Gr12 Chem Unit 2: Structure of the Atom, Lesson 4: Electron Configuration and Trends in the Periodic
Table
C12-2-06 Relate the electron configuration of an element to its valence electron(s)
and its position on the periodic table.
C12-2-07 Identify periodic trends among the properties of elements and relate to
electron configuration. Include: atomic radii, ionic radii, ionization energy,
electronegativity
1) Read notes and answer questions below.
2) Complete “Electron Configuration Worksheets 2-6”. Use answer key to correct.
3) Complete “Periodic Trends_Atomic and Ionic Radii”
Gr12 Chem Unit 2: Structure of the Atom, Lesson 4: Electron Configuration and Trends in the Periodic
Table
Noble Gas Simplification
Now, this is becoming a lot of work writing down these ever-expanding electron configurations! The
more electrons we have in the atom, the longer the electron configuration. We have a method we can
use to simplify writing these configuration as we become more familiar with them. If we look
closely, we notice that the electron configuration for rubidium is the same as the previous element,
argon, with a single 5s electron added on. For the electron configuration of argon, let us simply write
[Ar]. The simplified electron configuration for rubidium then becomes:
Rubidium
[Ar]5s1
We can do this for any element, BUT, we must use only noble gases in the brackets. I call this the
noble gas simplification. In this method of writing electron configurations, the last noble gas before
we get to the element of interest is the noble gas we put into the brackets. For instance, for the
element aluminum we write
Aluminum
Calcium
[Ne]3s23p1
[Ar]4s2
and for calcium we write
We may NOT use any element in the brackets, only noble gases. This notation for writing electron
configurations helps us to highlight 2 different types of electrons in the atom. Those electrons in the
brackets are called core electrons. These electrons do not participate in chemical reactions. The
electrons written after the noble gas in brackets are called valence electrons. In many cases, “d”
electrons will be present after the last noble gas, as in the element manganese : [Ar]4s23d5. We
typically do not consider “d” electrons as valence electrons and therefore a more specific definition is
needed: valence electrons are those electrons in the highest principal energy level. These
electrons are important because they are the ones that are gained, lost or shared in chemical reactions.
For the element aluminum, above, we see 2 electrons in the 3s orbital and 1 electron in the 3p orbital,
so aluminum has a total of 3 valence electrons. Using the same method, calcium has 2 valence
electrons. If we look at the electron configuration for manganese again:
Manganese
[Ar]4s23d5
Practice: Write the Noble Gas simplification for the following elements’ electron configuration:
Ti
Ga
F
Gr12 Chem Unit 2: Structure of the Atom, Lesson 4: Electron Configuration and Trends in the Periodic
Table
Electron Configurations and the Periodic Table
It will be helpful now to look at electron configurations also in the context of the periodic table. The
periodic table can be broken into “blocks” that show what the last electron added to the electron
configuration is.
The alkali metal electron configurations (group 1) always end with “s1” and the alkaline earth metals
(group 2) always end with “s2”.
These 2 groups are known as “s block” elements. “P block” elements are all those in groups 13-18
and always end with 1 or more “p” electrons.
For example, all the elements in group 13, beginning with boron, end with “p1”. All of the elements
in group 16, beginning with oxygen, end with “p4”.
The transition elements are called “d block” elements and always end with 1 or more “d electrons”.
For example, the all of the elements in group 3 beginning with scandium, all end in “d1”.
The “f block” elements are those at the bottom of the periodic table that we call the lanthanide and
actinide groups. (Note that there is room for 14 electrons in f orbitals, or 7 “seats”)
These elements’ electron configurations always end with one or more “f electrons.”
(Source: http://www.kentchemistry.com)
Gr12 Chem Unit 2: Structure of the Atom, Lesson 4: Electron Configuration and Trends in the Periodic
Table
1. Write the electron configuration for Br in regular and noble gas notation.
2. What element is represented by: [Ne] 3s23p5
3. How many electrons are in Carbon's 2s orbital?
4. How many orbitals does the d-sublevel have?
5. How many electrons fit in any orbital?
6. How many electrons can fit in principle energy level 3?
7. How many 3p electrons does Phosphorus have?
8. How many p electrons does Phosphorus have?
9. How many s electrons does Cesium have?
10. How many 5d electrons does Hg have?
11. How many d electrons does Hg have?
12. Identify periodic trends among the properties of elements and relate to electron configuration.
(Image source: www.tutorvista.com )
s-block elements tend to have….( Include: atomic radii, ionic radii, ionization energy, electronegativity)
d-block elements tend to have…
p-block elements tend to have…