Electron Configurations and the Periodic Table.

Configurations Within a Group Look at the electron configurations for the Halogens F 1s2 2s2 2p5 Cl 1s2 2s2 2p6 3s2 3p5 Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 I 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5 All of the elements in Group 7 end with 5 electrons in a p subshell. In fact, every Group ends with the same number of electrons in the highest energy subshell

Configurations and the Periodic Table s-block p-block d-block s1 s2 p1 p2 p3 p4 p5 p6 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 f-block f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14

How to remember the filling order? 1s 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d s subshells begin in level 1, so begin the s-block with “1s” p subshells begin in level 2, so begin the p-block with “2p” d subshells begin in level 3, so begin the d-block with “3d” f subshells begin in level 4, so begin the f-block with “4f”

How to remember the filling order? 1s 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d To see the filling order of subshells, read from left to right, top to bottom! Note that this tool shows that the 3d energy level is filled after the 4s energy level!

Where Does the Noble Gas Leave Off? How do you know where to start off after using a noble gas? Use the periodic table! 1s He 2s 2p Ne 3s 3p Ar 4s 3d 4p Kr 5s 4d 5p Xe 6s 4f 5d 6p Rn 7s 5f 6d The noble gas fills the subshell that it’s at the end of. Begin filling with the “s” subshell in the next row to show valence electrons.

Isotopes

What are isotopes? Isotopes - n. Atoms of the same element with a different number of neutrons Some isotopes are radioactive—but not all…many are quite stable!

Isotopes Example Hydrogen-2 Hydrogen-1 Mass # = 1 amu Mass # = 2 amu If they have different number of neutrons, and neutrons have a mass of 1 amu… Then isotopes of the same element will have different masses! But because their protons are the same, they are the same element!

C C Carbon-12 Carbon-13 Identifying Isotopes Isotopes can be differentiated by their different mass numbers in the element symbol 12 C 13 C Carbon-12 Carbon-13 Or by the mass number following their name.

Mass Number versus Atomic Mass Average Atomic Mass # of protons + # of neutrons Average of actual masses Always a whole number Not a whole number For one specific isotope only Weighted average of all isotopes Is not found on the periodic table Is found on the periodic table

Calculating Average Atomic Mass Average atomic mass is a weighted average (it takes into account how often each isotope occurs). Actual mass (not mass number) “Sum of” Average atomic mass  ( )  = Abundance of isotope Mass of isotope What fraction of the time is that isotope present?

Example of Finding Avg Atomic Mass Find the atomic mass of chlorine if Chlorine-35 has a mass of 34.969 amu and Chlorine-37 has a mass of 36.966 amu and is present 24.22% of the time. Remember that percents add up to 100. So they said the second isotope is present 24.22% of the time. This means that the first isotope is present 100-24.22 = 75.78% of the time Isotope Mass Percent Decimal 1 34.969 amu 75.78 0.7578 2 36.966 amu 24.22 0.2422 This chart summarizes the information in the problem: = 35.45 amu (this is what’s on the periodic table for Cl!)