OCR Chemistry 1.1.1 Atoms & Reactions
- Created by: Kayleigh
- Created on: 11-03-14 18:21
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- OCR AS Chemistry 1.1.1 Atoms
- History of the Atom
- Ancient Greeks
- all matter is made up of tiny particles (atoms)
- if you were to repeatedly divide matter, you would reach a point where you could not divide any further
- John Dalton 1808
- atoms in any given element are all of the same kind
- compound contains two or more elements combined in fixed proportions
- during chemical reactions, atoms in the reactants rearrange to form reactants in the products
- J.J Thompson 1897
- found the electron
- knew that atom is neutral, so part is - and part is +
- plum pudding model
- negatively charged electrons embedded in a large positively charged sphere
- plum pudding model
- Ernest Rutherford 1909-1920
- fired positive alpha particles at gold foil
- they surprisingly went straight through and some bounced back
- found the proton
- new model of atom with a very small positively charged nucleus in its centre
- they surprisingly went straight through and some bounced back
- proton did not account for the whole mass of the nucleus (not accepted by scientists)
- fired positive alpha particles at gold foil
- Henry Moseley 1914
- determined charges on nuclei
- atomic number is equal to the number of protons in the nucleus
- this was used to reorganize Periodic table based in atomic number instead of atomic mass
- Ancient Greeks
- Sub-Atomic Particles
- proton mass=1 charge=+1
- neutron mass=1 charge=0
- electron mass=1/2000 charge=-1
- behaviour in an electric field
- neutron unaffected (no charge)
- proton (+charge) attracted towards negative plate
- electron (-charge) attracted towards positive plate
- electron deflected more prominently than proton as it has a much lower mass
- Definitions
- atomic number = number of protons in the nucleus of an atom
- mass number = the combined number of protons and neutrons in the nucleus of an atom
- isotopes = atoms of the same element which have the same number of protons and electrons but different numbers of neutrons
- isotopes have the same chemical properties as they have same number of electrons
- isotopes have different physical properties because they have different masses
- relative isotopic mass = the mass of one isotope of an element relative to one twelfth of an atom of Carbon 12
- relative atomic mass = the weighted mean mass of an atom relative to one twelfth of an atom of Carbon 12
- to calculate do the mass number x %abundance for each isotope. Add answers together. Divide by abundances of all isotopes
- Mr or RFM?
- for covalent molecules (only non metals) Relative Molecular Mass (Mr)
- both calculated by adding up individual relative atomic masses of atoms
- for ionic compounds (metals and non metals and ammonium compounds) Relative Formula Mass (RFM)
- because they do not exist as molecules, formula represents ratio of positive to negative ions
- Ionic Equations
- focus only on ions that don't react together (spectator ions)
- 1. rewrite equation showing individual ions present in ionic compounds only
- 2. cancel out anything that is the same on both sides - must be identical including state
- History of the Atom
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