Download development of the atomic model

STRUCTURE OF AN ATOM
STRUCTURE OF AN ATOM
 ELECTRON - the
NEGATIVE particles
surrounding the
nucleus of an atom.
 discovered by JOSEPH
JOHN THOMPSON
STRUCTURE OF AN ATOM
 PROTON – positively
charged particle in the
nucleus of the atom
 Discovered by Eugene
Goldstein
STRUCTURE OF AN ATOM
 NEUTRON – a neutral
subatomic particle
present in the nucleus of
an atom
 Discovered by James
Chadwick in 1932
POEM ABOUT THE ATOM
I’m Penny the Proton and I’m pretty large,
I’ m considered a plus, with my POSITIVE charge.
My friends and I, in the nucleus we huddle,
It’s nice and cozy with neutrons to cuddle!
I’m Ned the Neutron and I’ pretty heavy,
I’m fat and lazy and take things steady.
You could call me “cheap” I’ve NO CHARGE at all,
I really am just a dense, NEUTRAL ball!
I’m Elvis the Electron and I’m pretty quick,
I fly round the nucleus at a fair old lick!
The protons and I, we tend to attract,
I’m NEGATIVE you see and that is a fact!
The Greek Model
 Democritus – Greek philosopher around the year
400 BC
 He concluded that atom could not be divided into
smaller and smaller pieces forever. Eventually,
the smallest piece of matter would be found.
 He used the word “atomos” to describe the
smallest possible piece of matter
The Dalton Model
 John Dalton – English chemist that proposed the
first atomic theory in 1803
Points of Dalton’s Atomic Theory
1) All elements are composed of indivisible particles
called atoms
2) Atoms of the same element are exactly
alike/identical. They are unique and
unchangeable.
3) During chemical reactions, there are changes in
the way the atoms combine, separate, or regroup.
Atoms are neither created nor destroyed.
4) Atoms combine to form compounds. They
combine in a definite ratio of small whole numbers.
Dalton’s Atomic Model
Thomson’s Discovery of Electron
The Thomson Model (1904)
 J.J. Thomson – English scientist who discovered
electrons in 1897
 Sometimes called the “plum pudding” model,
Thomson thought of an atom as being composed of
a positively charged material with the negatively
charged electrons scattered through it
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The Rutherford Model
 Ernest Rutherford – British physicist who, in
1908 proved the atom had a small, dense,
positively charged nucleus.
 Rutherford’s model proposed that an atom is
mostly empty space. There is a small, positive
nucleus with the negative electrons scattered
around the outside edge
Rutherford’s Experiment
•Over 98% of the _ particles went straight through.
•About 2% of the _ particles went through but were
deflected by large angles
•About 0.01% of the _ particles bounced off the gold foil
The Bohr Model
 Niels Bohr – Danish scientist who, in 1913,
proposed the “Planetary Model” of the atom
 Electrons move in definite orbits around the
nucleus, like planets moving around the sun.
Bohr proposed that each electron moves in a
specific energy level
 Sir James Chadwick discovered the neutron in
1935
Sample Atomic Structure
A Helium Atom
The Wave/Electron Cloud
Model
 Based on wave mechanics, this model
proposed that electrons have no definite path
in an atom
 The probable location of an electron is based
on how much energy it has.
 The more energy an electron has, the farther
it is from the nucleus
 The small positively charged nucleus is
surrounded by a large space in which there
are enough electrons to make the atom
neutral
Electron Cloud Model
Sample Atomic Structure
A Hydrogen
Atom
Hydrogen: a
proton
surrounded by an
electron cloud
Atomic Symbols
 Atomic Number (Z)  number of unit positive
charges
Number of Protons = Z
 Mass Number (A)  total number of protons and
neutrons
A = number of neutrons + number of protons
A = number of neutrons + Z
Atomic Symbols (Nuclide Notation)
Also called Element Notation
35
A
Symbol
Z
Cl
17
ISOTOPES are any of two or more forms of a chemical
element having the same number of protons (atomic
number) in the nucleus having different number of
neutrons.
Used for PET imaging and myocardial perfusion; investigation of a range
of diseases in human organs.
ISOTOPES OF HYDROGEN
Hydrogenation of
substances
Nuclear magnetic
Resonance - medicine
radioactive
IONS are atoms or molecules with a net electric
charge due to the loss or gain of one or more
electrons.
H+ : a positively charged
hydrogen ion
H : the
hydrogen
atom
H- : a negatively charged
hydrogen ion
References
 http://dbhs.wvusd.k12.ca.us/AtomicStructure/Atomic
Structure.html
 http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm