An isotope of an element has a slightly different number of particles to other isotopes of the element. So, the most common isotope of oxygen is oxygen-16, and it has 16 nucleons (both protons and neutrons) in its nucleus. Oxygen-18 has 18 nucleons.
Isotope
Fact of the Day
David I of Scotland gave tax rebates to subjects with good table manners.
Quote of the Day
"Is life not a hundred times too short - to get bored?
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~ Nietzsche
On This Day
1579 Thomas Gresham, merchant, financier, and founder of the Royal Exchange, died suddenly, apparently of apoplexy. He bequeathed his estate, after the death of his wife, to the Corporation of London and the Mercers' Company to set up a college to provide free lectures to the public; Gresham College thus became London's first institution of higher education.
1916 The hospital ship Britannic, sister-ship of Titanic, hit a mine and sank, killing 30.
1918 Ten days after the Armistice, the German navy surrendered to the British in the Firth of Forth.
1920 The assassinations of British intelligence officers ordered by Michael Collins in the Irish War of Independence led to thirty-one dead (from both sides) in what became known as 'Bloody Sunday'.
1974 21 people were killed and 182 injured when bombs exploded in two Birmingham pubs. The IRA was probably responsible, but the real culprits have never been found. The Birmingham Six, originally convicted of the bombings, were released because of dodgy police practices.
1981 The proceedings of the House of Commons were televised live for the first time.