Historical Development of the Atomic Theory

1
Historical Development of the Atomic Theory
2
Democritus (must know)

• Ancient Greek philosopher
• (circa 400 BC)
• Matter is made of tiny particles that we cant
  see
• Atomos means indivisible
• Thought these spheres of matter were solid and
  could not be broken down further

3
John Dalton (1766 1844)

• English scientist and teacher
• Performed experiments
• 4 points to his atomic theory

4
Daltons atomic theorydo not need to know his
name, you DO need to know the points of his
theory

• All elements are made of tiny indivisible atoms
• Atoms of the same element are the same as each
  other and different from other elements
• Atoms of different elements can mix together in
  whole-number ratios
• Chemical reactions occur when atoms change how
  they are arranged.

5
J.J. Thompson (1856 1940)you do not need to
know his name, you MUST KNOW the cathode ray
experiment.

• English Physicist
• Passes electric current through a cathode ray
  tube
• The cathode ray is a stream of negatively charged
  electrons
• Electrons are a sub-atomic particle
• Must be a corresponding positive part to the atom
• discovers the electron

6
Credited with the Plum Pudding Model
7
Ernest Rutherford (1871 1937)you must know
him, you must know his gold foil experiment, you
must know what he concluded from it

• New Zealander who worked in England
• Gold Foil experiment

8
Diagram the gold foil experiment
An alpha particle (a)is a Helium nucleus (2
protons, 2 neutrons)
9
What was learned from the gold foil experiment

• Small, massive center called the nucleus
• Nucleus has a positive charge ()
• Electrons (-) are outside the nucleus
• Most of atom is empty space

10
Neils Bohr (1885 1962)you may need to know his
name associated with his atomic model.

• Danish Physicist
• Used Spectral Line Data from hydrogen
• Organized electrons into discrete shells or
  orbitals.
• The Bohr Model is what is used to explain
  electron configurations in Regents Chemistry

11
Modern Atomic Theory
12

• All matter is composed of atoms
• An element is composed of only one type of atom
• Compounds are different kinds of elements bonded
  together in definite proportions

13

• Atoms can be broken down into smaller units
  called subatomic particles
• Proton
• Neutron
• Electron

14
Proton

• positively charged
• Mass of 1 amu
• Found in the nucleus
• Atomic protons

15
Finding Protons

• Drag out periodic table

16
Neutron

• No charge (electrically neutral)
• Mass of 1 amu
• Also in the nucleus
• Atomic mass atomic

17
Calculating neutrons
1 Find the atomic mass
2 Round it to the nearest whole number 3 subtract
the Atomic number from it
18
Electron

• Negatively charged
• Mass of 0 (zero) amu
• Found outside the nucleus
• Shells or energy levels
• For all neutral atoms
• electrons protons

19
There is another super-secret place you can find
the electrons
Add those numbers They are the electron
configuration Well talk about them again. Shhh.
Dont tell anyone else.
20
Wave-Mechanical Model

• AKA (Also Known As)
• Quantum Mechanical Model
• Electron Cloud
• Deals with the probability of finding an electron
  in a certain area of the atom outside the
  nucleus.

21
(No Transcript)
22
Electron Shells(energy levels)

• (crack out your Periodic Table)
• Row of electron shells.

23
(No Transcript)
24
(No Transcript)
25
Valence Electrons

• electrons in the outermost energy level
• Determine HOW atoms react
• Column of valence electrons sort of

26
(No Transcript)
27
(No Transcript)
28

• Column 1 1 valence electron
• Column 2 2 Valence electrons
• Columns 3 12 there is no obvious pattern

29
(No Transcript)
30

• Columns 13 -18 10 fewer valence electrons than
  column number
• e.g.
• Column 14 4 Valence electrons
• Columns 15 5 valence electrons
• Exception, He has 2 valence electrons.

31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)