# Formulae, Equations and Amounts of Substance

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## An Atom

The nucleus is made up of protons, neutrons.

Electrons occupy the space outside the nucleus.

Protons have a positive charge.

Electrons are negative.

Neutrons have no charge

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## Element

A substance that cannot be broken down chemically into a simpler substance,

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## Atomic Number

Number of protons in the nucleus.

This is equal to the number of electrons.

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## Mass Number

Number of protons plus the number of neutrons.

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## Isotopes

Atoms with the same number of protons and electrons, but a different number of neutrons.

Have different physical properties.

Always have the same chemical properties.

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## State Symbols

s - solid

l - liquid

g - gas

aq - solution in water

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## Relative Atomic Mass

The average mass of its isotopes compared with the mass of an atom of the carbon-12 isotope.

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## A mole The amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12

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## Avogadro Constant

The number of atoms in exactly 12g of carbon-12 is found from experiments to be 6.02 x 1023

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## Relative Formula Mass (Mr)

In a compound, the sum of the relative atomic masses of all the atoms in the chemical formula.

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## Reactions with gases

One mole of any gas occupies 24dmat 25 degrees C (298K) and 1 atmosphere pressure.

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## Empirical Formula

The simplest formula for a compound, showing the whole-number ratio of the number of atoms of each element present.

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## Moles in solution Percentage by mass = mass of solute / mass of solution x 100

Percentage by volume = volume of one component / total volume x 100

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## Parts per million (PPM)

Concentration = mass of component / mass of solution x 1000000

Can be useful for very low concentrations.

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## Double Salts

Crystals that contain different salts in a 1:1 ratio.

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## Double Salts

Crystals that contain different salts in a 1:1 ratio.

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## Calculating Yield

Percentage yield = actual yieldpredicted yield × 100

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## Atom Economy

Mass of atoms in desired products / mass of atoms in reactants x 100

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