BIOL-102 6/18 (unit 1)

Electron Configuration and the Octet Rule

• Oxygen has six electrons in its outer shell, placing it in column 16.
• Hydrogen has one electron in its outer shell, placing it in column 1.
• Most shells need eight electrons to be full, which is known as the octet rule. However, hydrogen only needs two electrons to fill its outer shell. Helium is an exception to the rule, as it is in row 18 but only has two electrons, yet it possesses a full outer shell, giving it properties similar to other elements with full shells.

Covalent Bonds

• Atoms share electrons to achieve a full outer shell. For example, oxygen bonds with two hydrogen atoms because it needs two electrons.
• Covalent bonds are the strongest type of bond and are prevalent in living organisms.
• Covalent bonds typically do not dissolve in water, unlike ionic bonds.

Polarity in Covalent Bonds

• Polarity refers to extreme opposites. In molecules, it indicates opposite charges on different sides, similar to magnets with positive and negative poles.
• Water is a polar molecule where oxygen has a negative charge, and hydrogen has a positive charge.
• The negative side of a water molecule is attracted to the positive side of another water molecule.
• Unequal sharing of electrons causes polarity. Oxygen, being larger, holds onto the shared electrons for approximately 80% of the time, resulting in a negative charge, while hydrogen has a positive charge since its electron spends less time around it.
• In polar molecules, part of the molecule has a positive charge, and part of the molecule has a negative charge. Nonpolar molecules have a neutral charge across the entire molecule.

Hydrogen Bonds

• Hydrogen bonds do not create new substances but cause existing substances to stick together. They are particularly significant in water.
• Hydrogen bonds link two H2O molecules; they are just 'holding hands'.
• Hydrogen bonds are weak because they do not create new substance. The are formed between polar covalent molecules containing hydrogen.
• Hydrogen bonds occur when the positive charge of a hydrogen atom is attracted to the negative charge of another molecule (e.g., the oxygen portion of another water molecule).
• Hydrogen bonds are why water exhibits unique life-assisting properties and behaves differently from other substances.

Van der Waals Interactions

• Van der Waals interactions are similar to hydrogen bonds but do not involve hydrogen, which nobody cares about outside of the industry.

Isotopes and Radioactive Decay

• Atoms of the same element with different numbers of neutrons are called isotopes.
• The mass number is a decimal because it represents the average weight of an element, considering the different isotopes. For example, carbon generally has six protons and six neutrons (carbon-12), but some carbon atoms have two extra neutrons (carbon-14).
• Carbon-14 is radioactive.
• Radioactivity: Toxicity is in the dose. We are constantly bombarded with radioactivity, and there is low-level radiation everywhere.
• Radioactive decay involves neutrons decaying into protons, changing the element. For example, over time, carbon turns into nitrogen because neutrons turn into protons.