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
Roman women would use lead and crocodile dung, among other things, as make-up.
Quote of the Day
"A Conservative government is an organised hypocrisy.
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~ Benjamin Disraeli
On This Day
303 St George, a possibly Greek, Palestinian, or non-existent Roman soldier, was executed for preaching Christianity. He is the patron saint of Aragon, Catalonia, England, Ethiopia, Georgia, Greece, Lithuania, Palestine, Portugal, and Russia.
1344 Or 1348. The Order of the Garter, the highest order of chivalry in England, was founded by Edward III.
1616 William Shakespeare, one of the greatest playwrights in English history, died at the age of 52 and within a month of signing his will where he was described as being 'in perfect health'.
1661 Charles II was crowned king of England, Scotland and Ireland, thereby officially restoring the monarchy. He chose St George's Day for his coronation, as did James II and Queen Anne.
1850 Poet William Wordsworth died of pleurisy, aged 80.
1915 Idealistic war poet Rupert Brooke died of an infected mosquito bite on his way to Gallipoli.
1945 Hitler's propaganda minister, Joseph Goebbels, and his wife committed suicide in Hitler's Berlin bunker, after killing their six children. Meanwhile, Hitler's private secretary, Martin Bormann, escaped from the bunker. He didn't make it far: his remains were discovered in Berlin in 1972.