Atomic structure

• How many elements are there?

  118
• All substances are made of atoms.
• Atoms


  Atoms are tiny particles that make up all substances on Earth.

  They contain a central nucleus with electrons orbiting around it.
• Protons, neutrons and electrons


  Protons, neutrons and electrons are not evenly distributed in an atom. The protons and neutrons exist in a dense core at the centre of the atom. This is called the nucleus. The electrons are spread out around the edge of the atom. They orbit the nucleus in layers called shells.
• Electrons


  Negatively charged particles that

  orbit the nucleus
• Protons

  Positively

  charged particles

  found inside the

  nucleus
• Neutrons

  Neutral (no charge) particles found

  inside the nucleus
• Atomic Number

  The atomic number is the number of protons in the nucleus of an atom.

  In the periodic table this is the smaller number

  The number of protons tells you which element it is.

  e.g. – An atom with 6 protons will always be a carbon atom

  Elements are neutral, so in a neutral atom, the number of protons = the number of electrons
• Mass Number

  The MASS number is the number of protons + neutrons in the nucleus.

  In the periodic table this is the bigger number

  This tells you how much the atom weighs

  To find the number of neutrons an atom has, take away the atomic number from the mass number

  Number of neutrons = mass number - number of protons = mass number - atomic number