Definition
An element is made up of entirely one type of atoms. All atoms of that element will have same number of protons (which carry a positive electrical charge) and electrons (which carry a negative electrical charge), same atomic number but they can have different number of neutrons (which carry no electrical charge) resulting in different masses. An element having different neutrons are called isotopes.
Arrangement
The protons and neutrons are packed together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus.
