Download Atomic Structure Power Point

An atom is the smallest
whole part of an element.
Democritus, a Greek
philosopher, was the
first person to realize
that all matter is
composed of atoms.
John Dalton (~1800) proposed the
Atomic Theory, which stated that:
All matter is composed of atoms.
Atoms cannot be created or
destroyed.
Atoms of elements combine to
form compounds.
Each element is made up of
different kinds of atoms.
are made up of:
Electrons, which have a negative
charge.
Protons, which have a positive
charge.
Neutrons, which have no charge.
A stable atom has a neutral charge.
It has an equal number of positive
and negative charges.
Atomic number = # of protons
Atomic mass = proton # + neutron #
All atoms of the same element have
the same no. of protons. The proton
determines the position, or element
no. on the periodic table.
Hydrogen has 1 proton,
so its atomic no. is 1.
Hydrogen is element #1
on the Periodic Table of
the Elements.
How many protons does gold have?
79
How many electrons
does one atom of gold
have?
79
How many neutrons
does one atom of gold
have?
196.97 – 79 = 117.97 neutrons
So how can you have part of a
neutron, such as 119.97 ?
Because of ISOTOPES ! An isotope
is a form of an element that has the
same number of protons, but different
numbers of neutrons. The atomic mass
on the periodic table reflects the
average mass of all of the known
isotopes of an element. Each isotope
may have different characteristics.
How many protons does aluminum have? 13
How many neutrons does this element
have? 26.98 – 13 = 13.98 neutrons
How many electrons does aluminum have? 13
This is a
Bohr model
of a lithium
atom. The
Bohr model is
named after
Niels Bohr.
e
e
n
pnp
np
e
Atoms are arranged with protons
and neutrons in the nucleus, with
electrons orbiting around the
nucleus in energy shells.
In a Bohr model, each energy level can hold a
characteristic number of electrons.
K= 2
L= 8
M = 16
N = 32
K
N
M
L
Draw a Bohr model of oxygen:
e
e
At. # = 8
e
e
K = 2
8p
e
8n
e
e
e
L = 6