Atomic Structure and the Periodic Table

Atomic Structure and the Periodic Table

1. The Atom

   • All substances are made of atoms. An atom is the smallest part of an element that can exist
   • There are around 100 different elements
     • An element is a substance that consists of only one type of atom
   • A compound is a substance that is made up of two or more elements chemically bonded together
     • Compounds are formed through chemical reactions
     • Compounds can only be separated through chemical reactions
   • A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.
     • Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography

2. History of the Atom

   • 1) Plum Pudding: 1900
     • DESC: Atoms comprise negative particles surrounded by a cloud of positive charge
   • 2) Rutherford's Experiment: 1911
     • DESC: Central positive Charge surrounded by orbiting electron clourd
     • Rutherford's gold foil experiment showed that there was a presence of a dense positive nucleus
   • 3) Bohr: 1913
     • DESC: Central positive nucleus with electrons moving in circular orbits. Orbits are ordered by energy levels

3. The Periodic Table

   • Mass number is the number of protons and neutrons
   • The atomic number is the number of protons or the number of electrons
     • Elements are arranged according to atomic number
   • Isotopes are elements that have the same atomic number but a different mass numbers. This is due to a difference in number of neutrons.
   • Relative atomic mass is the average mass with the abundance of isotopes
     • You can calculate it using the mass number of an element and the percentage of isotopes present
   • The maximum electron capacity for each shell is 2, 8, 8
   • The group number (vertical) gives the number of electrons in the outer shell
   • The period number (horizontal) gives the number of electron shells

4. Metals, Non-metals and Groups

   • Metals are shiny, malleable, dense, sonorous and are good conductors
     • Positive ions
   • Non-metals are dull, brittle and are good insulators
     • Negative ions (except hydrogen)
   • Group 0
     • These are the 'Noble Gases' which aren't reactive as they have a full outer electron shell
     • The boiling point increases down the group
   • Group 1
     • These are called the 'Alkali Metals'
     • The properties of these metals are defined by the fact that there is a single electron in the outer shell
     • The metals become more reactive down the group and react with water to form 'alkali' solutions
       • Hydrogen gas is released after the metal reacts with water and a metal hydroxide is produced
       • These are more reactive than group 2 metals which are similar
         • This is because less energy is required to lose 1 electron than 2
     • The metals get more reactive down the group because the outer electron is further from the positive nucleus.
       • This means that the force of electrostatic attractions between the positive nucleus and the negative electron decreases meaning that it is lost more easily.
   • Group 7
     • The 'Halogens'
     • 7 electrons in the outer shell
     • Exist in molecules with a pair of atoms
       • Diatomic
     • In Group 7, the further down the group an element is the higher its relative molecular mass, melting point and boiling point
       • In Group 7, the reactivity of the elements decreases going down the group
         • This is because the attraction between nucleus and electrons are weaker further away
           • It is more difficult to gain an electron
     • A more reactive halogen can displace a less reactive halogen
   • Transition Metals
     • Many transition metals can be used as catalysts
     • They form coloured compounds
     • They are good conductors
     • They have high melting points (except mercury)

Images and files in the map