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
King John used the fat from 40 pigs to blow up the southern wall of Rochester Castle during a siege in 1215
Quote of the Day
"I let down my friends, I let down my country. I let down our system of government,
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~ Richard Nixon
On This Day
1586 American colonists arrived in Plymouth with large quantities of tobacco. Smoking caught on quickly, though it was also used in tea.
1694 The Bank of England was founded by an act of parliament as a way to finance government debt by private subscription.
1943 The concentrated Allied bombing of Hamburg led to a three hour firestorm that killed approx 30,000 civilians.