.2 Mass number, atomic number and isotopes

• In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
• All atoms of a particular element have the same number of protons. The number of protons in an atom of an element is called its atomic number.
• The total number of protons and neutrons in an atom is called its mass number.
• Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that elemen
• Atoms turn into positive ions if they lose one or more outer electron(s)