Understanding Understanding Chemical Chemical ReactionsReactions

Lesson Covalent bondingLesson Covalent bonding

Covalent bondingCovalent bondingREMEMBER!• Two non-metals can both gain

electrons by sharing!• If their outer shells overlap, they

share some of each other’s electrons.• This ‘satisfies’ both atoms.

Covalent bondingCovalent bonding

Shared electrons form covalent bonds between non-metal atoms.

Another example of Another example of covalent bondingcovalent bonding

• Chlorine does not exist as single atoms.

• Virtually the only gases that exist as single atoms are the Noble gases – why?

Another example of Another example of covalent bondingcovalent bonding

• Chlorine Cl has 7 electrons in its outer shell.

• It needs 1 more electron to fill it.

• How can it manage to do this?

Another example of Another example of covalent bondingcovalent bonding

• Like many gases, it is di-atomic.

• Two Cl atoms bond together to make a Cl2 molecule.

Another example of Another example of covalent bondingcovalent bonding

Three ways to show the covalent bond in Cl2. The right-hand one is a ‘dot and cross’ diagram (showing the outer electrons only).

Another example of Another example of covalent bondingcovalent bonding

Count the electrons in the outer shell of each chlorine atom. Do they both have 8 electrons? Are they both ‘satisfied’?

OxygenOxygen• Oxygen, like hydrogen and chlorine

exists as a di-atomic molecule.• Each oxygen atom has six electrons

in the outer shell – two electrons short of the stable electron arrangement of a Noble gas.

OxygenOxygen

OxygenOxygen• Each oxygen atom gives two

electrons to be shared, so this makes two covalent bonds (called a double bond).

OxygenOxygen

Properties of covalent Properties of covalent compoundscompounds

Substance Appearance Does it melt?

Does it dissolve in water?

Does it conduct electricity?

Graphite

Candle wax

Sand

Glucose

Sulphur

Iodine

Properties of covalent compounds involving 2, 3, 4 Properties of covalent compounds involving 2, 3, 4 or 5 non-metal atoms bonded together to form a or 5 non-metal atoms bonded together to form a

molecule.molecule.

• They are usually gases (think methane, ammonia)

• Their melting points are low• They are poor conductors of

electricity• They do not dissolve easily in water

(except HCl)• They dissolve well in organic solvents

Properties of covalent compounds involving 2, 3, 4 Properties of covalent compounds involving 2, 3, 4 or 5 non-metal atoms bonded together to form a or 5 non-metal atoms bonded together to form a

molecule.molecule.

• The bonds within the covalent molecules are very strong.

• But the particles have no electric charge

• There are only very weak forces between the molecules.

• This explains their low melting and boiling points.

Properties of covalent compounds involving 2, 3, 4 Properties of covalent compounds involving 2, 3, 4 or 5 non-metal atoms bonded together to form a or 5 non-metal atoms bonded together to form a

molecule.molecule.

• Small molecules form gases at room temperature.

• Larger molecules may be liquids or soft solids.

Properties of covalent compounds involving 2, 3, 4 Properties of covalent compounds involving 2, 3, 4 or 5 non-metal atoms bonded together to form a or 5 non-metal atoms bonded together to form a

molecule.molecule.

• Sulphur reacts with oxygen to form sulphur dioxide (SO2) molecules. Is this likely to be a solid, liquid or gas?

Giant covalent structuresGiant covalent structures• Use the CHEMISTRY text book

• Read page 120 – 121 (up to but not including the section on ‘Plastics’).

• Answer the following questions in your own words…..

Giant covalent structuresGiant covalent structures• What is a ‘giant molecular structure’?• Give three examples of giant molecular

structures.• What are allotropes?• Describe the properties of diamond.• Describe the properties of graphite.• Explain why these two allotropes of carbon

have such different properties.