Transcript Atomic Theory

Atomic Theory
What is an Atom?
An ATOM is the smallest part of an
element that has all of the element’s
properties.
 Atoms of different elements are different
from each other.

Atomic Theory
This is the study of the nature of atoms
and how they combine to form all types of
matter.
 It explains how atoms make up their
elements and how they make up all other
forms of matter, including compounds and
mixtures.

Ancient Atomic Theories
The idea that matter is made up of
combinations of simpler forms of matter is
very ancient.
 Ancient Greeks – thought that matter was
all made up of 4 elements – Fire, Water,
Earth and Air
 Ancient China – thought there were 5
elements – Fire, Water, Wood, Metal and
Earth
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John Dalton
In the early 1800’s a scientist and teacher,
John Dalton, suggested that matter is
made up of atoms.
 He believed that atoms could vary in size,
mass or colour.

Dalton’s Atomic Theory
All matter is made up of small indivisible
particles called atoms
 All atoms of an element are identical to
each other in size and mass
 Atoms of different elements have different
properties
 Atoms of different elements combine in
specific ways to form new substances

Dalton’s Atoms
J.J. Thomson
In the late 1800’s an English physicist
researched atoms and decided that he
thought atoms might be made of a
combination of particles.
 He experimented with electric currents in
glass tubes called cathode ray tubes.
 Using this tube he was able to cause nonradioactive atoms to produce streams of
negatively charge particles that were later
found to be electrons.

J.J. Thomson
In 1897, Thomson proposed a
revolutionary new model for atoms, in
which each atom was composed of
smaller particles
 He discovered that atoms were composed
of both positive and negatively charged
particles.

Thomson’s Model of the Atom
This can be
compared to as a
blueberry muffin.
The blueberries
represent negative
charges, and the
batter of the muffin
represents positive
charges.

New Zealand born scientist tested
Thompson’s model of the atom while
working in England

Rutherford’s famous “Gold Foil”
experiment led him to include a nucleus in
his atomic model

Rutherford shot positively charged
particles at a very thin foil of pure gold
In the experiment most high speed
positive particles went right through the
gold foil, however some bounced back
WHY? …. Because of the gold’s NUCLEUS!

The nucleus
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Rutherford discovered the nucleus. The
nucleus is the centre of the atom
He also discovered that the nucleus
contains most of the atom’s mass. The
nucleus is far larger than the rest of the
atom.
He calculated that comparing the size of
the nucleus to other atomic sub-particles
was like comparing a football field to a
green pea.

Based on the “Gold Foil” experiment
Rutherford revised the existing atomic
model to include a nucleus

Similar to Thomson’s model except that
all of the atom’s positive charge and mass
were concentrated at a tiny point in the
centre of the atom and the electrons
surrounded this point

Chadwick was Rutherford’s student and
he refined the concept of the nucleus

He discovered that the nucleus contains
neutral (no charge) particles called
neutrons and positive charge particles
called protons

Each neutron has almost the same mass
as each proton in the atom

Danish physicist that helped transform
Rutherford’s model to a model that we use
today

Bohr suggested that electrons surround the
nucleus in specific energy levels called
energy shells

He found that electrons jump between these
energy shells by gaining or losing energy

The max number of electrons in the first
three energy shells are; 2, 8, and 8
respectively
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Most advanced and
accurate model of the
atom
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Electrons exist in
specific energy levels
that surround the
nucleus in a form
resembling a cloud