4.2 bonding, structure and properties of matter

gcse aqa chemistry

What is the calculation for relative atomic mass?

(mass number of isotope 1 x natural abundance of isotope 1) + (mass number of isotope 2 x natural abundance of isotope 2) / 100

What happens in ionic bonding?

A metal transfers electrons to a non-metal - the metal loses electrons to become a cation (positive) and the non-metal gains those electrons to become an anion (negative), meaning they both have full outer shell. They are held together by ionic bonding, the electrostatic attraction between oppositely charged ions.

What holds ions together in ionic bonding?

Oppositely charged electrostatic forces

What is the structure of ionic bonding?

Giant ionic lattice

Explain the giant ionic lattice structure

Ionic solids form regular crystals, with a shape reflecting the regular arrangement of ions within them. Each positive ion attracts the negative ion 6 ways and each negative ion attracts the positive ion in 6 ways, creating a regular cubic structure which is the lattice structure

What are the limitations of dot and cross diagrams in showing ionic and covalent bonding?

They do not show how the ions are arranged or the electrostatic forces holding the ions together/don’t show the shape of the lattice

What are the limitations of ball and stick and 3D diagrams in showing ionic and covalent bonding?

They are not to scale and give no information on the electrostatic forces holding the ions together

What are the limitations of 2D diagrams in showing ionic bonding?

They don’t show multiple layers of a giant ionic lattice or correct sizings

What are the limitations of 2D diagrams in showing covalent bonding?

They don’t show the correct sizing of the molecules or bonds

Explain the properties of ionic compounds using their structure

There are many strong bonds between ions which require a lot of energy to break, giving it high melting and boiling points. When they’re solid, the ions are held in place/together, meaning they can’t conduct electricity, however when they’re liquid or dissolved in water/polar solvent they can as they’re free to move and hold a charge

How do you use charges/valencies of ions to find the empirical formula?

Using the charges, figure out how many of each ion will be required to give the formula an overall charge of 0 (e.g. K⁺¹ and O^-2 = K₂O) OR use the valencies to drop and swap

What is covalent bonding?

The bonding between two or more non-metals to form molecules, involves the sharing of electrons, electrostatic attraction between protons in nuclei of each atom and shared pair of electrons

What are the two structures of covalent bonding?

Simple covalent molecule and giant covalent structure (diamond, graphite and silicon dioxide)

Do simple covalent structures have strong covalent bonds?

Yes

Do simple covalent bonds have strong intermolecular forces between molecules?

No - therefore they have low melting and boiling points

Do simple covalent molecules conduct electricity?

No - they don’t have charged particles or delocalised electrons

Define allotropes and give 2 examples of carbon’s allotropes

Allotropes are different structural forms of the same element in the same physical state, e.g. graphite and diamond for carbon

What is metallic bonding?

The electrostatic attraction between the positive metal cations and the delocalised electrons

Give an example of metallic bonding (the structure/formula)

Mg⁺² + 2e^-

Explain metallic bonding in a giant metallic structure.

A regular arrangement of metal cations with delocalised electrons inbetween the ions, with no bonds between the ions and electrons

Explain the differences in chemical and physical properties between metals and non-metals.

Metals are conductors, malleable, strong, shiny and ductile, and form cations (positive). Non metals are insulators, brittle, dull and weak, and form anions (negative).

Explain the properties of pure metals in terms of their structure and bonding.

They have delocalised electrons which carry charges, so they’re conductors. Regular arrangement allows metal ions to slip and slide, making them malleable and ductile. Electrostatic forces between metal ions and delocalised electrons are strong, so they have high melting and boiling points.

What are alloys?

Alloys are metal + another metal or metal + carbon, so they aren’t pure metals.

Why are alloys harder than pure metals?

Alloys contain different sized atoms, so the layers are distorted, making it harder for them to slide over each other. This makes them harder.

What are bronze, gold, steel and aluminium alloys used for?

Bronze - door handles. Gold - jewellery. Steel - knives. Aluminium - kitchen utensils.

Explain properties of graphene in terms of its structure and bonding.

Graphene is a single sheet of graphite, meaning it’s only one atom thick and is therefore a 2D structure. The carbon atoms are joined in hexagons which strong covalent bonds between them which are hard to break down, giving it a high boiling point, and each have one delocalised electron, meaning it can conduct electricity and thermal energy. It’s very light and can be added to composite materials to make them stronger without adding much weight

Explain properties of graphite in terms of its structure and bonding

Graphite is formed of hexagonal sheets of carbon atoms which each form 3 strong covalent bonds, meaning the layers are free to slip and slide over each other as there are no strong bonds between the layers, however it has a high boiling point as the covalent bonds require a lot of energy to break. Only 3 of carbon’s 4 electrons are used, so each carbon atom has a delocalised electron, meaning graphite can conduct electricity and thermal energy

Explain properties of diamond in terms of its structure and bonding

Diamond has a giant covalent structure with carbon atoms that each form four strong covalent bonds, meaning diamond is very hard and the bonds need a lot of energy to break, so has a high melting point. It doesn’t conduct electricity as there are no ions or free electrons

What are fullerenes?

Fullerenes are molecules of carbon, usually shaped like closed tubes or hollow balls.

What are fullerenes used for?

They’re catalysts, and can be used to cage other molecules, deliver drugs to the body and can form nanotubes, which are tiny carbon cylinders that are conductors and are used in nanotechnology.

Why does a single atom not have the same properties as bulk materials?

Properties are due to the forces and relationships between atoms, ions or molecules, so a single atom cannot have properties as they don’t have other atoms to interact with

What are the dimensions/sizes of nanoparticles?

Nanoparticles have a diameter of 1-100nm, and contain only a few hundred atoms

What are the properties of glass ceramics?

Brittle, transparent, strong

What are the properties of clay ceramics?

Brittle, strong

What are the properties of polymers?

Depends on what it’s made of, so can be flexible, strong, rigid, solid etc

What are the properties of composites?

Depend on reinforcement and matrix materials, but usually strong, stiff and light

What is an isotope?

Isotopes are different forms of the same element which all have the same number of protons but different numbers of neurons

What are nanoparticles?

Small particles ranging from 1 to 100nm in diameter with very large surface area to volume ratios

What are uses of nanoparticles (with mini explanations)?

Can make new catalysts (large SA:V), can be used in medications (tiny so easier absorbed into body, deliver drugs directly to cells), electronics (can conduct electricity, used in tiny electric circuits), cosmetics (nanoparticles in face creams, moisturisers etc are much better/deeper absorbed by skin), deodorants (silver nanoparticles have antibacterial properties), sun creams (titanium & zinc oxides much more effective at blocking UV rays, nanoparticle forms of these are clear)

What are the disadvantages of using nanoparticles?

Could catalyse harmful reactions in body, small size makes them easy to breathe in which could damage the lungs, nanoscience still in early stages of discovery/development so a lot of unknowns, could damage environment, large SA:V means a spark near them could cause an explosion

Nanometre to micrometre

Divide by 1000

Micrometre to nanometre

Multiply by 1000