1.2 The nuclear atom

Atomic number

The number of protons in the nucleus

Mass number

The total number of protons and neutrons

• Protons + Neutrons

Ion

An atom that has lost or gained an electron

Cation

Atoms that have lost electrons, forming a positive ion

Anion

Atoms that have gained electrons, so form negative ions

Isotope

Atoms of the same element with different numbers of neutrons

• Chemical properties are the same, but physical properties may differ

  • e.g, boiling point, melting point, density, etc

State and describe the purpose of a mass spectrometer

To determine the relative atomic masses of elements from their isotopic composition

• Sample is vaporized so individual atoms can be analysed

• Atoms are ionized to form a positively charged ion

• Positive ion is accelerated through the spectrometer toa negatively charged plate, and deflected by a magnetic field placed at right angles to their path

• Deflection is inversely proportional to their mass/charge ratio

Relative atomic mass

The average mass of an atom of the element, considering all its isotopes and their relative abundance, relative to one atom of carbon-12

Mass spectra

The results of the analysis by a mass spectrometer