Chemistry - History of the Atom

Dalton’s contributions to the atomn

• indivisible atoms (cannot be broke down)

• no positive or negative (no charges/subatomic particles)

Dalton’s picture of the atom

Thomson’s contributions to the atom

• atom has positive and negative charges inside

• net charge of zero

• equal number of subatomic particles

Thomson’s picture of the atom

Rutherford’s contributions

• gold foil experiment

• pos alpha beans would go through the gold foil since atoms are neutral

• concluded that positive nucleus and cloud of electrons

Rutherford’s picture of the atom

Two flaws of Rutherford’s atom?

• not organized

• positive and negative attract, so the cloud theory does not make sense

Why did some of the rays deflect in the gold-foil experiment?

• since the nucleus is positive, the rays would deflect off the positive nucleus

Gold Foil Experiment

Bohr’s contributions to the atom

• electrons orbit the nucleus in energy levels

Why did Bohr question Rutherford’s atom?

Questioned the attraction between the positive nucleus and the “cloud” of negative electrons.

How many electrons in 1st shell?

2

how many electrons for the 2nd shell

8

how many electrons for the 3rd shell

8

protons =

atomic number

neutrons =

atomic mass - atomic number

Bohr’s picture of the atom

What is an ion

an atom with a charge due to a loss or gain of electrons

What does the + for this lithium ion mean?

it lost an electron, so it is positively charged

How do you do lewis dot diagrams?

use the # of valence electrons (group #)