Unit 3 - Atomic Structure. Chapter 5 Addison/Wesley Textbook. Earliest Model. 450 BC – Democritis, a Greek philosopher, first uses the word “atomos” which means indivisible Definition of atom today – Smallest particle of an element that still retains properties of that element. Late 1700’s.
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This says that the same compound from any source always contains the same elements in the same proportion by mass
There are 3 major subatomic particles (protons, neutrons, and electrons).
There are basic particles that make these up but we will not discuss them
The proton also came from the cathode ray tube
The neutron was discovered by Chadwick, a student of Rutherford in 1935.
#protons = #electrons
(atomic mass unit)
# protons + # neutrons
that is why there are decimals