CHEM TOPIC 2

What are the three states of matter?

Solid, liquid, and gas.

What do state symbols (s), (l), (g), and (aq) represent in chemical equations?

(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water).

What happens to energy and particle arrangement during melting and boiling?

Energy is absorbed from the surroundings to overcome the forces of attraction between particles, changing a solid into a liquid (melting) or a liquid into a gas (boiling).

What are the main limitations of the simple particle model (spheres representing particles)?

It assumes all particles are solid, spherical, and inelastic, and it does not show the forces between particles, the space between them, or the fact that real particles are not spheres.

What are the three main types of chemical bonds?

Ionic bonds, covalent bonds, and metallic bonds.

Which types of elements form ionic bonds?

Metals combined with non-metals.

What happens to electrons during ionic bonding?

Electrons are transferred from the metal atoms to the non-metal atoms.

What charge do metal atoms form when they become ions, and why?

Positive ions (cations), because they lose electrons, leaving more protons than electrons.

What charge do non-metal atoms form when they become ions, and why?

Negative ions (anions), because they gain electrons, leaving more electrons than protons.

What are the ion charges formed by elements in Groups 1, 2, 6, and 7?

Group 1 = 1+, Group 2 = 2+, Group 6 = 2-, Group 7 = 1-.

Describe the structure of a giant ionic lattice.

A regular 3D arrangement of alternating positive and negative ions held together by strong electrostatic forces of attraction acting in all directions.

Why do ionic compounds have high melting and boiling points?

A large amount of thermal energy is required to overcome the strong electrostatic forces of attraction between oppositely charged ions.

Why can ionic compounds conduct electricity only when molten or dissolved in water, but not as solids?

In a solid, ions are fixed in position within the lattice and cannot move. When molten or dissolved, the ions are free to move and can carry electrical charge.

What are the main limitations of 2D and 3D dot-and-cross diagrams for ionic compounds?

• Scale: They only show a small, isolated section, failing to represent that a giant lattice continues endlessly in all directions.

• Bonds: They can make bonds look like solid objects instead of invisible forces of attraction.

• No 3D shape (2D diagrams): They are completely flat, so they don't show how the ions are actually arranged in three-dimensional space.

• No true size: They don't show the relative sizes of the ions (how big one ion is compared to another).

Which types of elements form covalent bonds?

Non-metals combined with non-metals.

What is a covalent bond?

A shared pair of electrons between two non-metal atoms.

Name the 8 small covalent molecules required for AQA GCSE Chemistry.

Hydrogen (H2), Chlorine (Cl2), Hydrogen chloride (HCl), Water (H2O), Ammonia (NH3), Methane (CH4), Oxygen (O2), Nitrogen (N2).

What type of covalent bonds are found in Oxygen (O2) and Nitrogen (N2)?

Oxygen contains a double covalent bond (O=O); Nitrogen contains a triple covalent bond (N#N).

Why do small covalent molecules have low melting and boiling points?

Although the covalent bonds inside the molecules are very strong, the weak intermolecular forces between molecules require very little energy to overcome.

What happens to the melting and boiling points of simple molecular substances as the molecules get larger?

They increase, because larger molecules have stronger intermolecular forces, requiring more energy to break.

Why do small covalent molecules not conduct electricity?

They do not have an overall electrical charge, free-moving ions, or delocalized electrons to carry charge.

What is a polymer and why are they solid at room temperature?

Polymers are very long chains of repeating units (monomers) joined by strong covalent bonds. Because they are massive molecules, the intermolecular forces between polymer chains are relatively strong, making them solids at room temp.

Describe the structure and properties of Diamond.

Each carbon atom forms 4 strong covalent bonds in a giant tetrahedral lattice. It is extremely hard, has a very high melting point, and does not conduct electricity because there are no free electrons.

Describe the structure of Graphite.

Each carbon atom forms 3 strong covalent bonds in hexagonal sheets/layers, leaving 1 delocalized electron per carbon atom. There are no covalent bonds between the layers.

Why is graphite soft/slippery and why can it conduct electricity?

Soft/slippery: Weak intermolecular forces between layers allow them to slide over each other. Electrical conductivity: Delocalized electrons are free to move through the structure carrying charge.

What is Graphene?

A single, 1-atom-thick layer of graphite. It is extremely strong, lightweight, flexible, and an excellent conductor of electricity, making it useful in electronics.

What are Fullerenes and give an example?

Hollow molecules of carbon atoms shaped as closed cages or tubes (based on hexagonal, pentagon, or heptagon rings). Example: Buckminsterfullerene (C60).

What are Carbon Nanotubes and what are their key properties?

Cylindrical fullerenes with a very high length-to-diameter ratio. They have high tensile strength (hard to break when pulled) and high electrical/thermal conductivity.

What are the main uses of fullerenes and carbon nanotubes?

Drug delivery in the body, lubricants, catalysts, and strengthening materials (like in tennis rackets or electronics).

Describe the structure of a giant metallic lattice.

A regular lattice of positive metal ions surrounded by a sea of delocalized (free) electrons originating from the outer shell of metal atoms.

Why are metals good conductors of electricity and thermal energy?

The delocalized electrons are free to move throughout the entire metallic structure, rapidly transferring thermal energy and carrying electrical current.

Delocalized electrons absorb thermal energy, move rapidly through the structure, and collide with other particles to transfer the heat

Why are pure metals malleable and ductile?

The atoms/positive ions are arranged in uniform, regular layers that can easily slide over one another when a force is applied, without breaking the metallic bond.

What is an alloy, and why are alloys harder than pure metals?

An alloy is a mixture of a metal with other elements (usually other metals or carbon). Alloys are harder than pure metals because the different-sized atoms distort the regular layers of the metal lattice, preventing the layers from sliding over each other.

What size are nanoparticles, and how do their surface area to volume ratios compare to bulk materials? (HT Only)

Nanoparticles are 1 to 100 nm in size. As particle size decreases by a factor of 10, the surface area-to-volume ratio increases by a factor of 10, giving them a huge SA:V ratio so smaller quantities are needed as more surface materials are on the surface to react.

What are the main uses and potential risks of nanoparticles? (HT Only)

Uses: Medicine (drug delivery), cosmetics, suncreams, electronics, catalysts. Risks: Could be absorbed into the skin/bloodstream, potential long-term toxicity to health or the environment.

intermoluclar forces

weak forces of attraction between separate molecules

what is forces of attraction

A pull that holds particles together

What’s electrostatic force

The force of attraction between opposite electric charges (positive and negative).

what does molecular substance mean

a substance made of small molecules, where the atoms inside each molecule are joined by strong covalent bonds, and the molecules are held to each other by weak intermolecular forces.