Topic 2 & 12 - Atomic structure

Question 1

What is an element?

Answer 1

A substance that cannot be broken down into simpler substances by a chemical reaction

Question 2

What is a compound?

Answer 2

A substance made by chemically combining two or more elements

Question 3

What is the atomic number, Z?

Answer 3

The number of protons in the nucleus

Question 4

What is the mass number, A?

Answer 4

The number of protons plus the number of neutrons in an atom

Question 5

What are isotopes?

Answer 5

Atoms of the same element with different mass numbers

Question 6

What can be said about isotopes’ chemical and physical properties

Answer 6

Isotopes have the same chemical properties but different physical properties

Question 7

What does the stability of a nucleus depend on?

Answer 7

The balance between the number of protons and neutrons

Question 8

What kind of nuclei emit alpha particles?

Answer 8

Nuclei which have too many protons to be stable

Question 9

What kind of nuclei emit beta particles?

Answer 9

Nuclei that have too many neutrons to be stable

Question 10

What are the uses of radioactive isotopes?

Answer 10

1. Generate eneryg in nuclear power plants
2. Sterilise surgical instruments
3. Preserve food
4. Fight crime
5. Detect cracks in structural materials

Question 11

How can carbon-14 be used in dating?

Answer 11

• The relative abundance of carbon-14 present in living plants is constant
• When organisms die, no more carbon-14 is abosrbed and the levels of it fall due to nuclear decay
• With the help of carbon-14s half-life, the time of death can be calculated

Question 12

How can cobalt-60 be used in radiotherapy?

Answer 12

• Highly energetic gamma rays are used
• The treatment damages the genetic material inside a cell by knocking off electrons and making it impossible for the cell to grow
• Normal cells are able to recover if the treatment is controlled

Question 13

How can iodine-131 be used as a medical tracer?

Answer 13

• Emits both beta and gamma rays
• Can be used in the form of the compound sodium iodide to investigate the activity of the thyroid gland and to diagnose and treat thyroid cancer
• Radiation levels from different parts of the body are then detected
• Short half-life → quickly eliminated from the body

Question 14

How can iodine-125 be used to treat prostate cancer?

Answer 14

• Pellets of the isotope are implanted into the gland
• Long half-life
• Destroys the cancer cells from within

Question 15

What are the stages of a mass spectrometer?

Answer 15

1. Vaporisation
   - Vaporised sample is inserted so that individual atoms can be analysed
2. Ionisation
   - Particles bombarder with high-energy electrons to produce positively charged ions
3. Acceleration
   - Ions accelerated by an electric field
4. Deflection
   - Ions deflected by a magnetic field
   - The amounf of deflection is proportional to the charge/mass ratio
   - Ions with smaller mass are deflected more than heavier ions
   - Ions with higher charges are deflected more than less charged ions
5. Detection
   - Positive ions of a particular mass/charge ratio are detected
   - The strength of the signal is a measure of the number of ions

VapIADeDe

Question 16

What is the mass spectrometer used for?

Answer 16

Measuring the mass of individual atoms

Question 17

How can the relative atomic mass be calculated from mass spectra?

Answer 17

Question 18

What is the relationship between the wavelength and frequency?

Answer 18

c = λf

Question 19

What is the difference between a continuous spectrum and a line spectrum?

Answer 19

Continuous spectrum = light

LIne spectrum has only lights accoring to the emission or absorption of an element

Question 20

What is the relationship between emission and absorption spectra?

Answer 20

The colours present in the emission spectrum are the same as those that are missing from the absorption spectrum

Question 21

What is the relationship between wavelength and energy?

Answer 21

The smaller the wavelength, the greater the energy

Question 22

What are emission and absorption spectra used for?

Answer 22

They can be used to identify elements like a bar code; every element has its unique abosrption and emission spectra

Question 23

How do electrons give out light?

Answer 23

When they fall back from their excited state to the ground state, the energy is given out as electromagnetic radiation

Question 24

What is the energy change of an electron when it is excited or returned to ground state?

Answer 24

∆E_electron = E_photon = hf

Question 25

When does hydrogen emit light?

Answer 25

When its electron falls to the second energy level (n = 2)

Question 26

What is the relationship between a photon's energy, frequency, and wavelength?

Answer 26

The energy is directly proportional to its frequency and inversely proportional to its wavelength

Question 27

What is the first ionisation energy?

Answer 27

The minimum energy needed to remove one mole of electrons from one mole of **gaseous** atoms in their ground state

Question 28

What is the difference in the format of electron arrangement and electron configuration?

Answer 28

Electron arrangement = 2.8.7 Electron configuration = 1s²2s²2p⁶

Question 29

What happens to the ionisation energy for ions closer to the nucleus?

Answer 29

They are harder to remove due to nuclear attraction and require a lot more energy

Question 30

What can be said about electron energy levels?

Answer 30

They are divided into further sub-levels

Question 31

What is the rule for the number of sub-levels?

Answer 31

The nth energy level is divided into n sub-levels (the 4th level has four sub-levels)

Question 32

How many electrons can each main level hold?

Answer 32

2n² electrons (3rd level can hold 2 X 3² = 18 electrons)

Question 33

How many electrons can n = 1, 2, 3, 4 levels hold?

Answer 33

n = 1 → 2 n = 2 → 8 n = 3 → 18 n = 4 → 32

Question 34

How many electrons can each sub-level hold?

Answer 34

s → 2 p → 6 d → 10 f → 14

Question 35

What sub-levels do n = 1, 2, 3, 4 levels have?

Answer 35

n = 1 → 1s n = 2 → 2s, 2p n = 3 → 3s, 3p, 3d n = 4 → 4s, 4p, 4d, 4f

Question 36

What does the Heisenberg's uncertainty principle state?

Answer 36

We cannot know where an electron is at any given moment in time

Question 37

What is an atomic orbital?

Answer 37

A region around an atomic nucleus in which there is a 90% probability of finding the electron

Question 38

Draw the shape of an s orbital and the shapes of the p_x, p_y, and p_z orbitals

Answer 38

Question 39

What is the Pauli exlusion principle?

Answer 39

No more than two electrons can occupy any one orbital, and if two electrons are in the same orbital they must spin in opposite directions

Question 40

What is true for the 3d sub-level fro elements Z \> 20

Answer 40

The 3d sub-level falls below the 4s for elements Z \> 20 (when the orbital is full)

Question 41

What is the Aufbau principle?

Answer 41

Electrons are placed into orbitals of lower energy first (they go parallel first)

Question 42

What is Hund's rule?

Answer 42

If more than one orbital in a sub-level is available, electrons occupy different orbitals with parallel spins

Question 43

Not a question but helps in remembering how the orbitals are filled:

Answer 43

Question 44

What is the electron configuration of chromium?

Answer 44

[Ar] 3d⁵4s¹

Question 45

What is the electron configuration of copper?

Answer 45

[Ar] 3d¹⁰4s¹

Question 46

Why are the electron configurations of chromium and copper different and stable?

Answer 46

The half-filled and filled 3d sub-levels are stable, thus the 3d has filled first instead of 4s

Question 47

What happens to the sub-levels of transition metals when positive ions are formed?

Answer 47

The outer 4s electrons are removed before the 3d electrons