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Module: BIOM – 1007

Lecturer: Dr Bhambra

Date: 07/10/16

Atoms, Elements and Isotopes
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To achieve consistent communication between chemists around the globe, the International Union of
Pure and Applied Chemistry (IUPAC) was formed

o

Of the 92 naturally occurring elements in the earth, 25 of these are required for life
 11 of these are vital for biological systems
 However, 4 of these, hydrogen, carbon, oxygen and nitrogen make up just under 97% of a
human’s total body mass
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In 440 B
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C this became known as the Aristotelian view of matter (from Aristotle)

o

In 1643, a pupil of Galileo, Evangelista Torricelli proved that air had a weight and that it was capable of
pushing down on liquid mercury
 This lead to the discovery of the barometer and further led to the theory that air and other gases
consists of loosely packed particles, too small to be seen
 Furthermore, during the late 18th and early 19th century a scientist, John Dalton developed
his atomic theory
 That all matter is made of atoms and that they cannot be broken down into
anything simpler
 That all atoms in a particular element are identical to each other and differ to
atoms of other elements
 In 1987 JJ Thompson discovered the electron
 He showed that atoms contain smaller pieces, known as subatomic particles
 This lead to the discovery by Earnest Rutherford in 1911, that an atom must
contain a central nucleus
 Niels Bohr used experimental evidence to show that electrons occupy orbits and
shells around the nucleus

o

Atoms can be arranged in different structures known as allotropes
 Both diamonds and graphene are made from carbon atoms
 The carbon in diamonds is a complex structure consisting of strong covalent bonds
 The carbon in graphene is arranged in layers being held together with weak bonds

o

Atoms with the same number of protons and electrons but a different number of neutrons is known as an
isotope
 For example, oxygen has 8 protons, 8 electrons and can either have 8, 9 or 10 neutrons
 This is written as 16O, 17O or 18O
 The number is the atomic mass of the atom, therefore, ‘normal’ oxygen is 16O
 Plants can discriminate between the 2 isotopes of CO2 in our atmosphere, 12C (98
...
1%)
 The difference in neutrons is enough to alter the diffusion of CO2 within the plants
chloroplast, therefore, 12CO2 is preferred
 Tracers used in metabolic studies also use isotopes such as PTOX tracers which are labelled with 13C
 Isotopes can also have severely negative effects
 D2O compared with H2O, studies show that a 90% replacement to D2O proved fatal to fish
and other organisms
 It impaired the organism’s haematopoiesis, inhibited mitosis, muscle and nervous function



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