Chapter 2 The Chemical Level of Organization

Atoms

Building blocks of matter

Atomic Nucleus

An atom's dense central core, containing protons and neutrons.

Protons

positively charged subatomic particles

Neutrons

the particles of the nucleus that have no charge

Electrons

negatively charged subatomic particles

Atomic Number

the number of protons in the nucleus of an atom

Mass Number

the sum of the number of neutrons and protons in an atomic nucleus

Element

A pure substance made of only one kind of atom

Atomic symbol

A one or two letter abbreviation for an element

Atomic Mass

the weighted average of the masses of the isotopes of an element

Molecule

two or more atoms held together by covalent bonds

Compound

A substance made up of atoms of two or more different elements joined by chemical bonds

Organic compound

a covalently bonded compound that contains carbon, excluding carbonates and oxides

Inorganic compound

A compound that does not contain the element carbon or contains carbon bound to elements other than hydrogen.

Electrons

negatively charged subatomic particles

Planetary model of the atom

Electrons move around the nucleus in fixed cylindrical orbits

Electron Orbitals

volumes of space surrounding the atomic nucleus where electrons are likely to be found

Electron Orbital model

a more modern model of atomic structure that depicts the general location of electrons outside the nucleus

Electron Energy level

a location of electrons surrounding the nucleus in the atom

Electron Shells

an energy level of electrons at a characteristic average distance from the nucleus of an atom

Isotopes

Atoms of the same element that have different numbers of neutrons

Radioisotopes

Isotopes that have unstable nuclei and undergo radioactive decay.

Mixtures

A combination of two or more substances that are not chemically combined

Solution

A mixture that forms when one substance dissolves another.

Solute

A substance that is dissolved in a solution.

Solvent

A liquid substance capable of dissolving other substances

Concentration

A measurement of how much solute exists within a certain volume of solvent

Homogenous

of the same kind

Colloid

A mixture containing small, undissolved particles that do not settle out.

Heterogenous

(adj.) composed of different kinds, diverse

Sol-gel transformation

Reversible change of a colloid from a fluid (sol) to a more solid (gel) state.

Suspension

A mixture in which particles can be seen and easily separated by settling or filtration

Molarity

the number of moles of solute per liter of solution

Avogadro's number

number of representative particles in a mole, 6.02 X 10^23

Molecular Weight

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

Chemical Bonds

An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.

Valence shell

The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.

Octet rule/ rule of eight

atoms react by gaining or losing electrons so as to acquire the stable electron structure of a noble gas, usually eight valence electrons

Ionic Bonds

Formed when one or more electrons are transferred from one atom to another; the electrostatic forces that hold ions together in ionic compounds

Ions

positively and negatively charged atoms

Anion

A negatively charged ion

Cation

A positively charged ion

Covalent Bonds

Bonds created by sharing electrons with other atoms.

Polar molecule

molecule with an unequal distribution of charge, resulting in the molecule having a positive end and a negative end

Nonpolar molecules

a molecule in which electrons are shared equally between atoms

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons

Electropositive

When an atom is not at all electronegative. In fact, it tends to lose electrons rather than to gain them. Elements that are electropositive are generally to the left and bottom of the periodic table with 1 or 2 valence shell electrons.

Dipole

a molecule that has two poles, or regions, with opposite charges

Hydrogen Bond

A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.

Chemical Reaction

process that changes one set of chemicals into another set of chemicals

Reactants

Starting material in a chemical reaction

Products

The elements or compounds produced by a chemical reaction.

Molecular formula

A chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of the atoms.

Synthesis Reaction

a chemical reaction in which two or more substances react to yield a single product

Decomposition Reaction

a reaction in which a single compound breaks down to form two or more simpler substances

Catabolic

A process in which large molecules are broken down

Exchange or displacement reaction

bonds are both made and broken

Oxidation-reduction Reaction (Redox reaction)

the movement of electrons from one molecule to another

Oxidized

loses electrons

Reduced

gains electrons

Dehydration synthesis

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule.

Hydrolysis

Breaking down complex molecules by the chemical addition of water

Exergonic reaction

Reaction that proceeds with a net release of free energy.

Endergonic reaction

A nonspontaneous chemical reaction, in which free energy is absorbed from the surroundings.

Chemical equilibrium

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

Catalysts

Chemical agents that selectively speed up chemical reactions without being consumed by the reaction.

Electrolytes

minerals that carry electrical charges that help maintain the body's fluid balance

Acids

substances that release hydrogen ions when dissolved in water

Bases

Compounds that reduce the concentration of hydrogen ions in a solution. They are proton (hydrogen) acceptors.

Buffers

weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH

Macromolecules

A very large organic molecule composed of many smaller molecules

Polymers

molecules composed of many monomers; makes up macromolecules

Monomers

building blocks of polymers

Carbohydrates

the starches and sugars present in foods

Monosaccharides

Single sugar molecules (e.g. glucose, fructose, galactose)

Disaccharides

Carbohydrates that are made up of two monosaccharides (e.g. sucrose, lactose, maltose)

Isomers

Two different molecules that have the same chemical formula

polysaccharide

Carbohydrates that are made up of more than two monosaccharides

Lipids

Energy-rich organic compounds, such as fats, oils, and waxes, that are made of carbon, hydrogen, and oxygen.

Fatty acids

chains of carbon atoms bonded to hydrogen atoms

Glycerol

A three-carbon alcohol to which fatty acids are covalently bonded to make fats and oils.

Triglycerides

an energy-rich compound made up of a single molecule of glycerol and three molecules of fatty acid.

Saturated Fatty acid

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that can attach to the carbon skeleton.

Unsaturated Fatty acid

A fatty acid possessing one or more double bonds between the carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.

Phospholipids

a lipid consisting of a glycerol bound to two fatty acids and a phosphate group.

Hydrophobic

Having an aversion to water; tending to coalesce and form droplets in water.

Hydrophilic

Having an affinity for water.

Steroids

A type of lipid characterized by a carbon skeleton consisting of four rings with various functional groups attached.

Eicosanoids

biologically active compounds that regulate body functions

Protein

A three dimensional polymer made of monomers of amino acids.

Peptide bond

The chemical bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid

Polypeptide

A polymer (chain) of many amino acids linked together by peptide bonds.

Amino acids

building blocks of proteins

Denature

A change in the shape of a protein (such as an enzyme) that can be caused by changes in temperature or pH (among other things).

Enzymes

Proteins that speed up chemical reactions

Apoenzyme

protein portion of an enzyme

Cofactor

Non-protein helpers that may be bound tightly to the enzyme as a permanent resident, or may bind loosely and reversibly along with the substrate.

Substrate

reactant of an enzyme-catalyzed reaction

Active site

a region on an enzyme that binds to a protein or other substance during a reaction.

Activation energy

Energy needed to get a reaction started