Unit 1

Question 1

What did Democritus theorize?

Answer 1

All matter was made up of tiny particles too small to be seen.

Question 2

How did Thomson determine that this beam consists of negatively charged particles?

Answer 2

Applied a positively and negatively charged plate and the electron ray deflected towards the positively charged plate (opposites attract - therefore the beam must have consisted of negatively charged particles)

Question 3

According to Thomson if there are six electrons in the atom, how many positvely charged particles are in the atom?

Answer 3

Zero - Electrons are stuck around a positively charged dough that balances out the negative charge of the electrons; together they don’t have any total net charge (atom is electrically neutral)

Question 4

What are Thomsons main discoveries?

Answer 4

Discovered the presence of electrons inside of atoms and calculate the charge to mass ratio of the electron

Question 5

Why was this experiment called the cathode ray tube experiment and not the anode ray tube experiment?

Answer 5

The electron beam appears to eminate from the cathode and not the anode.

Question 6

Q: What about the cathode ray experiment helped thomson to conclude that all atoms contain electrons?

Answer 6

Experimented with different cathode and anode metals; all of them emitted a cathode ray proving that all atoms/materials contain negatively charged particles (electrons)

Question 7

Explain the cathode ray tube. What did it help Thomson discover?

Answer 7

The cathode ray tube is a partially evacuated glass tube with a cathode and an anode (electrodes) at each end. Thomson applied high voltage between the two electrodes and found that the ray produced passed right through. When he applied a positively and negatively charged plate, the ray deflected towards the positively charged plate, proving that the beam consisted of negatively charged particles. (opposites attract

This experiment helped him to discover the electron and the charge-to-mass ratio of an electron.

Question 8

Fully explain the oil drop experiment.

Answer 8

Millikan performed the oil drop experiment to measure the size of of the charge of an electron. He used gravity and electricity to figure out how much negative charge each electron has.

Millikan suspended tiny charged droplets of oil (perependicular) through a very tiny hole between two metal electrodes, a negatively charged plate on the bottom and a positively charged plate on the top. When he balanced the downard force of gravity with the upward electric force (electric force = gravitational force), he used the telescope and found that the drop stayed still in mid air. Milikan determine the charge on an electron to be 1.6 x 10-19 C.

He then used Thomson’s work (charge-to-mass ratio) to calculate the mass of an electron to be 9.11 x 10-31 kg.

Question 9

What is an isotope?

Answer 9

A form of an element in which the atoms have the same number of protons as all the other forms of that element, but different number of neutrons.
*Same properties, different masses - depending on the number of neutrons

Question 10

What is a radioisotope?

Answer 10

A radioisotope is an isotope that emits high energy radioactive rays.
*An unstable ratio of protons to neutrons (too many in the nucleus) causes the nucleus of an isotope to be unstable, thus the atom becomes radioactive.

Question 11

Explain Rutherfords gold-foil experiment.

Answer 11

Surrounded a piece of goil-foil with a screen and aimed alpha particles (positively charged particles) straight at it. Most alpha particles went right through, showing that that the gold atoms were mostly empty space. Yet, some alpha particles were deflected at large angles and backwards. Proved that the atom is 99% space but contains a positive, dense nucleus, which surrounded by very small negative electrons that occupy most of the volume.

Question 12

If atoms are composed of the same particles (protons, neutrons, and electrons), why do different atoms have different chemical properties?

Answer 12

Dependent on the number of electrons in each atom. The number of electrons in an atom and their arrangement determine the chemical behaviour of the atom.

Question 13

T or F: Millikan performed the oil drop experiment to figure out the size of the electron.

Answer 13

F - He performed the experiment to measure the size of the charge of the electron

Question 14

What did Max Planck theorize? What did he discover?

Answer 14

He theorized that the energies of the oscillating atoms in the heated solid were multiples of a small quantity of energy. Basically energy is not continuous.

He discovered that the atom can absorb an infinite amount of energy, and that energy is not continous. It is quantized (comes in bursts)

Question 15

What was Einstein’s contribution to quantum theory?

Answer 15

Einstein ooked at Planck’s math and came up with quantification (the idea that energy comes in individual packets/bursts and not individual streams)

Question 16

Define quantum.

Answer 16

Quantum is a unit that represents a small, discrete, indivisible quantity (pl. quanta)

Question 17

What was Einstein’s contribution to the photoelectric effect?

Answer 17

Einstein reasoned that light consisted of a stream of energy packets (or quanta) – later called photons. He suggested that the ejection of an electron from the metal surface could be explained in terms of a photon–electron collision.

Photon – a small packet of energy corresponding to a specific frequency of light.

Question 18

Who came up with the photoelectric effect?

Answer 18

Hertz. Found that when light is shined on metals, electrons are given off.

Question 19

Can an electron be in two places at the same time?

Answer 19

Yes

Question 20

Continuous spectrum - where all wavelengths and frequencies are represented. White light viewed through a prism and a rainbow are examples of continuous spectra.

Atomic emission spectra - formed by the frequencies of emitted light when electrons return to ground state (more stable)
more proof of the quantized nature of light and led to a new model of the atom based on quantum theory.

Absorption line spectrum - forms the frequencies of light transmitted (with dark bands) when energy is absorbed by the electrons in the ground state to reach higher energy states.