Structure and Bonding Chemistry

AQA GCSE year 10

What are the 3 types of strong chemical bonds?

• Ionic

• Covalent

• Metallic

What is ionic bonding?

Force of (electrostatic) attraction between oppositely charged ions (metal + non-metal)

What is covalent bonding?

Atoms, specifically non-metals, that share pair(s) of electrons

What is metallic bonding?

Strong electrostatic attraction between a sea of negative delocalised electrons and positive metal ions. (metal + metal)

When does ionic bonding occur?

In compounds formed from metals combined with non-metals

When does covalent bonding occur?

In non-metallic elements and in compounds of non-metals

When does metallic bonding occur?

In metallic elements and alloys

Describe ionic structures

• Giant structure of ions

• Held together by strong electrostatic forces of attraction in all directions between oppositely charged ions

• These forces act in all directions in the lattice and this is called ionic bonding

• This forms a giant ionic lattice

Give 3 examples of giant covalent structures

• Diamond

• Graphite

• Silicon dioxide

What changes about the properties of group 7 elements going down the group?

Further down =:

• Higher relative molecular mass

• Higher melting point

• Higher boiling point

• Lower reactivity

Describe the structure of metals

• Consists of giant structures of positive ions arranged in a regular pattern, or neat layers (lattice).

• Electrons in the outer shell of metal ions are delocalised and so are free to move through the whole structure

• The sharing of delocalised electrons gives rise to strong metallic bonds

• This forms a giant metallic lattice

Describe simple covalent structures

• There are strong covalent bonds within the molecules (each atom belongs to each atom)

• There are weaker intermolecular forces between the molecules

Describe the structure of a giant covalent structure

• All atoms are linked to other atoms by strong covalent bonds

• Solids with very high melting points, a lot of energy is required to overcome the covalent bonds

• These bonds must be overcome to melt or boil these substances

What takes place at the melting point?

• Melting and freezing

What takes place at the boiling point?

Boiling and condensing

What does the amount of energy needed to change state depend on?

The strength of the forces between the particles of the substance

How does a change of state happen in simple molecular (simple covalent) structures

• While the covalent bond within the molecules is strong, this is not broken during changes of state.

• Instead, the weak, intermolecular forces are overcome (which requires little energy so simple molecular structures are usually gases or liquids)

What does the nature of the particles involved in a change of state depend on?

• Type of bonding

• Structure of substance

What are the limitations of the simple particle model?

• There are no forces between spheres

• All particles are represented as spheres

• The spheres are solid

What are some properties of ionic compounds and why?

• High melting and boiling point because of the large amounts of energy needed to break the many strong bonds

• When melted or dissolved in water, conduct electricity because the ions are free to move and so charge can flow

What state are small molecules (simple molecular)?

Usually gases or liquids that have relatively low melting and boiling points

Why are small molecules (simple molecular) usually gases or liquids?

• Only have weak intermolecular forces

• These are overcome when the substance melts or boils, requiring very little energy

• Intermolecular forces increase with size of the molecules so larger molecules have higher melting and boiling points

Do small molecules (simple molecular) conduct electricity and why?

No because there are no free electrons, no ions and a neutral charge (charges balance out unlike how in giant lattices the charge isn’t specifically to another ion but rather all around iyk what i mean)

Describe the structure of polymers

• Very large molecules

• Atoms within molecules are linked by very strong covalent bonds

• Intermolecular forces between molecules are relatively strong and so these substances are solid at room temp.

Why are metals more malleable than alloys?

• Layers of atoms are able to slide over each other

• So they can be bent and shaped (malleable)

• Different sizes of atoms in alloys distort the layers making it more difficult for them to slide over each other

• So alloys are harder than pure metals

Why are metals good conductors of electricity?

Delocalised electrons in the metal are free to carry charge through the metal when a voltage is applied

Why are metals good thermal conductors?

Because there are many delocalised electrons that can move freely and transfer heat energy throughout the structure (by vibrating, creating a chain reaction).

Describe the structure and properties of diamond

• Each carbon atom forms 4 covalent bonds with other carbon atoms in a giant covalent structure

• Very hard

• High melting point

• Doesn’t conduct electricity

Describe the structure and properties of graphite

• Each carbon atom forms 3 covalent bonds with 3 other carbon atoms, forming layers of hexagonal rings

• So high melting point

• Layers are free to slide over each other because there are no covalent bonds between the layers, just relatively weak intermolecular forces

• So soft and slippery

• 1 electron per atom is delocalised

• So conducts thermal energy and electricity

What is graphene?

A single layer of graphite (1 atom thick)

What are fullerenes? (check)

A layer of graphene formed as a sphere.

Molecules of carbon atoms with hollow shapes. ← check

Describe the structure of fullerenes

They are molecules of carbon atoms with hollow shapes.

• Based on hexagonal rings of carbon

• May also contain rings with 5 or 7 carbon atoms

What was the first fullerene to be discovered?

• Buckminsterfullerene

• Spherical shape

What are the properties of carbon nanotubes?

• Cylindrical fullerenes

• High tensile strength (if you pull from both sides ig, idk. like stretching a rubber band)

• High electrical and thermal conductivity

What are some uses of fullerenes?

• Drug delivery in the body

• Lubricants

• Catalysts

What are some uses of carbon nanotubes?

Reinforcing materials e.g. in tennis rackets

How big is a nanometre?

1 × 10^-9 m

How big is the nucleus of an atom?

1 × 10^-14 m

How big is the radius of an atom?

1 × 10^-10 m OR 0.1nm

How big are nanoparticles?

Between 1-100nm

How big are fine particles (also called PM2.5)?

Diameters between 100-2500nm

How big are coarse particles (also called PM10)?

Diameters between 2,500 and 10,000nm

(often referred to as dust)

What happens to the surface area:volume ratio of a cube if the side decreases by a factor of 10

The ratio increases by a factor of 10

Why might nanoparticles have different properties to the same materials in bulk?

Because of their higher surface area:volume ratio

Why might smaller quantities of nanoparticles be as effective as normal particles?

Because of their higher surface area:volume ratio

What are some uses of nanoparticles?

• Controlled drug delivery (in body)

• Synthetic skin

• Electronics

• Cosmetics and sun creams

• Development of new catalysts for fuel cell materials

• In deodorants and fabrics to prevent growth of bacteria

What are some benefits of nanoparticles in sun cream?

• Better skin coverage

• More effective protection from sun’s ultraviolet rays

What are some disadvantages of nanoparticles in sun cream?

• Potential cell damage

• Harmful effects on the environment