ATOMIC STRUCTURE + PERIODIC TABLE

ATOMIC STRUCTURE + PERIODIC TABLE

1. HISTORY OF THE ATOM

   • [1987] THE PLUM PUDDING MODEL
     • In 1897 JJ Thomson created the plum pudding model
     • It consisted of a cloud of positiveness and electrons dotted randomly around it.
   • [1909] THE NUCLEAR MODEL
     • In 1909, Ernest Rutherford performed an experiment based on the hypothesis that atoms are mostly just air space.
     • ALPHA PARTICLE SCATTERING EXPERIMENT:
       • A thin sheet of gold leaf was repeatedly shot at with alpha particles with a screen placed behind the leaf.
     • Although his hypothesis was mostly correct, he found that 1 in 10,000 of the alpha particles had been deflected back
     • New model consisted of a Nucleus of POSITIVE CHARGE in the centre surrounded by a cloud of electrons.
   • BOHR'S NUCLEAR MODEL
     • Bohr's speculated that electrons were organised in shells/energy levels
     • Each shell/energy level was a fixed distance from the nucleus
     • This helped explain a lot of scientific observations at the time
   • DISCOVERY OF THE SUBATOMIC PARTICLES
     • In 1920, the subatomic particle with the same charge as a hydrogen nuclei was named the PROTON
     • 20 years into referring to the mass in the middle as "nuclei", James Chadwick carried out an experiment that found neutral mass in the atom
       • These became known as NEUTRONS

2. THE PERIODIC TABLE

   • GROUP 1 ALKALI METALS
     • The first column of the periodic table: Lithium, sodium, potassium, etc
     • Each have 1 electron on its outer shell
     • Alkali metals are silvery solids that have to be handled and stored a certain way since they oxidise when exposed to oxygen.
     • REACTIVITY TREND: Increases down the column (e.g. Lithium is the least reactive and Francium is the most reactive.)
     • MELTING AND BOILING POINTS: Decreases down the column (e.g. Lithium has the highest melting/boiling point and Francium has the lowest melting/boiling point.)
     • With Non-metals, Alkali metals form IONIC COMPOUNDS
     • They react VIGOROUSLY with water and forms metal hydroxides
     • REACTION WITH CHLORINE: Alkali metal + Chlorine => Metal chloride
   • GROUP 7 HALOGENS
     • The 7th column on the periodic table: Fluorine, chlorine, bromine, iodine, etc
     • COLOURFUL VAPORS
       • Fluorine - poisonous yellow gas
       • Chlorine - poisonous, dense, green gas
       • Bromine - Dense, poisonous, red-brown volatile liquid/orange vapour
       • Iodine - Poisonous dark grey, crystalline solid/purple vapour
     • REACTIVITY TRENDS: Down the graph it gets less and less reactive, fluorine is the most reactive and astatine is the least reactive
     • BOILING/MELTING POINT: They increase down the group so the elements at the bottom have a higher boiling point than those do at the top
     • Halogen atoms can share electrons with NON-METALS through COVALENT BONDING
     • Halogen atoms form IONIC COMPOUNDS with metals. They gain one electron and become HALIDE IONS with a -1 CHARGE.
     • DISPLACEMENT REACTION: More reactive halogens can kick out less reactive halogens from an aqueous solution of its salt
   • GROUP 0 NOBLE GASES
     • The 8th column of the periodic table: Helium, neon, aragon, krypton, zenon and Radon
     • They have full outer shells meaning they don't react much if not at all
     • At room temperature they exist as MONATOMIC GASES (single atoms not bonded to anything else)
     • MELTING/BOILING POINT: Increase as you go down the column
   • TRANSITION METALS
     • These are the central block of the periodic table
     • They're good conductors of heat and electricity
     • They are very dense, strong and shiny, sink in water
     • In comparison to ALKALI METALS they don't react as vigorously with WATER. TRANSITION METALS are dense, stronger and harder than alkali metals. They have higher melting and boiling points.
     • They can form with different charges e.g. Iron (III), Iron (II) and Iron (I)
     • They form COLOURED COMPOUNDS
     • They are very good CATALYSTS