isotopes

• Atom


  The smallest part of an element that can exist
• Element


  A substance made of one type of atom only
• Proton


  Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1.
• Neutron


  Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.
• Nucleus


  The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom.
• Isotope


  Atoms of an element with the same number of protons and electrons but different numbers of neutrons.
• Atomic number


  The number of protons in the nucleus of an atom. Also called the proton number.
• Mass number


  The number of protons and neutrons found in the nucleus of an atom.
• Isotopes of hydrogen


  • Hydrogen-1
  • Hydrogen-2
  • Hydrogen-3
• All three isotopes of hydrogen have identical chemical properties
• Relative atomic mass


  The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.
• Relative atomic masses are given in the periodic table and have the symbol Ar
• Mass numbers are always whole numbers, but relative atomic masses are often rounded to the nearest whole number and are not whole numbers
• The relative atomic mass of chlorine is 35.5 rather than a whole number because chlorine contains two different isotopes, chlorine-35 and chlorine-37