Chapter 4: Elements and the Periodic Table

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atom

the smallest particle of an element

nucleus

tiny region in the center of the atom that has all of the atom's protons and neutrons

protons

positively charged particles in the nucleus

electrons

negatively charged particles that orbit the nucleus

neutrons

particles that have no charge found in the nucleus

energy level

determines the specific amount of energy that an electron has

atomic number

the number of protons in the nucleus of an atom

isotopes

atoms with the same number of protons but different numbers of neutrons

mass number

sum of the protons AND neutrons found in the nucleus of an atom

atomic mass

average mass of all of the isotopes of an element

periods

horizontal row on the periodic table

groups

a vertical column on the periodic table

chemical symbol

a one or two letter symbol used to designate each element

plasma

state of matter that consists of a gas-like mixture of free electrons and nuclei of atoms that have been stripped or electrons

nuclear fusion

process in which two atomic nuclei combine, forming a larger nucleus and releasing large amounts of energy

ductile

the ability to be stretched into wire

conductivity

the ability of an object to transfer heat or electricity to another object

reactivity

the ease and speed with which an element combines or reacts with other elements and compounds

corrosion

when a metal combines with oxygen in the air to weaken the metal (rusting is a form of this)

alkali metals

group 1 elements

alkaline earth metals

group 2 elements

transition metals

the elements in groups 3 thru 12

particle accelerators

move atomic nuclei faster and faster until they have reached very high speeds

nonmetal

element that lacks the properties of a metal

diatomic molecule

consists of two atoms

halogens

the highly reactive group 17 elements

noble gases

the nonreactive group 18 elements

metalloids

elements that have some properties of both metals and nonmetals

semiconductor

can conduct electricity under some conditions but not under other conditions

radioactive decay

the atomic nuclei of unstable isotopes release fast-moving particles and energy

radioactivity

spontaneous emission of radiation by an unstable atomic nucleus.

alpha particle

consists of 2 neutrons and 2 protons and is positively charged; same as a helium nucleus

beta particle

a fast moving electron given off by a nucleus during radioactive decay

gamma radiation

consists of high-energy waves similar to x-rays

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