1. Atomic Models Dalton - 1803 - round ball with a positive nucleus
Around 400 BC a Greek scientist 
called Democritus said that matter was 
made up of small particles he named 
'Atoma' (meaning indivisible).
Dalton round ball with a positive nucleus
Element made up of atoms that cannot be divided
Atoms of the same element are alike
Atoms of different elements can join in whole number 
ratios to form molecules

2. Thompson - discovered electrons in 1897
Rutherford - discovered the nucleus 1911
Based on his alpha-particle
scattering experiment on
gold, Rutherford concluded
that the atom consisted of
a hard central core where
most of the mass of the
atom rested.

3. http://web. visionlearning. com/ custom/chemistry/animations/ CHE1
Bohr - electrons 
travel in paths 
(energy levels) 
around the nucleus 
- 1913

4. Protons Electrons Neutrons Positive Mass = 1 amu = 1.67 x 10-24 g
Discovered by E. Goldstein in 
1886
Symbol – p+
Electrons
Negative charged
Mass = 1/1840 amu = 
9.11 x10-28
Discovered by J.J. Thompson in 1897 Symbol – e-1
Neutrons
Neutral
Mass = 1 amu = 1.67 x 10-24g
Discovered by James Chadwick in 1932
Symbol - no

5. The Atomic Nucleus P+ No Small Dense Positive charge Core of an atom
Contains protons and neutrons
Discovered by Ernest Rutherford 
in 1911 P+ No
Valence electron - an electron in the 
outermost energy level of an atom

6. Modern - electron cloud theory replaced Bohr’s model in 1925
Chadwick - discovered the neutrons in 1932
Modern Theory - electrons do not 
move in definite paths but the exact 
position, speeds and direction of 
electrons cannot be determined.
Modern - 
electron cloud 
theory replaced 
Bohr’s model in 
1925

7. e- enter lowest energy level first
p orbitals can hold a maximum of two electrons so all three together can hold a 
total of 6 electrons
As s orbital is shaped lie a sphere, so it has only one possible orientation in space. 
An s orbital can hold a maximum of two valence electrons

8. The Atom
2 protons = +2
2 neutrons = 0
2 electrons = -2
Net charge = 0

9. Atomic Number e - e - P+ no e - e -
Atoms are composed of 
protons, neutrons and electrons
Electrons surround the nucleus 
and occupies most of the volume 
of the atom
The number of protons in the 
nucleus of an atom
Each element has a different 
number of protons; therefore, a 
different atomic number
Number of protons = number 
of electrons
Therefore the atom is neutral
The Atom – 
mostly empty 
space
e
-
e
- P+ no
e
-
e
-

10. 6 Most of the mass of an atom is in the nucleus Protons = 1 amu
Mass Number
Mass Number
Most of the mass 
of an atom is in the 
nucleus
Protons = 1 amu
Neutrons = 1 amu
Electron = 1/1840 
amu
Mass Number = 
Protons + Neutrons
Neutrons = Mass 
number - Protons 12 C 6
Symbol
Atomic Number = p+

11. Neutrons = Mass Number - Atomic Number
Isotopes
3.2.9

13. Isotopes Same number of protons and electrons
Different number of neutrons
Therefore – Different mass numbers
10p+
12no
10p+
10no
10p+
11no 22 Ne 10 20 Ne 10 21 Ne 10

14. Atomic Mass Y-10 20% Y-21 80% mass X % = Relative Weight 10 X .20 = 2
Atomic mass = weighted average of the 
masses of its isotopes
You calculate the atomic mass based on 
relative abundance
Example: Copper atomic mass=
Isotopes – Cu and CU-65
Isotope Cu-63 more abundant
Y %
Y %
mass X % = Relative Weight
10 X .20 = 2
21 X .80 =16.8
Total = 18.8 amu

15. MASS Number Average Mass % Relative abundance Weigh Add Count
Kidney
Brown
Mac
Total
MASS
Weigh
Add
Number
Count
Average 
Mass
Mass/ Number
Don't do %
Part/Whole X100
Should equal 
100
Relative 
abundance
Divide % by 100
Should equal 1
Relative Weight
Relative 
Abundance X 
Average Mass

16. Hangman Atomic Structure Jeopardy http://www.quia.com/hm/110454.html