History of The Atom - Development of the Periodic Table

Question 1

What did the Greeks believe about atoms?

Answer 1

That matter was made out of small, indivisible, spherical atoms.

Question 2

What did John Dalton believe?

Answer 2

• Atoms are “tiny hard spheres”
• “cannot be divided or split”
• In chemical reactions, atoms re-arranged themselves and combined with other atoms

Question 3

What did JJ Thomson discover?

Answer 3

The Electron

Question 4

How did Thomson discover the electron?

Answer 4

He experimented by applying high voltages to gases at low pressure

Question 5

What was the name of the model by Thomson?

Answer 5

Plum Pudding

Question 6

Describe the plum pudding

Answer 6

Cloud/Sphere of positive charge embedded with negatively charged electrons

Question 7

What happend in the Geiger and Marsden experiment?

Answer 7

They were firing dense, positively charged particles (alpha particles) at a thin peice of gold foil.
They thought the particles would go straight through, but they didn’t.

Question 8

Why did some alpha particles go straight through?

Answer 8

Because of the mostly empty space in the atoms

Question 9

Why did some aplha particles deflect?

Answer 9

Because they have a concentration of positive charge in the atom

Question 10

Why did some aplha particle bounce back?

Answer 10

Positive charge and mass are concentrated in a tiny volume in the atom

Question 11

What did Rutherford believe?

Answer 11

That electrons were orbiting the nucleas which contains very dense positively charged protons

Question 12

What model did Rutherford make?

Answer 12

Nuclear model

Question 13

Explain the nuclear model

Answer 13

• Compact nucleas - contained all positive charge
• Electrons on the outside of the atom

Question 14

What did Niels Bohr suggest?

Answer 14

That the electrons orbitted the nucleas and are held in shells

Question 15

What did James Chadwick discover?

Answer 15

Neutrons

Question 16

What are the differences betwee the plum pudding and nuclear model?

Answer 16

• Mass in the nuclear model is concentrated in the nucleas - mass is spread out in the plum pudding
• Nuclear model is mostly empty space- plum pudding has no empty space
• Electrons and the nucleas are separate in the nuclear model - electrons are embedded in the plum pudding

Question 17

What changes did Bohr do to his model?

Answer 17

• Electrons orbit the nucleas
• At specific distances from nucleas

Question 18

Describe the Alpha scattering experiment

Answer 18

1. They got gold foil (because we can hammer gold into very thin foil)
2. They fired alpha particles at the foil (they have a positive charge)
3. They found out that most of the alpha particles passed straight through the gold foil without any change in direction (means that atoms are mainly empty space)
4. Some were deflected (changed direction)(Centre of atom has a positive charge)
5. Some bounced back (centre of atom has a great deal of mass)
6. They replaced the plum pudding model with the nuclearm model

Question 19

Order of people

Answer 19

1. Democritus
2. John Dalton
3. JJ Thomson
4. Rutherford
5. Niels Bohr
6. James Chadwick

Question 20

What did the neutron explain?

Answer 20

The imbalance between atomic and mass numbers

Question 21

Current model of the atom

Answer 21

• Nucleus = most mass, tiny, proton, neutron, radius is 10,000 times smaller than radius of atom
• Rest is empty space with -electrons (they give atom overall size)
• Radius of atom = 1X 10⁻¹⁰m
• Number of protons = electrons
• Gain energy by absorbing EM radiation, they go to a higher energy level, further away
• They lose/gain electrons = ion