2. HIROSHIMA 1945

3. August 6th, 1945

4. Part 1: Atomic Structure
ATOMIC THEORY
Day 1
Part 1: Atomic Structure

5. The Origin of the Atom
Day 1

6. Changes in the Model of the Atom
Day 1

7. 1. DALTON
- everything is made of atoms - different elements combine to form compounds in simple whole ratios - each element has its own unique type of atom with a characteristic weight - small indivisible solid particle model

8. 2. THOMSON
- discovery of subatomic particle (electron) Cathode ray experiment - rays are particles, not waves - new particles are negative, lighter than smallest atom (hydrogen) - plum pudding model

9. 3. RUTHERFORD Thin gold foil experiment
alpha particles mostly pass through foil
but sometimes deflected back when they hit something massive
thus, atom made mostly of empty space
core of positively charged material, where most of the mass of the atom is (nucleus)
why don’t negative electrons give in to the pull of the positive nucleus and collapse inwards?

10. 4. BOHR
- negatively charged electrons found in concentric circular orbits around the positive charged nucleus - electrons found at fixed energy levels orbiting at fixed distances from the nucleus - path closest to nucleus = lowest energy level - energy higher the farther the orbits are from the nucleus - the farther the electron is from the nucleus, the less attraction it feels - electrons can jump from one energy level to another, but are not found between levels - they lose or gain a discrete package of energy (quantum of energy) every time it jumps levels  quantum leap - explains why each element has a certain number of electrons available for reactions - the electrons found on the outer most orbit  valence electrons - planetary model

17. EXAMPLES Any atom containing 3 protons must be…?
2. A neutral sodium atom has _____ electrons

18. IONS
If electrons are added to or subtracted from a neutral atom, the resulting particle is called an ION
 Electrons have a NEGATIVE charge so:
SUBTRACTING a NEGATIVE charge produces a POSITIVE ion
ADDING a NEGATIVE charge produces a NEGATIVE ion

20. EXAMPLES
1. If an electron is added to a neutral F atom, then the ion is written as: 2. If two electrons are removed from a neutral Ba atom, then the ion is written as:

21. Atomic Mass
Since both neutrons and protons have a molar mass of approximately 1 g, then:
- Total mass of an atom = total number of protons and neutrons
*the electrons are too light to make an appreciable contribution to the mass of an atom
ATOMIC MASS = the total # of protons and neutrons
Thus,
NUMBER OF NEUTRONS = ATOMIC MASS – ATOMIC NUMBER

22. EXAMPLES
Find the number of protons, neutron and electrons in the following atoms: a) Al b) C

23. …But, then why is it that the atomic mass of some elements is not a whole number?... 

25. or..
- atomic species having the same atomic number, but different mass numbers

36. Now try it with ions!
Find the number of protons, neutron and electrons in the following ions:
56Fe3+
2) 76As3-
3) 201Au+
4) 82Br -

37. Extra Practice…

38. Extra Practice…

39. Natural Mixtures
The molar mass of chlorine is 35.5 g. Since there can’t be 0.5 of a proton or neutron, then this atomic mass MUST represent an AVERAGE value of a MIXTURE of isotopes… Example: Find the average atomic mass of 1) Cl, given that is composed of 75.77% Cl-35 and 24.23% Cl-37

40. Natural Mixtures
Now you try… Find the average atomic mass of: 2) B, given that is is composed of 18.8% B-10 and 81.2% B-11