Biology 1107; Topic 2: Chemistry of Life

element

the smallest distinct unit of matter; matter at its simplest level of functionality or usefulness to life

four main elements of life on earth (~96%)

carbon, hydrogen, oxygen, and nitrogen

orbital

the region of space where an electron is found most frequently; no more than two electrons occupy that region

“incomplete” orbital

an orbital filled with only one electron

“complete” orbital

an orbital filled with two electrons

the two types of chemical bonds

covalent and ionic bonds

common non-chemical bonds

hydrogen bonds and van der Waals forces

electronegativity

the attractive force that the protons in the nuclei of any atom have for electrons of other atoms

nonpolar covalent bond

the equal sharing of electrons between two chemically bonded atoms; atoms are equally electronegative

polar covalent bond

the unequal sharing of electrons between two chemically bonded atoms; atoms have different electronegativities

ionic bond

the transfer of electrons from one atom to another, resulting in the ionization of both atoms; strongest chemical bond over the greatest distance with a force extending in all directions

covalent bond

the sharing of electrons between two atoms

important properties of water

polarization, high specific heat, high heat of vaporization, ionization

polarity

the extent to which electrons in a covalent bond are shared unequally, creating a dipole

specific heat

the amount of heat energy required to increase the temperature of a substance by 1degC, measured in calories

heat of vaporization

the amount of heat energy required to change a gram of liquid water to water vapor

ionization

a property of a substance in which it readily dissociates into ions; notably seen in water (splits into hydrogen and hydroxyl ions)

pH

a quantitative measure of the concentration of positively charged hydrogen ions in solution

matter

anything that occupies space and has mass

atom

the smallest units that retain the chemical and physical properties of an element

molecules

the chemical combination of atoms in fixed numbers and ratios in living and nonliving matter

chemical formula

standard symbols used to represent elements, compounds, and the number of atoms in each; what molecular names are written as

atomic number

the number of protons in the nucleus, which does not vary between like atoms; how atoms are identified on the periodic table

mass number

the total number of protons and neutrons in the atomic nucleus

isotopes

distinct forms of atoms of an element with the same number of protons but different numbers of neutrons; some element’s isotopes have minimal variation in their properties, others have more

mass

the amount of matter in an object

weight

the measure of the pull of gravity on an object

valence electrons

electrons in an atom’s outermost energy level or shell

inert atoms

atoms with a completely filled outermost energy level; nonreactive atoms

polar associations

the attraction between different polarized or ionized particles and molecules; tend to exclude nonpolar molecules

hydrophilic

atoms or molecules that readily associate with water

nonpolar associations

clumps of nonpolar molecules, often resulting from exclusion by polar associations; they reduce the surface area that is exposed to surrounding polar environment

hydrophobic

nonpolar substances excluded by water and other polar molecules

hydrogen bonds

attractions between partially positive hydrogen atoms (sharing electrons unequally with oxygen, nitrogen, or sulfur) and partially negative atoms sharing in a different covalent bond; may be intramolecular (between atoms in the same molecule) or intermolecular (between atoms in different molecules)

van der Waals forces

weak forces that develop over short distances between nonpolar molecules (or regions of molecules) as temporary dipoles occur by chance

molecular geometry

the 3-d arrangement of atoms in molecules determined by the orbitals of the atoms; determines the function of a molecule

molecular weight

the sum of the atomic weights of all the atoms in the molecule

acids

proton donors that release H+ (and anions) when they are dissolved in water; increase the concentration of H+

bases

proton acceptors that reduce the H+ concentration of a solution; most release a hydroxide ion and a cation

buffer

substances that compensate for pH changes by absorbing or releasing H+; often are weak acids or bases that dissociate reversibly to absorb H+ or OH-; have specific ranges of greatest buffering capacity