Chemistry Exam 1

physical change

a type of change that alters the physical properties of a substance but does not change its composition

chemical change

a process involving one or more substances changing into new substances (chemical reaction)

physical property

characteristic of matter that can be measured or observed without changing the samples composition

element

a pure substance that cannot be broken down into simpler substances by physical or chemical means

compound

a chemical combination of two or more elements; can be broken down into simpler substances by chemical means and has properties different from those of its elements

periodic table

a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups) arranged by increasing atomic number

law of definite proportions

states that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass

mixture

a physical blend of two or more pure substances in any proportion

heterogeneous mixture

a mixture that does not have a uniform composition and in which individual substances remain distinct

homogeneous mixture

a mixture that has a uniform composition throughout and always has a single phase

atom

Smallest particle of an element

proton

A subatomic particle that has a positive charge and that is found in the nucleus of an atom

neutron

A subatomic particle that has no charge and that is found in the nucleus of an atom

electron

A subatomic particle that has a negative charge and that is found in the electron cloud

cathode ray

a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure

nucleus

center of an atom

atomic number

the number of protons in an atom

atomic mass unit

one twelfth the mass of a carbon-12 atom

average atomic mass

the weighted average mass of the isotopes of that element

isotope

atoms of the same element with different numbers of neutrons

mass number

the number after an element's name, representing the sum of its protons and neutrons

radioactivity

the process in which some substances spontaneously emit radiation

radiation

energy that comes from a source in the form of waves or particles

nuclear reaction

a reaction that involves a change in the nucleus of an atom

radioactive decay

a spontaneous process in which an unstable nuclei lose energy by emitting radiation

alpha radiation

radiation that is made up of alpha particles; its deflected toward a negatively charged plate when radiation from a radioactive source is directed between two electrically charged plates

alpha particle

a particle with two protons and two neutrons, with a 2+ charge; is equivalent to a helium-4 nucleus, can be represented by a; and is emitted during radioactive decay

nuclear equation

a type of equation that shows the atomic number and mass number of the particles involved

beta radiation

radiation made up of beta particles; is deflected toward a positively charged plate when radiation from a radioactive source is directed between 2 electrically charged plates

beta particle

a high-speed electron with a 1- charge that is emitted during radioactive decay

gamma ray

high energy radiation that has no electrical charge and no mass; is not deflected by electric or magnetic fields, usually accompanies alpha and beta radiation, and accounts for most of the energy lost during radioactive decay

radioisotope

isotopes of atoms with unstable nuclei

penetrating power

the ability of radiation to pass through matter

transmutation

the conversion of an atom of one element to an atom of another element

nucleon

the positively charged protons and neutral neutrons contained in an atom's nucleus

strong nuclear force

a force that acts on subatomic particles that are extremely close together

band of stability

the region on a graph within which all stable nuclei are found when plotting the number of neutrons versus the number of protons

positron emission

to decrease the protons, a proton can be converted into a neutron by emitting a positron

transuranium element

an element with an atomic number of 93 or greater in the periodic table

nuclear fission

the process in which a heavy nucleus divides to form smaller nuclei and one or two neutrons and produces a large amount of energy

nuclear fusion

the process of binding smaller atomic nuclei into a single, larger, and more stable nucleus

chain reaction

self sustaining process in which one reaction initiates the next

critical mass

the minimum mass of a sample of fissionable material necessary to sustain a nuclear chain reaction

electron capture

occurs when the nucleus of an atom draws in a surrounding electron, usually one from the lowest energy level

radioactive decay series

a series of nuclear reactions that starts with an unstable nucleus and results in the formation of a stable nucleus

half life

the time required for one half of a radioisotopes nuclei to decay into its products

radiochemical dating

the process of determining the age of an object by measuring the amount of a certain radioisotope remaining in that object

thermonuclear reaction

a nuclear fusion reaction

enriched uranium

uranium that has a higher percent of U-235 than its natural abundance of about 0.7%