All Chemistry Definitions to Learn for Leaving Certificate

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:… Continue Reading →

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… Continue Reading →

Hardness in Water

Hard water is any water that forms a scum with soap. Soft water forms lather with soap. Hardness is caused by dissolved calcium and magnesium icons (Ca2+ and Mg2+). Temporary hardness Temporary hardness can be removed by boiling the water. Problems caused by temporary hardness: forms scum (wastes soap), limescale… Continue Reading →

The Water Treatment Process

Water treatment plants convert the raw untreated water to consumable water that is available at your home. The stages of water treatment: Sedimentation: Large particles are screened out and smaller particles are left to settle to the bottom of the sedimentation tanks. Flocculation: Aluminium sulphate (which is a flocculating agent) is added… Continue Reading →

Differences in the Modern Periodic Table

Main differences between Mendeleev’s Periodic Table and the modern periodic table: In the modern periodic table, the elements are arranged in order of increasing atomic number. (In Mendeleev’s table, they were arranged in order of increasing atomic weight). More elements are in the modern periodic table which have been discovered since Mendeleev’s time. eg. the… Continue Reading →

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… Continue Reading →

The Mass Spectrometer

A mass spectrometer is used to: Identify the presence of isotopes. Measure the relative abundances of isotopes. Measure relative atomic masses and relative molecular masses. Identify unknown compounds. Five stages of the spectrometer Vaporisation. The sample is injected as a gas, or as a liquid that is heated to vaporise it. Ionisation. An electron… Continue Reading →

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… Continue Reading →


Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation. Background information: Radioactivity was discovered by Henri Becquerel with photographic paper. Pierre and Marie Curie discovered polonium and radium. Radiation types: alpha , beta , gamma . Alpha particles Groups of two protons and neutrons struck… Continue Reading →