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The Atom
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400BC ish
Indivisible, Solid Sphere
ModelDeveloped by Democritus. He
said all matter is composed of
indivisible tiny things made up
into small not being able to be
seen by the eye structures.
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400BC
Democritus
Democritus found that atoms are not all the same, they are eternal, and always moving. He made a theory on this to explain why and how atoms were so small, and what they were about. He proposed a more advance atomic theory.
http://www.philosophyprofessor.com/images/philosophers/democritus.jpg
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First person to name tiny particle of matter the
ATOM
His theory (not completely accurate):
•All elements are composed of indivisible atoms
•All atoms of a given element are identical
•Atoms of different elements are different,
meaning different mass-wise
•Compounds are formed by the combination of
atoms of different elements .
•Law of Definite Proportion or Composition or
Ratio.
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1803
John Dalton
He proposed the atomic theory. He inferred proportions of elements in compounds. He found the atomic weight, and chemical symbols. He also had the most useful atomic theory of matter. To come up with this, he tested gases and used evaporation to find out what the gases had on that mixture all together.
http://redescolar.ilce.edu.mx/redescolar/efemerides/septiembre2001/interna/dalton.gif
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Theory
a. Basic unit of matter is a tiny particle
called atom.
b. All elements are composed of indivisible
atoms
c. All atoms of a given element are
identical.
d. Compounds are formed by the
combination of atoms of different elements.
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1897
J.J. Thomson
He found electrons and subatomic particles
when he was working with cathode ray
tubes. He was working with glass tubes and
electricity and messed up and discovered
electrons.
http://www.phy.cam.ac.uk/cavendish/history/electron/jj_c1890.jpg
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1897
Plum Pudding Model
Discovered by J.J. Thomson. He said the
atom was a sphere of positive electricity,
with negative particles throughout. This
came around right after he discovered the
electron.
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Atomic Model Timeline
http://www.projectsharetexas.org/resource/
atomic-theory-dalton-thomson-and-
rutherfordontrack-chemistry-module-2-
lesson-1
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1911
Ernest Rutherford
He ionized gas using radiation, and found alpha and beta waves. He used his research and the magnetic properties of
iron to find radio waves. He also discovered the atomic
nucleus using others research and findings. To find this he did
the Rutherford experiment. Briefly, he used a thin foil made of
gold metal to find positive and negative charges in an atom.
http://www.newgenevacenter.org/portrait/rutherford.jpg
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Rutherford bombarded
gold foil with alpha
particles
Most passed through but
some were deflected
This is because alpha
particles are (+) and they
hit the dense (+) nucleus
of the gold atom thus
leading to the discovery of
the nucleus
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https://www.youtube.com/watch?v=kBgIM
RV895w
Rutherford’s Gold Foil
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1913
The Bohr Model
http://en.wikipedia.org/wiki/Bohr_model
Niels Bohr discovered this atom. It
shows a positively charged
nucleus surrounded by electrons.
This was mostly to explain the
Rydberg formula. The Bohr model
is a hydrogen model. It helps with
the learning of the quantum
theory.
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1913
Niels Bohr
Niels figured out the structure of the atom, and their radiations. He also started the basis of the quantum theory.
http://www.nrc-cnrc.gc.ca/education/elements/images/elements/Bohrium.jpg
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Most revolutionary model
Dense positive nucleus, with
electrons orbiting in shells
First model showing electrons
revolving around the nucleus
Based on past models and
experiments
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Sodium Atom
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Sodium atom shells
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Bohr’s Model of the atom
https://www.youtube.com/watch?v=CUk
3enr-m0w
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Discovered by
Thompson (-)
1/1836 amu
No charge,
subatomic particle
Subatomic particle,
1 amu (+)
An orbital is the area
where an electron can
most likely be found
Number of
protons+neutrons=atomic mass
Number of
protons=atomic numberAtomic
mass-atomic number=# of neutrons
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Wave- Mechanical ModelAlso called the charge cloud model, orbital
model, or quantum mechanical model.
Unlike the Bohr model does not show the
path of the electrons in definite, fixed
orbits it shows the most probable location
of an electron with distinct amount of
energy in areas called orbitals.
1. Orbital: Most probable region in which an
electron can be located.
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Wave-Mechanical Model
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Atoms of the same element
with different number of
neutrons (atomic mass),
same number of protons.
Example:
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Argon Isotopes
Naturally Occurring
Isotopes
Mass Number Natural
Abundance Half-life
36 0.3336% STABLE
38 0.0629% STABLE
40 99.6035%STABLE
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Isotopes
Isotope Atomic mass (ma/u) Natural abundance
(atom %)
Nuclear spin (I) Magnetic moment
(μ/μN)
32S 31.97207070 (25) 94.93 (31) 0 0
33S 32.97145843 (23) 0.76 (2)
3/2 0.643821
34S 33.96786665 (22) 4.29 (28) 0 0
36S 35.96708062 (27) 0.02 (1) 0 0
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1803
Dalton
1897
Thomson
1909
Rutherford
1913
Bohr
NOW
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Outer electrons are known as valence
electrons
Quantum numbers:
s,p,d,f- each represent a sublevel and
orbital.
Each letter has a coefficient to signify
which level it is in
s can hold 2 electron
p can hold 6 electrons
d can hold 10 electrons
f can hold 14 electrons
e.g, oxygen: 1s2 2s2 2p4
Each orbital can hold no more than 2
electrons
Orbital notation:
1s2 2s2 2p3
You are not allowed to fill up
the second set of arrows
until you have finished
putting an arrow in each box
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Ground State: in any given atom,
the electrons are found in the
lowest available energy level.
Excited State: when the
electrons move from lower
energy level to higher
energy levels. Unstable
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Electrons can
absorb specific
amount of energy
called quanta (sing.
Quantum)
When the electron falls back its releases a quantum of energy..
This energy appears as a photon of radiation of definite wavelength…
The light emitted by an element when its electrons return to a lower energy state can be viewed as a Bright –line emission spectrum.
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Bright Line Spectrum
The light emitted by an element when its
electrons return to a lower energy state
(excited state to the ground state)
Can be viewed as a bright-line spectrum
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When an electron jumps to a
shell at a higher level it is
know to be at an excited
state
When it returns to ground
state, it produces a light
spectrum
Each element produces a
different spectra
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http://science.hq.nasa.gov/kids/imagers/em
s/waves3.html
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BRIGHT – LINE SPECTRUM
https://www.youtube.com/watch?v=N8_S
iS8OlSU
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Homogenous Heterogeneous
Elements and compounds
are pure substance
(composition is same
throughout the material)
Law of Definite proportion:
atoms in compound exist in a
fixed ratio
Mixtures are like compounds
but can be separated
physically