Chapter 2: Chemical Context of Life

By weight, magnesium accounts for only 0.1% of most living things

when hydrogen is covalently bonded to an electronegative atom. Highly electronegative atoms attract shared electrons more strongly than hydrogen does, resulting in a slight positive charge on the hydrogen atom. The slightly positive hydrogen atom is then attracted to another electronegative atom, forming a hydrogen bond.

the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products remain the same

adhesion of water molecules to other kinds of molecules. Water adheres to the cellulose molecules in a paper towel, allowing the towel to pick up a puddle of water. This is similar to the adhesion between water molecules and cellulose in cell walls responsible for water transport in plants.

Dissociation of water produces equal numbers of OH- and H+. Water ionizes to form hydroxide and hydronium ions. Dissociation of water is reversible.

the element is required in very small amounts. Although all forms of life require iron, other elements are required only by certain species.

the existence of unpaired electrons in the valence shell.

Van der Waals interactions can form between atoms of equal electronegativity. Even nonpolar covalent bonds have temporary regions of partial positive and negative charge, due to the chance movements of electrons. Attractions between such transient positive and negative charges create weak Van der Waals interactions.

An electron orbital describes a three-dimensional space where an electron can be found 90% of the time.

Weak bonds are transient and easily reversible. Molecules that form weak bonds can come together, interact, and then separate. The combined effect of many weak and transient hydrogen bonds or Van der Waals interactions can produce important emergent properties. Read about the importance of the transience of weak bonds such as hydrogen bonds, ionic bonds, and Van der Waals interactions.

the nucleus decays spontaneously, giving off particles and energy

A parent isotope decays into its daughter isotope at a fixed rate, not affected by temperature, pressure or any environmental variable

scientists measure the ratio of different isotopes and calculate how many half lives, in years, have passed since an organism was fossilized or a rock was formed

energy that matter possesses because of its location and structure

Because they can be used as tracers to follow particular atoms and molecules through metabolic pathways

Covalent bond

Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules.

They involve the making and breaking of chemical bonds.