Chemistry

Chemistry

1. Atoms, elements, compounds and mixtures

   • Atoms
     • Smallest part of an atom
     • Makes all substances
   • Elements
     • One type of atom
     • Shown on periodic table
   • Compound
     • Formed by elements in chemical reactions
     • 2 or more elements chemically bonded together
   • Chemical reaction
     • Make new substances
     • Often energy/temperature change
   • Mixture
     • 2 or more elements NOT chemically bonded together
   • Separation techniques
     • Distillation
       • Separate liquids, part of the mixture evaporates
       • Mass at start = mass at end
     • Filtration
       • Separate the solid from a solution
     • Chromotography
       • Soluble solute, that dissolves in a solvent
     • Crystallisation
       • Solute in a solvent, left with a solid solute

2. The development of the atomic model

   • New experimental evidence can lead to new models or altered models
   • Atoms are tiny spheres that cannot be divided
     • Thoughts before electron discovery
   • Models
     • Plum pudding model
       • Atoms are balls of positive charge with negative electrons stuck inside
     • Nuclear model
       • Says mass of atom is in the centre (charged nucleus)
   • Scientists
     • Niels Bohr
       • Electrons orbit nucleus at specific distances
     • James Chadwick
       • Neutrons in nucleus (20 years to be approved)
   • The proton
     • Positive charge in nucleus, each particle has the same amount of positive cahrge

3. Subatomic particles

   • Relative electric charges
     • Proton = +1
     • Neutron = 0
     • Electron = -1
     • No. of electrons = no. of protons
     • No. of proton = atomic number
   • Atoms
     • Radius = 0.1 nm
     • Nucleus
       • Radius 1/10000
       • Almost all mass here
   • Relative masses
     • Proton = 1
     • Neutron = 1
     • Electron = 1/1836
     • Mass number = no. of protons + no. of neutrons
     • Average value that takes into account the abundance of isotope of the element
   • Isotope
     • Same no. of protons, different no. of electrons
   • Electrons
     • Occupy the lowest available energy levels
     • 2,8,8

4. The periodic table

   • Elements are in order of atomic (proton) number
   • Groups
     • Elements with similar chemical properties
     • Same number if electrons on the outer shell