Chemistry igcse revision topic one

Solute

The substance that dissolves into a liquid to form a solution.

Solvent

The liquid in which a solute dissolves.

Solution

A homogeneous mixture formed when a solute dissolves into a solvent without separating out.

Saturated solution

A solution in which the maximum possible amount of solute has dissolved at a specific temperature.

Element

A pure substance composed of only one type of atom that cannot be broken down into simpler substances.

Compound

A substance formed from two or more different elements chemically bonded together.

Mixture

A combination of two or more substances that are physically mingled but not chemically bonded.

Arrangement and movement of particles in a solid

Particles are arranged in a regular lattice, have strong forces of attraction, vibrate about fixed positions, and possess low energy.

Arrangement and movement of particles in a liquid

Particles are randomly arranged and closely packed, have weak forces of attraction, and are free to flow past one another.

Arrangement and movement of particles in a gas

Particles are far apart with very weak forces of attraction, have high energy, and move randomly at high speeds.

Filtration

A separation method used to separate an insoluble solid from a liquid using filter paper and a funnel.

Crystallisation

A separation method used to obtain a soluble solid from a solution by heating gently to concentrate it, cooling to form crystals, and drying.

Simple distillation

A technique used to separate and collect a pure solvent from a solution through boiling followed by condensation.

Fractional distillation

A technique used to separate a mixture of miscible liquids with different boiling points using a fractionating column.

Stationary phase in paper chromatography

The chromatography paper across which the solvent moves.

Mobile phase in paper chromatography

The solvent that travels up the chromatography paper.

$R_f$ value formula

$$\frac{\text{distance moved by substance}}{\text{distance moved by solvent front}}$$

Relative charges of protons, neutrons, and electrons

Proton: $+1$, Neutron: $0$, Electron: $-1$.

Atomic number

The total number of protons present in the nucleus of an atom.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Calculation for the number of neutrons

$$\text{mass number} - \text{atomic number}$$

Isotopes

Atoms of the same element that have the same number of protons and electrons, but a different number of neutrons.

Relationship between electronic configuration and Periodic Table position

The number of outer-shell electrons corresponds to the group number, and the number of occupied shells corresponds to the period number.

Atom

The smallest indivisible particle of an element that cannot be broken down into anything simpler by chemical means.

Molecule

A chemical particle formed from two or more atoms chemically joined together.

Difference in melting points between a pure substance and a mixture

A pure substance melts sharply at a single, fixed temperature, whereas a mixture melts over a range of temperatures.

Melting

The change of state from solid to liquid occurring when particles absorb thermal energy and break out of their fixed positions in a regular lattice.

Freezing

The change of state from liquid to solid occurring when particles lose kinetic energy and become locked into a fixed lattice structure.

Boiling

The rapid change of state from liquid to gas taking place throughout the entire liquid at a fixed temperature.

Condensation

The change of state from gas to liquid occurring when particles cool, lose kinetic energy, and draw closer together under attractive forces.

Sublimation

The phase transition directly from a solid to a gas without passing through the liquid state.

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration as a result of random particle motion.

Particle explanation for the dilution of coloured solutions

The solute particles break apart from one another and distribute uniformly among an increasing volume of solvent particles.

Residue in filtration

The insoluble solid left behind on the filter paper after the liquid passes through.

Filtrate

The liquid or solution that passes through filter paper into the receiving flask.

Reason for drawing the baseline in pencil in paper chromatography

Pencil lead is insoluble in the running solvent, preventing it from dissolving and running up the chromatogram to interfere with sample spots.

Reason the solvent level must start below the baseline in chromatography

To prevent the sample spots from dissolving directly into the solvent reservoir before the solvent travels up the paper.

Distinguishing a pure substance from a mixture on a chromatogram

A pure substance yields only a single spot, whereas a mixture separates into two or more distinct spots.

Relative masses of protons, neutrons, and electrons

Proton: $1$, Neutron: $1$, Electron: $\frac{1}{1836}$ (negligible).

Locations of sub-atomic particles within an atom

Protons and neutrons are bound together in the dense central nucleus, while electrons orbit around the nucleus in shells.

Reason an atom carries an overall neutral charge

The number of positively charged protons is exactly equal to the number of negatively charged electrons, canceling out any net charge.

Maximum electron capacities of the first three electron shells

First shell: $2$, second shell: $8$, third shell: $8$.

Relative formula mass ($M_r$)

The sum of the relative atomic masses ($A_r$) of every atom present in the chemical formula of a substance.