Summary EDEXCEL A LEVEL CHEMISTRY UNIT 1 ATOMIC STRUCTURE NOTES

1.1 ATOMIC STRUCTURE
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09:22
An atom is a particle of matter that uniquely defines a chemical element.
- Nucleus of protons and neutrons surrounded by electrons in energy levels.




1.2 ATOMIC NUMBER AND MASS NUMBER
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09:24
Atomic number/Z - Number of protons in its nucleus.
● The number of protons in the nucleus determines the element.
● In an atom, the number of electrons is equal to the number of protons.
- Atoms have no charge, so the charges counteract each other.

Mass number/A - Number of protons plus neutrons in the atoms nucleus.
● Doesn't include electrons as they are very light.

, 1.3 COMPARING THE MASSES OF ATOMS -
MASS SPECTROMETRY
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09:46
A mass spectrometer separates atoms and molecules according to their mass.
● Also shows relative numbers of different atoms and molecules present.

Using the data, chemists can deduce;
● Isotopic compositions of elements.
● Relative atomic mass of elements.
● Relative molecular mass of compounds.

A gaseous sample enters the ionisation chamber.
● Electron gun shoots high energy electrons.
● High energy electrons bombard the atoms or molecules of the sample,
knocking off electrons.
The ions are accelerated by an electric field.
The ions enter a magnetic field, which deflect the ions.
● Lower M/Z ratio deflects more.
The ions are detected electronically by electrical signals related to abundance by the
detector.




Bombarding molecules can cause some to break into fragments.
The peak with the highest mass is usually the whole molecule ionised.
● The mass of this molecular ion is the relative molecular mass of the
compound.