GCSE Chemistry: Atomic Structure, Periodic Table, and Bonding

A comprehensive set of practice questions covering mixtures, separation techniques, the periodic table, bonding, states of matter, and quantitative chemistry based on the lecture notes.

What is the fundamental difference between the components of a mixture and a compound?

In a mixture, there are no chemical bonds between the different parts, whereas compounds are formed by chemical bonds.

List four physical methods used to separate mixtures.

Filtration, crystallisation, simple distillation, and fractional distillation.

In paper chromatography, why must the baseline be drawn in pencil rather than pen?

Pencil marks are insoluble and will not dissolve in the solvent, whereas ink would dissolve and interfere with the results.

What is the 'solvent front' in the context of chromatography?

The point the solvent has reached as it moves up the paper.

Explain the difference between a soluble and an insoluble solid.

A soluble solid can dissolve in a liquid to form a solution, while an insoluble solid will not dissolve.

When should crystallisation be used instead of evaporation to separate a salt from a solution?

Crystallisation should be used if the salt decomposes when heated or if large crystals are required.

Outline the four steps for separating rock salt (a mixture of salt and sand).

1) Grind the mixture to decrease crystal size. 2) Stir the mixture into water to dissolve the salt. 3) Filter the mixture to remove the sand. 4) Evaporate the water from the salt solution to form dry crystals.

When is fractional distillation preferred over simple distillation?

Fractional distillation is used when the mixture contains liquids with similar boiling points.

How does the fractionating column work in a laboratory distillation setup?

The column is cooler at the top; liquids with higher boiling points condense partway up the column and run back down, while only the liquid with the lowest boiling point reaches the top when the temperature matches its boiling point.

Why do metals tend to form positive ions during reactions?

Metals generally have few outer electrons or have outer electrons far from the nucleus (weak attraction), meaning it takes less energy to lose them than to gain more.

Describe the special properties of transition metals.

They can form ions with different charges (e.g. $Cu^+$ and $Cu^{2+}$), form colourful compounds, and act as effective catalysts.

State the trends observed as you go down Group 1 (alkali metals).

They have higher relative atomic masses, lower melting and boiling points, and become more reactive.

What products are formed when an alkali metal reacts with water?

A metal hydroxide and hydrogen gas.

Provide the balanced symbol equation for the reaction of sodium with water.

$$2Na_{(s)} + 2H_2O_{(l)} \rightarrow 2NaOH_{(aq)} + H_{2(g)}$$

Describe the trends observed as you go down Group 7 (halogens).

They have higher relative atomic masses, higher melting and boiling points, and become less reactive.

What is a displacement reaction in the context of Group 7?

A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt.

Why are Group 0 elements (noble gases) inert?

They have a full outer shell of electrons (a stable electronic structure), meaning they do not need to lose or gain electrons.

How do the boiling points of noble gases change as relative atomic mass increases?

The boiling points increase because the increasing number of electrons leads to greater intermolecular forces that must be overcome.

Which groups in the periodic table are most likely to form ions?

Groups 1 and 2 (metals) and Groups 6 and 7 (non-metals).

What is the definition of an ionic bond?

The strong electrostatic attraction between oppositely charged ions.

State the limitations of dot and cross diagrams for representing ionic compounds.

They do not show the structure of the compound, the size of the ions, or how they are arranged.

Why do ionic compounds conduct electricity when molten or dissolved, but not when solid?

In solid form, ions are held in a fixed lattice; when molten or dissolved, the ions are free to move and carry electric charge.

Define a covalent bond.

A strong electrostatic attraction between the positively charged nuclei of the bonded atoms and a shared pair of electrons.

Compare the strength of covalent bonds versus intermolecular forces in simple molecular substances.

Covalent bonds within the molecules are very strong, while the intermolecular forces between the molecules are very weak.

Why do polymers generally have higher melting points than simple covalent molecules?

The intermolecular forces between polymer molecules are larger because the molecules are much longer, requiring more energy to break.

Describe the structure of diamond.

Each carbon atom forms four covalent bonds in a very rigid giant covalent structure, making it extremely hard.

Why can graphite conduct electricity?

Each carbon atom only forms three covalent bonds, leaving one delocalised electron per atom that is free to move and carry charge.

What is graphene?

A single layer of graphite that is one atom thick, making it a two-dimensional substance.

Name two potential uses for fullerenes.

Delivering drugs into the body (by 'caging' molecules) and acting as industrial catalysts due to their large surface area.

What makes metals malleable?

Metals have layers of atoms that can slide over each other.

Why are alloys harder than pure metals?

Different sized atoms in the alloy distort the regular layers of metal atoms, making it more difficult for them to slide over each other.

Define the three states of matter using the particle theory model.

Solids have strong forces and a fixed lattice; liquids have weak forces and random arrangement but stick together; gases have very weak forces and are far apart.

What is a nanoparticle?

A particle with a diameter between $1\text{ nm}$ ($1 \times 10^{-9}\text{ m}$) and $100\text{ nm}$ ($1 \times 10^{-7}\text{ m}$).

How does the surface area to volume ratio change as a particle decreases in size?

The surface area to volume ratio increases.

What is the formula for calculating the percentage mass of an element in a compound?

$$\text{Percentage mass} = \frac{A_r \times \text{number of atoms of that element}}{M_r \text{ of the compound}} \times 100$$

State the value of the Avogadro constant.

$$6.02 \times 10^{23}$$

What is the formula used to calculate the number of moles from mass?

$$\text{Number of moles} = \frac{\text{mass in g}}{M_r}$$

What volume does one mole of any gas occupy at room temperature and pressure ($20\text{ }^\text{o}\text{C}$ and $1\text{ atm}$)?

$$24\text{ dm}^3$$

What is the formula for calculating atom economy?

$$\text{Atom economy} = \frac{M_r \text{ of desired products}}{M_r \text{ of all reactants}} \times 100$$

List three reasons why the percentage yield of a reaction is always less than 100%.

1) The reaction is reversible and doesn't go to completion. 2) Side reactions occur with impurities or air. 3) Product is lost during separation or transfer between containers.