Terms
The sum of the protons and neutrons in the nucleus of a cell
Mass Number
First to argue that all matter was made from indivisible particles called atoms?
Democritus in 450 B.C.
Which subatomic particle has a negative charge?
Electron
In a periodic table, what are the rows called?
Periods
Gallium has a mass number of 68 and an atomic number of 31, how many neutrons are in its nucleus?
37 because 68-31=37
Electrons that are in the highest energy level of an atom
Valence electrons
JJ Thomson's experiments provided evidence that atoms contain __________ charged particles.
Negatively
The nuclei of isotopes contain different numbers of what?
Neutrons
The elements in Group 8A are called _______ gases.
Noble
Samples of a pure compound always have the same elements in the same mass proportions. This is the Law of ____________?
Law of Constant Composition
The number of protons in an atom
Atomic number
The number of which sub-atomic particle is unique for each element?
Protons
A region of space around the nucleus where electrons are most likely to be found
Orbitals
(Not electron cloud and not shell)
In a periodic table, the columns are called?
Groups
Matter cannot be created or destroyed, but it can change forms. This is the Law of ___________.
Law of Conservation of Mass
Atoms of an element with the same number of protons but different number of neutrons
Isotopes
What is the outer most shell called?
Valence Shell
While neutrons have no charge, they do have what?
Mass
Which group of elements on the periodic table are most reactive?
Group 1A elements, alkali metals
What determines an element's chemical properties?
The number of Valence Electrons
A region of space around the nucleus where electrons are most likely to be found
Orbitals
This represents all the orbitals in an atom
Electron Cloud
An atom in an excited state has more energy than an atom in the ground state, but it is less _______?
Stable
An orbital can contain a maximum of ___ electrons.
(Not to be confused with shells)
TWO
Note: Shells can hold more: 1N holds up to 2 electrons, 2N holds 8, 3N holds 18, etc.
All elements in the same group have the same number of _____________?
Valence Electrons