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ELECTRONS
• Negatively charged particle surrounding the
nucleus
• Electrons move quickly around the nucleus
at a rate of billions of times each second.
• In a neutral atom the number of electrons
equals the number of protons
Location of the electron
• Depends on how much
energy the electron has
• Arranged in energy
levels
• Lower energy levels
are closer to the
nucleus
Drawing Energy Levels
• Start with the lowest
energy level
• Fill energy level
completely before
placing electrons in
the next energy level
Energy levels
• 1st energy level can
hold 2 electrons
• 2nd energy level can
hold 8 electrons
• 3rd energy level can
hold 18 electrons
• 4th energy level can
hold 32 electrons
Energy Sublevels
• 1st energy level - S orbital 2 electrons
• 2nd energy level - S orbital 2 electrons
P orbital 6 electrons
• 3rd energy level - S orbital 2 electrons
P orbital 6 electrons
D orbital 10 electrons
• 4th energy level - S orbital 2 electrons
P orbital 6 electrons
D orbital 10 electrons
F orbital 14 electrons
Electron Shell Structure
•
The Octet Rule:
•
In general, atoms are most stable when
they have 8 electrons in their outermost shell. (Octet means 8.) The
exception is the first shell which is most
stable with TWO electrons. If you know
the Atomic Number and Mass Number
of an element and the maximum
number of electrons in each electron
shell you can draw a diagram of the
element.
Order of Orbital Filling
• Electron configuration
Electrons and light
• When electrons absorb
energy they move out
to the next energy
level
• When they lose energy
they drop down a level
and give off light
Colorado - univ of Bolder
• Cool site
• http://www.colorado.edu/physics/2000/inde
x.pl
Isotopes
• Atoms of the same element that have a
different number of neutrons
• Round the atomic mass to the nearest whole
number to find the number of neutrons in
the most common form of the atom
• Mass numbers of isotopes differ because the
number of neutrons is different