The Structure of the Atom

Atomic Theory Summary – the atom is the smallest particle of matter.

History of the Atom Cont.

JJ Thomson (1897) – Raison Bun Theory– Electrons (negative) distributed in a positive

sphere– Cathode Ray Tube used to measure the

mass of the electron

Ernest Rutherford (1911) – discovered that atoms have a positive nucleus– Gold Foil Experiment– Positive charge due to protons

James Chadwick (1932) – within the nucleus there are protons and neutrons (no charge)

Niels Bohr – came up with the current model of the atom taught in Grade 9 and 10 Science;- Bohr Rutherford Model (planetary model)

Bohr-Rutherford Model1. Electrons move around the nucleus in

circular paths called ORBITS / ENERGY LEVELS

2. Each Orbit / energy level can hold a specific # of electrons (always fill the closest orbit first and work out from the nucleus)

3. 1st – 2, 2nd – 8, 3rd – 8, 4th – 18 (2-8-8-18)

Examples

Mg He

N Ne

Summary of the Three Subatomic Particles

1. The Proton:- located inside the nucleus- is positively charged- symbol is p+

2. The Neutron:- located inside the nucleus- has no charge (neutral)- symbol is no

3. The Electron- orbits outside the nucleus- very tiny compared to the proton or neutron- is negatively charged- symbol is e-

Other Terms

Atomic Number- the number of protons- unique to each atom, use it to identify an

elementMass Number (Atomic Mass)

- the number of protons plus the number of neutrons

- measured in atomic mass units (amu)

Since atoms are neutral (ie. No charge), the number of protons in an atom must equal the number of electrons

SummaryAtomic # = #p+ = #e-

Mass # = #p+ + #no

• Read 179-190 (Ch 5.1 and Ch 5.2)• Questions pg. 186 2, 4, 5, 6

pg. 193 2, 3, 5, 7