Periodic trends, or patterns in the periodic table, are prevalent all throughout the periodic table. It is important to note here that these patterns and trends we will be discussing are most clearly seen in the main group elements (elements in Groups 1-2 and 13-18).
Groups 3-12 do not follow the periodic patterns and trends as easily. This has to do with the way their electrons are arranged in the atom, but you will learn more about that in a chemistry course one day!For now, just realize when we talk about a pattern or trend, we are talking about the main group elements.
The first pattern we will discuss are valence electrons. Valence electrons are the outer most electrons in an atom. They are the ones that are furthest from the nucleus.
The electrons in the outer ring of this atom are the valence electrons.
In our example image above, the electrons are shown in different energy levels. The electrons that are in the level furthest from the nucleus are considered valence electrons. So, this atom has 7 valence electrons.
Valence electrons are important because, since they are the outermost electrons, they are the electrons that interact with other atoms. Therefore, they are responsible for most of the properties (characteristics or behaviors) of an atom. In general, an atom can have from 1-8 valence electrons.
Look at the different elements shown above. They each have different numbers of valence electrons (circled in yellow on the image). See a larger version of the image here.
Pattern of Valence Electrons
Let's examine the pattern of valence electrons in the Periodic Table.
See a larger version of the periodic table here.
The number of valence electrons for each element actually varies directly with the group the element is in. The group number helps indicate the number of valence electrons. Review the list below to see this pattern:
- Group 1 has 1 valence electron.
- Group 2 has 2 valence electrons.
- Group 13 has 3 valence electrons.
- Group 14 has 4 valence electrons.
- Group 15 has 5 valence electrons.
- Group 16 has 6 valence electrons.
- Group 17 has 7 valence electrons.
- Group 18 has 8 valence electrons.
Notice that we skipped Groups 3-12. Again, it's because these groups do not follow the predicted patterns well.
The periodic trend of the number of valence electrons being linked to an element's group number only works for Groups 1-2 and 13-18.
How to Determine
To find the number of valence electrons, we simply determine what group an element is in. For example, the element sodium (Na) has 1 valence electron because it is in Group 1.
Now you try. How many valence electrons does sulfur (S) have?
Answer: Sulfur has 6 valence electrons because it is in Group 16. Remember, don't confuse valence electrons with total electrons! Sulfur has 14 total electrons (based on its number of protons) and then 6 of these are valence electrons.
Please do not block ads on this website. The table below for the main group elements is set out just like the Periodic Table of the elements. The electronic configuration in shell notation is given for an atom of each of the elements. The electrons in the valence shell (highest energy level) are given in red. Can you see a pattern, or trend, in the electronic configuration of the atoms in each group and in each period?
No ads = no money for us = no free stuff for you!Trends in the Number of Valence Electrons
symbol
electron configuration in shells
(valence shell electrons, the number of electrons in the highest energy level, shown in red) Group 1
(IA) Group 2
(IIA) Group 13
(IIIA) Group 14
(IVA) Group 15
(VA) Group 16
(VIA) Group 17
(VIIA) Group 18
(VIIIA or 0) Li
2,1Be
2,2 B
2,3C
2,4N
2,5O
2,6F
2,7Ne
2,8 Na
2,8,1Mg
2,8,2 Al
2,8,3Si
2,8,4P
2,8,5S
2,8,6Cl
2,8,7Ar
2,8,8 K
2,8,8,1Ca
2,8,8,2 Ga
2,8,18,3Ge
2,8,18,4As
2,8,18,5Se
2,8,18,6Br
2,8,18,7Kr
2,8,18,8 Rb
2,8,18,8,1Sr
2,8,18,8,2 In
2,8,18,18,3Sn
2,8,18,18,4Sb
2,8,18,18,5Te
2,8,18,18,6I
2,8,18,18,7Xe
2,8,18,18,8 Cs
2,8,18,18,8,1Ba
2,8,18,18,8,2 Tl
2,8,18,32,18,3Pb
2,8,18,32,18,4Bi
2,8,18,32,18,5Po
2,8,18,32,18,6At
2,8,18,32,18,7Rn
2,8,18,32,18,8 Fr
2,8,18,32,18,8,1Ra
2,8,18,32,18,8,2 1 valence electron 2 valence electrons 3 valence electrons 4 valence electrons 5 valence electrons 6 valence electrons 7 valence electrons 8 valence electrons
(EXCEPTION He has 2 valence electrons)
You should see two patterns, or trends:
- Elements in the same Group have the same number of valence shell electrons.
Group 1
(IA)2
(IIA)13
(IIIA)14
(IVA)15
(VA)16
(VIA)17
(VIIA)18
(VIIIA or 0)Number of
valence electrons1 2 3 4 5 6 7 8 2 - Across a period of the Periodic Table from left to right the number of valence electrons increases.2
Group 1
(IA)2
(IIA)13
(IIIA)14
(IVA)15
(VA)16
(VIA)17
(VIIA)18
(VIIIA or 0)Number of
valence electrons1 2 3 4 5 6 7 8 2 Trend: lowest number of
valence electrons→ → → → → → highest number of
valence electrons
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In the table below, the electronic configuration of only the valence electrons is given using subshell notation.
Can you find a pattern, or trend, in the energy levels occupied by the valence electrons?
symbol position of valence shell electrons (energy level of valence electrons shown in red) | ||||||||
Group 13 | ||||||||
He 1s2 | 1||||||||
Li 2s1 | Be 2s2 | B 2s22p1 | C 2s22p2 | N 2s22p3 | O 2s22p4 | F 2s22p5 | Ne 2s22p6 | 2|
Na 3s1 | Mg 3s2 | Al 3s23p1 | Si 3s23p2 | P 3s23p3 | S 3s23p4 | Cl 3s23p5 | Ar 3s23p6 | 3|
K 4s1 | Ca 4s2 | Ga 4s24p1 | Ge 4s24p2 | As 4s24p3 | Se 4s24p4 | Br 4s24p5 | Kr 4s24p6 | 4|
Rb 5s1 | Sr 5s2 | In 5s25p1 | Sn 5s25p2 | Sb 5s25p3 | Te 5s25p4 | I 5s25p5 | Xe 5s25p6 | 5|
Cs 6s1 | Ba 6s2 | Tl 6s26p1 | Pb 6s26p2 | Bi 6s26p3 | Po 6s26p4 | At 6s26p5 | Rn 6s26p6 | 6|
Fr 7s1 | Ra 7s2 | 7 |
You should see two patterns, or trends, in the energy levels of the valence electrons:
- The valence shell electrons of elements in the same period of the Periodic Table occupy the same energy level:
PeriodEnergy Level of
Valence ElectronsValence Shell1 1 K 2 2 L 3 3 M 4 4 N 5 5 O 6 6 P 7 7 Q - Down a Group of the Periodic Table from top to bottom, the energy of the valence electrons increases:
Energy Level of Valence Electrons in a Group
Trend2 lowest energy 3 ↓ 4 ↓ 5 ↓ 6 ↓ 7 highest energy
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