Structure and Bonding (3)

Why do elements in groups 1, 2, 6 and 7

readily form ions?

So they become more stable and

achieve the electron structure of the

noble gases (group 8).

What type of ions do elements in group 1

and 2 form?

Cations (positive)

- Group 1 metals will form 1+ ions

- Group 2 metals will form 2+ ions

What type of ions do elements in groups

6 and 7 form?

They are non-metals so form anions

(negative)

- Group 6 will form 2- ions

- Group 7 will form 1- ions

What does it mean if an ionic compound

ends in -ide?

The compound contains 2 elements.

What does it mean if an ionic compound

ends in -ate?

The compound contains at least three

elements, one of which is oxygen.

Describe the structure of an ionic

compound

(LIR)

Lattice structure.

Ions held together by strong electrostatic forces between ions with opposite charges.

Regular arrangement of ions.

What is the chemical formula of sodium

oxide, formed from Na+ and O2-?

Na2O

Charges must balance so 2 sodium ions

are required.

What is the chemical formula of

magnesium hydroxide, formed from Mg2+ and OH-?

Mg(OH)2

Charges must balance so 2 hydroxide

ions are required.

What is a covalent bond?

A bond formed when a pair of electrons is

shared between two atoms.

What forms as a result of covalent

bonding?

A molecule

Draw a dot and cross diagram for the

formation of methane (CH4

True or false?

‘Covalent bonds are weak’

FALSE

Covalent bonds are strong

Which is smaller, an atom or a molecule?

An atom.

Simple molecules consist of atoms

joined by strong covalent bonds within

the molecule.

Why do ionic compounds have high

melting points?

Strong electrostatic attraction between the positive and negative ions requires alot of energy to overcome.

When do ionic compounds conduct electricity and why?

When molten or aqueous (dissolved in water) because the ions are charged and

free to move.

When solid, the ions are fixed in an ionic lattice so they can’t move.

Why do simple molecular compounds

have low melting and boiling points?

They have weak intermolecular forces (forces between molecules) which only

require a little energy to overcome.

Do simple molecular compounds

conduct electricity? Why / why not?

No because there are no charged

particles.

Do giant covalent structures have a high

melting point? Explain your answer.

Yes because they have lots of strong

covalent bonds which require a lot of

energy to break

How do metals conduct electricity and

heat?

The positive ions are fixed in a sea of delocalised electrons.

These electrons are free to move and carry charge/energy.

True or false?

‘Metals are insoluble in water’

TRUE

Name two giant covalent structures

formed from carbon atoms

Graphite

Diamond

Describe the structure of graphite

Each carbon atom bonded to 3 other carbon atoms.

Layers of hexagonal rings of carbon atoms.

Weak intermolecular forces between layers.

One delocalised electron per carbon atom.

Describe and explain the properties of

graphite

Graphite is soft / slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another.

Graphite conducts electricity because there is one delocalised electron per carbon atom. The delocalised electrons are mobile charges.

Describe the structure of diamond

All carbon atom are covalently bonded to four other carbon atoms.

No delocalised electrons.

Describe the properties of diamond

Very hard.

Very high melting point.

Doesn’t conduct electricity as there are

no charged particles.

What are the uses of graphite? Why?

Electrodes because graphite conducts

electricity and has a high melting point.

Lubricant because it’s slippery (the layers

in graphite can slide over each other).

Why is diamond used in cutting tools?

It’s very hard.

What is a fullerene?

A molecule made of carbon shaped like a closed tube or hollow ball

Name two fullerenes

Graphene

C60 (buckminsterfullerene)

What are the properties of the fullerene

C60?

- Slippery due to weak intermolecular forces.

- Low melting point.

- Spherical.

- Strong covalent bonds between carbon atoms in a molecule.

- Large surface area.

What are the properties of graphene?

-High melting point due to covalent

bonding between carbon atoms.

- Conducts electricity because it has

delocalised electrons.

Why is graphene useful in electronics?

It is extremely strong and has delocalised

electrons which are free to move and carry

charge.

It is only one atom thick as it is a single layer of

graphite.

What is a polymer? Name a polymer

Long chain molecules formed from many

monomers.

E.g. poly(ethene)

Draw the structure of poly(ethene)

What bond is formed between carbon

atoms in polymer molecules?

Covalent bonds

What are the properties of metals?

- High melting point.

- Good conductors of electricity.

- High density.

- Malleable and ductile.

- Generally shiny.

Explain why metals are malleable

The atoms are arranged in uniform rows

which can slide over one another.

Explain why metals can conduct

electricity

The electrons in the metal are charges

that can move.

What are the properties of non-metals?

-Low boiling points.

- Brittle when solid.

- Poor conductors of electricity.

List the limitations of the following

models when representing ionic

compounds: dot and cross, 2D diagrams

and 3D diagrams

● Dot and cross - no lattice structure or ionic bonds.

● 2D diagrams - only shows one layer, doesn’t show

formation of ions.

● 3D diagrams - shows spaces between the ions,

doesn’t show charges.

List the limitations of the following

models when representing covalent

molecules: dot and cross and ball and

stick

Dot and cross - doesn’t show relative sizes of

atoms or intermolecular forces.

● Ball and stick - bonds shown as sticks rather

than forces, doesn’t show how covalent bonds

form.