OCR Gateway Chemistry (separate, higher)

GCSE resource for paper 1

Melting Point

The temperature at which a solid turns into a liquid.

Boiling Point

The temperature at which a liquid turns into a gas.

A change of state is…

the transformation of a substance from one physical state to another, such as solid to liquid or liquid to gas.

New substances are made in…

A chemical reactions and involve chemical changes. Not often reversible (except in reversible reactions)

Dalton’s Model 1803

• Atoms cannot be broken down

• Atoms are different for each element

• Smallest particle

Thomson’s Model 1897

• Discovered electrons as negative particles

• Atoms contain positive charge with electrons embedded

• Plum pudding model

Gold Foil Experiment

Alpha particles fired at gold foil, proved that the atom is made up of a positive nucleus surrounded by a cloud of negative electrons

Rutherford’s Model 1911

• Planetary Model

• Central positive nucleus containing most of the mass

• Electrons orbit the nucleus

Bohr’s Model

• Electrons occupy energy levels (shells)

Sub-atomic particles

Name	Relative Mass	Charge
Electrons	1/2000 (ish)	-1
Protons	1	+1
Neutrons	1	0

Isotopes

Same number of protons, different number of neutrons resulting in different atomic masses.

Ions

Different number of electrons than the element, can have different chemical properties. Charged Particles

Element

Contains atoms with the same atomic number

Compound

Contains two or more elements bonded together

Mixture

Contains two or more different substances, not bonded, can contains elements and/or compounds

Formulation

A mixture designed to be useful, contains specific amounts of each substance

Purity

A pure substance consists of only one compound or element, has a set boiling point

Simple distillation

Used to separate a compound from a solution based on different boiling points.

Fractional distillation

Used to separate liquids from a mixture of liquids, as they all have different boiling points.

Crystallisation

Used to produce solid crystals from a solution by evaporating the liquid leaving solid crystals behind

Filtration

Used to separate a mixture of an insoluble solid from a liquid

Paper chromatography

Thin layer chromatography

Rf value

Difference travelled by substance divided by the distance travelled by solvent.

Mendeleev’s periodic table 1869

Arranged elements in order of increasing mass, & arranged elements with similar properties below each other, leaving gaps for undiscovered elements

Modern periodic table

Horizontal rows are periods in order of increasing atomic number. Vertical columns are groups, arranged by similar properties. Metals on the left hand, non-metals on the right, transition metals in the middle

Physical properties of metals

Shiny

High BP

Good Conductors of electricity & heat

High Density

Malleable

Physical properties of non-metals

Dull

Low BP

Poor Conductors (insulators)

Low Density

Brittle

Ionic Bonds

Ionic bonds are formed when a metal atom transfers one or more of its electrons to a non-metal atom, to have a full outer shell, resulting in the formation of positively and negatively charged ions that are held together by electrostatic forces. Ions in an ionic compound are arranged in an ionic lattice.

Covalent Bonds

Covalent bonds are formed when two non-metal atoms share one or more pairs of electrons, achieving full outer electron shells.

Simple molecular

Elements or compounds, held together by covalent bonds. These substances often have low melting and boiling points and may exist as gases or liquids at room temperature. Only contains a few covalent bonds

Giant covalent

Contains many atoms and covalent bonds

Usually consists of carbon

e.g Diamond,graphite and fullerenes

Usually very high mp and bp

Metallic bonding

Electrons leave outer shells, forming positive metal ions & a sea of de-localised electrons. Regular arrangement forming a metallic lattice.

Avagadro’s Constant

6.022 × 10²³ atoms per mole.

The mole is

A unit of measurement for the amount of a substance. E.G. 12g of Carbon is 1 mole of carbon

Mass of an atom =

Ar of substance / Avagadro’s constant

Molar mass

The mass of one mole of that substance

Is equal to the Ar or Mr of the substance

Mass (g) =

Molar mass (g/mol) * amount (mol)

Limiting reactants

The substance used up in a reaction

Exothermic

Gives out energy (hot)

e.g. combustion

Endothermic

Takes in energy, temperature decreases

e.g. electrolysis

When bonds break

energy is taken in, energy is released when these bonds reform. If endothermic more energy is taken in then given out. If exothermic more energy released than taken in.

Reaction profile, endo or exo?

Endothermic

Product line higher than reactant line - meaning more energy taken in then given out

Reaction profile, endo or exo?

Exothermic

Product line lower than reactant line - meaning more energy is released than taken in.

Bond energies

used to calculate energy changes in reactions.

Energy change = energy in - energy out

Oxidation (reactions)

Gain of oxygen

Reduction (reactions)

Loss of oxygen

Oxidation (electrons)

Loss of electrons

Reduction (electrons)

Gain of electrons

OILRIG

oxidation is loss, reduction is gain

Acids

Sources of H+ ions

Acidic solutions

Alkalis

Sources of OH- ions (hydroxide)

Alkaline solutions

pH scale

Less than 7 = acidic (Often red - orange with universal indicator

Equal to 7 = neutral (Green)

More than 7 = alkaline (Turquoise - blue)

A pH meter can also be used to measure the pH of a solution

A base

A substance that reacts with acid to from exclusively an acid and water

An alkali is a soluble base

Neutralisation

A chemical reaction where an acid reacts with a base forming a salt and water

Usually an acid+metal hydroxide = salt + water

Acid + metal

Salt + hydrogen

Acid + carbonate

salt + water + carbon dioxide

Nitric acid

Nitrate salt

Phosphiric acid

Phosphate

Hydrochloric acid

Chloride

Strong acids

Completely dissociate in a solution

Weak acids

Partially dissociates in a solution

Electrolytes

Ionic compounds, either molten or dissolved in water

Cations

Positively charged ions

Anions

Negatively charged ions

Cathode

Negatively charged electrode, attracts the cations

Anode

Positively charged electrode, attracts the anions

At the cathode…

Cations gain electrons

At the anode…

Anions lose electrons

At the cathode (solutions)

Metals are produced if it is less reactive than hydrogen

Hydrogen will be produced if it is more reaction than the metal

At the anode (solutions)

Oxygen is produced unless halide (group 7) ions are present & will form their respective halogens

Electroplating

Uses electrolysis to put a thin layer of metal onto a metal object

This can be to prevent corrosion or for appearance

Purifying copper

Uses electroplating

The cathode is pure copper

The anode is impure copper

The solution is copper (III) sulfate
This allows for the transfer of copper ions from the anode to the cathode, resulting in purified copper.