A scientific law that states that mass is neither destroyed nor created during ordinary chemical reactions or physical changes
Law of definite Proportions
the fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
Law of Multiple Proportions
If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.
atoms of the same element that have different masses.
an electron occupies the lowest-energy orbital that can receive it
Pauli exclusion principle
no two electrons in the same atom can have the same set of four quantum numbers.
orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin.