Atomic structure and the Periodic table

Atomic structure and the Periodic table

1. Atoms, elements and compounds

   • An atoms is the smallest part of an element that can exist
     • An element is a substance made up of one type of atom
     • the relative atomic mass is the average mass of an atom (rma)
       • relative charge
         • proton= +1 neutron= 0 electron= -1
       • relative mass
         • proton= +1 neutron= 0 electron= -1
         • relative atomic mass= sum of (isotope abundance x isotope mass number) / sum of abundances of all isotopes
           • isotopes are different forms of atoms, as they have different number of neutrons
   • A compound contains two or more elements, chemically bonded

2. Mixtures

   • a mixture is an impure substance that contains two or more elements or compounds, that are mixed together but not chemically bonded
   • physical processes to seperate
     • filtration
       • separating an insoluble solid from a liquid reaction mixture. useful for purification.
     • distillation
       • simple
         • Used to separate out a liquid from a mixture. Used in industry to get pure water from sea water
       • fractional
         • Used for separating a mixture of different liquids and is especially useful when boiling points of the liquids are close together
     • crystallisation
       • Separating a soluble solid from a solution.
     • chromatography
       • used to separate mixtures made up of liquids of different colours.

3. development of the atom

   • The atoms was described as a solid sphere and that different spheres made different elements
     • JJ Thomson's measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles-electrons
     • Ernest Rutherford and Marsden conducted the famous alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold.
       • expected particles to go through or be slightly deflected at most. More than expected deflected.
       • Rutherford came up with the theory that in the atom, there's a tiny positively charged nucleus at the centre, where most of the mass is concentrated. A 'cloud' of negative electrons surrounds this nucleas. This became the nuclear model
     • Scientists realised that electrons in a 'cloud' would be attracted to the nucleus of an atom, causing the atom to collapse
       • Bohr's nuclear model suggested that all the electrons were contained in shells, and that electrons orbit the nuclead in fixed shells.
         • Helped explain the observations of a lot of other scientists
         • later experiments led to the conclusion that the positive charge of any nucleus could be subdivided into smaller particles, each particle having the same amount of positive charge-protons. and james chadwick carried out experiments that said there were neutral paricles- neutrons

4. the periodic table

   • elements placed according to properties(similarities) and atomic mass
     • Rows called period show how many shells an elements atom has
     • Group number shows how many electrons in outer shell
   • used to arranged according to atomic mass only, and by doing so, a periodic pattern was revealed
     • Mendeleev overcame some of the problems by taking the 57 known elements and placing them in his table
       • put elements in order of atomic mass but switched order of some elements if properties meant it should be changed
       • Gaps were left to make sure elements with similar properties stayed in the same groups
         • indicated that there were undiscovered elements and Mendeleev could predict what their properties might e
         • when these elements were found and their properties fitted with Mendeleev's predictions, it helped confirm his ideas
       • when isotopes were discovered, Mendeleev was right to not place elements in strict order of atomic mass but also to take into account their properties.
         • isotopes have different atomic masses

5. Metals and non metals

   • elements that react to form + IONS are metals and -IONS means non metal

6. group 0

   • unreactive
     • non-flammable
   • do not easily form molecules because their atoms have stable arrangements of electrons
   • eight electrons in outer shell, except for helium(only 2).
   • boiling points increase with increasing relative atomic mass.
   • room temp=colourless monatomic gases