Chemistry

States of matter: What are the three states of matter?

Solid (fixed shape and volume), Liquid (fixed volume, no fixed shape), Gas (no fixed shape or volume)

States of matter: Particle arrangement in solids

Closely packed in a regular arrangement, vibrate in fixed positions

States of matter: Particle arrangement in liquids

Close together but irregular, can move/slide past each other

States of matter: Particle arrangement in gases

Far apart, random arrangement, move rapidly in all directions

States of matter: Changes of state definitions

Melting (solid → liquid), Freezing (liquid → solid), Boiling (liquid → gas), Condensation (gas → liquid)

States of matter: Explain melting using particles

Particles gain energy, vibrate more, overcome forces holding them in fixed positions

States of matter: Explain boiling

Particles gain enough energy to overcome intermolecular forces and form gas bubbles

States of matter: Diffusion definition

The net movement of particles from high concentration to low concentration

States of matter: Factors affecting diffusion

Temperature (higher = faster), concentration gradient, state (fastest in gases)

Elements: Definition

A substance made of only one type of atom

Compound: Definition

A substance made of two or more elements chemically bonded in fixed ratios

Mixture: Definition

Two or more substances not chemically bonded and can be separated physically

Difference between compound and mixture

Compounds have fixed composition and chemical bonds; mixtures have variable composition and no bonding

Separation technique: Filtration

Separates insoluble solid from liquid

Separation technique: Crystallisation

Obtains dissolved solid from solution by evaporating solvent

Separation technique: Simple distillation

Separates solvent from solution based on boiling point

Separation technique: Fractional distillation

Separates liquids with different boiling points

Chromatography: What does it separate?

Mixtures of soluble substances (e.g. inks)

Chromatography: Rf value formula

Distance travelled by substance ÷ distance travelled by solvent

Atomic structure: What is an atom?

The smallest part of an element that retains its properties

Subatomic particles: Proton

Relative charge +1, mass 1, found in nucleus

Subatomic particles: Neutron

Relative charge 0, mass 1, found in nucleus

Subatomic particles: Electron

Relative charge -1, very small mass, found in shells

Atomic number definition

Number of protons in an atom

Mass number definition

Total number of protons + neutrons

Isotopes definition

Atoms of same element with different numbers of neutrons

Electronic configuration rule

Electrons fill shells: 2,8,8 (for first 20 elements)

Why atoms are neutral

Number of protons = number of electrons

Ion formation

Atoms gain or lose electrons to achieve full outer shell

Periodic Table: Arrangement principle

Elements arranged by increasing atomic number

Group definition

Vertical columns with similar chemical properties

Period definition

Horizontal rows showing number of electron shells

Metals location

Left and centre of Periodic Table

Non-metals location

Right side of Periodic Table

Trend: Atomic size down a group

Increases due to more electron shells

Trend: Reactivity of Group 1

Increases down the group

Trend: Reactivity of Group 7

Decreases down the group

Ionic bonding: Definition

Bonding between metal and non-metal involving transfer of electrons

Ionic bonding: How ions form

Metals lose electrons (positive ions), non-metals gain electrons (negative ions)

Ionic compound structure

Giant ionic lattice with strong electrostatic forces

Properties of ionic compounds

High melting/boiling points, conduct electricity when molten or dissolved, brittle

Why ionic compounds conduct electricity

Ions are free to move when molten or in solution

Example ionic bond (NaCl)

Sodium loses 1 electron, chlorine gains 1 electron → Na⁺ and Cl⁻

Covalent bonding: Definition

Bonding between non-metals involving sharing of electron pairs

Single covalent bond

One shared pair of electrons

Double covalent bond

Two shared pairs of electrons

Simple molecular substances

Small molecules with weak intermolecular forces

Properties of simple covalent molecules

Low melting/boiling points, do not conduct electricity

Giant covalent structures

Large networks of atoms bonded covalently (e.g. diamond, graphite)

Diamond structure

Each carbon bonded to 4 others → very hard, high melting point, no conductivity

Graphite structure

Each carbon bonded to 3 others, layers slide, conducts electricity due to delocalised electrons

Group 7: Name

Halogens (e.g. chlorine, bromine, iodine)

Group 7: State at room temperature

Chlorine gas, bromine liquid, iodine solid

Group 7: Trend in colour

Gets darker down the group

Group 7: Trend in boiling point

Increases down the group

Group 7: Trend in reactivity

Decreases down the group

Why halogens react

Gain 1 electron to achieve full outer shell

Displacement reactions definition

A more reactive halogen displaces a less reactive halogen from a compound

Example displacement reaction

Chlorine + potassium bromide → potassium chloride + bromine

Halogens as diatomic molecules

Exist as X₂ (e.g. Cl₂, Br₂)