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chemistry igcse acapprinted 11 · PDF 11
145 pagesrevision 46934
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electrons in shell 1 . electrons in shell 2 . electrons in shell 3 etc until the valence shell
Subatomic Particle
Relative Mass
Charge
Proton
1
+1
Neutron
1
0
Electron
1/1840
-1
The Proton Number and Atomic Mass of an element
• The proton number of an element, also known as the atomic number of an element, is the number of
protons one atom of an element contains.
• The atomic mass of an element, also known as the mass number or nucleon number of an element, is the
number of protons and neutrons contained in the nucleus of one atom of the element.
• The relative atomic mass of an element is the average mass of an atom relative to the mass of a carbon-12
atom where a carbon 12 atom has a mass of exactly 12 units