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Main
Energy Levels
1) Electrons follow paths called orbits, shells, or levels.
2)
Each shell can hold a specific maximum number of electrons. 3)
Each electron possesses a definite amount of energy. 4)
The radius of the orbit depends on the amount of energy that electron has and
on the attractive force the nucleus has for that electron.
Bohr model of the atom (with main energy levels
identified by number: 1 --> 7) shell
#1
closest to nucleus
can hold a maximum of 2 e shell
#2
next shell outward can hold a maximum of 8 e shell
#3
next shell outward
for elements Z = 1 --> 20, this shell can hold a shell
#4
next shell outward can hold a maximum of 32 e and
so forth
When scientist started measuring energy given off or taken in by atoms more closely they found: 1)
when e- absorb energy they move to higher energy levels (become
`excited e') this was found by spectrum analysis and the scattering
effects of Rutherford's alpha particles
2) when e- fall back to lower energy levels they must
lose this energy by emitting radiation, usually as photons of light 3)
if e- absorb too much energy they can be ionized (which
means completely removed from the electron cloud)
4) *** e- in the highest energy level (greatest
distance from nucleus) require the least energy to escape from the atom and
are usually the e‑ involved in chemical reactions
5) Bohr's model of fixed electron paths has now been changed to an
`electron cloud' model which describes areas of space around the nucleus where
electrons of various energy levels are to be found
See example of electrons shells on board
Match
example: 1)
the match itself contains potential energy (stored as chemical energy in
bonds) 2)
to release this fuel (by way of oxidation) and given off light and heat the
match must absorb energy which comes from the heat of kinetic energy of motion
(friction) as match is scratched across strike plate 3)
as energy is absorbed electrons become excited (absorb energy and move to
higher energy levels) and perhaps ionized (have absorbed enough energy to
break free from the electron cloud entirely) 4)
as kindling temperature is reached and oxidation takes place electrons
begin to fall back down the stair step energy levels and the electrons that
were ionized begin to recombine with ions left behind in such a way that they
must radiate away this excess energy as photons of light that we see or as
heat energy we can feel 5) continued combustion takes place as wood, oxygen in the air, and other chemicals in the match oxidize rapidly Subshells
The
electrons that are closest to the nucleus are held most strongly. In the
energy levels (shells) at the greatest distance from the nucleus, the number
of electrons .that each level can hold increases, and their attraction for
the nucleus decreases. a) 4 subsbells (found by spectral lines) have these names and symbols: sharp (s), principal (p), diffuse (d), fundamental (f) b)
these subshells differ in size, shape, and orientation in space
c) first main shell =
s subshell only = max. of 2 electrons in s subshell second main shell =
sand p subshell = max. of 6 electrons in p subshell third main shell =
s and p and d = max. of 10 electrons in d subshell fourth main shell =
s and p and d and f = max. of 14 electrons in f subshell
d)
filling order (example of tantalum with 73 electrons)
1s2 2s2 2p6
3s2 3p6 4s2 3d10 4p6 5s2
4d10 5p6 6s2 4f14 5d3
or in the core configuration [Xe] 6s2 4f14 5d3
2p3
2 is specific main energy level, p is subshell shape, and 3 is the
number of electrons in that subshell
e) Rules: 1)
main energy levels are numbered 1, 2, 3, 4, 5, 6, 7 2)
the larger the number of mainshell, the greater the volume of orbital (2s
orbital is larger than ls) 3)
the order in which subshells are filled usually follows energy ranking
starting with subshell lowest in energy and then working up the filling order
(with exceptions) 4)
within a given sublevel, each orbital is usually occupied by a single electron
before any orbital has 2 electrons (its maximum)
f) Added hints: 1)
the number of sublevels within a main. level is numerically equal to the
number of that main level 2)
the square of the main level number gives the number of orbitals in that level
3)
the number of orbitals multiplied by 2 gives the maximum number of electrons
in that main energy level. 4)
symbol used for electron spin up 5)
¯
symbol used for electron spin down
6) electrons can stay close together (in orbital) if spins are opposite 7)
*** NO more than 2 electrons (spin opposed) will occupy any one region of
space, orbital, or bond. *** |
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Page Last Updated: Friday March 02, 2007 Webmaster: Larry Jones Pickens County School District |