1. Atomic Structure

2. Early Models of the Atom
Democritus (460 – 370 BCE)
Among first to suggest existence of atoms
Believed atoms were indivisible and indestructible
John Dalton ( )
Used experimental methods to observe atoms
Studied the ratios in which elements combine in chemical reactions
Formulated an atomic theory

3. Dalton’s Atomic Theory
All elements are composed of tiny indivisible particles called atoms
Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
Atoms of different elements can physically mix together or can chemically combine in simple whole number ratios to form compounds
Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another.

4. What happens to atoms in chemical reactions according to Dalton?
Checkpoint:
What happens to atoms in chemical reactions according to Dalton?

5. JJ Thomson ( )
Discovered the electron as a negatively charged subatomic particle
Performed experiments that involved passing electric current through gases at low pressure (a cathode ray tube) and used a magnet to show particles with a charge

6. Thomson Model
Negative electrons embedded in a sphere of positive charge
“plum-pudding”

7. Ernest Rutherford (1871-1937) Student of Thomson
Conducted the famous “gold-foil experiment”
Discovered the nucleus as a dense center to the atom
Electrons move around the nucleus

9. Niels Bohr (1885-1962) Student of Rutherford
Electrons moved in fixed circular paths around the nucleus
Each path was dependent upon the energy of the electron (the energy needed to move one electron from one energy level to the next is called a “quantum”)

11. Erwin Shrödinger ( )
Focused his attention on the energy of electrons
Found electrons do not travel in fixed paths, but are randomly moving in certain areas around the nucleus
The quantum-mechanical model (electron-cloud model) is the current one we use today.
Predicts how likely an atom can be found in a certain location of the electron-cloud

13. Today’s model Electron-Cloud model/quantum-mechanical model
Nucleus: dense center with protons and neutrons
Electrons: moving randomly and rapidly around the nucleus in no fixed path but rather in probable areas.

15. Left Page Activity
On a left page, you are going to create a timeline of the atom. Make sure to include the author of the model, a description, and a picture of each.