Atomic structure
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What does an atom contain?
Protons and neutrons.
Why is an atom neutral?
It has an equal number of protons and electrons. The positive charge balance out the negative charge.
Electron mass
0.0005
Proton mass
1
Neutron mass
1
Electron charge
-1
Proton charge
+1
Neutron charge
0
Radius of an atom
About 1 x 10-10 m
Mass of an atom
1 x 10-23 g
What is an isotope?
Elements with the same atomic number but different mass numbers are isotopes.
Elements with the same group
With the same number of electrons in the outer shell are arranged vertically.
Elements with the same period
In order of how many shells the electrons occupy are arranged horizontally.
Development of atomic theory?
• An early theory of atoms was developed by John Dalton. His explanation was provisional, but later was confirmed by later evidence. When J.J. Thompson, Romford and Bohr found new evidence, their explanation changed the model of the atom. With later evidence their predictions were confirmed. • Ideas can also change rapidly falling on expected results. Geiger and Marsden had some unexpected results which made significant contributions to Rutherford and Bohr’s idea.