Topic 2: Atomic Structure

Question 1

What is an atomic number?

Answer 1

Atomic number, Z, is the number of protons in the nucleus of an atom of an element.

Question 2

What is a mass number?

Answer 2

Mass number, A, is the number of protons and neutrons in the nucleus of an atom.

Question 3

What is used in radiotherapy to treat cancer?

Answer 3

Cobalt-60

Question 4

Which radioisotope is used in cosmic, geological and archeological dating?

Answer 4

Carbon-14

Formed from nitrogen-14 being bombarded highly penetrating cosmic rays from outer space.

Question 5

What is half-life?

Answer 5

Half-life, t 1/2, is the time it takes for an amount of radioactive isotope to decrease to one-half of its initial value.

Question 6

What is the mass of an electron?

Answer 6

1/1836 amu

Question 7

What is a mass spectrometer?

Answer 7

A mass spectrometer is an instrument used to determine the relative atomic mass of an element. It can also show its isotopic composition.

Question 8

What are the five stages in the process occurring in a mass spectrometer?

Answer 8

1) vaporisation - sample enters the instrument, where it is heated and vaporised, producing gaseous atoms or molecules
2) ionisation - the gaseous atoms are bombarded by high-energy electrons, generating positively charged species:
X (g) + e -> X+(g) + 2e
3) acceleration - positive ions are attracted to negatively charged plates and accelerated in the electric field
4) deflection - positive ions are deflected by the magnetic field perpendicular to their path. The degree of deflection depends on the mass-to-charge ratio
5) detection - detector detects species of particular ratio

Question 9

What is the electromagnetic spectrum (EMS)?

Answer 9

Electromagnetic spectrum is a spectrum of wavelengths that comprised the various types of electromagnetic radiation, such as radio waves, microwaves, infrared radiation.

Question 10

What is electromagnetic radiation?

Answer 10

E.g. radio waves, microwaves, infrared radiation, ultraviolet radiation

The energy, E, of electromagnetic radiation is inversely proportional to the wavelength.

High-energy radiations, such as gamma rays and x-rays, have small wavelengths.

Wavelength is related to the frequency of the radiation, v.

Question 11

What is the range of visible light wavelengths?

Answer 11

400-700nm

Question 12

What are flame tests?

Answer 12

Flame tests are used to identify certain metals. The colour of the flame varies for different elements and can be used to identify unknown substances. The colours are due to the excitation of electrons in the metals by heat of the flame, which emit photons of light.

Question 13

What is a photon?

Answer 13

A photon is a quantum of radiation. Wavelength and energy of a photon are related.
Equation is in the data booklet.

Question 14

What is Bohr’s atomic model?

Answer 14

Model of atom structure that depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits, defined by their energy levels.

Question 15

What are the limitations to Bohr’s atomic model?

Answer 15

Model assumes that:

• the position of the electron orbits is fixed
• energy levels are circular or spherical in nature
• suggests an incorrect scale for the atom

Bohr limited his calculations to just one element, hydrogen.

Question 16

What is an atomic orbital?

Answer 16

An atomic orbital is a region in space where there is a high probability of finding an electron. Any orbital can hold maximum 2 electrons. There are several types of orbitals, called s, p, d and f, etc. Each has a characteristic shape and associated energy.

Question 17

Describe the s orbital.

Answer 17

S orbital is spherically symmetrical. Within the sphere there is a 99% chance or probability of finding an electron.

Question 18

Describe p atomic orbital.

Answer 18

A p orbital is dumbbell shaped. There are three p atomic orbitals, px, py and pz. All with boundary surfaces conveying probable electron density pointing in different directions along the three Cartesian axes, x, y and z.

Question 19

What is the Aufbau principle?

Answer 19

The Aufbau principle states that electrons fill the lowest energy orbital that is available first.

Question 20

What is the Pauli exclusion principle?

Answer 20

Pauli exclusion principle states that any orbital can hold a maximum of two electrons and these electrons have opposite spin.

Question 21

What is Hund’s rule of maximum multiplicity?

Answer 21

Hund’s rule states that when filling degenerate orbitals (orbitals of equal energy), electrons fill all the orbitals singly before occupying them in pairs.

Question 22

What is a continuous spectrum?

Answer 22

A continuous spectrum is a full range of wavelengths emitted by an object such as an incandescent light bulb.

Question 23

What is an emission spectrum?

Answer 23

An emission spectrum is a series of lines emitted against a dark background. E.g. when a pure gaseous element, such as hydrogen, is subjected to an electrical discharge, the gas will glow.

Question 24

What is an absorption spectrum?

Answer 24

An absorption spectrum can be observed when a cloud of cold gas is placed between a hot metal and a detector. It consists of a pattern of dark lines against a coloured background. The gaseous atoms absorb certain wavelengths of light from the continuous spectrum.

Question 25

To which region of EMS do Lyman series belong to?

Answer 25

Transition from 2, 3, 4, 5.. to n=1, belongs to UV region.

Question 26

To which region of EMS do Balmer series belong to?

Answer 26

Transition from 3, 4, 5, 6.. to n=2, belongs to visible and UV regions.

Question 27

To which region of EMS do Paschen series belong to?

Answer 27

Transition from 4, 5, 6, 7.. to n=3, belong to IR regions.