1.2 Basic Ideas About Atoms

Question 1

What is the plum pudding model?

Answer 1

The plum pudding model was J J Thomson’s model of an atom and it consisted of a sphere of positive charge, with small negative electrons distributed throughout it.

Question 2

In terms of an atomic nucleus, what is radioactive decay?

Answer 2

Radioactive decay is the process that takes place when an unstable atomic nucleus loses energy by emitting radiation.

Question 3

What is alpha decay?

Answer 3

Alpha decay is a type of radioactive decay, during which an atomic nucleus loses two protons and two neutrons. An alpha particle is equivalent to a helium nucleus. It reduces the atomic number by two and the mass number by four, making the element more stable.

Question 4

What is beta decay?

Answer 4

Beta decay is a type of radioactive decay, during which a beta particle is lost, which is equivalent to an electron, and a neutron turns into a proton or a proton turns into a neutron. This changes the atomic number by one, but the mass number remains the same.

Question 5

What is positron emission?

Answer 5

Positron emission, also known as beta plus decay, is a subcategory of beta decay. A beta plus particle is the antiparticle to an electron, meaning it has the same mass but opposite charge. Therefore, when released, it increases a nucleus’ proton number by one and has no effect on mass number.

Question 6

What is electron capture?

Answer 6

Electron capture is a process that can be used by unstable atoms to make them more stable. The process involves an electron being drawn into the nucleus where it reacts with a proton to form a neutron and a neutrino.

Question 7

Compare the ionising power of alpha, beta and gamma radiation

Answer 7

Alpha - very strong ionising power
Beta - medium ionising power
Gamma - weak ionising power

Question 8

Compare the penetrating strength of alpha, beta and gamma radiation

Answer 8

Alpha - stopped by thin paper
Beta - stopped by thin metal
Gamma - stopped by thick lead

Question 9

Compare the range in air of alpha, beta and gamma radiation

Answer 9

Alpha - less than 5 cm range
Beta - less than 1 m range
Gamma - infinite range

Question 10

How are alpha, beta and gamma particles affected by electric fields?

Answer 10

Alpha particles are positively charged and beta particles are negatively charged so alpha and beta radiation can be deflected by an electric field. Gamma radiation is neutral so is not affected by an electric field.

Question 11

What is radioactive half life?

Answer 11

Half life is the time it takes for the radioactivity or the number of unstable nuclei present in an sample to halve.

Question 12

Why should people limit the exposure they have with certain types of radiation?

Answer 12

When radiation interacts with molecules in living cells, it can damage them and cause a mutation in DNA. The cell can become cancerous if the DNA in the nucleus of a cell is damaged.

Question 13

Give some uses of radioisotopes

Answer 13

• Used to examine metal structures like piping to identify any defects.
• Used in tracers for diagnostic purposes.
• Radio-dating (a technique used to date materials
  like rocks).
• Used medically to treat cancerous tumours.

Question 14

Define first ionisation energy

Answer 14

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions.

Question 15

Define first ionisation energy

Answer 15

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions.

Question 16

Is ionisation energy exothermic or endothermic?

Answer 16

Endothermic

Question 17

What factors influence ionisation energy?

Answer 17

• The number of protons in the nucleus.
• The subshell from which the electron is removed.
• Electron shielding.

Question 18

How do successive ionisation energies tell you which group an element belongs to?

Answer 18

A large increase between two different successive ionisation energies, for example between 7th and 8th ionisation energy, suggests the 8th electron is being taken from a new, full, stable shell (and hence this requires more energy to remove).
There are therefore 7 electrons in its outer shell so the element belongs to Group 7 (new group 17).

Question 19

What is the trend in ionisation energy across a period?

Answer 19

Ionisation energy increases across a period because the number of protons increases and electron shielding remains very similar. This means across the period the electrons require more energy to overcome the strengthening nuclear attraction.

Question 20

What is the trend in ionisation energy down a group?

Answer 20

onisation energy decreases down a group. This is because the atomic radius and electron shielding increases so the nuclear attraction with the electron gets increasingly weaker making the electron easier to remove.

Question 21

What is an Orbital

Answer 21

A region within an atom that can hold up to two electrons with opposite spins.

Question 22

What is a subshell?

Answer 22

A division of electron shells separated by orbitals.
Subshells are called s, p, d, and f.

Question 23

What rules do electrons follow when filling up orbitals?

Answer 23

Electrons always enter the lowest energy orbital available.
Electrons prefer to occupy orbitals on their own and will only pair up if there is no empty orbital of the same energy available.

Question 24

How many orbitals (and therefore electrons) are there in each type of subshell?

Answer 24

● s-subshell: 1 orbital (2 electrons)
● p-subshell: 3 orbitals (6 electrons)
● d-subshell: 5 orbitals (10 electrons)
● f-subshell: 7 orbitals (14 electrons)

Question 25

Which electron shells, from 1-4, contain which subshells?

Answer 25

Shell – Subshell(s) – Max e-
1 s 2
2 s,p 3
3 s,p,d 18
4 s,p,d,f. 32

Question 26

Why are the 4s orbitals generally filled before the 3p orbitals?

Answer 26

The 4s orbitals are at a lower energy level so they are filled first

Question 27

What is the electron configuration of calcium?

Answer 27

1s(2) - 2s(2) - 2p(6) - 3s(2) - 3p(6) - 4s(2)

Question 28

Which two elements in the periodic table are exceptions to the rule that the 4s orbital is filled before the 3p orbital?

Answer 28

Chromium and copper. The 4s orbital only fills with one electron as this gives them more stable configurations in the 3d orbital.
Chromium: [Ar]4s(1) - 3d(5)
Copper: [Ar]4s(1) - 3d(10)

Question 29

What determines the chemical properties of an element?

Answer 29

The electron configuration.

Question 30

What shapes are the s- and p-orbitals?

Answer 30

Question 31

Explain the origin of emission and absorption spectra in terms of electron transitions

Answer 31

When an electron experiences a change in energy so that it moves down an energy level, a photon is released to help conserve energy. When an electron gains energy to move up an energy level, photons are absorbed to provide the energy for this.
The specific wavelengths and energies of photons that are involved in the interactions can be seen using emission and absorption spectra.

Question 32

What is the difference between absorption spectra and emission spectra?

Answer 32

Question 33

What is the equation that links energy and frequency?

Answer 33

Energy (J) =
Planck’s constant (m2kgs-1) x Frequency of photon (Hz)
(E = hv)

Question 34

What is the equation that links frequency and wavelength?

Answer 34

Frequency (Hz) =
Speed of light (m/s) Wavelength (m)

Question 35

Put in order of increasing energy:
UV light, visible light and infrared radiation

Answer 35

Infrared radiation < visible light < UV light

Question 36

What is the significance of the frequency of the convergence limit of the Lyman series when related to the ionisation energy of the hydrogen atom?

Answer 36

The frequency of the convergence limit of the Lyman series can be used in the equation E=hv to calculate the first ionisation energy for hydrogen.