Helium Atom

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Helium Atom electrons, which have a negative
charge and are the least massive of the three
protons, which have a positive charge and are
about 1836 times more massive than electrons and
neutrons, which have no charge and are about 1839
times more massive than electrons.
The darkness of the Electron cloud protons in
pink and neutrons in purple.
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Electrons (yellow) Protons (grey) Neutrons
(pink) up quarks (red) down quarks (blue)
Gluons (black) which hold the quarks together
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An electron shell can hold up to 2n2 electrons,
where n is the principal quantum number of the
shell.The occupied shell of greatest n is the
valence shell, even if it only has one electron.
In the most stable ground state, an atom's
electrons will fill up its shells in order of
increasing energy. Under some circumstances an
electron may be excited to a higher energy level
(that is, it absorbs energy from an external
source and leaps to a higher shell), leaving a
space in a lower shell. An excited atom's
electrons will spontaneously fall into lower
levels, emitting excess energy as photons, until
it returns to the ground state.
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s, p, d describes the shape of the atomic
orbital. principal quantum number is at the
right of each row. the azimuthal quantum number
is denoted by letter at top of each column.
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