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LC Chemistry
LC Chemistry

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All Chemistry Definitions to Learn for Leaving Certificate - Higher Level

The Atom

  • Dalton’s Atomic Theory: All matter is made up of indivisible atoms which cannot be created or destroyed.
  • William Crookes discovered the Electron. Cathode ray tube.
  • JJ Thomson determined that electrons were negative. Found E/M ratio.
  • Robert Millikan’s Oil drop experiment discovered size of electron’s charge.
  • Plum Pudding Model: Solid positive sphere with electrons embedded.
  • Rutherford discovered the Nucleus. Fired alpha particles at gold foil. Proton.
  • Chadwick discovered the neutron by firing alpha particles at beryllium.
  • Energy level is the fixed energy value that an electron in an atom may have.
  • Heisenberg’s Uncertainty Principle states that it is... (More)
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The Atom

Matter is composed of very small particles which may be atoms, molecules or ions.

The History of the Atom

The Greek philosophers first proposed that there were indivisible particles which they called ‘atoms’ which means ‘indivisible’ in Greek. This is where we get the word atom.

John Dalton

In 1808, an English chemist called John Dalton was able to provide indirect evidence for the existence of atoms.

Dalton’s Atomic Theory:

  1. All matter is made up of very small particles called atoms.
  2. All atoms are indivisible. They cannot be broken down into simpler particles.
  3. Atoms cannot be created or destroyed.... (More)
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Arrangement of Electrons in the Atom

To understand the arrangement of electrons in atoms, Neils Bohor understood the spectra. When white light (eg. sunlight or light from an ordinary electric light bulb) is passed through a prism, the white light is broken up into many different colours. This called a continuous spectrum. But when Bohor carried out this experiment with a hydrogen discharge tube (a glass tube filed with hydrogen at low pressure through which an electric current is passed) instead of white light, he found that instead of seeing a continuous spectrum, he saw a series of narrow lines. These lines are called line... (More)

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Oil Refining: Organic Chemistry – Summary

Fractional Distillation: This involves the heating of crude oil, and separating the various mixtures in the basis of their boiling points.

Octane Number

The Octane Number of a fuel is a measure of the tendency of the fuel to resist knocking.

  • Heptane = 0
  • 2,2,4 Trimethylpentane = 100
  • Shorter the alkane chain, higher the octane number.
  • More branched the chain, higher the octane number.
  • Cyclic compounds have higher octane numbers than straight chain compounds.

Increasing the Octane Number

  • Isomerisation – Changing straight chain alkanes into their isomers.
  • Catalytic Cracking is the breaking down of long-chain hydrocarbon molecules into short... (More)