Particle and atomic theory pt.2

Question 1

Electron shells

Answer 1

• Electrons move in a region of space surrounding the nucleus called electron shells.
• These shells are labelled K, L, M, N and numbered 1, 2, 3, 4

Question 2

Electron configuration

Answer 2

• Electron configuration refers to the arrangement of electrons in the shells around the nucleus
  eg. Calcium (20) - 2, 8, 8, 2

1. Electrons fill from the shells closest to the nucleus out.
2. The electron capacity of each shell is limited. The maximum number of electrons each shell can hold can be found using 2n^2
   where n = shell number.
3. The maximum number of electrons in the outer shell of any atom is 8.

Question 3

The maximum no. of electrons in the first 4 shells

Answer 3

2, 8, 18, 32

Question 4

Valence electrons

Answer 4

Valence electrons are the electrons found in the outermost shell.

Question 5

Rule for the outside shell

Answer 5

• Atoms need eight electrons in their outermost shell in order to be stable
• This is known as the octet rule.

Question 6

Atomic emission spectrum

Answer 6

• Every element emits light if it is heated by passing an electric discharge through its gas or vapour.
• This happens because the atoms of the element absorb energy, then lose it and emit it as light.
• Passing the light emitted by an element through a prism will produce an atomic emission spectrum for that element.

Question 7

Bohr’s energy levels (reason for the emission spectrum)

Answer 7

• Bohr proposed that electrons of specific energy move around the central nucleus in circular orbits or energy levels.
• Although an electron cannot lose energy when circulating around the nucleus, it can gain energy through an external source (e.g. flame or electric current) and would move to a higher energy level.
• When electrons move to a higher energy level, it has moved from the ground state (lowest energy level) to an excited state (highest energy level).
• When it drops back down to a lower, more stable orbit, this excess energy is given out as a photon or quantum of light.

Question 8

The energy levels and the emission spectrum

Answer 8

• The excess energy is seen as a line of a particular colour on the visible spectrum.
• The energy given out is the difference in energy between the two energy levels
• Some metallic elements can be identified simply by their characteristic flame colours when heated:
  Copper burns with a blue-green flame
  Sodium burns with a yellow flame.

Question 9

Forming ions

Answer 9

• the number of protons = the number of electrons,
  except when the atom forms an ion and becomes charged (there is an imbalance).
• This happens when the atom either loses an electron to become positively charged (called a cation) or gains an electron to become negatively charged (called an anion).

Question 10

Examples of ions

Answer 10

Sodium cation- a sodium atom (2, 8, 1) loses it’s outermost valence electron to achieve a full outer shell (stablility) and becomes a positively charged ion (2,8).

Chlorine anion- a chlorine atom (2, 8, 7) gains an electron to achieve a full outer shell (stablility) and becomes a negatively charged ion (2, 8, 8).