John Dalton
William Crookes
J.J. Thomson
Ernest Rutherford
ATOMS
Early Theories About ATOMS
Ancient Greeks- 4 Materials:
(2500 years ago)
-Earth -Fire
-Air -Water
-Ex. Wood= Earth+Fire
Early Theories About ATOMS
Democritus (Greek thinker) – All
matter is made up of Atoms
“Cannot be
divided” solid
spheres(No one believed
him) (930 BC)
1808 John Dalton
-Proved that matter is made up of
Atoms
- Different elements
have different masses
1808 - John Dalton
(By putting substances
together to form new
substances and taking them
apart chemists discovered that
ALL matter is made of
elements)
-Element – matter made of atoms of
only one kind (periodic table of elements)
1870 - William Crookes
-Used a cathode ray tube to show
streams of particles
1897 - J.J. Thomson
-Discovered the Electron
(opposite side)
- Bent Crookes stream with a magnet
did this with many gases and many elements
Plum Pudding
model
http://www.aip.org/history/electron/jjsound.htm
-The Nuclear Atomic Model
1911 - Ernest Rutherford
Used by
modern
scientists
1911 - Ernest Rutherford
-The Nucleus – the small central core
of an atom where most of the mass is
located
-protons & neutrons
- positive charge
-(electrons found in a cloud around it)
Electron Cloud -
-Region around the nucleus in which
the electrons travel
Dalton
Thomson
Rutherford
Dalton
Thomson
Rutherford
Atomic Particles-The basic building blocks of atoms
Particle
charge
found
Electron
- negative outside nucleus
Proton
+ positive inside nucleus
Neutron No charge inside nucleus
Proton
Neutron
Electron
Size of Atomic Particles-Sooooo small that scientists use:
Atomic Mass Unit (u) – A unit used to
express the masses of atomic particles
and atoms (1u=1.66 x 10-27Kg)
Electron
Proton
Neutron
0 u (1/1836)
1u
1 u (1837/1836)
Scientific Models -Used when objects can’t be studied
directly
Ex. Stars, Atoms
-Many experiments
-(how do atoms behave under different
conditions)
Atomic Number - The number of
protons in the nucleus of an atom
Element #of protons # of electrons
Hydrogen
1
1
Oxygen
8
8
Sulfur
16
16
Gold
79
79
In a normal atom positive charges (proton)
cancel out negative charges (electrons)
Electrons in motion
1913 –Niels Bohr –
electrons can follow
only certain orbits
Electron Arrangement
Energy Level – A region around an
atomic nucleus in which electrons
move
Ex. He
+
Ex. C
Nucleus
2 8 18 32
+
Symbols of Elements -
Berzelius
(Swedish Scientist)
Atomic Symbol – 1 or 2 letters used
to represent an atom of an element
1st letter – ALWAYS CAPITALIZED
2nd letter (if there is one) – ALWAYS
lower case
- Based on the element name
(sometimes the Latin name)
The Periodic Table of Elements
Symbols of Elements
Hydrogen
1
H
1.008
Name of Element
Atomic Number
Symbol
Atomic Mass
The Number of Particles in a Nucleus
Protons = Electrons
Mass Number = Protons + Neutrons
Mass Number – The sum of the
protons and Neutrons in an atom
(different atoms have different mass #’s)
Element
Atomic Mass # Proton Neutron Electron
#
#
#
#
Lithium
3
7
3
4
3
Boron
5
11
5
6
5
Nitrogen
7
14
7
7
7
10
20
10
10
10
Neon
Isotopes- Atoms whose nuclei contain
the same # of protons, but different #s
of Neutrons
Ex. Hydrogen-1, Hydrogen-2, Hydrogen-3
(deuterium) (tritium)
+
+
+
Atomic Mass- The average of all the
masses of the isotopes of a particular
element
-Round to the nearest whole #= Mass #