Chemistry In Biology

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Matter

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Anything that occupies space and has mass.

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Mass

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A measure of the amount of matter in an object.

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Element

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Asubstance that cannot be broken down into other substances by chemical means.Scientists recognize 92 chemical elements that occur naturally and several morethat have been created in the laboratory.

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Periodic table of elements

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A tablelisting all of the chemical elements (both natural and human-made) ordered byatomic number (the number of protons in the nucleus of a single atom of thatelement).

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Trace elements

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Anelement that is essential for the survival of an organism but is needed in onlyminute quantities. Examples of trace elements need by people include iron andzinc.

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Compounds

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Asubstance containing two or more elements in a fixed ratio; for example, tablesalt (NaCI) consists of one atom of the element sodium (Na) for every atom ofchlorine (CI).

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Atom

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The smallest unit of matter than retains the properties of an element.

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Proton

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Asubatomic particle with a single unit of positive electrical charge, found inthe nucleus of an atom.

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Electron

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Asubatomic particle with a single unit of negative electrical charge. One ormore electrons move around the nucleus of an atom.

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Neutron

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A nervecell; the fundamental structural and functional unit of the nervous system,specialized for carrying signals from one location in the body to another.

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Nucleus

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(plural,nuclei) (1) An atom's central core, containing protons and neutrons. (2) Thegenetic control center of a eukaryotic cell.

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Atomic number

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Thenumber of protons in each atom of a particular element. Elements are ordered byatomic number in the periodic table of elements.

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Mass number

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The sum of the number of protons and neutrons in an atoms nucleus.

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Atomic mass

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Thetotal mass of an atom.

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Isotopes

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Avariant form of an atom. Different isotopes of an element have the same numberof protons and electrons but different numbers of neutrons.

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Radioactive isotope

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Anisotope whose nucleus decays spontaneously, giving off particles and energy.

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Chemical bonds

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Anattraction between two atoms resulting from a sharing of outer-shell electronsor the presence of opposite charges on the atoms.

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Ions

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Anatom or molecule that has gained or lost one or more electrons, thus acquiringan electrical charge.

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Ionic bond

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Anattraction between two ions with opposite electrical charges. The electricalattraction of the opposite charges holds the ions together.

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Covalent bond

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Anattraction between atoms that share one or more pairs of electrons.

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Molecule

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Agroup of two or more atoms held together by covalent bonds.

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Polar molecule

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Amolecule containing an uneven distribution of charge due to the presence ofpolar covalent bonds (bonds having opposite charges on opposite ends). A polarmolecule will have a slightly positive pole (end) and a slightly negative pole.

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Hydrogen bonds

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Atype of weak chemical bond formed when a partially positive hydrogen atom fromone polar molecule is attracted to the partially negative atom in anothermolecule (or in another part of the same molecule).

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Chemical reaction

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A process leading to chemical changes inmatter, involving the making and/or breaking of chemical bonds. A chemicalreaction involves rearranging atoms, but no atoms are created or destroyed.

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Reactant

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Astarting material in a chemical reaction.

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Product

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Anending material in a chemical reaction.

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Cohesion

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Theattraction between molecules of the same kind.

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Evaporative cooling

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Evaporative cooling A property of water whereby a body becomes cooler as water evaporates from it.

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Solution

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Aliquid consisting of a homogeneous mixture of two or more substances: adissolving agent, the solvent, and a substance that is dissolved, the solute.

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Solvent

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Thedissolving agent in a solution. Water is the most versatile known solvent.

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Solute

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Asubstance that is dissolved in a liquid (which is called a solvent) to form asolution.

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Aqueous solution

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Asolution in which water is the solvent.

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Acid

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Asubstance that increases the hydrogen ion (H+) concentration in a solution.

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Base

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Asubstance that decreases the hydrogen ion (H+) concentration in a solution.

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pH scale

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A measure of the relative acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic).

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Buffer

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Achemical substance that resists changes in pH by accepting hydrogen ions fromor donating hydrogen ions to solutions.