An element's atomic number equals the number of what in each atom?
AnswerProtons
The number of protons defines the element; carbon always has 6, for example.
Science · Facts & stats
Atom facts & stats
7 fact-checked facts about atoms, each with the reason behind it. 5 more are in today's round and join this page after it closes.
The basics
Which element has the lightest atoms?
AnswerHydrogen
Hydrogen, element 1, usually has just one proton and one electron.
Going deeper
Which scientist discovered the electron in 1897?
AnswerJ. J. Thomson
J. J. Thomson found the electron by studying cathode rays at Cambridge in 1897.
Who led the gold foil experiments that revealed the atomic nucleus?
AnswerErnest Rutherford
Rutherford's team saw a few alpha particles bounce back from gold foil, showing a tiny dense nucleus.
The word 'atom' comes from a Greek word meaning what?
AnswerUncuttable
Atomos means uncuttable or indivisible, reflecting the old idea that atoms could not be split.
Expert level
A proton has roughly how many times the mass of an electron?
AnswerAbout 1,836
A proton is about 1,836 times as massive as an electron, so nearly all an atom's mass is in its nucleus.
Who discovered the neutron in 1932?
AnswerJames Chadwick
James Chadwick identified the neutral neutron in 1932 and received the 1935 Nobel Prize in Physics.
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