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empirical formula
A formula for a compound that gives the smallest whole-number ratio of each type of atom.
mole
6.022 x 10^23 particles--especially of atoms, ions, or molecules. For any element, it has a mass in grams that is numerically equivalent to its atomic mass in amu.
molecular mass
The sum of the molar masses of all the atoms in an empirical formula.
molecular formula
A formula for a compound that gives the specific number of each type of atom in a molecule.
avogadro’s number
The number of particles in a mole, 6.022 x 10^23.
molar mass
The mass of one mole of atoms of an element or one mole of molecules (or formula units) for a compound.
mass percent
The percentage, by mass, of each element in a compound.
binary acid
An acid containing only hydrogen and a nonmetal.
oxyanion
An anion containing oxygen.
formula mass
The average mass of the molecules (or formula units) that compose a compound.
binary compound
A compound containing only two different kinds of elements.
molecular formula
A formula for a compound that gives the specific number of each type of atom in a molecule.
molecular model
A three-dimensional representation of a molecule.
chemical formula
A way to represent a compound, indicating the elements present in the compound and the relative number of atoms of each element.
oxyacid
An acid containing hydrogen, a nonmetal, and oxygen.
space-filling model
A way to represent molecules in which atoms are represented with spheres that overlap with one another.
molecular element
An element that does not normally exist in nature with single atoms as the basic unit.
polyatomic ion
An ion composed of a group of atoms with an overall charge.
molecular compound
A compound formed from two or more nonmetals, having distinct molecules as their simplest identifiable units.
formula unit
The basic unit of ionic compounds; the smallest electrically neutral collection of cations and anions that compose the compound.
law of definite proportions
A law stating that all samples of a given compound have the same proportions of their constituent elements.
law of constant composition
A principle stating that a given compound always contains the same proportion of elements by mass.
law of conservation of mass
A principle stating that mass is neither created nor destroyed in a chemical reaction.
law of conservation of energy
A principle stating that energy cannot be created or destroyed, only transformed from one form to another.
kinetic molecular theory
A theory that explains the behavior of gases in terms of the motion of their particles.
ionic compound
A compound formed between a metal and one or more nonmetals.
atomic element
An element that exists in nature with single atoms as the base unit.
structural formula
A two-dimensional representation of molecules that shows the number and type of atoms and how the atoms are bonded together.
ball-and-stick model
A way to represent molecules in which an atom is represented with a ball and a bond is represented with a stick.
acid
A molecular compound that dissolves in solution to form H+ ions.
anion
A negatively charged ion.
nonmetals
Elements that tend to gain electrons in chemical reactions, found at the upper right side of the periodic table.
atomic mass unit
The unit commonly used to express the masses of protons, neutrons, and nuclei, equal to 1.66 x 10^-24 grams.
mass number
The sum of the number of neutrons and protons in an atom.
isotope
One of two or more atoms with the same number of protons but different numbers of neutrons.
metals
Elements that tend to lose electrons in chemical reactions, found at the left side and in the center of the periodic table.
metalloids
Elements that fall along the boundary between the metals and the nonmetals in the periodic table; their properties are intermediate between those of metals and those of nonmetals.
semiconductor
A compound or element exhibiting intermediate electrical conductivity that can be changed and controlled.
electron
A negatively charged particle that occupies most of the atom's volume but contributes almost none of its mass.
nuclear radiation
The energetic charged particles or electromagnetic waves emitted from the nucleus of an atom when it is undergoing a nuclear process.
atomic mass
A weighted average of the masses of each naturally occurring isotope of an element.
atomic number
The number of protons in the nucleus of an atom.
periodic law
The law that states that when the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically.
ion
An atom (or group of atoms) that has gained or lost one or more electrons, so that it has an electric charge.
neutron
A nuclear particle with no electrical charge and nearly the same mass as a proton.
proton
A positively charged nuclear particle.
periodic table
An arrangement of the elements in which atomic number increases from left to right and elements with similar properties fall in columns called families or groups.
periodic table
A tabular arrangement of the chemical elements, organized by their atomic number, electron configuration, and recurring chemical properties.
Rutherford diagram
A representation of the structure of an atom, showing a dense nucleus surrounded by electrons.
periodic law
The law stating that the properties of elements are a periodic function of their atomic numbers.
orbital diagram
A visual representation of the distribution of electrons in an atom's orbitals.
transition metals
The elements in the middle of the periodic table whose properties tend to be less predictable based simply on their position in the periodic table.
group
Elements that have similar outer electron configurations and therefore similar properties, occurring in vertical columns in the periodic table.
radioactive
Describes a substance that emits tiny, invisible, energetic particles from the nuclei of its component atoms.
halogens
The Group 17 elements, which are very reactive nonmetals.
noble gases
The Group 18 elements, which are chemically unreactive.
chemical symbol
A one- or two-letter abbreviation for an element.
percent natural abundance
The percentage amount of each isotope of an element in a naturally occurring sample of the element.
cation
A positively charged ion.
nucleus
The small core containing most of the atom's mass and all of its positive charge, made of protons and neutrons.
nuclear theory of the atom
A theory stating that most of the atom's mass and all of its positive charge are contained in the small, dense nucleus.
atom
The smallest identifiable unit of an element.
alkali metals
The Group 1 elements, which are highly reactive metals.
alkaline earth metals
The Group 2 elements, which are fairly reactive metals.
main-group elements
Groups 1-2 and 13-18 on the periodic table. These groups have properties that tend to be predictable based on their position in the periodic table.
chemical change
A change in which matter changes its composition.
matter
Anything that occupies space and has mass.
Kelvin
The temperature scale that assigns 0 degrees to the coldest temperature possible, absolute zero.
physical change
A change in which matter does not change its chemical composition, even though its appearance might change.
decanting
A way to separate a mixture in which one layer is carefully poured off of another layer.
Calorie
The amount of energy required to raise the temperature of 1 gram of water by 1 Celsius degree.
potential energy
The energy of a body that is associated with the position or the arrangement of its parts.
exothermic
A process that releases heat energy.
work
The result of a force acting on a distance.
property
A characteristic we use to distinguish one substance from another.
gas
A state of matter in which atoms or molecules are widely separated and free to move relative to one another.
thermal energy
A type of kinetic energy associated with the temperature-dependent random movement of atoms and molecules.
specific heat capacity
The heat capacity of a substance in joules per gram per degree Celsius.
amorphous
A type of matter in which atoms or molecules do not have a long-range order, such as glass and plastic.
product
A final substance produced in a chemical reaction represented on the right side of a chemical equation.
law of conservation of energy
A law stating that energy can be neither created nor destroyed.
homogeneous
A mixture, such as salt water, that has the same composition throughout.
compressible
Able to occupy a smaller volume when subjected to increased pressure.
reactant
An initial substance in a chemical reaction, represented on the left side of a chemical equation.
chemical reaction
The process by which one or more substances transform into different substances through a chemical change.
heat
The transfer or exchange of thermal energy caused by a temperature difference.
endothermic
A process that absorbs heat energy.
electrical energy
Energy associated with the flow of electric charge.
chemical property
A property that a substance can display only through changing its composition.
solid
A state of matter in which the atoms or molecules are packed close to each other in fixed positions.
liquid
A state of matter in which atoms or molecules are packed close to each other but are free to move around each other.
Calorie
A unit of energy equal to 3.6 million joules.
volatile
Tending to vaporize easily.
crystalline
A type of solid matter with atoms or molecules arranged in a well-ordered, three dimensional array with long-range, repeating order.
pure substance
A substance composed of only one type of atom or molecule.
heterogeneous mixture
A mixture, such as oil and water, that has two or more regions with different compositions.
Celsius
A temperature scale, often used by scientists, for which water freezes at 0 degrees and boils at 100 degrees.
temperature
A measure of the thermal energy in a sample of matter.
Calorie
An energy unit equivalent to 1000 chemistry calories.
molecule
Two or more atoms joined in a specific arrangement by chemical bonds.
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