Atomos is an ancient Greek word meaning 'indivisible' or 'cannot be cut'. Atoms are the building blocks of matter; they are the smallest particles that when combined together have the properties of a particular chemical element, or compound.
The electron configuration, that is the distribution or arrangement of electrons in the atom, can be described by the Bohr model of the atom and the quantum mechanical model of the atom.
First ionisation energies provide evidence for our quantum mechanical model of the atom.
This section is the foundation of atomic structure and explains the numerical values given on the periodic table.