9. Relationships Between the Elements
Families on Periodic Table
Lesson Objectives
•
Describe the patterns that exist in the electron configurations for the main group elements.
•
Identify the columns in the periodic table that contain 1) the alkali metals, 2) the alkaline earth metals,
3) the halogens, and 4) the noble gases, and describe the differences between each family's electron
configuration.
•
Given the outermost energy level electron configuration for an element, determine its family on the periodic
table.
Introduction
With the introduction of electron configurations, we began to get a deeper understanding of the periodic table.
An understanding of these electron configurations will prove to be invaluable as we look at bonding and
chemical reactions. The orbital representation method for representing electron configuration is shown below.
The orbital representation was learned in an earlier chapter but like many of the skills you learn in chemistry,
it will be used a great deal in this chapter and in several chapters later in the course.
In this lesson, we will focus on the connection between the electron configuration and the main group elements
of the periodic table. We will need to remember the sub-level filling groups in the periodic table. Keep the
following figure in mind. We will use it for the next two chapters.
265
1
Elements Ending with s = Alkali
In the periodic table, the elements are arranged
in order of increasing atomic number. In previous
material we learned that the atomic number is
the number of protons in the nucleus of an atom.
For a neutral atom, the number of protons is
equal to the number of electrons. Therefore, for
neutral atoms, the periodic table is also arranged
in order of increasing number of electrons. Take
a look now at the first group or column in the
periodic table. It is the one marked “1A” in Figure
1. The groups or families are the vertical rows of Figure 1: Group 1A of the Periodic Table (Created by:
elements. The first group has seven elements Richard Parsons, License: CC-BY-SA)
representing the seven periods of the periodic
table. Remember that a period in the periodic
table is a horizontal row. Group 1A is the only
group with seven elements in it.
Table 1: Electron Configurations for Group 1 Metals
Element
Atomic Number Electron Configuration
Lithium (Li)
3
2
1
2
2
6
1
2
2
6
2
6
1
2
2
6
2
6
2
10
6
1
2
2
6
2
6
2
10
6
2
10
6
1
2
2
6
2
6
2
10
6
2
10
6
2
1s 2s
Sodium (Na) 11
1s 2s 2p 3s
Potassium (K) 19
1s 2s 2p 3s 3p 4s
R u b i d i u m 37
(Rb)
1s 2s 2p 3s 3p 4s 3d 4p 5s
Cesium (Cs) 55
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s
Francium (Fr) 87
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s
14
10
6
1
1
What do you notice about all of the elements in Group 1? They all have s as the outermost energy level
electron configuration. The whole number in front of the “s” tells you what period the element is in. For ex2
2
6
1
ample sodium, Na, has the electron configuration 1s 2s 2p 3s , so it is in period 3. It is the first element of
this period.
This group of elements is called the alkali metals. They get their name from ancient Arabic (al kali) because
“scientists” of the time found that the ashes of the vegetation they were burning contained a large amount
of sodium and potassium. In Arabic, al kali means ashes. We know today that all alkali metals have electronic
1
configurations ending in s . You might want to note that while hydrogen is often placed in group 1, it is not
266
considered an alkali metal. The reason for this will be discussed later.
2
Elements Ending with s = Alkaline Earth
Taking a look at Group 2A in the figure below, we can use the same analysis we used with group 1 to see
if we can find a similar trend. It is the second vertical group in the periodic table and it contains only six elements.
Table 2: Electronic Configurations for Group 2A Metals
Element
Atomic Number Electron Configuration
Beryllium (Be)
4
2
2
2
2
6
2
2
2
6
2
6
2
2
2
6
2
6
2
10
6
2
2
2
6
2
6
2
10
6
2
10
6
2
2
2
6
2
6
2
10
6
2
10
6
2
1s 2s
M a g n e s i u m 12
(Mg)
1s 2s 2p 3s
Calcium (Ca)
20
1s 2s 2p 3s 3p 4s
Strontium (Sr)
38
1s 2s 2p 3s 3p 4s 3d 4p 5s
Barium (Ba)
56
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s
Radium (Ra)
88
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s
14
10
6
2
What do you notice about all of the elements in group 2A? They all have an outermost energy level electron
2
configuration of s . The whole number in front of the “s” tells you what period the element is in. For example,
2
2
6
2
magnesium, Mg, has the electron configuration 1s 2s 2p 3s , so it is in period 3 and is the second element
in that period. Remember that the s sublevel may hold two electrons, so in Group 2A, the s orbital has been
filled.
Elements in this group are given the name alkaline earth metals. They get their name because early “scientists” found that all of the alkaline earths were found in the earth’s crust. Alkaline earth metals, although
not as reactive as the alkali metals, are still highly reactive. All alkaline earth metals have electron configu2
rations ending in s .
2 6
Elements Ending with s p = Noble Gases
The first person to isolate a noble gas was Henry
Cavendish, who isolated argon in the late 1700s.
The noble gases were actually considered inert
gases until the 1960’s when a compound was
formed between xenon and fluorine which
changed the way chemists viewed the “inert”
gases. In the English language, inert means to
be lifeless or motionless; in the chemical world,
inert means does not react. Later, the name "noble gas" replaced "inert gas" for the name of
Group 8A.
When we write the electron configurations for these elements, we see the same general trend that was observed with groups 1A and 2A; that is, similar electron configurations within the group.
Table 3: Electron Configurations for Group 8A Gases
Element
Atomic Number Electron Configuration
267
Helium 2
(He)
1s
Neon (Ne) 10
1s 2s 2p
Argon (Ar) 28
1s 2s 2p 3s 3p
K r y p t o n 36
(Kr)
1s 2s 2p 3s 3p 4s 3d 4p
Xenon (Xe) 54
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
Radon (Rn) 86
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
2
2
2
6
2
2
6
2
6
2
2
6
2
6
2
10
6
2
2
6
2
6
2
10
6
2
10
6
2
2
6
2
6
2
10
6
2
10
6
2
14
10
6
Aside from helium, He, all of the noble gases have outer energy level electron configurations that are the
2
6
same, ns np , where n is the period number. So Argon, Ar, is in period 3, is a noble gas, and would therefore
2
6
have an outer energy level electron configuration of 3s 3p . Notice that both the s and p sublevels are filled.
Helium has an electron configuration that might fit into Group 2A. However, the chemical reactivity of helium,
because it has a full first energy level, is similar to that of the noble gases.
2 5
Elements Ending with s p = Halogens
The halogens are an interesting group. Halogens
are members of Group 7A, which is also referred
to as 17. It is the only group in the periodic table
that contains all of the states of matter at room
temperature. Fluorine, F2, is a gas, as is chlorine,
Cl2. Bromine, Br2, is a liquid and iodine, I2, and
astatine, At2, are both solids. What else is neat
about Group 7A is that it houses four (4) of the
seven (7) diatomic compounds. Remember the
diatomics are H2, N2, O2, F2, Cl2, Br2, and I2. Notice that the latter four are Group 17 elements.
The word halogen comes from the Greek meaning salt forming. French chemists discovered that
the majority of halogen ions will form salts when
combined with metals. We all know some of these
already: LiF, NaCl, KBr, and NaI.
Taking a look at Group 7A in the figure, we can find the same pattern of similar electron configurations as
th
found with group 1A, 2A, and 8A. It is the 17 group in the periodic table and it contains only five elements.
Table 4: Electron Configurations for Group 7A Elements
Element
Atomic number Electronic configuration
Fluorine (F) 9
1s 2s 2p
C h l o r i n e 17
(Cl)
1s 2s 2p 3s 3p
B r o m i n e 35
(Br)
1s 2s 2p 3s 3p 4s 3d 4p
Iodine (I)
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
53
Astatine (At) 85
268
2
2
5
2
2
6
2
5
2
2
6
2
6
2
10
5
2
2
6
2
6
2
10
6
2
10
5
2
2
6
2
6
2
10
6
2
10
6
2
14
10
5
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
What is the general trend for the elements in Group 7A? They all have, as the outermost energy level electron
2
5
configuration, ns np , where n is the period number. You should also note that these elements are one group
away from the noble gases (the ones that generally don’t react!) and the outermost electron configuration
of the halogens is one away from being filled. For example, chlorine (Cl) has the electron configuration [Ne]
2
5
3s 3p so it is in period 3, the seventh element in the main group elements. The main group elements,
as you recall, are equivalent to the s + p blocks of the periodic table (or the teal and purple groups in the
diagram above).
2 4
Elements Ending with s p = the Oxygen Family
Oxygen and the other elements in Group 6A have
a similar trend in their electron configurations.
Oxygen is the only gas in the group; all others
are in the solid state at room temperature. Oxygen was first named by Antoine Lavoisier in the
late 1700s but really the planet has had oxygen
around since plants were first on the earth. Taking
a look at Group 6A in the figure below, we find
the same pattern in electron configurations that
we found with the other groups. Oxygen and its
th
family members are in the 16 group in the periodic table. In Group 16, there are, again, only five
elements.
Table 4: Electron Configurations for Group 6A Elements
Element
Atomic Number Electron Configuration
Oxygen (O)
8
1s 2s 2p
Sulfur (S)
16
1s 2s 2p 3s 3p
2
2
4
2
2
6
2
4
2
2
6
2
6
2
10
4
2
2
6
2
6
2
10
6
2
10
4
2
2
6
2
6
2
10
6
2
10
6
S e l e n i u m 34
(Se)
1s 2s 2p 3s 3p 4s 3d 4p
Tellurium (Te) 52
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
P o l o n i u m 84
(Po)
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
2
14
10
4
When we examine the electron configurations of the Group 6A elements, we see that all of these elements
2
4
have the outer energy level electron configuration of ns np . We will see that this similar electron configuration
gives all elements in the group similar properties for bonding.
These elements are two groups away from the noble gases and the outermost electron configuration is two
2
2
6
2
4
away from being filled. Sulfur, for example, has the electron configuration 1s 2s 2p 3s 3p so it is in period
3. Sulfur is the sixth element in the main group elements. We know it is the sixth element across the period
269
of the main group elements because there are 6 electrons in the outermost energy level.
2 3
Elements Ending with s p = the Nitrogen Family
Just as we saw with Group 16, Group 5A has a
similar oddity in its group. Nitrogen is the only
gas in the group with all other members in the
solid state at room temperature. Nitrogen was
first discovered by the Scottish chemist Rutherford in the late 1700’s. The air is mostly made of
nitrogen. Nitrogen has properties that are different
in some ways from its group members. As we will
learn in later lessons, the electron configuration
for nitrogen provides the ability to form very
strong triple bonds. Nitrogen and its family
th
members belong in the 15 group in the periodic
table. In Group 15, there are also only five elements.
Table 6: Electronic Configurations for Group 5A Elements
Element
Atomic Number Electron Configuration
Nitrogen (N)
7
2
2
3
2
2
6
2
3
2
2
6
2
6
2
10
3
2
2
6
2
6
2
10
6
2
10
3
2
2
6
2
6
2
10
6
2
10
6
1s 2s 2p
P h o s p h o r u s 15
(P)
1s 2s 2p 3s 3p
Arsenic (As)
1s 2s 2p 3s 3p 4s 3d 4p
33
Antimony (Sb) 51
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
Bismuth (Bi)
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
83
2
14
10
3
What is the general trend for the elements in group 5A? They all have, as the electron configuration in the
2
3
outermost energy level, ns np , where n is the period number. These elements are three groups away from
the noble gases and the outermost energy level electron configuration is three away from having a completed
outer energy level. In other words, the p sublevel in the Group 15 elements is half full. Arsenic, for example,
2
2
6
2
6
2
10
3
has the electron configuration 1s 2s 2p 3s 3p 4s 3d 4p so it is in period 4, the fifth element in the main
group elements. We know it is the fifth element across the period of the main group elements because there
are 5 electrons in the outermost energy level.
Lesson Summary
•
Families in the periodic table are the vertical columns and are also referred to as groups.
•
Group 1A elements are the alkali metals and all have one electron in the outermost energy level because
1
their electron configuration ends in s .
•
Group 2A elements are the alkaline earth metals and all have two electrons in the outermost energy
2
level because their electron configuration ends in s .
•
Group 5A elements all have five electrons in the outermost energy level because their electron configu2
3
ration ends in s p .
•
Group 6A elements all have six electrons in the outermost energy level because their electron configu2
4
ration ends in s p .
270
•
Group 7A elements are the halogens and all have seven electrons in the outermost energy level because
2
5
their electron configuration ends in s p .
•
Group 8A elements are the noble gases and all have eight electrons in the outermost energy level because
2
6
their electron configuration ends in s p .
•
Elements in group 8A have the most stable electron configuration in the outermost shell because the
sublevels are completely filled with electrons.
Review Questions
2
3
1. If an element is said to have an outermost electronic configuration of ns np , it is in what group in the
periodic table?
(Beginning)
(a) Group 3A
(b) Group 4A
(c) Group 5A
(d) Group 7A
2. What is the general electronic configuration for the Group 8A elements?
(Beginning)
(Note: when we wish to indicate an electron configuration without specifying the exact energy level, we
2
3
use the letter "n" to represent any energy level number. That is, ns np represents any of the following;
2
3
2
3
2
3
2s 2p , 3s 3p , 4s 4p , and so on.)
2
6
2
5
2
1
(a) ns np
(b) ns np
(c) ns np
2
(d) ns
3. The group 2 elements are given what name?
(Beginning)
(a) alkali metals
(b) alkaline earth metals
(c) halogens
(d) noble gases
271
4.
Using the diagram, identify:
(Beginning)
(a) The alkali metal by giving the letter that indicates where the element would be located and write the
outermost electronic configuration.
(b) The alkaline earth metal by giving the letter that indicates where the element would be located and write
the outermost electronic configuration.
(c) The noble gas by giving the letter that indicates where the element would be located and write the outermost electronic configuration.
(d) The halogen by giving the letter that indicates where the element would be located and write the outermost
electronic configuration.
2
3
2
1
(e) The element with an outermost electronic configuration of s p by giving the letter that indicates where
the element would be located.
(f) The element with an outermost electronic configuration of s p by giving the letter that indicates where
the element would be located.
5. In the periodic table, name the element whose outermost electronic configuration is found below. Where
possible, give the name of the group.
(Intermediate)
2
1
(a) 5s
(e) 3s
2
10
2
3
2
10
1
2
(b) 4s 3d 4p (f) 1s
(c) 3s 3p
2
10
2
4
5
(g) 6s 5d 6p
2
(d) 5s 4d 5p (h) 4s 4p
Further Reading / Supplemental Links
http://en.wikipedia.org
Vocabulary
group
period
272
Vertical columns of the periodic table.
Horizontal rows of the periodic table.
alkali metals
alkaline earth metals
noble gases
halogens
main group elements
Group 1 in the periodic table (Li, Na, K, Rb, Cs, Fr).
Group 2 in the periodic table (Be, Mg, Ca, Sr, Ba, Ra).
Group 18 in the periodic table (He, Ne, Ar, Kr, Xe, Rn).
Group 17 in the periodic table (F, Cl, Br, I, At).
Equivalent to the s + p blocks of the periodic table, also known as "representative
elements."
Review Answers
1. (c) Group 5A
2
6
2. (a) ns np
3. (b) alkaline earth metals
4.
1
a. Element E: outermost electronic configuration = ns
2
b. Element B: outermost electronic configuration = ns
2
6
2
5
c. Element C: outermost electronic configuration = ns np
d. Element G: outermost electronic configuration = ns np
e. Element H
f. Element I
5.
2
1
(a) 5s Sr: Alkaline earth metals: Group 2A (e) 3s Na: Alkali metals: Group 1A
2
10
2
3
2
10
1
(b) 4s 3d 4p Ga: Group 3A
(c) 3s 3p P: Group 5A
2
(d) 5s 4d 5p Sn: Group 4A
2
(f) 1s He: Noble Gases: Group 8A
2
10
2
4
5
(g) 6s 5d 6p At: Halogens: Group 7A
(h) 4s 4p Se: Group 6A
Electron Configurations
Lesson Objectives
•
Convert from orbital representation diagrams to electron configuration codes.
•
Distinguish between outer energy level (valence) electrons and core electrons.
•
Use the shortcut method for writing electron configuration codes for atoms and ions.
Introduction
In the last section, we determined that the members of the chemical families (vertical columns on the periodic
table) all have the same electron configuration in their outermost energy levels. In the next section, we will
273
review the orbital representation for electron configuration and the electron configuration code. Then we will
learn a shortcut for writing electron configuration codes.
Shortcut for Writing Electron Configurations
The diagram below represents the orbital representation diagram used in earlier chapters. The orbital
representation diagram has a few different variations but all are used to draw electron configurations. Most
show the orbitals in groups (or even in boxes or circles) with orbitals having their own line (or box) within
each sublevel. The sublevel 2p has 3 orbitals (2px, 2py, and 2pz) and each of these orbitals has its own line
(or box).
Let’s begin this section with the orbital box (or the orbital representation diagram) for a neutral atom. Draw
the electronic configuration for potassium using the electron configuration diagram below. Remember that
potassium is element number 19 so has 19 electrons. Every line in the energy diagram below holds 2 electrons
of opposite spins.
Now we can simplify this by excluding all of the levels and sublevels that are not in use or do not hold electrons.
274
Writing the electron configuration code for potassium, we would get:
2
2
6
2
6
1
K: 1s 2s 2p 3s 3p 4s .
Remember, the noble gases are the elements that are nearly non-reactive, partially due to the fact that the
2
6
outermost energy level electron configuration was full (ns np ). Look at potassium on the periodic table and
then find the preceding noble gas. Drag you finger counting backward from potassium to the nearest noble
gas. What do you get? Argon (Ar) is correct. Now, let’s draw the electron configuration for Argon and place
the electron configuration for potassium beside it.
What do you notice looking at the two diagrams? Potassium has the same electron configuration as argon
+ 1 electron. We can make this point when we write electronic configuration codes.
2
2
6
2
6
1
K: 1s 2s 2p 3s 3p 4s
2
2
6
2
6
Ar: 1s 2s 2p 3s 3p
Therefore
1
K: [Ar] 4s . {This is known as the noble gas configuration code system or the “short-cut”}
Let’s try another. Draw and write the electron configuration of gallium (Ga). Gallium is number 31 and
th
therefore has 31 electrons. It is also in the 4 period, the third element in the period of main group elements.
2
1
From this information, we know that the outermost electrons will be 4s 4p .
275
Electron configuration of Gallium (Ga).
2
2
6
2
6
2
10
1
Writing the electron configuration code for gallium, we get: Ga: 1s 2s 2p 3s 3p 4s 3d 4p . In numerical
2
2
6
2
6
10
2
1
order, the electronic configuration for gallium is: Ga: 1s 2s 2p 3s 3p 3d 4s 4p .
Now, go back to the previous noble gas. Again, we find the previous noble gas is argon. Remember argon
2
2
6
2
6
has electronic configuration of 1s 2s 2p 3s 3p .
2
2
6
2
6
2
10
1
Ga: 1s 2s 2p 3s 3p 4s 3d 4p
2
2
6
2
6
Ar: 1s 2s 2p 3s 3p
Therefore
2
10
1
Ga: [Ar] 4s 3d 4p .
This seems to work well for neutral atoms, what about ions? Remember that a cation is formed when electrons
are removed from a neutral atom and anions are formed when electrons are added to a neutral atom. But
where do the electrons get added to or removed from? The electrons that are involved in chemical reactions
are the ones that are in the outer shell. Therefore if electrons are to be removed or added, they get removed
from or added to the shell with the highest value of n.
Let’s now look at an example. Draw the electron configuration for Fe. Then, write the reaction for the formation
2+
of Fe .
276
2+
2+
-
The reaction for the formation of the Fe ion is: Fe
Fe + 2e . Therefore we have to remove 2 electrons.
From where do we remove the two electrons? The rule is to remove from the highest n value first which, in
this case, means we remove from the electrons from the 4s sublevel first.
Fe
2
2+
-
Fe + 2e
2
6
2
6
2
6
2
1s 2s 2p 3s 3p 4s 3d
2
6
2
6
6
-
1s 2s 2p 3s 3p 3d + 2e
Remember that when we write electron configuration codes using noble gas configurations we use the
2+
previous noble gas. In writing the electron configuration code for Fe or Fe , we would use the symbol [Ar]
2
2
6
2
6
to substitute for 1s 2s 2p 3s 3p .
Fe
2+
-
Fe + 2e
6
2
6
[Ar] 3d 4s
-
[Ar] 3d + 2e
2+
3+
In addition to forming Fe ions, iron atoms are also capable of forming Fe ions. Extra stability is gained
by electron configurations that have exactly half-filled d orbitals. The third electron that is removed from an
3+
iron atom to form the Fe ion is removed from the d orbital giving this iron ion a d orbital that is exactly halffilled. The extra stability of this configuration explains why iron can form two different ions.
Fe
3+
-
Fe + 3e
6
2
[Ar] 3ds 4s
5
-
[Ar] 3ds + 3e
Now what about negative ions, the anions? Remember that negative ions are formed by the addition of
electrons to the electron cloud. Look at bromine, Br. Neutral bromine has atomic number 35 and therefore,
holds 35 electrons.
277
-
-
-
The reaction for the formation of the Br ion is: Br + e
Br . The bromide ion is formed by the addition of
one electron. If you look at the electron configuration for bromine, you will notice that the 4p sublevel needs
-
one more electron to fill the sublevel and if this sublevel is filled, the electron configuration for Br is the
same as that of the noble gas krypton (Kr). When adding electrons to form negative ions, the electrons are
added to the lowest unfilled n value.
Br
+ e2
2
6
2
6
2
10
5
1s 2s 2p 3s 3p 4s 3d 4p + e
Or
Br
+ e2
2
6
2
6
2
10
5
1s 2s 2p 3s 3p 4s 3d 4p + e
-
Br
2
2
6
2
6
2
10
6
1s 2s 2p 3s 3p 4s 3d 4p
-
Br
[Kr]
-
Notice how Br has the same electron configuration as Kr. When this happens, the two are said to be isoelectronic.
Sample Question: Write the electron configuration codes for the following atoms or ions using the noble gas
electron configuration shortcut.
(a) Se
(b) Sr
2-
(c) O
2+
(d) Ca
3+
(e) Al
Solution:
10
4
[Ar] 4s 3d 4p
(b) Sr :
[Kr] 5s
2-
(c) O
278
2
(a) Se :
:
2
[Ne]
2+
(d) Ca
3+
(e) Al
:
:
[Ar]
[Ne]
Core Electrons
When we look at the electron configuration
for any element we can distinguish that there are two different types of electrons. There are electrons that
work to do the reacting and there are those that don’t. The outer shell electrons are the valence electrons
and these are the electrons that are responsible for the reactions that the atoms undergo. The number of
valence electrons increases as you move across the periodic table for the main group elements.
In older periodic tables, the groups were numbered using an A and B group numbering system. The representative groups (s and p blocks) were numbered with A and the transition elements were numbered with
B. The table on the right has both numbering systems. The A numbering is shown for you in the diagram in
red; this is all we will be concerned with for this lesson. The number of valence electrons in the A groups
increases as the group number increases. In fact, the number of the A groups is the number of valence
electrons. Therefore, if an element is in group 3A, it has 3 valence electrons, if it is in group 5A, it has 5 valence electrons.
All electrons other than valence electrons are called core electrons. These electrons are in inner energy
levels. It would take a very large amount of energy to pull an electron away from these full shells, hence,
they do not normally take part in any reactions. Look at the electron configuration for gallium (Ga). It has 3
valence electrons and 28 core electrons.
Sample Question: How many core electrons and valence electrons are in each of the following?
(a) V
279
(b) As
(c) Po
(d) Xe
Solution:
(a) 23V :
Core Electrons = 18, Valence electrons = 5
(b) 33 As :
Core Electrons = 28, Valence electrons = 5
(c) 84 Po :
Core Electrons = 78, Valence electrons = 6
(d) 54 Xe :
Core Electrons = 46, Valence electrons = 8
Lesson Summary
•
An orbital box diagram can be used to draw electron configurations for elements.
•
The noble gas configuration system is the shorthand method for representing the electron configuration
of an element.
•
The noble gas symbol represents all of, or most of, the core electrons.
•
For cations, the electrons are removed from the outermost sublevel having the greatest n value.
•
For anions, the electrons are added to the unfilled energy level having the lowest n value.
•
Isoelectronic species have the same electron configurations.
•
Using an orbital box diagram, the core electrons and the valence electrons can easily be visualized.
•
The valence electrons are those electrons that are in the outermost shell.
Review Questions
1. What is the difference between the standard electron configuration code and the electron configuration
code using noble gas configurations?
(Beginning)
2. The standard electron configuration is often called the ground state electron configuration.
Why do you think this is so?
(Beginning)
3. How is it possible to have the same number of core electrons and valence electrons for two different ions?
(Challenging)
4. Draw the orbital representation for the electron configuration of potassium, K.
5. Write the electron configuration code for potassium, K.
(Intermediate)
6. Write the noble gas electron configuration code for potassium, K.
(Intermediate)
7. How many core electrons and valence electrons are in potassium, K?
+
8. Write the electron configuration for potassium, K .
(Intermediate)
(Intermediate)
+
9. Write the noble gas electron configuration code for potassium, K .
280
(Intermediate)
(Intermediate)
+
10. With what species is K isoelectronic?
(Intermediate)
11. The electron configuration below is for which element?
10
2
(Intermediate)
2
[Kr] 4d 5s 5p
(a) Sb
(b) Sn
(c) Te
(d) Pb
12. The electron configuration below is for which element?
10
2
(Intermediate)
4
[Xe] 5d 6s 6p
(a) Pb
(b) Bi
(c) Po
(d) Tl
13. What is the noble gas electron configuration for the bromine element?
2
2
6
2
6
2
2
6
2
6
2
5
2
(Intermediate)
5
(a) 1s 2s 2p 3s 3p 4s 4p
10
2
5
(b) 1s 2s 2p 3s 3p 3d 4s 4p
(c) [Ar] 4s 4p
10
2
5
(d) [Ar] 3d 4s 4p
14. Write the noble gas electron configuration for each of the following.
(Intermediate)
(a) Al
3-
(b) N
2+
(c) Sr
2+
(d) Sn
(e) I
15. How many core electrons and valence electrons are in each of the following?
(Intermediate)
a. Mg
b. C
c. S
281
d. Kr
e. Fe
Vocabulary
orbital box diagram A diagram for drawing the electron configurations where sub-levels are shown in
groups (or even in boxes) and each orbital has its own line (or box) within each sublevel.
isoelectronic
Having the same electron configuration.
core electrons
Electrons that occupy energy levels below the outermost energy level.
valence electrons Electrons that occupy the outer shell of the atom or ion.
Review Answers
1. The noble gas configuration includes all of the full orbitals up to the nearest shell to the element. For example for sodium, Na:
2
2
6
1
Na: 1s 2s 2p 3s
11
6
The noble gas configuration would include everything up to and including the 2p .
Therefore Na would become:
1
Na: [Ne] 3s
11
2. The standard electronic configuration is probably called the ground state electronic configuration because
it starts at the ground level (n = 1).
3. If you have an element and an ion or two ions, these can have the same number of core electrons and
+
2+
the same number of valence electrons. Look at Na and Mg
A sodium atom has 11 electrons, 10 core electrons and 1 valence electron. When the sodium atom becomes
a +1 ion, it has 10 core electrons and zero valence electrons. A magnesium atom has 12 electrons, 10 core
electrons and 2 valence electrons. When the magnesium atom becomes a 2+ ion, it has 10 core electrons
and zero valence electrons. Both ions have the same electron configuration as a neon atom.
4.
2
2
6
2
6
1
5. 1s 2s 2p 3s 3p 4s
282
1
6. [Ar] 4s
7. 18 core electrons and 1 valence electron
2
2
6
2
6
8. 1s 2s 2p 3s 3p
9. [Ar]
10. argon
11. (b) Sn
12. (c) Po
10
2
5
13. (d) [Ar] 3d 4s 4p
2
1
14. (a) Al: [Ne] 3s 3p
3-
(b) N : [Ne]
2+
(c) Sr : [Kr]
2+
10
2
(d) Sn : [Kr] 4d 5s
10
2
5
(e) I: [Xe] 4d 5s 5p
15.
(a) 12Mg: Core Electrons = 10, Valence electrons = 2
(b) 6C: Core Electrons = 2, Valence electrons = 4
(c) 16S: Core Electrons = 10, Valence electrons = 6
(d) 36Kr: Core Electrons = 28, Valence electrons = 8
(e) 26Fe: Core Electrons = 18, Valence electrons = 8
Lewis Electron Dot Diagrams
Lesson Objectives
•
Explain the meaning of an electron dot diagram.
•
Draw electron dot diagrams for given elements.
•
Describe the patterns of electron dot diagrams in the periodic table.
Introduction
This chapter will explore yet another shorthand method of representing the valence electrons. The method
explored in this lesson will be a visual representation of the valence electrons. We will, as we observed in
the previous lesson, finish the lesson with a look at how this visual representation flows in a pattern
283
CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook
materials for the K-12 market both in the U.S. and worldwide. Using an open-content, webbased collaborative model termed the “FlexBook,” CK-12 intends to pioneer the generation
and distribution of high-quality educational content that will serve both as core text as well
as provide an adaptive environment for learning.
Copyright © 2009 CK-12 Foundation, www.ck12.org
Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material)
is made available to Users in accordance with the Creative Commons Attribution/NonCommercial/Share Alike 3.0 Unported (CC-by-NC-SA) License (http://creativecommons.
org/licenses/by-nc-sa/3.0/), as amended and updated by Creative Commons from time
to time (the “CC License”), which is incorporated herein by this reference. Specific details
can be found at http://about.ck12.org/terms.