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# Mass of Atoms and Moles, Relative Formula and Empirical Formula

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## Polly Henshaw

on 25 February 2015

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#### Transcript of Mass of Atoms and Moles, Relative Formula and Empirical Formula

A mole is the number used in calculations involving atoms and molecules, to simplify calculating in terms of number of atoms.
A mole is equal to 6.022 x 1023 atoms or molecules.
What is a Mole?
NO.
Mass of Atoms & Moles,
Relative Formula Mass & Empirical Formula

Mass of Atoms
What is an Atom?
An atom is a basic unit of an element. An atom includes a nucleus, made up of protons and neutrons. Its has energy shells surrounding it, with electrons in them.
The Mass of an Atom
The mass if an atom varies depending on the element its made of.
The relative atomic mass is a measure of the mass of one atom of the element.
Protons =1
Neutrons =1
Electron =0
If the atom is made up of Lithium it will have an atomic mass of 7.
This is because it has 3 protons and 4 neutrons and 3 electrons.
The relative formula mass of a substance is the sum of the relative atomic masses of the elements present in a formula unit.The symbol for relative formula mass is Mr (Subtext 'r').
If the substance is made of simple molecules, this mass may also be called the relative molecular mass.
Relative Formula Mass
Empirical Formula
CH COOH has two carbons, four hydrogens and two oxygens. So we could write the formula like this:
C H O and so it reduces to CH O.
What is Empirical formula?
How do you work it out?
The formula of a compound expressed as the smallest possible whole-number ratio of subscripts of the elements in the formula
3
2
4
2
2
How do you work it out?
For example: Hydrogen's relative atomic mass is H=1. So, the formula for hydrogen gas is H2 (subtext '2'). As each molecule contains 2 hydrogen atoms.
This means that the relative mass formula of hydrogen gas is;
To work out the Relative Formula Mass you simply add up the relative atomic masses of each atom in the molecule.
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