Atomic structure.

• Dalton model of an atom has changed over time because of the discovery of subatomic particles.
• Atoms have a central nucleus containing protons and neutrons surrounded by one or more electron shells.
• What is the relative charge and mass of a proton?

  Charge: +1 Mass: 1
• What is the relative charge and mass of a neutron?

  Charge: 0 Mass: 1
• What is the relative charge and mass of an electron?

  Charge: -1 Mass: 0.0005
• why do atoms contain equal numbers of protons and electrons?

  Atoms contain the same number of protons and electrons so that they have a neutral electrical charge.
• The nucleus of an atom is very small compared to the overall size of the atom. Atoms are mostly empty space.
• most of the mass of an atom is concentrated in the nucleus
• What is the mass number of an atom?

  The mass number of an atom is the total number of protons and neutrons in its nucleus.
• The atomic number tells you how many protons an element has.
• To work out the number of neutrons in an element, you subtract the mass number from the atomic number.
• What is an isotope?

  An isotope is a variant of an element that has the same number of protons but a different number of neutrons in its nucleus.
• the existence of isotopes results in relative atomic masses of some elements not being whole numbers.
• What is the formula for the relative atomic mass?

  The relative atomic mass of each element is calculated from the mass number and relative abundances of all the isotopes of a particular element.