Formulae, Equations and Amounts of Substance


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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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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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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