Atomic Structure

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The mass number is the total amount of Protons and Neutrons in an atom.

Isotopes are atoms in an element with different numbers of neutrons.

The relative formula mass of a compound is found by adding together the relative atomic masses of all the atoms in the formula of the compound.

The relative formula mass of a substance in grams is one mole of that substance.

Subatomic Particles

Each atom contains a nucleus containing Protons and Neutrons with Electrons surrounding it in energy levels.

Masses of Sub atomic particles

Proton = 1

Neutron = 1

Electron = Very Small (1/1836)

Mass Number and Atomic Number

The mass number is never smaller than the Atomic number, it can be the same but is usually bigger.

The mass number is the amount of Protons and Neutrons it contains

The atomic number is the amount of Protons it contains

Isotopes

The atoms of a particular element will always have the same amount of protons as each other. Their atomic number will be the same.

Atoms in an element can have different amounts of Neutrons so their Mass number can be different.

Atoms of the same element with different amount of Neutrons are called Isotopes

The different isotopes in a element have identical chemical properties

Some isotopes are Radioactive

Chemical Symbols

The chemical symbol for an element shows its Mass number at the top and its atomic number at the bottom.. Here is the Chemical symbol for Carbon

It tells us carbon has 6 protons, from that we can work out from the mass number that carbon has 6 neutrons

For your exam, you will need to know what relative formula mass is.

You should also be able to work out the relative formula mass of a substance when given its formula.

The symbol for relative formula mass is Mr. The symbol for relative atomic mass is Ar.

You will be given any Ar values you need in the examination.

Working out Mr

To find the relative formula mass of a substance, you just add together the relative atomic mass values for all the atoms in its formula.

Moles

The relative formula mass of a substance - shown in grams - is called one mole of that substance. For example, the Mr of carbon monoxide (CO) is 28. This means that one mole of Carbon Monoxide is 28g

Atomic Structure

Isotopes

Relative Formula Mass