1. Chapter 3 – Atomic Structure
Development of the Atomic Theory

2. Democtritus
Greek
First coined the term “Atom” which means invisible and indivisible.
Came up with the theory while trying to starve himself to death.
Aristotle had opposing theory which was believed for 2000 years

3. Boyle & Newton Robert Boyle Isaac Newton
Began ‘experimental chemistry’
Studied gases
Worked with Newton to bring alchemy out of the “dark ages” . Eventually became Chemistry.
Isaac Newton was one of the first people to propose a “mechanical universe.” He believed that the universe is made up of small solid masses that are constantly in motion. This idea is known as “The Mechanical Universe” idea.
Wrote article “Skeptycal Chemyst”

4. John Dalton
John Dalton formulated the Atomic Theory which states that:
atoms cannot be divided or separated
atoms of one element are the same
atoms of an element are different than atoms of other elements
atoms of different elements can be combined in whole number ratios to form compounds
Used actual experimental work from Antoine Lavoisier (Law of conservation of Mass) and Joseph Proust (Law of Definite Proportions) to support his theory.

5. Atomic Mass
The atomic mass on the Periodic Table of Elements is a WEIGHTED AVERAGE.
Measured in atomic mass units (amu)
The amu is based on 1/12 the mass of a carbon-12 atom
1 amu = 1.66 x kg

6. The Mole SI unit for amount of a substance is the mole
1 mole = 6.02 x 1023 particles
A particle can be an atom, ion, molecule, compound or formula unit
This is called Avogadro’s Constant
1 mole of a substance = mass of substance from PTE in grams
6.02 x 1023 particles of a substance = mass of substance from PTE in grams

7. Modern Atomic Structure

8. JJ Thomson
Experimented with Cathode rays.
Based on the work that he did, he discovered electrons, the first subatomic particle
He also developed a model of the atom called the “plum pudding” model.
Because of Thomson’s work, Dalton’s theory was adjusted.

9. Rutherford Student of Thomson.
Designed gold Foil Experiment to prove Thomson’s model.
His experiment disproved Thomson and he proposed his own theory, the nuclear model of the atom.

10. Modern Atomic Structure
Scientists now know that there are three major subatomic particles: protons, neutrons and electrons.
Particle
Location
Mass
Charge
proton
nucleus
1 amu +
neutron
none
electron
orbit nucleus
(in the electron cloud)
1/2000 amu -

11. How does this relate to the PTE?
You can use the periodic table of elements (PTE) to figure out how many protons, neutrons and electrons are in any atom on the table.
Neutrons can be found by subtracting the atomic mass from the atomic number:
N = A - Z
Atomic mass (A) = p + n in the nucleus Au
197 79
Atomic number (Z) = number of protons in the nucleus

12. Atoms, Ions and Isotopes
The number of protons in an atom NEVER changes. This is how you identify an element. If the number of protons are changed, you have a whole new element. Atoms are electrically neutral (protons = electrons).
If an atom is heavier/lighter than expected (greater or lower atomic mass than on the PTE), neutrons have been added or lost. This is now an isotope.
If an atom becomes charged, it has lost (+) or gained (-) electrons. It is now an ion.

13. Rb+1 Ni Name Symbol A Z P N E Atom, Ion or Isotope? uranium 92 148 5046 85 37 59 28 48 62
Rb+1 Ni

14. Name
Symbol A Z P N E
Atom, Ion or Isotope?
carbon 8 54 33 40 28
gold
207 43 19 18

15. ELEMENT
SYM A Z P N E
ATOM, ION OR ISOTOPE 13 14 79
114 48 17 18
197 80 7 3 2 83
130
240 92 74 58 88 38 36 24 25 19 20 51 54

16. ELEMENT SYM A Z P N E ATOM, ION OR ISOTOPE Aluminum Al 27 13 14 Atom
Gold Au
197 79
118
Cadmium Cd
114 48 66
Isotope
Chlorine Cl 36 17 19 18
Ion
Mercury Hg 80
117
Lithium Li 7 3 4 2
Bismuth Bi
213 83
130
Uranium U
240 92
148
Tungsten W
184 74
110
Cerium Ce
140 58 82
Strontium Sr 88 38 50
Chromium Cr 49 24 25
Potassium K 39 20
Antimony Sb
122 51 71 54
ion 27 13
197 79
114 48 36 17 -1
197 80 7 3 +1
213 83
240 92
184 74
140 58 88 38 +2 49 24 39 19
122 51 -3