1. History of the discovery of Atomic Structure

2. Democritus and Aristotle
Atomos—greek for indivisible
Earth wind fire and water—4 elements

3. John Dalton
English Chemist

4. History
Dalton: Comes up with earliest definitions of elements and compounds
Dalton: model of atom is a solid sphere
Dalton: comes up with the definition of law of constant composition

5. Law of constant composition

6. A. Dalton’s Atomic Theory
Dalton’s Atomic theory states:
All elements are composed of atoms.
All atoms of a given element are identical.
Atoms of different elements are different.
Compounds consist of the atoms of different elements.
Atoms are not created or destroyed in a chemical reaction.

8. JJ Thomson
British Physicist

9. A. The Structure of the Atom
Experiments by J.J. Thomson showed that atoms contain electrons.
Cathode ray tube

10. JJ Thomson: Discovers the electron with the cathode ray tube,
JJ Thomson: Model of atom is a plum pudding

11. A. The Structure of the Atom
The Plum Pudding Model

12. Ernest Rutherford
British/New Zealand Chemist

14. A. The Structure of the Atom
Rutherford’s Experiment

15. More History Rutherford: Gold Foil Experiment
Rutherford: Discovers positively charged nucleus, atom mostly space
Rutherford: Model of small positively charged nucleus, electrons in space

16. A. The Structure of the Atom
Results of the Rutherford experiment
(a) The results that the metal foil
experiment would have yielded if the
plum pudding model had been correct
(b) Actual results

17. Introduction to the Modern Concept of Atomic Structure
Ernest Rutherford showed that atoms have internal structure.
The nucleus, which is at the center of the atom, contains protons (positively charged) and neutrons (uncharged).
Electrons move around the nucleus.

18. Niels Bohr
Niels Bohr studied the spectrum lines from hydrogen gas that was excited. He determined that when a Quantum of energy hit an electron, it would jump a specific amount to a different orbit.
His model basically said the electrons orbit the nucleus in specific energy levels, like a planet orbits the sun
The problem was that this only worked for hydrogen

19. Schrodinger
Erwin Schrodinger took Bohr’s idea, but said that instead of electrons orbiting in specific energy levels, they acted as waves and orbited in orbitals. This was supported by A LOT OF MATH.
Therefore, instead of electrons orbiting in specific energy shells/levels, they were found in electron clouds. Energy still defined which orbital they were found in.

21. James Chadwick 1891-1974 English Physicist
In studying alpha particles he found evidence of a new type of radiation with no charge and a mass similar to the proton
This he called the neutron

22. Protons
positively charged subatomic particle
found in the nucleus of an atom.
charge of 1+
Mass of 1 a.m.u.

23. Atomic Number
equals the number of protons in an atom of that element.
Atoms of different elements have different numbers of protons

24. Neutrons
neutral subatomic particle
found in the nucleus
mass 1 a.m.u.

25. Mass Number
Mass Number is protons + neutrons.
Sodium =
Or can say sodium-23

26. Electrons
negatively charged subatomic particle
found in the space outside the nucleus (electron cloud)
charge of 1−
So small virtually no mass

27. Isotopes Two atoms of same element with different masses:
What is the same about each group of elements? What is different?

28. Count: How many
Neon-22
Neon-20
Neon-21
What percentage is this of
100?
What would the average
Mass of these be?

29. Atomic Weight
Atomic weight = calculated using % isotope abundance for each isotope and the mass of each isotope.

30. Atomic Weight 2 isotopes of Bromine:
one has mass of amu, and abundance of 50.69%
one has mass of amu, and abundance of 49.31%
What is the atomic weight of Bromine?

31. Atomic Mass Unit
Masses of the fundamental atomic particles are expressed in atomic mass units, or amu. One atomic mass unit, 1 u, is 1/12 of a carbon atom.
1 amu = x g

32. Niels Bohr
1911
Developed solar system model
Electrons orbit in specific paths

33. Bohr Model Simplified model of electrons
2 electrons fit in first energy level
8 electrons fit in second energy level
8 electrons fit in third energy level**
***I just lied to you