# OCR Gateway Science C3 Revision Cards

Run through of the additional science OCR gateway module

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## What are atoms like?

Atoms are found in the Periodic table.
Approximately 80% of atoms are metals.
Metals found on left of Periodic table.

Elements made of 1 type of atom only.
Atoms have nucleus and outer shells.
Nucleus houses neutrons (no charge) and protons (positive charge).
Shells hold electrons (negative charge).

Periodic table shows Atomic number / Proton number and Relative atomic mass (RAM).
Proton number smallest of two. States number of protons + also shows number of electrons.
RAM = protons + neutrons.

To calculate the number of electrons use the proton number. To calculate the number of neutrons take the proton number from the RAM

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## Wha are atoms like?

DO NOT FORGET - PERIODIC TABLE ON THE BACK OF THE EXAM PAPER.

ATOMIC PARTICLE RELATIVE CHARGE RELATIVE MASS

PROTON +1 (POSITIVE) 1

NEUTRON 0 (NEUTRAL) 1

ELECTRON -1 (NEGATIVE) 0.0005 (ZERO)

Isotopes

• all atoms have of an element have the same number of protons
• isotopes of an atom have different numbers of neutrons
• therefore they have the same atomic number but different mass
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## How atoms combine - atomic bonding

Ion - charged particle or group of particles
Molecule - has more than one atom in formula so no charge
Ionic bonds are formed between metals and non-metals
Metals
- lose electrons so become positive in charge
Non-metals - gain a negatively charged electron so become negative in charge

Poor joke to remeber the charge of ions

Two atoms walking down a street. One pats its pockets. The other says "Have you lost something". The first atom responds "Yes I've lost an electron". The second atom asks "Are you sure?"

The first atom says "Yes, I'm positive!"

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## How atoms combine - ionic bonding

Dot and cross diagrams.

Dot and cross diagrams in square brackets show the ions that have been made.

Examples of ionic bond equations

Sodium + Chlorine = Sodium chloride

2Na + Cl2 = 2NaCl

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## Covalent Bonding and the Structure of the Periodic

Molecule - two or more non-metal atoms bonded together.

Molecular formula - shows number of atoms. e.g.
O2 F2 Cl2 N2

The atoms shown are called diatomic

Covalent bonding -

• sharing electrons complete outer shell
• dot and cross diagrams
• number of electrons needed shown by Periodic table group
• covalent bonding occurs between non-metals
• bonds between the different atoms are strong
• bonds between different covalent molecules are weak
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## Covalent Bonding and The Structure of the Periodic

Periodic Table

• 100 or so elements
• arranged in order of ascending number
• then arranged in rows (periods) and columns groups
• group shows number of electrons in outer shell. Group 1 elements have 1 electron in their outer shell, group 2 elements have 2 electrons etc
• period shows number of shells. Helium and hydrogen are on the first row so only have 1 shell. The second row has 2 shells ans so on.
• relative atomic mass (protons + neutrons) top
• proton (and electron) number bottom
• atomic structure can be shown as numbers lithium 2.1, sodium 2.8.1
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## Group 1 Elements - Alkali Metals

Alkali metals

• group 1 metals form hydrogen gas and alkali with water (hydroxides)
• violent reaction with water
• more reactive as go down table
• reactivity because of outer electron distance from nucleus
• melting points and boiling points decrease as go down group.
• density increases as go down group
• form positive ions
• flame tests - lithium red
sodium orange
- potassium lilac

Example of equation

Lithium + water = Lithium Hydroxide + Hydrogen

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## Group 7 Elements - Halogens

Group 7 elements

• halogens
• react violently with alkali metals
• reaction with metal makes halide
• more reactive as go up group
• make salts ending with ide
• form diatomic molecules
• undergo displacement Fluorine displaces all
• melting point and boiling points increase down group
• electrons gained to form negative ions (reduction)

OILRIG - OXIDATION IS LOSS - REDUCTION IS GAIN OF ELECTRONS

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## Electrolysis

Definitions

• Electrolysis - process passing DC through molten solution to break it down and obtain useful products.
• Electrolyte - molten solution
• Electrodes - anode (positive charge) and cathode (negative charge)
- opposites attract - negative ions go to anode
- positive ions to cathode

Electrolysis of sulphuric acid hydrogen made at cathode

Electrolysis of aluminium oxide bauxite (aluminium ore) melted
- electrons free to move
- molten aluminium forms at bottom
- oxygen formed at carbon anodes causing decomposition of anodes into carbon dioxide

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## Transition Elements

Transition metals - found in central block with no group number between groups II and III. Contains iron, gold, copper etc

Properties - same as all metals - shiny, sonorous, conductors etc

Compounds - transition metal compound coloured

Catalysts - speed up reaction - iron in Haber process
- nickel in margarine

Precipitates - form coloured precipitates with sodium hydroxide
- copper = blue solid
- iron (2+) = grey green solid
- iron (3+) = orange gelatinous solid

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## Metal structure and Properties

Properties

• lustrous (shiny), hard, high density, ductile, high melting point, good conductors
• conduct electricity delocalised (free flowing) electrons

Metallic bonds -

• holds particles together
• reason for conductivity
• metal structure contains crystals

Superconductors

• super fast circuits and levitate magnets
• little or no electrical resistance
• occurs at very low temperatures (known as critical temperature)
• Meissener effect - floating magnets
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