In summary, the greater the mass the more energy is needed to break bonds. A heavier isotope forms a stronger bond. The resulting molecule has less of a tendency to dissociate. The increase in energy needed to break the bond results in a slower reaction rate and the observed isotope effect.

Medical Applications

It is the electrons that determine the chemical behaviour of a particular element. Isotopes of an element share the same number of protons but have different numbers of neutrons. This means that all three isotopes have different atomic masses (carbon-14 being the heaviest), but share the same atomic number (Z=6).

Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons and electrons. The difference in the number of neutrons between the various isotopes of an element means that the various isotopes have different masses.

Drawbacks of Dalton’s Atomic Theory The indivisibility of an atom was proved wrong: an atom can be further subdivided into protons, neutrons and electrons. However an atom is the smallest particle that takes part in chemical reactions. According to Dalton, the atoms of same element are similar in all respects.

Dalton’s atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.

He remained a faithful Quaker all of his life, living modestly. In 1810, he declined an invitation to become a member of the Royal Society. In 1822, he was elected without his knowledge. In 1826, he was awarded the Society’s Royal Medal for his Atomic Theory.

Royal Medal

Dalton did many experiments that provided evidence for the existence of atoms. For example: He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random motion.