Chapter Two

• actinide is an inner transition metal in the bottom of the bottom two rows of the periodic table
• an alkali metal is an element in group 1
• an alkaline earth metal is an element in group 2
• an alpha particle (α particle) is a positively charged particle consisting of two protons and two neutrons
• an anion is a negatively charged atom or molecule (contains more electrons than protons)
• atomic mass is the average mass of atoms of an element, expressed in amu
• atomic mass unit (amu)(also, unified atomic mass unit, u, or Dalton, Da) is a unit of mass equal to 112112 of the mass of a 12C atom
• atomic number (Z) is the number of protons in the nucleus of an atom
• a binary acid is a compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
• a binary compound is a compound containing two different elements.
• a cation is a positively charged atom or molecule (contains fewer electrons than protons)
• a chalcogen is an element in group 16
• a chemical symbol is a one-, two-, or three-letter abbreviation used to represent an element or its atoms
• a covalent bond is an attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms
• a covalent compound(also, molecular compound) is composed of molecules formed by atoms of two or more different elements
• a Dalton (Da) is an alternative unit equivalent to the atomic mass unit
• Dalton’s atomic theory is a set of postulates that established the fundamental properties of atoms
• an electron is a negatively charged, subatomic particle of relatively low mass located outside the nucleus
• the empirical formula is a formula showing the composition of a compound given as the simplest whole-number ratio of atoms
• the fundamental unit of charge(also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 ×× 10−19 C
• a group is the vertical column of the periodic table
• a halogen is an element in group 17
• a hydrate is a compound containing one or more water molecules bound within its crystals
• an inert gas(also, noble gas) is an element in group 18
• an inner transition metal(also, lanthanide or actinide) is an element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide
• an ion is an electrically charged atom or molecule (contains unequal numbers of protons and electrons)
• an ionic bond is an electrostatic forces of attraction between the oppositely charged ions of an ionic compound
• an ionic compound is a compound composed of cations and anions combined in ratios, yielding an electrically neutral substance
• isomers are compounds with the same chemical formula but different structures
• isotopes are atoms that contain the same number of protons but different numbers of neutrons
• lanthanide is an inner transition metal in the top of the bottom two rows of the periodic table
• the law of constant composition(also, law of definite proportions) is where all samples of a pure compound contain the same elements in the same proportions by mass
• the law of definite proportions(also, law of constant composition) is where all samples of a pure compound contain the same elements in the same proportions by mass
• the law of multiple proportions is when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers
• a main-group element(also, representative element) is an element in groups 1, 2, and 13–18
• mass number (A) is the sum of the numbers of neutrons and protons in the nucleus of an atom
• a metal is an element that is shiny, malleable, good conductor of heat and electricity
• a metalloid is an element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals
• a molecular compound(also, covalent compound) is composed of molecules formed by atoms of two or more different elements
• a molecular formula is a formula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound.