Hydrogen has one electron in a 1s orbital and we write its electron configuration as 1s1. ”Spin” is responsible for a number of properties of matter including magnetism. The spin quantum number “ms“ can have values of either + ½ or – ½.

So what property is different? This property is called spin. But because they are in the same orbital they must have the same energy and the same probability distribution. Since each electron is described by a unique set of quantum numbers, the two electrons within a particular orbital must be different in some way. As they are typically drawn, each orbital defines the space in which the probability of finding an electron is 90%. Each orbital in an atom is described by the three quantum numbers n, l, ml, and each orbital can contain a maximum of 2 electrons. There are a few generalizations we can make. While this may seem confusing (it is!), it is the result of these calculations that we are really interested in, that is the types orbitals (electron density distributions) designated by the set of quantum numbers. The allowable values of l and ml for each value of n are shown in Table 2.1. For each value of n there are only certain allowable values of l, and for each value of l only certain values of ml are allowed. The higher the value of n, the higher the overall energy level of the electron shell. The principal quantum number “n”, is a non-zero, positive integer: n = 1, 2, 3, 4, etc these are often referred to as 'shells'.

Basically we can describe the wave function for each individual electron in an atom by a distinct set of three quantum numbers, known as n, l, and ml. The answer to our dilemma is provided by quantum numbers (whose derivation we will not consider). Chemistry, life, the universe and everything Chapter 2.7: Quantum numbers

Atomic orbitals quantum numbers