Chapter 2 Vocab Flashcards
Substance
A type of matter, either an element or a compound, that has a fixed composition.
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.
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.
Molecule
A structure consisting of two or more atoms that are bound chemically and behave as an independent unit.
Compound
A substance composed of two or more elements that are chemically combined in fixed proportions.
Mixture
Two or more elements and/or compounds that are physically intermingled but not chemically combined.
Law of mass conservation
A mass of law stating that the total mass of substances does not change during a chemical reaction.
Law of definite (or constant) 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.
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.
Percent by mass (mass percent, mass %)
The fraction by mass expressed as a percentage.
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.
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.
Nucleus
The tiny, central region of the atom that contains all the positive charge and essentially all the mass.
Proton (p+)
A subatomic particle found in the nucleus that has a unit positive charge (1.602176634x10^-19 C).
Neutron (n0)
An uncharged subatomic particle found in the nucleus, with a mass slightly greater than that of a proton.
Electron (e-)
A subatomic particle that possesses a unit negative charge (-1.602176634x10^-19 C) and occupies the space around the atomic nucleus.
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.
Mass number (A)
The total number of protons and neutrons in the nucleus of an atom.
Atomic symbol
(Also element symbol) A one- or two-letter abbreviation for the English, Latin, or Greek name of an element.
Isotopes
Atoms of a given atomic number (that is, of a specific element) that have different numbers of neutrons and therefore different mass numbers.
Atomic mass unit (u)
A mass exactly equal to 1/12 the mass of a carbon-12 atom.
Dalton (Da)
A unit of mass identical to atomic mass unit (u).