Chapter 2 Definitions Flashcards
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.
Electron Shell
The region surrounding the atomic nucleus at a fixed energy level in which electrons orbit.
Molecule
A chemical substance made up of two or more atoms joined by covalent bonds or ionic attractions.
Ionic Bond
An electrostatic attraction between positively and negatively charged ions.
Anion
A negatively charged ion. (Contrast with cation.)
Cation
An ion with one or more positive charges. (Contrast with anion.)
Covalent Bond
Chemical bond based on the sharing of electrons between two atoms.
Electronegativity
The tendency of an atom to attract electrons when it occurs as part of a compound.
Polar Covalent Bond
A covalent bond in which the electrons are drawn to one nucleus more than the other, resulting in an unequal distribution of charge.
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.
Heat of Vaporization
The energy that must be supplied to convert a molecule from a liquid to a gas at its boiling point.
Hydrophillic
Having an affinity for water. (Contrast with hydrophobic.)
[Gk. hydro: water + philia: love]
Hydrophobic
Having no affinity for water. Uncharged and nonpolar groups of atoms are hydrophobic. (Contrast with hydrophilic.)
[Gk. hydro: water + phobia: fear]
Cohesion
The tendency of molecules (or any substances) to stick together.
Functional Group
A characteristic combination of atoms that contribute specific properties when attached to larger molecules.
Macromolucule
A giant (molecular weight > 1,000) polymeric molecule. The macromolecules are the proteins, polysaccharides, and nucleic acids.
Polymer
A large molecule made up of similar or identical subunits called monomers. (Contrast with monomer.)
Monomer
A small molecule, two or more of which can be combined to form oligomers (consisting of a few monomers) or polymers (consisting of many monomers).
Saturated fatty acid
A fatty acid in which all the bonds between carbon atoms in the hydrocarbon chain are single bonds—that is, all the bonds are saturated with hydrogen atoms. (Contrast with unsaturated fatty acid.)
Unsaturated fatty acid
A fatty acid whose hydrocarbon chain contains one or more double bonds. (Contrast with saturated fatty acid.)
Hydrolysis
A chemical reaction that breaks a bond by inserting the components of water (AB + H2O → AH + BOH). (Contrast with condensation reaction.)
Condensation
A chemical reaction in which two molecules become connected by a covalent bond and a molecule of water is released (AH + BOH → AB + H2O.) (Contrast with hydrolysis reaction.)
