Chapter 5 Electron Configuration and Periodic Trends 5.6 Periodic Trends of the Elements

Valence Electrons The valence electrons • determine the chemical properties of an element • are the electrons in the s and p sublevels in the highest energy level • are related to the group number of the element Example: Phosphorus has 5 valence electrons 5 valence electrons

1s22s22p6 3s23p3

P Group 5A(15)

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Group Number and Valence Electrons

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Periodic Table and Valence Electrons

All the elements in a group have the same number of valence electrons. Example: Elements in Group 2A (2) have two (2) valence electrons. Be 1s2 2s2 Mg 1s2 2s2 2p6 3s2 Ca 1s2 2s2 2p6 3s2 3p6 4s2 Sr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 3

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Learning Check

Learning Check

State the number of valence electrons for each: A. O 1) 4 2) 6 3) 8

State the number of valence electrons for each.

B. Al 1) 13 C. Cl 1) 2 5

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2) 3

2) 5

3) 1

3) 7 Copyright © 2011 Pearson Education, Inc.

A. Calcium 1) 1

2) 2

3) 3

B. Group 6A (16) 1) 2

2) 4

3) 6

C. Tin 1) 2

2) 4

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Learning Check

Electron-Dot Symbols

State the number of valence electrons for each. A. 1s22s22p63s23p3

An electron-dot symbol • indicates the valence electrons as dots around the symbol of the element • for Mg shows two valence electrons placed as single dots on the sides of the symbol Mg . . ·Mg · or Mg · or · Mg or · Mg ·

B. 1s22s22p63s23p64s23d104p4 C. 1s22s22p5

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Writing Electron-Dot Symbols The electron-dot symbols for • Groups 1A (1) to 4A (14) use single dots

· Na ·

· Mg ·

· · Al · ·

·C·

• Groups 5A (15) to 7A (17) use pairs and single dots

·· ·P· · 9

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··

:O· · Copyright © 2011 Pearson Education, Inc.

Periodic Table and ElectronDot Symbols

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Groups and Electron-Dot Symbols • In a group, all the electron-dot symbols have the same number of valence electrons (dots). Example: Atoms of elements in Group 2A (2) each have two valence electrons. 2A (2) · Be · · Mg · · Ca · · Sr · · Ba · 10

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Learning Check 

A.

X is the electron-dot symbol for 1) Na

2) K

3) Al



B.



X 

1) B

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is the electron-dot symbol of 2) N

3) P

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Atomic Radius

Atomic Radius within a Group

The atomic radius • is the distance from the nucleus to the valence electrons

The atomic radius increases • going down each group of representative elements • as the number of energy levels increases

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Atomic Radius across a Period The atomic radius decreases • going from left to right across a period • as more protons increase the nuclear attraction for valence electrons

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Learning Check Select the element in each pair with the larger atomic radius. A. B. C.

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Ionization Energy Ionization energy • is the energy it takes to remove a valence electron

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Li or K K or Br P or Cl

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Ionization Energy Metals have • 1-3 valence electrons • lower ionization energies

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Ionization Energy

Noble gases have • complete octets (He has two valence electrons) • the highest ionization energies in each period

Nonmetals have • 5-7 valence electrons • higher ionization energies

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Ionization Energy

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Learning Check

Sizes of Metal Atoms and Ions

Select the element in each pair with the higher ionization energy.

A positive ion • has lost its valence electrons • is smaller than the corresponding metal atom (about half the size)

A. B. C.

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Li or K K or Br P or Cl

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Size of Sodium Ion The sodium ion Na+ • forms when the Na atom loses one electron from the third energy level • is smaller than a Na atom

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Sizes of Nonmetal Atoms and Ions A negative ion • has a complete octet • increases the number of valence electrons • is larger than the corresponding nonmetal atom (about twice the size)

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Size of Fluoride Ion F-

The fluoride ion • forms when a valence electron is added • has increased repulsions due to the added valence electron • is larger than a F atom

Learning Check 1. Which is larger in each of the following? A. K or K+ B. Al or Al3+ C. S2- or S 2. Which is smaller in each of the following? A. N3- or N B. Cl or ClC. Sr2+ or Sr

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Concept Map

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Electronegativity Electronegativity • is the relative ability of atoms to attract shared electrons • is higher for nonmetals, with fluorine as the highest with a value of 4.0 • is lower for metals, with cesium and francium as the lowest with a value of 0.7 • increases from left to right going across a period on the periodic table • decreases going down a group on the periodic table

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Some Electronegativity Values for Group A Elements

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Learning Check Using the periodic table, predict the order of increasing electronegativity for the elements O, K, and C.

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