Chemistry - Topic 2 — Bonding, Structure and Properties

How are particles arranged in solids?

Close together in fixed positions; they vibrate but cannot move past each other.

How do particles behave in a liquid?

Close together but able to move past each other.

How do particles behave in a gas?

Far apart, moving rapidly and randomly.

What do (s), (l), (g) and (aq) mean?

Solid, liquid, gas and dissolved in water (aqueous).

Why do substances have different melting points?

Different strengths of forces or bonds between particles need different energy.

What limits the simple particle model?

Solid spheres omit forces, their true structure and particle properties.

When is a substance liquid relative to melting/boiling points?

Above its melting point but below its boiling point.

Name the three main types of strong chemical bonding.

Ionic, covalent and metallic.

What is ionic bonding?

Strong electrostatic attraction between oppositely charged ions.

How are positive ions formed in ionic bonding?

Metal atoms lose outer-shell electrons.

How are negative ions formed in ionic bonding?

Non-metal atoms gain electrons.

Which charges do Group 1 and Group 2 metal ions form?

Group 1: +1; Group 2: +2.

Which charges do Group 6 and Group 7 non-metal ions form?

Group 6: −2; Group 7: −1.

What is the formula of magnesium chloride?

MgCl₂: Mg²⁺ is balanced by two Cl⁻ ions.

What is the formula of aluminium oxide?

Al₂O₃: two Al³⁺ ions balance three O²⁻ ions.

What structure do solid ionic compounds have?

A giant ionic lattice of alternating positive and negative ions.

Why do ionic compounds have high melting points?

Many strong electrostatic attractions require much energy to overcome.

When do ionic compounds conduct electricity?

When molten or dissolved, because ions can move and carry charge.

Why does solid sodium chloride not conduct electricity?

Its ions are held in fixed positions in the lattice.

What should ionic dot-and-cross diagrams show?

Transferred outer electrons and resulting ions in brackets with charges.

What is a limitation of dot-and-cross diagrams?

They show electron transfer but not actual 3D size or spatial arrangement.

How do you determine the formula of an ionic compound?

Balance the positive and negative charges to give an overall neutral formula.

What is a covalent bond?

A shared pair of electrons attracted to the nuclei of both atoms.

What type of elements usually form covalent bonds?

Non-metals bonded to other non-metals.

How many covalent bonds normally form around carbon?

Four.

How many covalent bonds normally form around oxygen?

Two.

How many covalent bonds normally form around nitrogen?

Three.

How many covalent bonds normally form around hydrogen or chlorine?

One each.

What is a single, double and triple bond?

One, two and three shared pairs of electrons respectively.

Which molecules contain double or triple bonds: O₂ and N₂?

O₂ has a double bond; N₂ has a triple bond.

What is the formula of methane?

CH₄: carbon makes four single covalent bonds to hydrogen.

What is the formula of ammonia?

NH₃: nitrogen makes three single covalent bonds to hydrogen.

How many bonds are in a water molecule?

Two O–H single covalent bonds.

How are polymers represented?

A repeating unit in brackets, with n showing many repeats.

Why do small covalent molecules usually melt or boil at low temperatures?

Only weak intermolecular forces need to be overcome.

What is overcome when a simple molecular substance boils?

Intermolecular forces, not the covalent bonds within molecules.

Why do simple molecular substances not conduct electricity?

They have no free charged particles to carry current.

Why can larger simple molecules have higher boiling points?

They usually experience stronger intermolecular forces.

Why are many polymers solids at room temperature?

Large molecules have relatively strong intermolecular forces.

What joins the atoms along a polymer chain?

Strong covalent bonds.

Why do giant covalent substances have very high melting points?

Many strong covalent bonds must be broken.

Why is diamond very hard?

Each carbon bonds to four others in a rigid 3D network.

Why does diamond not conduct electricity?

It has no delocalised electrons or mobile ions.

How many covalent bonds does each carbon make in graphite?

Three, in flat hexagonal layers.

Why is graphite slippery?

Layers slide over each other because forces between layers are weak.

Why does graphite conduct electricity?

Each carbon provides a delocalised electron able to carry charge.

What is the bonding in silicon dioxide?

A giant covalent network with strong bonds throughout.

What is graphene?

A single atom-thick layer of carbon atoms arranged in hexagons.

Why does graphene conduct electricity?

Delocalised electrons can move across the layer.

Why can graphene strengthen composites?

It is strong with a high tensile strength and low mass.

What are fullerenes?

Hollow carbon molecules shaped as cages or tubes.

What is a carbon nanotube?

A cylindrical fullerene with a very high length-to-diameter ratio.

Give one use of fullerenes or nanotubes.

Drug delivery, catalysts or reinforcing lightweight composites.

What is metallic bonding?

Electrostatic attraction between positive metal ions and delocalised electrons.

Why can metals conduct electricity?

Delocalised electrons move and carry charge.

Why do metals conduct thermal energy well?

Mobile delocalised electrons transfer energy rapidly.

Why can pure metals be bent?

Layers of ions slide while attraction to electrons remains.

Why are alloys usually harder than pure metals?

Different-sized atoms distort layers, making sliding more difficult.

Why do most metals have high melting points?

Strong metallic bonding needs substantial energy to overcome.

What size range defines nanoparticles?

Approximately 1–100 nanometres (nm).

How many metres are in one nanometre?

1 × 10⁻⁹ metres.

Why do nanoparticles have a large surface-area-to-volume ratio?

Much of their material is exposed at the surface relative to their volume.

What happens to SA:V when the side length of a cube halves?

Its surface-area-to-volume ratio doubles.

How do you calculate SA:V for a cube of side a?

Surface area = 6a²; volume = a³; SA:V = 6/a.

Give uses of nanoparticles.

Catalysts, cosmetics, sunscreens, electronics and some medical applications.

What is a potential disadvantage of nanoparticles?

Their small size may cause unknown health or environmental risks.

Why can less nanoparticle material be needed for a task?

Its larger surface-area-to-volume ratio increases exposed active surface.