Number Of Electrons

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How would you find out the number of electrons from just the 4 quantum numbers?

1 Answer


If a complete set of quantum numbers is given to you, then you can say for a fact that you're only dealing with one electron.

The Bohr model for silver explains the number of electrons, protons and neutrons that are present in the atom, and it diagrams the placement of the electrons within silver's five energy levels. Its second energy level holds eight electrons, and its third and fourth energy levels each hold 18 electrons.

  • Generally, the number of electrons—alongside with protons and neutrons—in an atom can be determined from a set of simple rules. The number of protons in the nucleus of the atom is equal to the atomic number (Z).
  • Same number of valence electrons. Group 1: Li, Na, K, Rb, Cs, Fr Group 16: O, S, Se, Te, Po. Excited State 36 (e-have absorbed energy to move to a higher energy level).

As you know, quantum numbers are used to describe the location and spin of an electron that surrounds an atom's nucleus.

More specifically, the four quantum numbers will tell you

  • the energy level on which the electron resides - given by #n#, the principal quantum number
  • the subshell in which the electron resides - given by #l#, the angular momentum quantum number
  • the exact orbital in which you can find the electron - given by, #m_l#, the magnetic quantum number
  • the spin of the electron - given by #m_s#, the spin quantum number
Number Of Electrons

Now, each complete set of quantum numbers can only describe one electron. This means that if you're given something like this

#n=2, l=1, m_l = 0, m_s = +1/2#

then you know for a fact that only one electron can have that set of quantum numbers.

Now, let's assume that you are not given all four quantum numbers. These are some rules to help you figure out how many electrons can share an incomplete set of quantum numbers

  • You are given the value of#n#

If this is the case, then use the fact that the number of electrons you get per energy level is equal to

#color(blue)('no. of electrons' = 2n^2)#

  • You are given#n#and#l#

Number Of Electrons 8

This time, you know the energy level and the subshell in which the electrons can be found. To determine how many electrons can share these quantum numbers, use #m_l#, which can take values from #-l# to #l#.

Once you know how many orbitals you have per subshell, multiply that value by #2# to get the number of electrons

Number Of Electrons

#color(blue)('no. of electrons' = 2 xx 'no. of subshells')#

  • You are ginve#n#, #l#, and#m_l#

Now you know the energy level, subshell, and specific orbital in which the electrons can reside.

Number Of Electrons In Nitrogen

Since the only possible values for #m_s# are #+-1/2#, it follows that every orbital can hold a maximum of two electrons.

Number Of Electrons 1s

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