Atomic Theory 6

What is a mass spectrometer?

An instrument used to identify isotopes and their relative abundances and to determine atomic or molecular masses.

What is the principle of the mass spectrometer?

Different ions are separated according to their masses or mass charge ratios when moving in a magnetic field.

What is relative abundance?

The percentage or proportion of each isotope present in a sample.

Why is there a vacuum inside a mass spectrometer?

So ions can be produced and studied without colliding with air particles.

What is the first stage in a mass spectrometer?

Vaporisation.

What happens during vaporisation?

The substance is heated so that it becomes a gas.

What is the second stage in a mass spectrometer?

Ionisation.

What happens during ionisation?

High energy electrons knock electrons out of atoms or molecules forming positive ions.

What is the third stage in a mass spectrometer?

Acceleration.

What happens during acceleration?

Positive ions are attracted to negatively charged plates and move at high speed.

What is the fourth stage in a mass spectrometer?

Deflection

What causes deflection in a mass spectrometer?

A magnetic field separates ions according to mass charge ratio.

How are lighter ions deflected?

Lighter ions are deflected more.

How are heavier ions deflected?

Heavier ions are deflected less.

What is the fifth stage in a mass spectrometer?

Detection.

What happens during detection?

Ions hit a detector and signals are recorded as a mass spectrum.

What does the detector measure?

The number of ions of each type hitting it.

What are two uses of the mass spectrometer?

Identify isotopes and calculate relative atomic masses.

Name all five stages in order.

Vaporisation ionisation acceleration separation detection.

Why must particles be gaseous in the mass spectrometer?

They must be able to move through the machine.