Energy levels in atom

Question 1

What is an ion?

Answer 1

• An ion is a charged atom. The number of electrons in an ion is not equal to the number of protons.
• An ion is formed from an uncharged atom by adding or removing electrons from the atom.
  
  • Adding electrons makes the atom into a negative ion.
  • Removing electrons makes the atom into a positive ion.

Question 2

When does ionisation occur?

Answer 2

Ionisation occurs when an electron is given enough energy for it to escape from the atom

Question 3

Examples of ionisation.

Answer 3

• Alpha, beta, and gamma radiation create ions when they pass through substances and collide with the atoms of the substance.
• Electrons passing through a fluorescent tube create ions when they collide with the atoms of the gas or vapour in the tube.

Question 4

What is an electron volt?

Answer 4

The amount of energy equal to 1.6 × 10–19 J defined as the work done when an electron is moved through a pd of 1 V.

Question 5

If a colliding electron loses all its kinetic energy when it causes excitation:

Answer 5

The current due to the flow of elections through the gas is reduced

Question 6

If the colliding electron does not have enough kinetic energy to cause excitation:

Answer 6

It is deflected by the atom, with no overall loss of kinetic energy.

Question 7

What are the excitation energies?

Answer 7

The energy values at which an atom absorbs energy are known as its excitation energies.

Question 8

Gas filled tube and electrons.

Answer 8

• Using gas-filled tubes with a metal grid between the filiament and the anode, we can show that gas atoms can absorb energy from colliding electrons without being ionised.
• This process, known as excitation, happens at certain energies, which are characteristic of the atoms of the gas.
• We can determine the excitation energies of the atoms in the gas-filled tube by increasing the potential difference between the filament and the anode and measuring the pd when the anode current falls.

Question 9

When excitation by collision occurs:

Answer 9

• The colliding electron makes an electron inside the atom move from an inner shell to an outer shell.
• Energy is needed for this process, because the atomic electron moves away from the nucleus of the atom.
• The excitation energy is always less than the ionisation energy of the atom, because the atomic electron is not removed completely from the atom when excitation occurs.