The Atom

Question 1

Describe Rutherford’s gold foil experiment.

Answer 1

• Alpha particles (helium nuclei) were fired at extremely thin gold foil
• The helium nuclei were positive and the thin foil was just a few atoms thick
• Any alpha particles that hit the fluorescent screen caused a scintillation

Question 2

State the results of Rutherford’s gold foil experiment.

Answer 2

• Most particles went straight through and caused flashes directly behind the foil
• A few alpha particles were deflected at a small angle
• An extremely small amount of particles bounced straight back

Question 3

What are the conclusions of Rutherford’s gold foil experiment.

Answer 3

• The atom is mostly empty space and most alpha particles just passed straight through
• Very few particles managed to pass close enough to a positive nucleus to be repelled and deflected by a small angle
• An extremely small amount of particles were about to actually hit the nucleus head on and thus were repelled straight back
• The atom is mostly empty space with a small dense positive nuclues at its centre and the electrons must orbit outside the nucleus

Question 4

What is the approximate radius of an atom and an atom nucleus?

Answer 4

Atom - 10-¹⁰m
Nucleus - 10-¹⁵m

Question 5

What is excitation of electrons?

Answer 5

When an atom is given energy, the electrons may absorb and use the energy to jump to another, higher energy level/shell. When the electrons fall back to their original level, they will emit the energy they no longer need.

Question 6

What is a continuous emission spectrum?

Answer 6

Continuous spectra are produced by an incandescent solid or liquid. They consist of all visible wavelengths of various strengths.

Question 7

What is a line emission spectrum?

Answer 7

When a gaseous element recieves energy, the electrons are excited to a higher energy state. When the energy source is removed, the electron returns to its original state and emits a photon frequency. This creates a line emission spectrum unique to the element.

Question 8

What is spectroscopy?

Answer 8

Identifying an element based on its line emission spectrum.

Question 9

What is the atomic number?

Answer 9

Denoted by A, it is the nuber of protons in the nucleus of an atom.

Question 10

What is the mass number?

Answer 10

Denoted by Z, it is the number of protons and neutrons in the nucleus of an atom.

Question 11

What is an isotope?

Answer 11

Isotopes are atoms with the same atomic number but different atomic mass.

Question 12

State an application of energy emission from excited electrons.

Answer 12

Lasers (Light Amplification by Stimulated Emission of Radiation)

Question 13

Important things to note about atoms.

Answer 13

• The atomic number defines the element
• Adding or removing neutrons makes isotopes
• If you add or subtract electrons, the atom becomes an ion
• To calculate the number of neutrons subtract the atomic number from the mass number
• Atomic numbers can be written on the top or bottom, the smaller number is always the atomic number.