0.1 Fundamentals of physics and chemistry important to microbiology  (Page 2/6)

Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons. Many elements have several isotopes with one or two commonly occurring isotopes in nature. For example, carbon-12 ( ¹² C), the most common isotope of carbon (98.6% of all C found on Earth), National Oceanic and Atmospheric Administration, “Stable and Radiocarbon Isotopes of Carbon Dioxide.” Web page. Accessed Feb 19, 2016 [http://www.esrl.noaa.gov/gmd/outreach/isotopes/chemistry.html] contains six protons and six neutrons. Therefore, it has a mass number of 12 (6 protons + 6 neutrons) and an atomic number of 6.

There are two additional types of isotopes in nature: heavy isotopes, and radioisotopes. Heavy isotopes have one or more extra neutrons while still maintaining a stable atomic nucleus. An example of a heavy isotope is carbon-13 ( ¹³ C) (1.1% of all carbon). ibid. ¹³ C has a mass number of 13 (6 protons + 7 neutrons). Since the atomic number of ¹³ C is 6, it is still the element carbon; however, it has more mass than the more common form of the element, ¹² C, because of the extra neutron in the nucleus. Carbon-14 ( ¹⁴ C) (0.0001% of all carbon) ibid. is an example of a radioisotope. ¹⁴ C has a mass number of 14 (6 protons + 8 neutrons); however, the extra neutrons in ¹⁴ C result in an unstable nucleus. This instability leads to the process of radioactive decay. Radioactive decay involves the loss of one or more neutrons and the release of energy in the form of gamma rays, alpha particles, or beta particles (depending on the isotope).

Heavy isotopes and radioisotopes of carbon and other elements have proven to be useful in research, industry, and medicine.

Chemical bonds

There are three types of chemical bonds that are important when describing the interaction of atoms both within and between molecules in microbiology: (1) covalent bonds, which can be either polar or non-polar, (2) ionic bonds, and (3) hydrogen bonds. There are other types of interactions such as London dispersion forces and van der Waals forces that could also be discussed when describing the physical and chemical properties of the intermolecular interactions of atoms, but we will not include descriptions of these forces here.

Chemical bonding is determined by the outermost shell of electrons, called the valence electrons (VE), of an atom. The number of VE is important when determining the number and type of chemical bonds an atom will form.

Covalent bonds

The strongest chemical bond between two or more atoms is a covalent bond . These bonds form when an electron is shared between two atoms, and these are the most common form of chemical bond in living organisms. Covalent bonds form between the atoms of elements that make up the biological molecules in our cells. An example of a simple molecule formed with covalent bonds is water, H ₂ O, with one VE per H atom and 6 VE per O atom. Because of the VE configuration, each H atom is able to accept one additional VE and each O atom is able to accept two additional VE. When sharing electrons, the hydrogen and oxygen atoms that combine to form water molecules become bonded together by covalent bonds ( [link] ). The electron from the hydrogen atom divides its time between the outer electron shell of the hydrogen atom and the outermost electron shell of the oxygen atom. To completely fill the outer shell of an oxygen atom, two electrons from two hydrogen atoms are needed, hence the subscript “2” indicating two atoms of H in a molecule of H ₂ O. This sharing is a lower energy state for all of the atoms involved than if they existed without their outer shells filled.