Transcript Atom Model History

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Fifth century B.C. Greek
philosopher
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All matter composed of
indivisible and
indestructible particles
called atoms (Greek for
uncuttable).
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Though later
challenged, many ideas
agreed with later theory
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Early 1800’s - Billiard Ball Model
Viewed the atom as a small, solid, indivisible
sphere.
Atoms of each element identical in mass and
properties.
Atoms of one element differ from another
atom.
Got the "ball" rolling for modern chemistry!
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Late 1800’s-Plum Pudding Model
Atom was a sphere of positive electricity which
was diffuse with negative particles imbedded
throughout
Discovered the electron
Experiments that passed electric currents
through gases at low pressure
Attracted to + charge so particles of current
must be –
Nobel Prize in physics in 1906.
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Solar System Model
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Discovered the nucleus- Gold Foil Experiment
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Atom mostly empty space with dense positively
charged nucleus surrounded by negative
electrons.
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Nobel Prize in chemistry in 1908
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flying dots = Alpha particles( +) emitted
green wall = detecting screen (where particles
hit)
yellow window in the middle = gold foil
as you see, 1/8000 alpha particles are repelled
backwards, that's because the nucleus is
VERY small, only few alpha particles hit it
completely and repel back.
Thus Rutherford knew that the nucleus was
super duper small!
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Modified Rutherford model- why electrons don’t crash into
the nucleus if + attract –
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Energy levels - electrons traveled in circular orbits and that
only certain orbits were allowed.
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Close to nucleus- lower energy level e- occupies
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Far from nucleus- higher energy level e- occupies
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Electron in one energy level or another not in between – like
a ladder
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Electrons gain or lose energy by changing energy level
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Difference in energy between levels (to move e-) = quantum
of energy
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Nobel Prize in physics in 1922
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Light- moving waves and particles
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Frequency- occurrences per time (1/s or s-1)
(v measured in Hz or cycles/second)
Speed- of light ( c ) 2.998 x 10 8 m/s
Wavelength- distance wave repeats – 2 consecutive
peaks (λ measured in m)
Stream of particles – energy Is determined by light’s
frequency To remove e-, particle of light needs min.
energy and a min frequency
Electromagnetic Spectrum – broad range of
wavelengths
Visible Spectrum: 400 nm (violet) to 700 nm (red)
Red: low frequency/ long wavelength
Violet: high frequency/ short wavelength
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The product of frequency and wavelength always
equals a constant, c, the speed of light
C = λv
Frequency and wavelength are inversely
proportional
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Ground State – lowest possible energy
Excited State - electron absorbs energy &
moves levels
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A quantum of energy in the form of light is
emitted when the electron drops back to a
lower energy level – an abrupt step.
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The light emitted by an electron from a higher
to lower energy level has a frequency directly
proportional to the energy change of the
electron.
Or….
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E=hxf
Where
E = energy measured in Joules (J)
h = Planck’s constant in J/Hz (J-s) = 6.63 x 10-34 J-s
f = frequency of light measured in Hz
If, c = λv
Then f = c
λ
And, E = h c
λ
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How likely to find an electron in various locations –
probability
Uncertainty Principle:
-exact position and momentum of e- is unknown;
instead look at probability … think of blades on an
airplane propeller or ceiling fan
Quantum Number – specifies the properties of
electrons
Electron Configuration- specific dispersal of
electrons among subshells (or sublevels)
Follow 3 principles:
1. Aufbrau- electrons occupy lowest
energy orbital first
1. Pauli Exclusion- orbital may describe
at most two electrons
1. Hund’s Rule – orbital of a sublevel fill
up by a single electron before pairing
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2n2 where n = quantum number designation
and indicates energy level
Quantum Number (n)
Shell Capacity (2n2 )
1
2
2
8
3
18
4
32
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The left-most columns include the alkali metals and the
alkaline earth metals. In these elements the valence
s orbitals are being filled
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On the right hand side, the right-most block of six
elements are those in which the valence p orbitals
are being filled
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These two groups comprise the main-group
elements
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In the middle is a block of ten columns that contain
transition metals. These are elements in which d
orbitals are being filled
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Below this group are two rows with 14 columns. These
are commonly referred to the f-block metals. In these
columns the f orbitals are being filled
Quantum #
Principle
Angular
Momentum
(Azimuthal)
Magnetic
Spin
Symbol
n
l
ml
ms
Possible Values 1,2,3,4,…
s, p, d, f
… -1,0,+1…
+,- 1/2
Characteristics
Shape
Orientation in
space
Magnetic spin
Size and
energy level *
*bigger number,
higher energy
level
n=1, ground
state
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Address of Atom
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Periodic Table is the Map
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Ions-Isoelectronic
Cations  Previous noble gas as core
Anions  next noble gas as core
Paramagnetic-one or more unpaired electrons
Diamagnetic – all electrons paired
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