Answer to Question #332934 in General Chemistry for Peanut Butter

Question

I am trying to understand electron configuration backfilling because I see that there is 2,8,16,2 for NI then it skips to 2,8,18,1 for CU

some say CU is 2, 8, 18, 1 and others say CU is 2, 8, 17, 2

Then I heard the atoms holds 8 electrons and fills 17 (What is the difference between hold and fill)

also don't see how the 3rd row when move it up to the 3rd row, how the numbers fit in sequence?

• From 1 part of the question, which is the hold and fill. I think it means that to fill would be referring to bonding with other atoms 

• but then again according to this definition I still don't understand: A stable arrangement is attended when the atom is surrounded by eight electrons. This octet can be made up by own electrons and some electrons which are shared. Thus, an atom continues to form bonds until an octet of electrons is made. This is known as octet rule by Lewis.

Answer 1

To help describe the appropriate notation for electron configuration, it is best to do so through example. For this example, we will use the iodine atom. There are two ways in which electron configuration can be written:

I: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁵

or

I: [Kr]5s²4d¹⁰5p⁵

In both of these types of notations, the order of the energy levels must be written by increased energy, showing the number of electrons in each subshell as an exponent. In the short notation, you place brackets around the preceding noble gas element followed by the valence shell electron configuration. The periodic table shows that kyrpton (Kr) is the previous noble gas listed before iodine. The noble gas configuration encompases the energy states lower than the valence shell electrons. Therefore, in this case [Kr]=1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶.