Gen Chem I - Chapter 2 Keyterms

amu

anion

A negatively charged ion.

atom

The smallest unit of an element that retains the chemical nature of the element. A neutral, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electrons.

atomic mass

The average of the masses of the naturally occurring isotopes of an element weighted according to their abundances.

amu

A mass exactly equal the mass of 1/12 a carbon-12 atom.

atomic number Z

The unique number of protons in the nucleus of each atom of an element (equal to the number of electrons in the neutral atom). An integer that expresses the positive charge of a nucleus or subatomic particle in multiples of the electronic charge.

atomic symbol

A one- or two-letter abbreviation for the English, Latin, or Greek name of an element.

binary covalent compound

A compound that consists of atoms of two elements, typically nonmetals, in which bonding occurs primarily through electron sharing.

binary ionic compound

A compound that consists of the oppositely charged ions of two elements.

cathode ray

The ray of light emitted by the cathode (negative electrode) in a gas discharge tube; travels in a straight line, unless deflected by magnetic or electric fields.

cation

A positively charged ion.

chemical bond

The force that holds two atoms together in a molecule (or formula unit).

chemical formula

A notation of atomic symbols and numerical subscripts that shows the type and number of each atom in a molecule or formula unit of a substance.

compound

A substance composed of two or more elements that are chemically combined in fixed proportions.

covalent bond

A type of bond in which atoms are bonded through the sharing of electrons; the mutual attraction of the nuclei and an electron pair that holds atoms together in a molecule.

chromatography

A separation technique in which a mixture is dissolved in a fluid (gas or liquid) and the components are separated through differences in adsorption to (or solubility in) a solid surface (or viscous liquid).

covalent compound

A compound that consists of atoms bonded together by shared electron pairs.

crystallization

A technique used to separate and purify the components of a mixture through differences in solubility, resulting in a component coming out of solution as crystals.

dalton da

A unit of mass identical to atomic mass unit (amu).

distillation

A separation technique in which a more volatile component of a mixture vaporizes and condenses separately from the less volatile components.

electron

A subatomic particle that possesses a unit negative charge (− 1.60218 × 10^−19 C) and occupies the space around the atomic nucleus.

element

The simplest type of substance with unique physical and chemical properties. An element consists of only one kind of atom, so it cannot be broken down into simpler substances.

filtration

A method of separating the components of a mixture on the basis of differences in particle size.

formula mass

The sum (in amu) of the atomic masses of a formula unit of a (usually ionic) compound.

formula unit

The chemical unit of a compound that contains the relative numbers of the types of atoms or ions expressed in the chemical formula.

fraction by mass

also mass fraction; The portion of a compound's mass contributed by an element; the mass of an element in a compound divided by the mass of the compound.

group

A vertical column in the periodic table; elements in a group usually have the same outer electron configuration and, thus, similar chemical behavior.

heterogeneous mixture

A mixture that has one or more visible boundaries among its components.

homogenous mixture

A mixture that has no visible boundaries among its components. (also solution)

hydrate

A compound in which a specific number of water molecules are associated with each formula unit.

ion

A charged particle that forms from an atom (or covalently bonded group of atoms) when it gains or loses one or more electrons.

ionic compound

A compound that consists of oppositely charged ions.

isotopes

Atoms of a given atomic number (that is, of a specific element) that have different numbers of neutrons and therefore different mass numbers.

isotopic mass

The mass (in amu) of an isotope relative to the mass of carbon-12.

law of definite composition

A mass law stating that, no matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass.

law of mass conservation

A mass law stating that the total mass of substances does not change during a chemical reaction.

law of multiple proportions

A mass law stating that, if elements A and B react to form two or more compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers.

mass number A

The total number of protons and neutrons in the nucleus of an atom.

mass spectrometry

An instrumental method for measuring the relative masses of particles in a sample by creating charged particles and separating them according to their mass/charge ratios.

metal

A substance or mixture that is relatively shiny and malleable and is a good conductor of heat and electricity. In reactions, metals tend to transfer electrons to nonmetals and form ionic compounds.

metalloid

An element with properties between those of metals and nonmetals.

mixture

Two or more elements and/or compounds that are physically intermingled but not chemically combined.

molecular mass

the sum (in amu) of the atomic masses of the elements in a molecule (or formula unit) of a compound.

molecule

A structure consisting of two or more atoms that are bound chemically and behave as an independent unit.

monatomic ion

The tiny, central region of the atom that contains all the positive charge and essentially all the mass.

neutron

An uncharged subatomic particle found in the nucleus, with a mass slightly greater than that of a proton.

non-metal

An element that lacks metallic properties. In reactions, nonmetals tend to share electrons with each other to form covalent compounds or accept electrons from metals to form ionic compounds.

nucleus

The tiny, central region of the atom that contains all the positive charge and essentially all the mass.

oxyanion

An anion in which an element, usually a nonmetal, is bonded to one or more oxygen atoms.

percent by mass/mass percent

The fraction by mass expressed as a percentage.

period

A horizontal row of the periodic table

periodic table of elements

A table in which the elements are arranged by atomic number into columns (groups) and rows (periods).

polyatomic ion

An ion in which two or more atoms are bonded covalently.

proton

A subatomic particle found in the nucleus that has a unit positive charge (1.60218 × 10^−19 C).

substance

A type of matter, either an element or a compound, that has a fixed composition.

volatility

The tendency of a substance to become a gas.