Electron Configuration and Periodic Trends Periodic Trends of the Elements Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Valence Electrons The valence electrons Determine the chemical properties of the elements. Are the electrons in the s and p sublevels in the highest energy level/outermost energy level Are related to the Group Number of the element. Example: Phosphorus has 5 valence electrons 5 valence electrons P = Group (15) 1s22s22p6 3s23p3

Group Number and Valence Electrons All the elements in a group have the same number of valence electrons…this is why those elements behave similarly! Example: Elements in Group (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

Periodic Table and Valence Electrons: Add this info to your periodic table

Learning Check State the number of valence electrons for each: A. O 1) 4 2) 6 3) 8 B. Al 1) 13 2) 3 3) 1 C. Cl 1) 2 2) 5 3) 7

Solution State the number of valence electrons for each. A. O 2) 6 2) 6 B. Al 2) 3 C. Cl 3) 7

Learning Check State the number of valence electrons for each. A. Calcium 1) 1 2) 2 3) 3 B. Group (16) 1) 2 2) 4 3) 6 C. Tin 1) 2 2) 4 3) 14

Solution State the number of valence electrons for each. A. Calcium 2) 2 B. Group (16) 3) 6 C. Tin 2) 4

Learning Check State the number of valence electrons for each. Hint—look at the sublevel/s of the highest energy level A. 1s2 2s2 2p6 3s2 3p3 B. 1s2 2s2 2p6 3s2 3p64s2 3d104p4 C. 1s22s22p5

Solution State the number of valence electrons for each. A. 1s2 2s2 2p6 3s2 3p3 5 B. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 6 C. 1s22s22p5 7

Atomic Size / Radius Atomic radius Is the distance from the nucleus to the valence electrons Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Atomic Radius Within A Group Atomic radius increases Going down each group of representative elements. More energy levels = bigger size Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Atomic Radius Across a Period Atomic radius decreases Going from left to right across a period. Each proton added increases nuclear attraction for valence electrons. This attraction causes the atom to shrink.

Learning Check Select the element in each pair with the larger atomic radius. A. Li or K B. K or Br C. P or Cl

Solution Select the element in each pair with the larger atomic radius. A. K B. K C. P

Ion Size/Radius An ion is an atom that has lost or gained electrons Losses and gains occur to create filled outer energy levels…causes stability We will do more with ions when we get to the next chapter so for now just listen and think…

Sizes of Metal Atoms and Ions A positive ion Has lost its valence electrons. Metals lose VE Is smaller (about half the size) than its corresponding metal atom. The protons there can pull harder when there are fewer electrons, making the ion shrink in comparison Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Example: Size of Sodium Ion The sodium ion Na+ Forms when the Na atom loses one electron from the 3rd energy level. Is smaller than a Na atom. Both have 11 protons, but those 11 protons can pull harder on 10 electrons than they can on 11.

Sizes of Nonmetal Atoms and Ions A negative ion Has a complete octet. Is an atom that gained valence electrons. Nonmetals gain VE Is larger (about twice the size) than its corresponding nonmetal atom. Since the # of protons is the same, there is an imbalance in how hard they can pull…this expands the size of the ion Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Example: Size of Fluoride Ion The fluoride ion F- Forms when a valence electron is added. Has increased repulsions due to the added valence electron. Is larger than F atom

Learning Check Which is larger in each of the following? 1. a. K or b. K+ 2. a. Al or b. Al3+ 3. a. S2- or b. S Which is smaller in each of the following? 4. a. N3- or b. N 5. a. Cl or b. Cl- 6. a. Sr2+ or b. Sr

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

Ionization Energy Ionization energy Is the energy it takes to remove a valence electron. IE tells us how difficult it is to take a valence electron Large IE means it is HARD to take an electron; Small IE means it is EASY to take an electron Na(g) + Energy of Na+(g) + e- Ionization +

Ionization Energy Metals have 1-3 valence electrons. Lower ionization energies. They “want” to lose electrons, so the IE will be lower If they lose their valence electrons, their new outermost energy levels will be full Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionization Energy Nonmetals have 5-7 valence electrons. Have higher ionization energies. They “need” more electrons to get an octet, so it is harder to take electrons from them…higher IE’s. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionization Energy Nobel gases have Complete octets or full outer energy levels (He has two valence electrons.) Have the highest ionization energies in each period. Very hard to take an electron from an element with the octet! Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Select the element in each pair with the higher Ionization energy. 1. A. Li or B. K 2. A. K or B. Br 3. A. P or B. Cl

Solution Select the element in each pair with the higher Ionization energy. A. Li B. Br C. Cl

Electronegativity

Electronegativity EN = how much an element wants to NOT share electrons equally when it forms a bond with another atom…wants to hog them! METALS—not very EN; don’t want more e- NONMETALS—very EN; want more e- Fluorine is the MOST electronegative element. Why are there no EN’s listed for noble gases????

Electronegativity