21 terms

# 7th Grade Science: Atomic Structure Key Terms

Atomic Structure

#### Terms in this set (...)

atom
The smallest particle of matter that retains all the characteristics of an element. It is the basic unit of matter and is made of three sub-atomic particles (neutrons, protons, and electrons)
nucleus
The positively charged dense center of an atom that contains protons and neutrons.
subatomic particle
Particles found within the atom, mainly protons, neutrons, and electrons.
proton
Subatomic particle in the nucleus that has a positive charge (+).
The number of this particle is always the same for every ion, isotope, or atom of a given element.
neutron
A subatomic particle in the nucleus which has no charge.
Atoms of a given element which contain more or less of of these particles are called isotopes.
electron
A subatomic particle that has a negative charge (-).
Atoms of a given element which contain more or less of these particles are called ions.
ion
An atom or molecule that has a charge because it has gained or lost electrons
charge
A measure of the electrical force that occurs whenever the number of protons in the nucleus is different from the number of electrons.
isotope
Atoms of the same element that have different mass because they have a different number of neutrons.
atomic mass unit
A measure of the mass of atoms and subatomic particles; is based on the carbon atom
atomic number
The number of Protons in an atom.
This is the "smaller number" on the Periodic Table.
This number never changes for atoms of a given element.
atomic mass
The sum of Protons + Neutrons in an individual atom.
On the Periodic Table this number represents the average mass of all isotopes of an element and is the "larger number"
electron cloud
A region around the nucleus of an atom where electrons are likely to be found.
energy level
A region of an atom in which electrons of the same energy are likely to be found.
quark
Fundamental particles that are smaller than protons and neutrons that do not normally exist on their own.
electromagnetic force
A force between all objects and subatomic particles that causes attraction or repulsion because of charge.
Opposite charges attract, Like charges repel.
strong nuclear force
A powerful force between particles in the nucleus of the atom that holds neutrons and protons together.
weak nuclear force
A force between particles in the nucleus of the atom that is effective at the shortest distance and is involved with a process called radioactive decay.
gravity
A force that increases with mass and that can act at great distances. This is the force that pulls an object toward Earth and holds planets in their orbits around stars.
indirect evidence
Evidence gathered about something we can not see
model
A representation of an object or system
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