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45 terms

Chapter 2 - Small Molecules and the Chemistry of Life

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atoms
[Gk. atomos: indivisible] The smallest unit of a chemical element. Consists of a nucleus and one or more electrons.
nucleus
[L. nux: kernel or nut] 1. In cells, the centrally located compartment of eukaryotic cells that is bounded by a double membrane and contains chromosomes. 2. In the brain, and identifiable group of neurons that share common characteristics or functions.
electrons
A subatomic particle outside the nucleus carrying a negative charge and very little mass.
protons
[Gk. protos: first, before] 1. A subatomic particle with a single positive charge. The number of protons in the nucleus of an atom determine its element. 2. A hydrogen ion, H+.
neutrons
One of the three fundamental particles of matter (along with protons and electrons), with mass approximately 1 amu and no electrical charge.
atomic mass unit (amu)
A mass of a proton that serves as a standard unit of measure.
element
A substance that cannot be converted to simpler substances by ordinary chemical means.
atomic number
The number of protons in the nucleus of an atom; also equals the number of electrons around the neutral atom. Determines the chemical properties of the atom.
mass number
The sum of the number of protons and neutrons in an atom's nucleus.
isotopes
[Gk. isos: equal + topos: place] Isotopes of a given chemical element have the same number of protons in their nuclei (and thus are in the same position on the periodic table), but differ in the number of neutrons.
atomic weight
The average of the mass numbers of a representative sample of atoms of an element, with all the isotopes in their normally occurring proportions. (Also called atomic mass)
radioisotopes
A radioactive isotope of an element. Examples are carbon-14 (¹⁴C) and hydrogen-3, or tritium (³H).
molecules
A chemical substance made up of two or more atoms joined by covalent bonds or ionic attractions.
orbital
A region in space surrounding the atomic nucleus in which an electron is most likely to be found.
electron shells
The region surrounding the atomic nucleus at a fixed energy level in which electrons orbit.
chemical bond
An attractive force stably linking two atoms.
covalent bond
Chemical bond based on the sharing of electrons between two atoms.
compound
1. A substance made up of atoms of more than one element. 2. Made up of many units, as in the compound eyes off arthropods.
molecular weight
The sum of the atomic weights of the atoms in a molecule.
electronegativity
the tendency of an atom to attract electrons when it occurs as part of a compound.
polar
Having separate and opposite electric charges at two ends, or poles. (Contrast with nonpolar.)
ions
[Gk. ion: wanderer] An electrically charged particle that forms when an atom gains or loses one or more electrons.
cations
An ion with one or more positive charges. (Contrast with anion.)
anions
[Gk. ana: upward progress] A negatively charged ion. (Contrast with cation.)
ionic bonds
An electrostatic attraction between positively and negatively charged ions.
hydrogen bond
A weak electrostatic bond which arises from the attraction between the slight positive charge on a hydrogen atom and a slight negative charge on a nearby oxygen or nitrogen atom.
hydrophilic
[Gk. hydro: water + philia: love] Having an affinity for water (Contrast with hydrophobic.)
hydrophobic
[Gk. hydro: water + phobia: fear] Having no affinity for water. Uncharged and nonpolar groups of atoms are hydrophobic. (Contrast with hydropholic.)
van der Waals forces
Weak attractions between atoms resulting from the interaction of the electrons of one atom with the nucleus of another. This type of attraction is about one-fourth as strong as a hydrogen bond.
chemical reaction
The change in the composition or distribution of atoms of a substance with consequent alterations in properties.
reactants
A chemical substance that enters into a chemical reaction with another substance.
energy
The capacity to do work or move mater against an opposing force. The capacity to accomplish change in physical and chemical systems.
specific heat
The amount of energy that must be absorbed by a gram of a substance to raise its temperature by one degree centigrade. By convention, water is assigned a specific heat of one.
heat of vaporization
The energy that must be supplied to convert a molecule from a liquid to a gas at its boiling point.
cohesion
The tendency of molecules (or any substances) to stick together.
solution
A liquid (the solvent) and its dissolved solutes.
solute
A substance that is dissolved in a liquid (solvent) to form a solution.
solvent
Liquid in which a substance (solute) is dissolved to form a solution.
mole
A quantity of a compound whose weight in grams is numerically equal to its molecular weight expressed in atomic mass units. Avogadro's number of molecules 6.023x10²³ molecules.
Avogadro's number
The number of atoms or molecules in a mole (weighed out in grams) of a substance, calculated to be 6.022x10²³
acids
[L. acidus: sharp, sour] A substance that can release a proton in solution. (Contrast with base.)
bases
1. A substance that can accept a hydrogen ion in solution. (Contrast with acid.) 2. In nucleic acids, the purine or pyrimidine that is attached to each sugar in the sugar-phosphate backbone.
reversible reaction
A reaction that can proceed in either direction-left to right or right to left-depending on the relative starting concentrations of the reactants and products
pH
The negative logarithm of the hydrogen ion concentration; a measure of the acidity of a solution. A solution with pH=7 is said to be neutral; pH values higher than 7 characterize basic solutions, while acidic solutions have pH values less than 7.
buffer
A substance that can transiently accept or release hydrogen ions and thereby resist changes in pH.