1. EARLY HISTORY OF ATOMIC THEORIES

2. DALTON’S THEORY Matter is made up of indestructible atoms.
Law of definite proportions:
Elements combine in a characteristic ratio
Law of multiple proportions:
Some elements have more than one combining
capacity
Law of conservation of mass:
Atoms cannot be created nor destroyed

3. THOMSON’S THEORY “The Raisin Bun model: e Raisin Bun” model:
+ and – charges are mixed together
Gave us electrons
Atoms can gain or lose electrons to form ions
Said that the identity of an element was based on its number of electrons

4. RUTHERFORD’S THEORY
Atoms have a tiny nucleus which contains positive & neutral charges and makes up the majority of the mass of the atom
Electrons are negative and occupy most of the volume of the atom.
Protons tell us the identity of the element

5. The Big Problem with Rutherford’s Model
e-are traveling in a circular orbit always changing directions and are therefore accelerating.
So…if these e- emitted photons they should lose energy and fall into the nucleus.
Using spectroscopy (analyzing spectra) it was shown that each element has a unique line spectra.

6. Planck’s Hypothesis
Max Planck ( ) started the quantum revolution by studying light emitted by blackbodies
an ideal black object: does not reflect light but emits light as a result of its temperature
Recall that as you heat a solid it begins to glow
– red at first then white.
White light is a combination of all light so the hotter object the more colours of light it emits.
The light intensity can be measured using instruments – produces a curved graph

7. ISOTOPES Have the same number of protons and
electrons but have different amounts of neutrons.
Radioisotopes – give off radioactivity when they decay