8 atoms (2 atoms of C, 6 atoms of H)

Practice: True or False1. All molecular compounds are composed of

atoms of two or more elements.

2. Molecular compounds are composed of two or more nonmetals.

3. Atoms in molecular compounds exchange electrons.

4. Molecular compounds have higher melting and boiling points than ionic compounds.

Ionic versus CovalentIONIC COVALENT

Name of fundamental particle

Formula Unit Molecule

Bonding Type Transfer e- Share e-

Types of Elements Metal & Nonmetal Nonmetals

Physical State Solid Solid, Liquid, or Gas

Melting Point High (above 300ºC)

Low (below 300 ºC)

Solubility Dissolves in Water Varies

Conductivity Good Poor

Chapter 8.2 – Covalent BondingRemember that ionic compounds transfer electrons in order to attain a noble gas electron configuration Covalent compounds form by sharing

electrons to attain a noble gas electron configuration

Regardless of the type of bond, the Octet Rule still must be obeyed (8 valence electrons)

Single Covalent BondA Single Covalent Bond consists of two atoms held together by sharing 1 pair of electrons (2 e-)

Electron Dot Structure

Double Covalent Bonds

A Double Covalent Bond is a bond that involves 2 shared pairs of electrons (4 e-)

Sometimes atoms attain noble gas configuration by sharing 2 or 3 pairs of electrons

Triple Covalent Bond

A Triple Covalent Bond is a bond that involves 3 shared pairs of electrons (6 e-)

Chapter 8.4 – Polar Bonds and Molecules

There are two types of covalent bonds Nonpolar Covalent Bonds (share equally) Polar Covalent Bonds (share unequally)

Polar Covalent• A Polar Covalent Bond is unequal sharing of electrons between two atoms (HCl)• In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge

Nonpolar Covalent Bond• A Nonpolar Covalent Bond is equal sharing of

electrons between two atoms (Cl2, N2, O2)

Classification of Bonds

You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements

Type of Bond Electronegativity Difference

Nonpolar Covalent 0 0.4

Polar Covalent 0.5 1.9

Ionic 2.0 4.0

• The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.

• Electronegativity decreases down a group and increases left to right across a period.

Electronegativity

PracticeWhat type of bond is HCl? (H = 2.1, Cl = 3.1)

Your Turn To Practice

N(3.0) and H(2.1)

H(2.1) and H(2.1)

Ca(1.0) and Cl(3.0)

Mg(1.2) and O(3.5)

H(2.1) and F(4.0)

Difference = 3.1 – 2.1 = 1.0

Therefore it is polar covalent bond.

Intermolecular forces

Intermolecular attractions are weaker than ionic, and covalent bonds

Besides ionic and covalent bonds, there are also attractions between molecules

Hydrogen Bond A hydrogen bond is the attraction between polar

molecules. It occurs when hydrogen (H) atom in one molecules is attracted to nitrogen (N), oxygen (O) or fluorine (F) in another molecule.

Hydrogen Bond

Hydrogen Bonds have about 5% of the strength of an average covalent bond

Hydrogen Bond is the strongest of all intermolecular forces

Intermolecular forcesHydrogen Bonds

Weak Dipole Forces- van der Waal’s forces

London’s Dispersion forces

Chapter 8.3 – VSPER TheoryValence shell electron pair repulsion (VSEPR) theory

VSEPR Theory

VSEPR Theory predicts the 3D shape of molecules

According to VSEPR, the repulsion of electrons causes the shape of the molecule to adjust so that the electrons are far apart

Shared versus Unshared ElectronsA Shared Pair is a pair of valence electrons that is shared between atoms and participates in the formation of covalent bond

An Unshared Pair is a pair of valence electrons that is not shared between atoms

VSEPR TheoryBoth shared and unshared pairs of

electrons are important in predicting the shapes of molecules

Each bond (single, double, or triple) or unshared pair is considered a steric number

Use the steric number to predict the molecular geometry

Practice

Methane (CH4) – tetrahedral

Ammonia (NH3) – pyramidal

Water (H2O) – bent

Carbon Dioxide (CO2) - linear