I do not understand this at all

Question

Write the electron configurations for the elements below. Use the following format with spaces between each sublevel in the configuration: 1s2 2s2 2p6.

What is the electron configuration of phosphorus? 

What is the electron configuration of iron? 

Answer 1

Electrons surround the nucleus of atoms at different energy levels (aka "shells"). These shells are named numerically starting with "1" closest to the nucleus. Each shell can only "hold" a certain number of electrons but they can exist in the shell is sub-groups called "orbitals". These orbitals are named with letters, the first being "s", the second being "p", the third being "d", then "f". In the first shell, there is only 1 orbital and it can hold only 2 electrons, hence the designation 1s2. That is the electron configuration for Helium, an atom with 2 protons and 2 electrons.

As you move up the periodic table, you add another proton for each element and, consequently another electron. The added electron first fills the "s" orbital in the shell, then begins filling the p orbitals. s-orbitals always max out with 2 electrons while p-orbitals max out at 6 electrons, d-orbitals max out at 10 electrons and f-orbitals max out at 14 electrons.

Phosphorus is in the 3rd row of the periodic table and so consequently has electrons filling the 3rd shell. Beginning at the left side of the periodic table in the 3rd row, we have Sodium (Na) which will have 11 electrons, 2 of them fill 1s, 2 of them fill 2s, 6 of them fill 2p and 1 of them is in orbital 3s. The next element to the right of Na is Magnesium (Mg) which has one more proton and consequently one more electron. That additional electron will fill up 3s with it's 2nd electron. The next element to the right Aluminum will begin to fil 3p with one more electron. That makes the electron configuration of Aluminum 1s2 2s2 2p6 3s2 3p1. Then to the right of Al is Si which will add one more electron to the 3p orbital and then to the right of that is Phosphorus. The electron configuration of P is then 1s2 2s2 2p6 3s2 3p3

Iron is in the next row (row 4). This gets a little tricky. Orbital 4s is a lower energy level than 3d. So Potassium begins filling 4s and Calcium completes orbital 4s HOWEVER, orbital 3d begins to fill after that so Scandium has an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d1. Counting to the right from there, Iron (Fe) has an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d6