ERSC 1F90 Lecture Notes - Lecture 2: Richard Feynman

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9 Oct 2011
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"All Things Are Made of Atom" - Richard Feynman
Atoms
Building blocks of all matter
To be more precise:
An atomic mass of 1u = 1.67262158 ×10-24 grams
An electron has 0.05% of the mass of a proton.
(20 electrons would have 1% of the mass of a proton).
A proton has a mass equal to 99.8% of a neutron.
A Brief Review Of Chemistry
Monday, September 19, 2011
7:22 PM
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To be more precise:
An atomic mass of 1u = 1.67262158 ×10-24 grams
An electron has 0.05% of the mass of a proton.
(20 electrons would have 1% of the mass of a proton).
A proton has a mass equal to 99.8% of a neutron.
The number of electrons equals the number of protons in an atom’s nucleus (their charges balance so that they are electrically neutral).
Electrons occur in spherical "shells" about the nucleus.
A shell is a particular region where electrons are most likely to be at a given instant in time as the orbits are not simple as shown below
Electron shells are also termed "energy levels" and each contains a specific number of electrons
When electrons are added or lost, the atom is no longer neutral, it has a charge that is either positive or negative
Such charged atoms are termed IONS
Neutral atom:
Number of protons (+) equal to number of electrons (-)
(net charge is 0)
Positive ion (Cation):
(net charge is +, ion has a positive charge
number of protons (+) is greater than number of electrons (-)
Negative ion (Anion):
(net charge is -, ion has a negative charge)
number of protons (+) is less than number of electrons (-)
An atom of sodium (Na) has 11 protons, 11 neutrons and 11 electrons; 2 electrons in the inner shell, 8 filling the 2nd shell and one electron in the
valence shell.
Electrical Charge
6 protons - +6
6 neutrons - 0
6 electrons - -6
Net charge - 0
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