CHEMICAL BONDING

K. FALING

EDITED: R. BASSON

SUTHERLAND HIGH SCHOOL

GRADE 10

PHYSICAL SCIENCE

TB . 103

HOW DOES BONDING WORK?

• The chemical reaction between elements leads to compounds, which have new

physical and chemical properties.

• A bond is the force that holds atoms together to form molecules. This happens so that the

millions of different substances found on earth can be formed.

• Intermolecular bonds/forces – between MOLECULES

Intramolecular bonds/forces – between ATOMS

• There are ATTRACTIVE forces between the nucleus of one atom (+) and the electrons of

the other atom and there are REPULISIVE forces between the electrons of different atoms.

When the attractive force is GREATER than the REPULSIVE force that exists between them.

• Elements will bond with each other to become stable = full energy levels.

• Only valence electrons are involved in bonding.

TB . 103

3 TYPES OF INTRAMOLECULAR BONDING

1. COVALENT BONDS - Between atoms of non-metals

2. IONIC BONDS - Between atoms of metals and non – metals

3. METALLIC BONDS - Between atoms of metals

O O

Na Cl

Cu Cu

TB . 103

REPRESENTING BONDING

•Bonding is illustrated by using LEWIS DIAGRAMS.

Requirements

• Only valence electrons are drawn.

• Electrons are represented as dots or crosses around

the symbol of the element.

EXAMPLEVALENCE

ELECTRONS?

GROUP

NUMBER?TB . 103

IMPORTANT INFO ABOUT LEWIS DIAGRAMS

• VALENCE ELECTRONS ARE DRAWN.

• THEY ARE REPRESENTED AS DOTS BUT ALSO CONTAINS LINES TO

REPRESENT SHARED PAIRS IN A CHEMICAL BOND.

• EXCESS ELECTRONS THAT FORM LONE PAIRS ARE REPRESENTED AS PAIRS

OF DOTS, AND ARE PLACED NEXT TO THE ATOMS.

• EACH ELEMENT WILL GAIN, LOOSE OR SHARE ELECTRONS UNTIL THEY

HAVE RECEIVED AN OCTET OF ELECTRONS = FULL VALENCE SHELL

ELECTRON CONFIGURATION.

PRACTICEDRAW LEWIS DIAGRAMS FOR THE FOLLOWING STRUCTURES

Ar

H

Ca

Zn

HOMEWORK

EXERCISE 8

1. COVALENT BONDS

• BETWEEN NON-METAL ATOMS

• ORBITALS WITH HALF-FILLED ORBITALS WILL OVERLAP AND ELECTRONS ARE SHARED

• SMALLEST PARTICLE IS A MOLECULE

• THE TYPE OF COVALENT BOND IS DETERMINED BY THE DIFFERENCE IN ELECTRONEGATIVITY

• NON-POLAR COVALENT - DIFFERENCE < 0.9 Attraction is shared equally

• POLAR COVALENT - 0.9 < DIFFERENCE < 1.7 One atom attracts the

shared pair more than the

other.

• IONIC - DIFFERENCE > 1.7

• EXAMPLE:𝐻20

• Single

• Double

• Triple

TB . 104

PRACTICEDRAW LEWIS DIAGRAMS FOR THE FOLLOWING BONDS

Hydrogen 𝐻2

Water 𝐻20

Nitrogen 𝑁2

TB . 104

IONIC BONDS

• OCCUR BETWEEN A METAL AND NON-METAL ATOMS

• INVOLVES THE TRANSFER OF ELECTRONS

• METALS TEND TO GIVE AWAY ELECTRONS AND BECOME POSITIVE IONS (CATIONS) AND THE NON-

METALS TEND TO ACCEPT THE ELECTRONS AND BECOME NEGATIVE IONS (ANIONS)

• SO: METALS – LOW IONISATION ENERGY AND NON-METALS: HIGH ELECTRON AFFINITY.

• THE CATIONS AND ANIONS ATTRACT EACH OTHER WITH STRONG ELECTROSTATIC OR

COULOMBIC FORCES

• LARGE CRYSTAL LATTICES ARE FORMED

• THE SMALLEST PARTICLE MAKING UP AN IONIC CRYSTAL LATTICE IS AN ION

• EXAMPLES INCLUDE: NACℓ; KMNO4; MGSO4; CACO3

TB . 106

DRAWING LEWIS DIAGRAMS THE IONIC BONDS

𝐶𝑙2𝑁𝑎

TB . 106

METALLIC BONDS• OCCUR BETWEEN METAL ATOMS

• THE ATOMIC NUCLEI WITH THE INNER ELECTRON SHELLS ARE TIGHTLY PACKED

• TOGETHER IN AN ORGANISED CRYSTAL STRUCTURE

• THE OUTERMOST ORBITALS OVERLAP

• THE VALENCE ELECTRONS ARE DELOCALISED AND CAN MOVE INTO ADJACENT ORBITALS

OF NEARBY ATOMS.

• THE SMALLEST PARTICLE OF A METALLIC CRYSTAL IS A POSITIVE METAL ION

• EXAMPLE: PIECES OF ZN, FE, CU AND AG

TB . 107

QUICK SUMMARY

Property Ionic bond Covalent

bond

Metallic bond

Smallest particle Ion Molecules Atom

Types of

elements

Metals &

non-metals

Non-metals Metals

How does bond

occur?

Electron

transfer

Sharing of

electrons

Positive atomic

core with sea of

delocalized

electrons

TB . 110

HOMEWORK

EXERCISE 9

• ALL MATTER IS MADE UP OF SMALL PARTICLES CALLED ATOMS

• A MOLECULE (NON-METALS) CONSISTS OF 2 OR MORE ATOMS THAT ARE BOUND

TOGETHER BY STRONG ATTRACTIVE FORCES

• A CHEMICAL COMPOUND IS A GROUP OF TWO OR MORE ATOMS OF DIFFERENT

TYPES THAT ARE HELD TOGETHER BY STRONG FORCES OR BONDS. THESE ATOMS

ALWAYS BOND IN A SPECIFIC RATIO.

TB . 111

• MOLECULAR FORMULA

• The actual number and type of atoms in the compound.

• Example: 02 03 𝐻20 𝐶8𝐻18

• EMPIRICAL FORMULA

• The simplest ratio in which atoms combine.

• STRUCTUAL FORMULA

• Shows the arrangement of the atoms and bonds

TB . 117

BALL AND STICK SPACE FILLING DIAGRAM LEWIS STRUCTURE

TB . 118

HOMEWORK

EXERCISE 10

TEST EXAMPLES

• Molecules (molecular

substances) are due to covalent

bonding.

• Ionic substances are due to ionic

bonding.

When the electrons of atoms are transferred from one atom to

another atom to form positive and negative ions, the ions bond

with ionic bonds and the resulting solid is called an ionic

substance (or salt or ionic compound).

As a general rule ionic substances are usually composed of both

metallic elements (usually forming positive ions) and nonmetallic

elements (usually forming negative ions)

• When metal atoms lose their outer electrons to form a

lattice of regularly spaced positive ions and the outer electrons

form a delocalized “pool” of electrons that surround the positive

ions, the atoms are bonded by metallic bonding and the resulting

collection of atoms is called a metal • Give examples of

molecules based on the above description e.g. • Covalent

molecular structures consist of separate molecules: oxygen,

water, petrol, CO2, S8, C60 (buckminsterfullerene or buckyballs)