Download Introduction to the Atom

Introduction to the
Atom
Understanding the basis for all
matter in the known world.
Development of the atomic theory
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430 BC Democritus proposed
the idea that matter is formed
of pieces that are so small
they could not be seen.
Democritus was the first to
describe these small pieces
as “atomos” which is Greek
for “uncuttable”. We today
use a variation of this word
called the “Atom”.
Daltons Atomic theory
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John Dalton used evidence
from a variety of experiments
and inferred that atoms in
nature had different
characteristics.
Dalton theory stated that
atoms of the same element
are the same, atoms of
different elements have
different masses, and that
one atom can not be changed
into another type of atom.
The Thomson model of the atom
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Thomson figured out that
atoms themselves had no
electrical charge, so he
figured that each atom
must have both a positive
and a negatively charged
particle within them which
allows the atom to remain
neutral. The negative
portion of an atom became
known as the electron.
Rutherford’s atomic model
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Rutherford figured out that not all
portions of an atom weighed the
same. The heaviest part of the
atom was the nucleus.
Rutherford’s work allowed us to
understand how the atomic
weight of an atom is always
determined by the contents of the
nucleus, and that electrons carry
almost no mass or weight.
The nucleus consists of protons
and neutrons.
Cloud model
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Established in the 1920’s
Based on the understanding of
how electrons do not orbit
around the nucleus like planets
around the sun.
Electrons can be found in a
cloud which surrounds the
nucleus in a unpredictable
manner. The electron cloud is a
visual model. The electrons
movement is related to the
energy level of the electron
itself.
The modern atomic theory
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1932 the neutron is
discovered in the nucleus.
The neutron has no
electrical charge.
With the discovery of the
neutron and the
understanding of the
protons and electrons the
atomic theory was
established.
electron
neutron
proton
The Atomic Theory
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The atomic theory has five
important points.
1) Elements are made of atoms.
2) Atoms of a single element are
identical and have the same
properties.
3) Atoms of different elements
combine to form compounds.
4) Compounds contain atoms in
given ratios
5) Atoms can combine in different
ratios to form multiple atoms.
Particles of an atom
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Atoms consist of three
types of particles.
Electrons, protons and
neutrons.
Protons and Neutrons
are found in the
nucleus.
Electrons are found in
the “shell” which
surrounds the outside
of the nucleus.
Particle
Symbol
Charge
Mass
(amu)
Proton
P+
1+
1
Neutron N
1
1
Electron e-
1-
1/1836
What is the amu and the Atomic
number?
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The amu is the measurement of
weight of an atom. The amu is
the atom mass units. The amu
system of measurement
assigns one (1) amu to both
protons and neutrons.
The atomic number represents
the number of protons an atom
contains in the nucleus.
An example is oxygen. The
atomic number of oxygen is
eight.
What are isotopes
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Isotope
Protons
Neutrons Mass
Number
Carbon
12
6
6
12
Carbon
13
6
7
13
Carbon
14
6
8
14
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Isotopes are atoms of an
element which have
different number of
neutrons which has an
effect on the weight of the
atom.
Isotopes are identified by
the mass number which is
the number of protons and
neutrons in the nucleus.
An example is on the left
which are all variations of
the element carbon.