atomic structure

• An element is a substance which contains only one type of atom. Each element has a different symbol and atomic number.
• The Periodic Table is arranged in horizontal rows called periods and vertical columns called groups.
• The elements are arranged by atomic number and based on their chemical properties.
• Elements in the same group of the Periodic Table have similar chemical properties.
• The alkali metals are all soft and reactive metals that will react with water to produce an alkaline solution (Group 1).
• The halogens are all reactive non-metal elements (Group 7).
• The noble gases are all colourless and extremely unreactive elements (Group 0).
• Atoms are made up of three subatomic particles; protons, neutrons and electrons.
• Protons and electrons are found inside the nucleus of the atom.
• Electrons are found orbiting the nucleus in electron/energy levels.
• Each of the particles have a specific mass and charge.
• Protons have a charge of 1+ and a mass of 1 amu.
• Neutrons have a charge of 0 and a mass of 1 amu.
• Electrons have a charge of -1 and a mass that is almost 0 or negligible.
• Overall, an atom is neutral. This is because the number of positive protons equals

  the number of negative electrons. The charges cancel out.
• Atomic Number = Number of Protons
• Mass Number = Number of Protons + Number of Neutrons
• Electrons are found orbiting the nucleus.
• Electrons are arranged in energy levels (shells).
• Electrons always fill the first energy level first.
• The first energy level holds 2 electrons.
• The second energy level holds 8 electrons.
• The third energy level holds 8 electrons.
• Once there are 4 electrons on one shell, the electrons start to pair off.
• Isotopes are atoms with the same atomic number but different mass number.

  Each has the same number of protons but a different number of neutrons.
• Elements are made up of isotopes.
• The relative atomic mass is calculated from the masses of all the isotopes of an element taking into account the percentage proportion of each.
• There are two isotopes of chlorine, chlorine-35 and chlorine-37.
• The RAM of chlorine is 35.5, therefore chlorine-35 must be more abundant because the mass number is closer to the RAM.
• There is a limit to the number of electrons each energy level can hold.

  The first energy level holds 2 electrons.

  The second energy level holds 8 electrons

  The third energy level holds 8 electrons