What are the quantum numbers for the first electron in #"H"#, #"He"#, #"Li"#, and #"Be"#?

1 Answer

Quantum numbers refer to electrons, so I'll assume you mean the electron number that would correspond with the atomic number of the element. Quantum numbers are basically like an address for electrons, giving us information about the location of an electron from most general to most specific.

We need to apply the Aufbau principle, Hund's rule and the Pauli exclusion principle to answer this question.

Quantum numbers are listed in the following order: n, l, #m_l#, #m_s#

n = principal number - tells us which energy level an electron is in
l = angular number - tells us which sublevel and electron is in
#m_l# = magnetic number - tells us which orbital the e- is in
#m_s# = spin number - tells us if the electron is spin up or spin down

The quantum numbers for electron 1 (hydrogen) are: 1,0,0,+1/2
2 (He): 1,0,0,-1/2
3 (Li): 2,0,0,+1/2
4 (Be): 2,0,0,-1/2

There is a lot of info you'll need to understand... - I'll recommend this video to help. Quantum numbers are discussed in the final minute but there is info through the entire video you'll use to determine quantum numbers.