Chemistry - History of the Atom

Who coined the term, atom?

Democritus

What did Democritus think about atoms in regards to how they were different from object to object?

He thought that each object had its own atom

Is Dalton’s first postulate true or false: elements are composed of atoms.

True

In his second postulate, Dalton says all atoms of a given element are identical. Is this true or false?

False

In his second postulate, Dalton says atoms of different elements are different. Is this true or false?

True

Which subatomic particle gives an element identity?

Proton

In his third postulate, Dalton says that compounds are composed of more than one element. T/F?

True

In his third postulate, Dalton says that the ratio of particles in an element are an integer or a fraction. T/F?

True

In his fourth postulate, Dalton says that a chemical reaction involves the separation, combination, or rearrangement of atoms without creating or destroying mass. T/F?

True

What is the Law of definite proportions?

In a compound, the ratios of elements is always the same

What is the Law of multiple proportions?

If multiple atoms occur in different compounds, then adding the mass of the elements in each compound will form ratios of small whole numbers.

What is the law of conservation of mass?

Mass cannot be created nor destroyed

What particle did JJ Thompson discover?

Electrons

What ratio did JJ Thompson discover?

Charge-to-mass ratio

When JJ placed positive and negative charges, the electrons bended towards which?

Positive

What model did JJ create?

Plum Pudding Model

What did Crooke add to his experiment compared to JJ?

He added a pinwheel

What did Crooke prove with his experiment?

Electrons have mass

Would Crooke agree with the Plum Pudding Model?

Yes

What numerical value did Millikan figure out?

He found the magnitude of the charge of an electron

Millikan used a positive plate to counteract gravity. This was placed in a chamber with electrons that would stick to _____ droplets (what material)?

oil

Millikan would increase the charge of the positive plate until some droplets were ________

suspended

Millikan determined the total mass of the droplet. Why was it ok for him to not subtract the mass of the electrons?

Electrons have almost no mass

Would Millikan agree with the Plum Pudding Model?

Yes

An alpha particle is made of what?

2 protons and 2 neutrons

Rutherford’s experiment was called…

Gold Foil Experiment

With the plum pudding model, any given positively charged area would have a very weak charge, therefore going through the gold foil. What actually happens?

Some alpha particles bounce off the foil in a random direction

What does Rutherford’s experiment prove about protons?

They aren’t spaced out, but are concentrated densely together.

Approximately how much heavier are protons compared to electrons?

about 1840 times

Would Rutherford agree with plum pudding? if not, what would he change

No, he would add a nucleus

Why did Chadwick conduct his experiment?

He thought there was another subatomic particle contributing to the mass of an atom

Chadwick shot alpha particles through a variation of elements along with what? (term for wax)

Paraffin

What did Chadwick conclude to exist?

neutrons

how does the mass of a neutron compared to a proton?

slightly heavier

Where did chadwick assume the neutron to be located and why?

In the nucleus because neutral charges could stabilize the proton

how can you compare the size of the nucleus to the whole atom?

marble to football stadium