Chapter 3: Molecules & Compounds

aqueous solution

solution for which water is the solvent

Avogadro's number (NA)

experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 x 1023

mol-1

concentrated

qualitative term for a solution containing solute at a relatively high concentration

concentration

quantitative measure of the relative amounts of solute and solvent present in a solution

dilute

qualitative term for a solution containing solute at a relatively low concentration

dilution

process of adding solvent to a solution in order to lower the concentration of solutes

dissolved

describes the process by which solute components are dispersed in a solvent

empirical formula mass

sum of average atomic masses for all atoms represented in an empirical formula

formula mass

sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass

mass percentage

ratio of solute-to-solution mass expressed as a percentage

mass-volume percent

ratio of solute mass to solution volume, expressed as a percentage

molar mass

mass in grams of 1 mole of a substance

molarity (M)

unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution

mole

amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of 12c

parts per billion (ppb)

ratio of solute-to-solution mass multiplied by 10⁹

parts per million (ppm)

ratio of solute-to-solution mass multiplied by 10⁶

percent composition

percentage by mass of the various elements in a compound

solute

solution component present in a concentration less than that of the solvent

solvent

solution component present in a concentration that is higher relative to other components

volume percentage

ratio of solute-to-solution volume expressed as a percentage

lonic bond

A chemical bond formed between two oppositely charged ions, generally a metallic cation and a nonmetallic anion, that are attracted to each other by electrostatic forces.

lonic compound

A compound composed of cations and anions bound together by electrostatic attraction.

Covalent bond

A chemical bond in which two atoms share electrons that interact with the nuclei of both atoms, lowering the potential energy of each through electrostatic interactions.

Molecular compounds

Compounds composed of two or more covalently bonded nonmetals.

Chemical formula

A symbolic representation of a compound that indicates the elements present in the compound and the relative number of atoms of each.

Empirical formula

A chemical formula that gives the relative number of atoms of each element in a compound.

Molecular formula

A chemical formula that shows the actual number of atoms of each element in a molecule of a compound.

Structural formula

A molecular formula that uses lines to represent covalent bonds and shows how the atoms in a molecule are connected or bonded to each other.

Ball-and-stick molecular model

A model that represents atoms as balls and chemical bonds as sticks; how the two connect reflects a molecule's shape.

Space-filling molecular model

A representation of a molecule in which atoms fill the space between each other to more closely represent how a molecule might appear if scaled to visible size.

Atomic elements

Elements that exist in nature with single atoms as their basic units.

Molecular elements

Those elements that do not normally exist in nature with single atoms as their basic units; elements with diatomic or polyatomic molecules as their basic unit.

Formula unit

The smallest, electrically neutral collection of ions in an ionic compound.

Polyatomic ion

An ion composed of two or more atoms.

Systematic names

An official name for a compound, based on well-established rules, that can be determined by examining its chemical structure.

Binary compounds

A compound that contains only two different elements.

Oxyanions

A polyatomic anion containing oxygen and another element.

Hydrates

An ionic compound that contains a specific number of water molecules associated with each formula unit.

Binary acids

An acid composed of hydrogen and a nonmetal.

Oxyacids

An acid composed of hydrogen and an oxyanion.

formula mass

sum of the atomic weights of atoms in a molecule.

Mass percent composition 

relative quantities of elements in a chemical compound as a percentage of the total mass

Empirical formula molar mass

The sum of the masses of all the atoms in an empirical formula.

Combustion analysis

A method of obtaining empirical formulas for unknown compounds, especially those containing carbon and hydrogen, by burning a sample of the compound in pure oxygen and analyzing the products of the combustion reaction.

Organic compounds

A compound composed of carbon and hydrogen and possibly a few other elements, including nitrogen, oxygen, and sulfur.

Hydrocarbons

An organic compound that contains only carbon and hydrogen.

Alkanes

A hydrocarbon containing only single bonds.

Alkenes

A hydrocarbon containing one or more carbon-carbon double bonds.

Alkynes

A hydrocarbon containing one or more carbon-carbon triple bonds.

Functional group

A characteristic atom or group of atoms that impart certain chemical properties to an organic compound.

Alcohols

A member of the family of organic compounds that contain a hydroxyl functional group (-OH).

Family

(group) A group of organic compounds with the same functional group.