Transcript Atomic Structure

The History of Atomic
Structure
Democritus
 Named the atom
from the Greek
word “atomos”
meaning indivisible.
 Wrote that atoms
were the smallest
unit of matter to
keep its identity.
John Dalton
 England 1780’s
 All matter is made
up of atoms.
 All atoms of the
same element are
the same.
 Atoms combine in
specific ratios.
 There is nothing
smaller than an
atom.
J. J. Thomson
 Discovered the
electron while
running electricity
through a gas.
 Discovered that
electrons were
negative.
 “Plum pudding”
model of the atom.
Marie & Pierre
Curie
 Provided evidence
for the existence of
protons and
neutrons.
 Discovered radium
and polonium.
 Marie Curie was the
first female winner
of the Nobel prize
and the first double
winner.
Ernest
Rutherford
 Discovered that the
nucleus was
positively charged
and very tiny.
 Found that the
atom is mostly
empty space.
Niels Bohr
 Developed the
“solar system”
model of the atom.
 The nucleus in the
center of the atom
is made of protons
(+) and neutrons.
 Electrons (-) orbit
the nucleus like the
planets around the
sun.
Electron
Cloud Model
 The current model
of the atom.
 Electrons do not
orbit the nucleus in
orderly paths.
 Electrons move
around the nucleus
at near the speed
of light in a general
area.
 Research continues.
Summary
Protons
 Found in the
nucleus of the
atom.
 Have a charge of +1
 Have a mass of 1
atomic mass unit
(amu)
Neutrons
 Found in the
nucleus of the
atom.
 Mass of 1 amu
 Neutrons have no
charge.
Electrons
 Found in orbits
(energy levels or
shells) around the
nucleus.
 Travel at near the
speed of light.
 Charge is –1
 Mass is 1/1800th
amu.
What makes one element different
from another?
 The number of protons
is always the same as
the atomic number.
 The number of
electrons is usually the
same as the atomic
number.
 To find the number of
neutrons: take the
atomic mass, rounded
to the nearest whole
number, and subtract
the atomic number.
Finding the number of neutrons
The mass number of
this isotope of
lithium is 7.
Notice that 7 is
equal to the total
number of protons
and neutrons.
If you remove the
protons (atomic
number), the
neutrons are left.
Isotopes of Hydrogen
What do they have in common?
What are the differences?