Aims

Class workCovalent Bonds

LO’s• What are covalent bonds?

Write it down!! Page 45© C Meyer

All• Know what a covalent bond is• Know covalent bonds can be

either small or large moleculesMost• Draw dot and cross diagrams for

covalent bondSome• Draw dot and cross diagrams for

complex molecules

Aims

Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:

1. Lithium (2.1) and fluorine (2.7)2. Magnesium (2.8.2) and chlorine (2.8.7)3. Aluminium (2.8.3) and fluorine (2.7)

Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by

the non-metal

Homework

Sodium Fluoride

Sodium atom Fluorineatom

Copy the diagram and draw another box showing the electron configuration in sodium fluoride.

2.82.8

FNa

2.8.1. 2.7

Na+ F-

+ -

Bonding in Aluminium Fluoride

In aluminium fluoride it is the non-metal atoms that we need more of.

F

F

F

Al Al

F

F

F

Brackets??

COVALENT BONDING

Hydrogen chloride

molecule

HClCount the electrons in the outer shell of

each atom. Are they full?Click

Cl

What is differentto ionic bonding??

H

Cl17

H1

What are covalent bonds?Info

Box

m1

Now lets look at a more complicated molecule

MethaneMethane

Click

Methane (found in natural gas)

CH4

Info

Box

H1

C6

C

H

m1

Title - Covalent compounds

• Formed when non-metal atoms react together.

• Atoms share outer shell electrons.• Shared electrons count towards

filling shells of both atoms to make full 2, 8, 8 pattern.

What are covalent bonds?

m3

You need to know different ways to show covalent bonds:-

• A pair of electrons shared like this is a covalent bondcovalent bond..

• Shown in full bonding diagrams (see figure 1). Or just shown as a pair of electrons (xx) or even just a line (see figure 2).

m4

FX

X F FF-Figure 1 Figure 2

Ways to show covalent bonds

What are covalent bonds?

Small covalent structures

• Can be simple!• Sometimes just a few atoms join together in

this way. • This produces small covalent molecules –

often known as simple molecular structures.

a simple molecularstructure

covalent bonds

Giant covalent structures

• Can be complex!!• Sometimes millions of atoms are

joined together by covalent bonds. • This produces a rigid 3-D network

called a giant latticegiant lattice..

a giant lattice

covalent bonds

Covalent bonding and electron structures

• Covalent bonding wants outer electron shells that are completely full.

• Done by sharing electrons where shared electrons are in outer shells of both atoms.

• Can be done with more than 2 atoms

Cl Cl C

H

H H

H

N

H

HH Cl H

Covalent bonding in chlorine

Chlorine (2.8.7) needs 1 more electron to attain a full electron shell.

Cl

(2,8,7)

Cl

(2,8,7)

Cl

(2,8,8)

Cl

(2,8,8)

Draw it!Cl-Cl

Covalent bonding in hydrogen chloride

Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. Another example

H

(2)

Cl

(2,8,8)

H-ClCl

(2,8,7)

H

(1)

Electronic structure of H and Cl??

Electronic structure of HCl??

m2

Covalent bonding in water

What are we going to do with water??Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more.

O H

H

O H

H

O

H

H

Electronic structure of H and O??

• Hydrogen (1) needs 1 more electron.

• How many does nitrogen (2.5) need?

• How many hydrogens per 1 nitrogen?

• Draw bonding diagrams for ammonia.

N H

H

HN H

H

H

3

3

• Hydrogen (1) needs 1 more electron.

• How many does carbon (2.4) need to make 8?

• How many hydrogens per 1 carbon?

• Draw bonding diagrams for methane.

4

4

C H

H

H

H

C H

H

H

H

How could we draw this with lines?

Covalent bonding - multiple bonds

• Mostly electrons are shared as pairs.• In some compounds they are shared in

fours or even sixes.• This gives rise to double and triple

covalent bonds.• Again, each pair of electrons is often

represented by a single line when doing simple diagrams of molecules.

Cl-ClSingle bond

O=ODouble bond

N=NTriple bond

Covalent bonding in oxygen

Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell.

OO O=O

OO

4 electrons

Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond.Draw a bonding diagram of nitrogen.

6 electrons

NN

N N

N=N

Giant covalent structures: diamond

• One form of carbon is diamond.

• Each diamond consists of millions of carbon atoms bonded into a single giant structure.

• It is veryvery hard.

Diamondstrong

covalentbonds

carbon atoms

Giant covalent structures: sand

• Sand is an impure form of silicon dioxide.

• Although it is a compound, it has a giant covalent structure with certain similarities to diamond.

silicon atoms

oxygen atoms

Ionic or covalent bonds??1. Methane2. Sodium Chloride3. Oxygen4. Water5. Magnesium Oxide6. Carbon7. Calcium Chloride8. Explain covalent bonding

What have I learnt?

What have I learnt?

The End