Any compound that gives up protons or accepts electrons during a chemical reaction or that releases hydrogen ions when dissolved in water.
The tendency of certain dissimilar molecules to cling together due to attractive forces. Compare with cohesion.
A negatively charged ion.
The number of protons in the nucleus of an atom, giving the atom its identity as a particular chemical element.
Ball and Stick Model
A representation of a molecule where atoms are shown as balls—colored and scaled to indicate the atom's identity—and covalent bonds are shown as rods or sticks connecting the balls in the correct geometry.
Any compound that acquires protons or gives up electrons during a chemical reaction or accepts hydrogen ions when dissolved in water.
A substance that, in solution, acts to minimize changes in the pH of that solution when acid or base is added.
A positively charged ion.
An attractive force binding two atoms together. Covalent bonds, ionic bonds, and hydrogen bonds are types of chemical bonds.
The potential energy stored in covalent bonds between atoms.
A dynamic but stable state of a reversible chemical reaction in which the forward reaction and reverse reactions proceed at the same rate, so that the concentrations of reactants and products remain constant.
The theory that simple chemical compounds in the ancient atmosphere and ocean combined by spontaneous chemical reactions to form larger, more complex substances, eventually leading to the origin of life and the start of biological evolution.
Any process in which one compound or element is combined with others or is broken down; involves the making and/or breaking of chemical bonds
The tendency of certain like molecules (e.g., water molecules) to cling together due to attractive forces. Compare with adhesion.
A type of chemical bond in which two atoms share one or more pairs of electrons. Compare with hydrogen bond and ionic bond.
A unit of mass equal to 1/12 the mass of one carbon-12 atom; about the mass of 1 proton or 1 neutron.
A group of orbitals of electrons with similar energies. Electron shells are arranged in roughly concentric layers around the nucleus of an atom, with electrons in outer shells having more energy than those in inner shells. Electrons in the outermost shell, the valence shell, often are involved in chemical bonding.
A measure of the ability of an atom to attract electrons toward itself from an atom to which it is bonded.
A substance, consisting of atoms with a specific number of protons, that cannot be separated into or broken down to any other substance. Elements preserve their identity in chemical reactions.
Referring to a chemical reaction that absorbs heat. Compare with exothermic.
The capacity to do work or to supply heat. May be stored (potential energy) or available in the form of motion (kinetic energy).
A quantitative measure of the amount of disorder of any system, such as a group of molecules.
Referring to a chemical reaction that can occur spontaneously, releasing heat and/or increasing entropy, and for which the Gibbs free-energy change (DG) < 0. Compare with endergonic.
Referring to a chemical reaction that releases heat. Compare with endothermic.
First Law of Thermodynamics
The principle of physics that energy is conserved in any process. Energy can be transferred and converted into different forms, but it cannot be created or destroyed.
Free Energy/ Gibbs Free Energy Change
A measure of the change in potential energy and entropy that occurs in a given chemical reaction. Calculated as DG = DH - T DS, where DH is the change in potential energy, T is the temperature in kelvins, and DS is the change in entropy. DG < 0 for spontaneous reactions and >0 for nonspontaneous reactions.
Any substance containing one or more atoms with an unpaired electron. Unstable and highly reactive.
A small group of atoms bonded together in a precise configuration and exhibiting particular chemical properties that it imparts to any organic molecule in which it occurs.
Thermal energy that is transferrred from an object at higher temperature to one at lower temperature.
Heat of Vaporization
The energy required to vaporize 1 gram of a liquid into a gas.
The array of relatively stable chemical and physical conditions in an animal's cells, tissues, and organs. May be achieved by the body's passively matching the conditions of a stable external environment (conformational homeostasis) or by active physiological processes (regulatory homeostasis) triggered by variations in the external or internal environment.
A weak interaction between two molecules or different parts of the same molecule resulting from the attraction between a hydrogen atom with a partial positive charge and another atom (usually O or N) with a partial negative charge. Compare with covalent bond and ionic bond.
A single proton with a charge of 1 + ;typically, one that is dissolved in solution or that is being transferred from one atom to another in a chemical reaction.
Interacting readily with water. Hydrophilic compounds are typically polar compounds containing charged or electronegative atoms. Compare with hydrophobic.
Not interacting readily with wter. Hydrophobic compounds are typically nonpolar compounds that lack charged or electronegative atoms and often contain many C - C and C - H bonds. Compare with hydrophilic.
An oxygen atom and a hydrogen atom joined by a single covalent bond and carrying a negative charge; formed by dissociation of water.
An atom or a molecule that has lost or gained electrons and thus carries an electric charge, either positive (cation) or negative (anion), respectively.
A chemical bond that is formed when an electron is completely transferred from one atom to another so that the atoms remain associated due to their opposite electric charges. Compare with covalent bond and hydrogen bond.
Any of several forms of an element that have the same number of protons but differ in the number of neutrons.
The energy of motion. Compare with potential energy.
The total number of protons and neutrons in an atom.
A common unit of solute concentration equal to the number of moles of a dissolved solute in 1 liter of solution.
The amount of a substance that contains 6.022 × 1023 of its elemental entities (e.g., atoms, ions, or molecules). This number of molecules of a compound will have a mass equal to the molecular weight of that compound expressed in grams.
A notation that indicates only the numbers and types of atoms in a molecule, such as H2O for the water molecule. Compare with structural formula.
The sum of the mass numbers of all of the atoms in a molecule; roughly, the total number of protons and neutrons in the molecule.
Nonpolar Covalent Bond
A covalent bond in which electrons are equally shared between two atoms of the same or similar electronegativity. Compare with polar covalent bond.
The spherical region around an atomic nucleus in which an electron is present most of the time.
Organic/ Organic Molecule
For a compound, containing carbon and hydrogen and usually containing carbon-carbon bonds. Organic compounds are widely used by living organisms.
A measure of the concentration of protons in a solution and thus of acidity or alkalinity. Defined as the negative of the base-10 logarithm of the proton concentration: pH = -log[H+].
A discrete packet of light energy; a particle of light.
Polar Covalent Bond
A covalent bond in which electrons are shared unequally between atoms differing in electronegativity, resulting in the more electronegative atom having a partial negative charge and the other atom, a partial positive charge. Compare with nonpolar covalent bond.
Energy stored in matter as a result of its position or molecular arrangement. Compare with kinetic energy.
Any of the final materials formed in a chemical reaction.
Any of the starting materials in a chemical reaction.
Second Law of Thermodynamics
The principle of physics that the entropy of the universe or any closed system increases during any spontaneous process.
Any substance that is dissolved in a liquid.
A liquid containing one or more dissolved solids or gases in a homogeneous mixture.
Any liquid in which one or more solids or gases can dissolve.
A representation of a molecule where atoms are shown as balls—color-coded and scaled to indicate the atom's identify—attached to each other in the correct geometry.
The amount of energy required to raise the temperature of 1 gram of a substance by 1°C; a measure of the capacity of a substance to absorb energy.
A two-dimensional notation in which the chemical symbols for the constituent atoms are joined by straight lines representing single (-), double (=), or triple (º) covalent bonds. Compare with molecular formula.
The cohesive force that causes molecules at the surface of a liquid to stick together, thereby resisting deformation of the liquid's surface and minimizing its surface area.
In biology, a more complex organization resulting from the combination of various components, such as a group of organs that work together to perform a physiological function.
A measurement of thermal energy present in an object or substance, reflecting how much the constituent molecules are moving.
The kinetic energy of molecular motion.
The number of unpaired electrons in the outermost electron shell of an atom; determines how many covalent bonds the atom can form.
An electron in the outermost electron shell, the valence shell, of an atom. Valence electrons tend to be involved in chemical bonding.