GCSE Chemistry · Edexcel 1CH0 · Topic 1A
Atomic structure
Key points
- Atoms have a tiny central nucleus containing protons (relative charge +1, mass 1) and neutrons (charge 0, mass 1), with electrons (charge −1, very small mass) in shells around it.
- Atoms are neutral because they have equal numbers of protons and electrons. Most of an atom is empty space.
- Atomic number = number of protons; mass number = protons + neutrons.
- Isotopes are atoms of the same element with different numbers of neutrons, e.g. carbon-12 and carbon-14.
- Relative atomic mass () is the mean mass of an element's atoms, weighted by isotope abundance: . E.g. 75% Cl-35 and 25% Cl-37 gives 35.5.
- The model of the atom developed from Dalton's solid spheres, through discoveries of the electron and the nucleus, to today's model.
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Everything in chemistry is made of atoms, and their structure explains how elements behave. These notes cover the parts of an atom, how to work out the numbers of each particle, isotopes and relative atomic mass, and how the model of the…
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