4.2 The Atom Flashcards
a subatomic particle that has a positive charge and that is found in the nucleus of the atom
proton
a unit of mass that describes the mass of an atom or molecule
atomic mass unit
a subatomic particle that has no charge and that is found in the nucleus of an atom
nuetron
the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element
atomic number
an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)
isotope
the sum of the numbers of protons and neutrons in the nucleus of an atom
mass number
the mass of an atom expressed in atomic mass units
atomic mass
Probably the most familiar force of the four forces is the gravitational force. This acts between all objects all the time. The amount of gravitational force between objects depends on their masses and the distance between them. This pulls objects toward one another. Because the masses of atoms are so small, this force is small.
gravitational force
Objects that have the same charge repel each other, while objects with opposite charge attract each other. This is due to the – force. Protons and electrons are attracted to each other because they have opposite charges. This force holds the electrons around the nucleus.
electromagnetic force
Protons push away from one another because of the electromagnetic force. A nucleus containing two or more protons would fly apart if it were not for the – force. At the close distances between protons and neutrons in the nucleus, the – force is stronger than the electromagnetic force, so the nucleus stays together.
strong force
The – force is an important force in radioactive atoms. In an unstable atom, a neutron can change into a proton or electron. The – force plays a key role in this change.
weak force
