LEARNING OBJECTIVES recognize the variety of valence electron in an atom. Draw an electron dot framework for an atom.

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Valence Electrons

As was mentioned in a previous ar of this chapter, electron are highly important, since a specific subset that electrons, calledvalence electrons, space solely-responsible because that determininghow elements bondwith one another.The number of valence electrons that are present in an atom can be established from that atom\"s electron configuration. Valence electron are discovered in the orbitals linked with one atom\"s highest possible occupied power level. The continuing to be electrons, which are called inner shell electrons, carry out not take part in bonding and are, therefore, not important to study.

Consider sulfur\"s electron configuration, i beg your pardon was established in the previous section and also is replicated below.

1s22s22p63s23p4

Recall the the power levelsin an electron configuration room theleading red numbers the denotethe begin of a brand-new energy level/orbital combination. Sulfur has electrons in the first, second, and third energy levels, as suggested by the top red 1, 2\"s, and also 3\"s, respectively.Valence electrons space those uncovered in thehighest occupiedenergy level. Therefore, in this case, just those electrons connected with anenergy level/orbital mix beginning through a3need to it is in considered. Because two energy level/orbital combine beginwith a3, both orbitals space selected for further consideration:

3s23p4

The superscripts linked with these orbitals full to 6. Therefore, sulfur has actually 6 valence electrons.

Example \\(\\PageIndex1\\)

Determine how countless ofnitrogen\"s electrons space classified together valence electrons. Nitrogen\"s electron configuration, i m sorry was established in the previous section, is displayed below.

1s22s22p3

Solution

Nitrogen has electrons in the very first andsecondenergy levels, as shown by the top red 1and2\"s,respectively.Valence electrons space those found in thehighest occupiedenergy level. Therefore, in this case, only those electrons associated with anenergy level/orbital combination beginning through a2need to it is in considered. Since two energy level/orbital combine beginwith a2, both orbitals room selected for more consideration:

2s22p3

The superscripts linked with these orbitals complete to 5. Therefore, nitrogen has 5valence electrons.

Exercise \\(\\PageIndex1\\)

Determine how many of the electron in each of the following elements are classified as valence electrons. Every element\"s electron configuration, which was identified in the previous section, is shown below.

Neon

1s22s22p6

Calcium

1s22s22p63s23p64s2

Answer a Neon has electrons in the very first andsecondenergy levels, as shown by the top red 1and2\"s,respectively.Valence electrons are those found in thehighest occupiedenergy level. Therefore, in this case, only those electrons linked with anenergy level/orbital combination beginning with a2need to it is in considered. Since two power level/orbital combinations beginwith a 2, both orbitals space selected for more consideration:

2s22p6

The superscripts linked with this orbitals full to 8. Therefore, neon has actually 8valence electrons. Answer b Calcium has actually electrons in the first,second, third, and fourthenergy levels, as shown by the top red 1,2\"s,3\"s, and4,respectively.Valence electrons space those discovered in thehighest occupiedenergy level. Therefore, in this case, just those electrons associated with anenergy level/orbital mix beginning v a4need to it is in considered. Because only oneenergy level/orbital combinationbegins through a 4, only one orbitalis selected for further consideration:

4s2

The superscriptassociated with thisorbitalis a2. Therefore, calcium has actually 2valence electrons.

While an electron construction representsallof the electrons current in an atom of one element, chathamtownfc.netists are just truly interested in an atom\"svalenceelectrons, since, as indicated above, those space the electrons that are solely-responsible because that determininghow aspects bondwith one another. Therefore, finding a \"shortcut\" because that determining how plenty of valence electrons are present in one atom would be extremely convenient. Together a \"shortcut\" does, indeed, exist. In a previous ar of this chapter, three systemsfor labeling the groups, or columns, on the periodic table to be presented. The 2nd system, i beg your pardon is dubbed the \"A/B System,\" was indicated to provide insight right into the digital character of elements found within that group.

Again, consider sulfur, S, which,based ~ above its electron configuration, has6 valence electrons.

Sulfur is located in the 16thcolumnof the regular table. However, the \"A/B System\"is used to labelthemain team elements. Group 16 is the 6thcolumn in the main group, or \"A-Block,\" columnsof the routine tableandsois labeling asGroup 6A. Keep in mind that sulfur\"s valence electron counting matches its team number in the \"A/B System.\" This connection uses tonearlyallelements uncovered in themain groupcolumns that the regular table. Helium is the only exception to this rule, together itis uncovered in group 8A, yet only has two complete electrons. This inconsistency invalidates the \"A/B shortcut\" method, and also the electron configuration technique must it is in employed to recognize that both that helium\"s electrons are valence electrons.

Since the \"A/B System\" team number coincides to the variety of valence electrons that are present in an atom, all elements found in ~ the same columnhave the same variety of valence electrons. Because an atom\"s valence electrons space solely-responsible because that determininghow elementsbondwith one another, this commonality in digital character defines why all of the elements within the same group share comparable properties.

Example \\(\\PageIndex2\\)

Based top top its ar on theperiodic table, determine how numerous ofnitrogen\"s electrons space classified as valence electrons.

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Solution

The \"A/B System\" group number shows the number of valence electrons that are existing in an atom. Nitrogen (N) is situated in the 15thcolumnof the periodic table. However, the \"A/B System\"is supplied to labelthemain group elements. Team 15 is the 5thcolumn in the key group, or \"A-Block,\" columnsof the routine tableandsois labeled asGroup 5A.Therefore, nitrogen has actually 5 valence electrons. (This answer is consistent with the systems to instance \\(\\PageIndex1\\).)

Exercise \\(\\PageIndex2\\)

Based top top theperiodic table, identify how many of the electron in each of the following aspects are classified as valence electrons.

Neon Calcium Answer a The \"A/B System\" group number suggests the number of valence electrons the are present in one atom. Neon (Ne) is situated in team 18, which islabeled asGroup 8A, utilizing the \"A/B System.\" Therefore, neon has actually 8 valence electrons. (This prize is continual with the systems to practice \\(\\PageIndex1\\texta\\).) Answer b Calcium(Ca) is located in team 2, which islabeled asGroup 2A in the \"A/B System.\" Therefore, calcium has 2 valence electrons. (Again, this prize is continuous with the equipment to exercise \\(\\PageIndex1\\textb\\).)