1. Atomic structure chp 3 sec 2
The Greek model, Dalton’s Model, Thomson’s model, Rutherford’s model, Bohr’s Model and the Modern Model

2. The Greek Model
Democritus said matter could not be divided into smaller and smaller pieces for ever .
He proposed the atoms
and called it Atomos
which means not divisible.
He was an Atomist.

3. Atomist used Indirect Evidence
Greek philosophers had only indirect evidence in which to study from. There were no microscopes,
This is evidence you get without seeing or touching

4. Modern Atomic Theory (Dalton)
All matter is composed of atoms
Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!
Atoms of an element have a characteristic average mass which is unique to that element.
Atoms of any one element differ in properties from atoms of another element

5. Thomson’s Atomic Model
Thomson believed that there were negative particles like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

6. Conclusions from the Study of the Negative particle
Atoms are neutral, so there must be positive particles in the atom to balance the negative charged particles
The negative particles are called electrons and they have so little mass that atoms must contain other particles that account for most of the mass (the positive pudding)

7. Rutherford’s Gold Foil Experiment
Alpha () particles are helium nuclei
Particles were fired at a thin sheet of gold foil
Particle hits on the detecting screen (film) are recorded

8. Rutherford’s Findings
Most of the particles passed right through
A few particles were deflected
VERY FEW were greatly deflected
“Like howitzer shells bouncing off of tissue paper!”
Conclusions:
The nucleus is small
The nucleus is dense
The nucleus is positively charged

9. Bohr’s Model
Bohr stated that electrons orbited around the nucleus like planets around the sun and each orbit was a different energy level.

10. The Modern Model
Electrons are behaving more like waves than planets and they vibrate back and forth.
They are like bees around a hive.

11. Electron shell configuration
The number of the shell denotes how many can fit

12. Atomic Particles Particle Charge Mass # Location Electron -1
9.109 x
Electron cloud
Proton +1
1.673 x 1
Nucleus
Neutron
1.675 x10-27

13. Amu= SI unit for atomic mass 6 C Carbon 12.0107
Atomic number (Z)
Protons &
electrons Symbol
Element name
Atomic Mass (A)
Protons Neutrons
Amu= SI unit for atomic mass 6 C
Carbon
amu

14. Atomic Number
Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
Element
# of protons
Atomic # (Z)
Carbon 6
Phosphorus 15
Gold 79

15. Mass # = p+ + n0 Mass Number
Mass number is the number of protons and neutrons in the nucleus of an isotope.
Mass # = p+ + n0
Nuclide p+ n0 e-
Mass #
Oxygen - 10 - 33 42
- 31 15 18 8 8 18
Arsenic 75 33 75
Phosphorus 16 15 31

16. Ions
Ions gain/lose electrons to become happy and by using the oxidation number you can determine how many.

17. Isotopes
Isotopes are atoms that
gain/lose neutrons and their mass changes.
The mass on the periodic table is the average of all isotopes

18. Composition of the nucleus
Atomic Masses
Atomic mass is the average of all the naturally occurring isotopes of that element.
Isotope
Symbol
Composition of the nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
7 neutrons
1.11%
Carbon-14
14C
8 neutrons
<0.01%
Carbon =