1.1 Ions

Atoms do not have any overall charge because the number of protons is always the same as the number of electrons and both have equal, but opposite, charges. If an atom loses or gains electrons it becomes an ion. The addition of electrons produces a negative ion while the loss of electrons gives rise to a positive ion. The loss of an electron is called oxidation, while the gain of an electron is called reduction. The atom losing an electron is said to be oxidized, while that gaining an electron is said to be reduced. The loss of an electron from a hydrogen atom, for instance, would leave a hydrogen ion, comprising just a single proton. Having an overall positive charge it is written as H⁺. Where an atom, e.g. calcium, loses two electrons its overall charge is more positive and it is written Ca²⁺. The process is similar where atoms gain electrons, except that the overall charge is negative, e.g. Cl^-. Ions may comprise more than one type of atom, e.g. the sulphate ion is formed from one sulphur and four oxygen atoms, with the addition of two electrons, SO₄^2-.

1.2 Isotopes

The properties of an element are determined by the number of protons and hence electrons it possesses. If protons (positively charged) are added to an element, then an equivalent number of electrons (negatively charged) must be added to maintain an overall neutral charge. The properties of the element would then change - indeed it now becomes a new element. For example, the addition of one proton, one electron and one neutron to the carbon atom, transforms it into a nitrogen atom.

If, however, a neutron (not charged) is added, there is no need for an additional electron and so its properties remain the same. As neutrons have mass, the element is heavier. Elements which have the same chemical properties as the normal element but have a different mass are called isotopes.

Isotopes can be traced by various means, even when incorporated in living matter. This makes them exceedingly useful in tracing the route of certain elements in a variety of biological processes.

Translation

Biology in medicine. Using isotopes as traces

Isotopes are varieties of atoms which differ in their mass. They are usually taken up and used in biological systems in the same way as the 'normal' form of the element, but they can be detected because they have different properties. Isotopes have been used to study photosynthesis, respiration, DNA replication and protein synthesis. Isotopes such as ¹⁵C and ¹³C are not radioactive and so do not decay but they can be detected using a mass spectrometer or a nuclear magnetic resonance (NMR) spectrometer.

To use a mass spectrometer the sample to be studied is vaporized is such a way that the molecules become charged. They then pass through a magnetic field which deflects them and the machine records the abundance of each ion with a particular charge: mass ratio. Isotopes with an uneven number of protons or electrons spin, like spinning bar magnets. A NMR spectrometer detects each type of spinning nucleus.

Radioisotopes can be used both for diagnosis and treatment of disease as well as for research into possible causes. A particularly important isomer used to study lung and heart complaints is ^99mtechnetium. It has a halt life of only 6 hours and so decays very rapidly. It can be used as an aerosol, in very low concentrations, to show up available air spaces in patients' lungs. It may be used to label red blood cells so that the distribution of blood within the spaces of the heart or in deep veins can be shown. This is useful if there is a possibility of blood clots having formed.

The radiation emitted by a radioisotope can be used to destroy damaged tissue. For example ¹³¹iodine is taken up selectively by the thyroid gland and can be used in carefully calculated doses to destroy a specific amount of that gland.