atomic structure and periodic table

• isotope: atom of the same element with a different number of neutrons
• rutherford perfomed the alpha scattering experiment to prove the nucleus was made up of protons
• Bohr suggested that all electrons were in shells and the shells were fixed whilst the electrons orbit
• James chadwick discovered neutral particles (neutrons)
• periodic table used to be organised by atomic weight, but now it is organised by atomic number
• Mendeleev organised them by leaving various gaps
• Mendeleev organised them mostly by atomic weight but did switch them around to be grouped with elements with similar properties
• group 1 elements are reactive, soft metals
• group one metals have a low density
• as you go down group one, the reactivity increases because its easier to lose the outer electron
• group one form ionic compounds which are usually white solids that dissolve in water to form colourless solutions
• group 1 react vigorously with water
• group one react vigorously when heated with chlorine gas to form white metal chloride salts
• as you go down group 7, the reactivity decreases
• halogens form molecular compounds and ionic bonds (with metals)
• more reactive halogens will replace less reactive ones
• all group 0 elements are inert, colourless gases
• group 0 boiling point increases as you go down the list
• noble gases have no electron affinity so they don't gain electrons easily
• transition metals have high melting points due to strong metallic bonding
• noble gases can be used as carrier gases in chromatography