Electron Configurations - Wikispaces-+Shell... · Electron Configurations ... What does the...
Transcript of Electron Configurations - Wikispaces-+Shell... · Electron Configurations ... What does the...
LESSON
24 Shell GameElectron Configurations
Think About ItRecall that the chemistry of the elements is closely related to the number ofvalence electrons in their atoms. The valence electrons are found in the outermostelectron shell of an atom.
What does the periodic table indicate about the arrangements of electrons?To answer this question, you will explore
o Subs hells in Atoms
f) Electron Configurations
e Connecting the Periodic Table to Electron Arrangements
o Noble Gas Shorthand
Exploring the Topic
o Subshells in AtomsElectrons are arranged into shells numbered11 = I, 2, 3, and so on. The number of electronshells in an atom is the same as the number ofthe period where the element is located on theperiodic table. Each shell has a maximum numberof electrons. For instance, the 11 = 2 shell cannothave more than 8 electrons.
Scientific evidence has led chemists to proposethat electron shells are further divided intoelectron subshells. Imagine magnifying the basicatomic model and finding that each shell iscomposed of subshells. Notice that the number ofsubshells that a shell has is equal to n.
n = 4 maximum: 32 e-n = 3 maximum: 18 e-[I" =, maximum 8 e-
~ n = I maximum; 2 e-
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Electron shells are further dividedinto subshells.
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Lesson 24 Shell Game 117
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118 Unit I Alchemy
The s, p, d, and f SubshellsThe subshells have special names. They are called the s, p, d, and f subshells. Justlike the basic shells, each subshell has a maximum capacity of electrons. Thes subshells can have a maximum of 2 electrons, p subshells can have a maximumof 6 electrons, and d subshells can have a maximum of 10 electrons. Finally,f subshells can have a maximum of 14 electrons.
Na
Issubshell
Sodium, Na, hasII electrons,located in thesubshells as shown.
Key
0 s subshells
0 p subshells
0 d subshells
0 f subshells
25 subshell2p subshell
35 subshell3p subshell3d subshell
Notice that the name of each subshell is labeled using both the basic shell numberand the subshell letter (Is, 2s, 2p, and so on).
Example IElectron ArrangementsUse the illustration of the subshells in a sodium atom above to help you answerthese questions:a. How many total electrons are there in a sodium, Na, atom? Which shells are
they in?b. How many valence electrons does sodium have? Which subshell are they in?c. How many electrons are there in the 3s subshell of sodium? In the 3p subshell?
SolutionThe atomic number of sodium is 11.
a. There are a total of 11 electrons in a neutral sodium atom. The electrons are inshells, n = I, n = 2, n = 3.
b. Sodium has one valence electron, located in the 3s subshell.c. There is one electron in the 3s subshell of sodium, and none in the 3p subshell.
'e Electron ConfigurationsIt can be time consuming to draw subshell models of the atoms to show thearrangements of the electrons, especially for atoms. with large atomic numbers.Chemists have developed a shorthand notation called an electron configurationto keep track of the electrons in an atom. The electron configurations for the firstten elements are shown here.
H Is1 C Is22s22p2He Is2 N Is22s22p3
Li Is22s1 0 Is22s22p4Be Is22s2 F Is22s22p5
B ls22s22pl Ne ls22s22p6
Nitrogen has atotal of 7 electrons.
Section IV Moving Electrons
Topic: ElectronConfiguration
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Each subshell is written using the shell numberand the subshellietter. In addition, the numberof electrons in each subshell is indicated with asuperscript number.
Notice that the superscript numbers add up tothe total number of electrons for that atom.
The sequence in which electrons fill up thesubshells is Is, 2s, 2p, 3s, 3p. After the elementargon the pattern changes slightly.
Electrons in each subshell
1Li: 2s
Subshells
SolutionSulfur is located in the third row in Group 6A. The atomic number of sulfur is 16,so there are 16 electrons that need to be distributed in subshells beginning withthe Is subshell.
The electron configuration of sulfur is Is22s22p63s23p4.
Example 2Electron Configuration of SulfurWrite the electron configuration for sulfur, S.
e Connecting the Periodic Table to Electron ArrangementsAn outline of the periodic Periodic Table-subshellstable appears here withcolor-coding to show thesubshell for the outermostelectron of each elemen t.For example, any elementlocated in the green areawill have its outermostelectron (s) in a p subshell.
As you proceed across theperiodic table from oneelement to the next, oneadditional proton and oneadditional electron are added, along with one or more neutrons. Each additionalelectron goes into a specific subshell. If an atom is located in the orange areas ofthe table, the last electron is placed into an s subshell. If an atom is located in theblue area of the table, the last electron is placed into a d subshell, And so on.
The elements in each block have related properties. The elements in the s-block arereactive metals. The elements in the d-block tend to form colorful compounds thatare used as pigments. The elements in the p-block tend to form colorless compounds.
Key~s-block I
~ p-blockd-block
• f-block
Decoding the TableIn order to write out an electron configuration for a specific element, you cansimply "read" from the periodic table, moving across from left to right and then
Lesson 24 Shell Game 119
down to the next row. For example, the sequence of subshells for argon, Ar, is Is,2s, 2p, 3s, 3p. The electron configuration for argon is Is22s22p63s23pfi.
Periodic Table-subshells
2
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Everything runs smoothly until you reach the fourth row of the periodic table.After argon, you might expect the next electron to be in the 3d subshell. However,this does not happen. The next element is potassium, K. Like the other elements inGroup lA, potassium has one electron in the s subshell. Thus, you place an electronin 4s before 3d. The electron configuration for potassium is ls22s22pfi3s23p64sl.Theelectron configuration for arsenic is Is22s22p63s23p64s23d104p3.
You may have noticed that you only have to look at the ending of each electronconfiguration in order to figure out the identity of the element associated with it.The ending provides you with the exact spot on the periodic table where you canfind the element.
Important The s subshells fill with electrons before the d subshells from the previousto Know shell. For example, the 4s subshell fills before the 3d subshell, the 5s subshell
fills before the 4d subshell, and so on. ~
Example 3Electron Configuration of CobaltWrite the electron configuration for cobalt, Co.
SolutionLocate cobalt on the periodic table. It is element number 27 and is located in fhefourth period of the periodic table. "_,"
Simply trace your finger across the periodic table of subshells, writing thesubshells as you go. When you get to cobalt, stop writing. Every subshell up to the4s subshell is completely filled. In addition, cobalt has seven electrons in the 3dsubshell. The answer is Is22s22p63s23p64s23d7.
You can check that you have the correct electron configuration by adding thesuperscript numbers to make sure there are 27 electrons.
120 Unit I Alchemy Section IV Moving Electrons
o Noble Gas ShorthandDepending on the element, the electron configuration can be lengthy to write.Plus, each element just repeats the electron configuration of the previous element,but adds one more electron.
Rather than repeat the same thing every time, chemists have devised a quicker wayto write out electron configurations. They use the noble gas at the end of each periodas a placeholder to symbolize all of the filled subshells before that place on the table.Using this "shorthand" method, the electron configuration of cobalt is [ArJ4s23d7
.
Shorthand notation allows you to make some interesting comparisons. Noticethat the noble gas shorthand notation emphasizes the valence electrons. Usingthis method, it is easy to see that each element in Group 2A has two valenceelectrons, both located in an s subshell.
Group 2A Elements
Element Symbol Elec tron configuration
beryllium Be [He]2s2
magnesium Mg [Ne]3s2
calcium ea [Ar]4s2
strontium Sr [Kr]Ss2
~ barium Ba [Xe]6s2
radium Ra [Rn]7s2
Ii
Key Termelectron configuration
Example 4Electron Configuration of SeleniumFind the element Selenium, Se, element 34, on the periodic table.a. What is the electron configuration of selenium?b. Write the electron configuration using noble gas shorthand.c. In what subshells are selenium's valence electrons?
Solutiona. Selenium is in the p-blcck, in Period 4. The electron configuration of
selenium is Is22s22p63s23p64s23dJ04p4.
b. The noble gas that comes before selenium is argon, Ar. Thus, the noble gasshorthand for this configuration is tA~]4s23d104p4.
c. Selenium's valence electrons are in subshells 4s and 4p.
Lesson SummaryWhat does the periodic table indicate about the arrangements of electrons?Electrons in atoms are arranged into basic shells labeled n = I, 2, 3, and so on. Theseshells are divided into subshells. The number of subshells in each shell is equal to n.
Lesson 24 Shell Game 121
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The subshells are referred to as s, p, d, and f subshells. The s, p, d, and f subshells canhave a maximum of2, 6, 10, and 14electrons, respectively. Chemists use electronconfigurations to specify the arrangements of electrons in subshells. The periodictable provides the information needed to write electron configurations.
r EXERCISES 1 _Reading QuestionsI. What are electron subshells?
2. What is an electron configuration?
3. How is the arrangement of electrons in an atom related to the location of theatom on the periodic table?
Reason and Apply4. How many subshells are in each shell: n = 1, n = 2, n = 3, n = 4?
5. What is the total number of subshells for elements in Period 5 of theperiodic table?
6. Draw a subshell model for each of the following elements, putting theelectrons in their appropriate places.a. sodium, Na b. neon, Ne c. carbon, C d. vanadium, V
7. What is the outermost subshell for bromine, Br?
8. Name an element with electrons in the f subshell.
9. Consider the element with the atomic number 13.a. What is the electron configuration for the element with atomic number 13?b. How many valence electrons does element 13 have? How do you know?c. How many core electrons does element 13 have? How did you figure
that out?
Explain why the chemical properties of argon, krypton, and xenon aresimilar, even though there are 18 elements between argon and krypton, and32 elements between krypton and xenon.
II. Write the electron configurations for each of these atoms. Then write itusing the noble gas shorthand method.a. oxygen b. chlorine
10.
C. Iron d. calcium
h. mercurye. magnesmm f. silver g. silicon
12. You should be able to figure out the identity of an atom from its electron·-configuration alone. Describe at least two ways you could do this.
13. Which elements are described by these electron configurations?a. Is22s22p63s23p64s23d4 b. Is22s22p63s23p2C. ls22s22p3 d. IS22s22p63s23p64s23d104p6SS24dloSp66s1e. Is22s22p63s23p64s23d104p6Ss24dlOSp66s24fl4SdlO6p2f. [Kr]Ss24d9
122 Unit I Alchemy Section IV Moving Electrons
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98 Unit I AlchemyLesson 24 • Transparency
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r=; :tf-e-- Electron Configurations
H lS1
~ He ls2
3 Li ls2 2S1
If Be ls2 2S2s: B ls2 2S2 2p1(, C ls2 2S2 2p2
7 N ls2 2S2 2p3
~ 0 ls2 2S2 2p4er F ls2 2S2 2pS
r'----"'" ID Ne ls2 2S2 2p6
tt Na ls2 2S2 2p6 3s1
t~ Mg ls2 2S2 2p6 3s2
/3 Al ls2 2S2 2p6 3s2 3p1l L{ Si ls2 2S2 2p6 3s2 3p2IS P ls2 2S2 2p6 3s2 3p3
/(; S ls2 2S2 2p6 3s2 3p4
I 7 CI ls2 2S2 2p6 3s2 '3ps- , ..
It Ar ls2 2S2 2p6 3s2 3p6
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Unit I Alchemy 99Lesson 24 • Transparency