Atomic structure (chem)

• Atoms are neutral, so they have an equal amount of protons (positive charge) and electrons (electrons).
• Isotopes are atoms with different numbers of neutrons but the same number of protons.
• Atoms where the electrons and protons are not equal are called ions. 
• An ion is an electrically charged particle produced by either removing electrons from a neutral atom to give a positive ion or adding electrons to a neutral atom to give a negative ion.
• Protons and neutrons exist in the nucleus while electrons stays in the electron shells.
• Atoms of the same element always have the same number of protons, but often have different numbers of neutrons
• The electronic configuration of atoms with electrons lesser than 20 is 2.8.8
• Elements in the same group (vertical), have similar chemical properties and same number of valence shells.