Electron Configuration

Periodic Table It is arranged so that similar chemical properties were arranged in vertical columns called groups. Because chemical properties are based on electronic structure (electron configurations) we can use the table to predict electron configurations for elements along with orbitals.

Looks like…

Periodic Table On the left is a block of 2 columns, then on the right is a block of 6 columns. In the center is a block of 10 columns, and on the bottom there is a block of 14 columns. s subshell = _______ electrons p subshell = _______ electrons d subshell = _______ electrons f subshell = _______ electrons

The 1st energy level (row) Has only 1 sublevel (1s) Has 1 orbital called 1s and can have 2 electrons

The 2nd energy level (row) has 2 sublevels (2s and 2p) 2s, has 1 orbital called 2s and can have 2 electrons 2p, has 3 orbitals called 2p and can have 6 electrons

The 3rd energy level (row) Has 3 sublevels 3s, has 1 orbital called 3s and can have 2 electrons 3p, has 3 orbitals called 3p and can have 6 electrons 3d, has 5 orbitals called 3d and can have 10 electrons

4 th energy level (row) Has 4 sublevels: 4s, has 1 orbital called 4s and can have 2 electrons 4p, has 3 orbitals called 4p and can have 6 electrons 4d, has 5 orbitals called 4d and can have 10 electrons 4f, has 7 orbitals called 4f and can have 14 electrons

Patterns For atoms with just a few electrons, the order in which the electrons fill up the energy levels is exactly the way we would predict: the first two electrons fill up the 1s sublevel, the next two electrons go into the 2s sublevel, the next six go into 2p, and so on. However, once we get to the third energy level, things get a little strange. It turns out that it takes a little less energy for an electron to go into a 4s orbital than into a 3d orbital, and so the 4s fills up before electrons fill the 3d.

Helium The atomic number of helium is 2, so a neutral atom of helium must have 2 electrons. The electron configuration would be 1s 2.

You try now…… What is the electron configuration of Beryllium?

Beryllium Be has 4 electrons, 1s 2 2s 2

You try now What is the electron configuration of Oxygen?

Oxygen O has 8 electrons, 1s 2 2s 2 2p 4

You try now What is the electron configuration of Argon?

Argon Ar has 18 electrons, 1s 2 2s 2 2p 6 3s 2 3p 6

Is this element calcium? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 - Is this element calcium?

Ways to check The total of all exponents should equal the atomic number of the atom.

The master sequence 1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p, …….don’t worry about the rest right now

Applet /electron.htm /electron.htm

Remember that Chemical properties of an elements are basically how different elements bond to each other to form compounds. The valence shell or the outer shell (the shell with the highest energy level) is the one mainly responsible for how an element reacts to form compounds. The rest of the electrons are the “core” electrons.

Elements with similar properties They should have similar valence shell electron configurations. Going down one column of the periodic table, one can see that the valence shell electron configurations are similar.