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Science

Atomic structure

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The mass number of an atom is its total number of protons and neutrons. Isotopes are atoms of an element with different numbers of neutrons. The relative formula mass of a compound is found by adding together the relative atomic masses of all the atoms in the formula of the compound. The relative formula mass of a substance in grams is one mole of that substance.

Subatomic particles

the proton and neutron are within the nucleus which is within the centre of the atom, the elctrons are on the edges of the atom

Structure of the atom

Each atom consists of a nucleus [nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. ] containing protonsproton: A proton is a small particle with a positive charge found in the nucleus of the atom. and neutronsneutron: ###TODO###, with electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ] arranged around it in energy levels.

Relative masses of subatomic particles

Name of particleRelative mass
Proton1
Neutron1
ElectronVery small (1/1836)

Mass number and atomic number

The mass number of an atom is never smaller than the atomic number. It can be the same, but is usually bigger:

  • The mass number of an atom is the total number of protons and neutrons it contains
  • The atomic number of an atom is the number of protons it contains

Notice that most of the mass of an atom is found in the nucleus.

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