Science Key Terms

Electrically neutral

having an equal number of protons (positively charged) and electrons (negatively charged)

Electron

a subatomic particle that orbits the nucleus of an atom; it is negatively charged

Electron configuration

the number of electrons in each shell of an atom, starting with the smallest; for example, 2, 8, 8, 2

Electron shell

the space around an atom’s nucleus, in which electrons circulate

Matter

any substance that has mass and takes up space

Molecule

a unit made up of two or more atoms chemically bonded to each other

Neutron

a subatomic particle located in the nucleus of an atom; it is neutrally charged

Nucleus

the center of an atom, which contains protons and neutrons

Proton

a subatomic particle located in the nucleus of an atom; it is positively charged

Subatomic particles

particles that make up atoms

Valence shell

the electron shell furthest away from the nucleus of an atom; occupied by electrons

Alpha particle

a positively charged particle that is four times larger than a proton

Cathode ray

a stream of electrons observed in a high-vacuum tube

Spectral line

a dark or bright line in an otherwise uniform spectrum

Atomic mass

the average mass of the atoms in a sample of an element

Atomic number

the number of protons in an atom

Chemical symbol

a symbol of one or two letters used to represent an element

Periodic table

a table of all known elements and their chemical symbol

Group

a column in the periodic table

Period

a row in the periodic table

Reactive

undergoes chemical reactions easily

Valence electron

an electron in the valence shell

Chemical formula

an expression of the elements that make up a chemical compound, usually presented as a ratio using chemical symbols and numbers; for example H₂O

Energy

the ability to do work

Kinetic energy

the energy of movement

Mass

the amount of matter that a physical body contains

Motion

the change in position of an object over time

Potential energy

stored energy; has the ability to cause movement

Transfer

to move from one place or object to another

Transform

change from one type to another

Work

when a force applied to an object causes the object to move

Conduction

the transfer of energy through a substance

Conductor

a substance that allows the transfer of energy

Convection

the transfer of energy by movement of a liquid or gas

Heat

the flow of thermal energy between objects

Insulator

a substance that resists the transfer of energy

Matter

a substance that has mass and takes up space

Radiation

the transfer of energy that does not require contact with matter

System

a set of simple things that work together to perform a function

Closed system

a system from which energy can flow in and out but matter cannot

Conservation of energy

the scientific law that states that energy cannot be created or destroyed

Isolated system

a system from which neither energy nor matter can flow in or out

Open system

a system that allows energy and matter to transfer in and out

Chemical change

a change in properties with a new substance formed

Physical change

a change in appearance with no new substance formed

Property

a characteristic of a substance that affects what it looks like and how it behaves

Reversible

can be changed back to its previous state

Chemical reaction

a process in which one or more substances are changed to form new substances

Conservation of mass

the scientific law that states that mass cannot be created or destroyed

Product

a substance formed in a chemical reaction

Reactant

a substance that undergoes a chemical change

Word equation

a representation of a chemical change in words

Combustion

the reaction of a substance with oxygen to give off heat

Corrosion

the reaction of a metal and oxygen

Endothermic

a reaction that absorbs energy in the form of heat

Exothermic

a reaction that releases energy in the form of heat

Asthenosphere

the portion of Earth’s mantle underneath the lithosphere that can flow

Atmosphere

the layer of gas that surrounds Earth

Core

Earth’s central layer, made up of a liquid outer core and solid inner core

Crust

Earth's thin outer layer, made up of continental crust and oceanic crust

Density

how heavy something is for its size; mass divided by volume

Lithosphere

Earth's rigid outer zone (crust and most of the upper mantle), made up of tectonic plates

Mantle

Earth's middle layer, made up of an upper mantle and a lower mantle

Tectonic plate

a section of Earth's lithosphere

Continental drift

the theory that the continents have moved overtime

Mid-ocean ridge

a long chain of mountains under the ocean formed by plate tectonics

Rift valley

a valley formed when a continent was pulled apart

Subduction

where one tectonic plate moves underneath another

Convergent boundary

where two tectonic plates are moving towards each other and colliding

Divergent boundary

where two tectonic plates are moving away from one another

Transform boundary

where two tectonic plates slide past each other