PERIODIC TRENDS - Honors Chemistry€¦ · PERIODIC TRENDS Author: Ythol Arul Created Date:...

CHAPTER 6.3PERIODIC TRENDS

Atomic Radius: Trends Within Groups

Definition:Distance from nucleus to outer energy level of atom

Trend: Generally increases as you move down a group

WHY?

Electrons added to energy levels

In other words, as you move down a group, more energy levels are added

Order in Increasing Atomic Radius

C, Pb, Si

1 = C

2 = Si

3 = Pb

Largest = Pb


Fr, Na, Rb

1 = Na

2 = Rb

3 = Fr

Largest = Fr

Atomic Radius: Trends Within Periods

Trend: Generally decreases moving left-to-right across a period

WHY?

Caused by an effect called: Zeff or Zeffective

I’m not really

smiling!

What Does This Mean? Increased nuclearcharge = increased # of protons pulling outermost electrons (valence electrons)closer to nucleus


Ti, Kr, Se

1 = Kr

2 = Se

3 = Ti

Largest = Ti


W, Cs, Po

1 = Po

2 = W

3 = Cs

Largest = Cs

Ionization Energy: Trends Within Groups

Definition: Energy required to remove an electron from an atom

A high ionization energy value indicates atom has a strong hold on valence electrons

Trend: Generally decreases as you move down a group

WHY?Atomic radius

increases moving down a group, therefore valence e-are farther from nucleus, requiring less energy to remove them

Order in Increasing Ionization Energy

Cd, Zn, Hg

1 = Hg

2 = Cd

3 = Zn

Largest = Zn


N, Bi, As

1 = Bi

2 = As

3 = N

Largest = N

Ionization Energy: Trends Within Periods

Trend: Generally increases moving left-to-right across a period

WHY? Zeff! Increased nuclear

charge of each atom produces an increased hold on valence electrons due to smaller radius


Mn, Cu, Ca

1 = Ca

2 = Mn

3 = Cu

Largest = Cu


Cl, Al, Na

1 = Na

2 = Al

3 = Cl

Largest = Cl

Electronegativity: Trends Within Groups

Definition:Ability of atoms to attract electrons in a chemical bond

Trend: Generally decreases as you move down a group

WHY?

Shielding Effect

Outer electrons are shielded from pull of nucleus due to distance, so not a strong attractionfor these electrons

Order in Increasing Electronegativity

F, Br, At

1 = At

2 = Br

3 = F

Largest = F


Ca, Ra, Sr

1 = Ra

2 = Sr

3 = Ca

Largest = Ca

Electronegativity: Trends Within Periods

Trend: Generally increases moving left-to-right across a period

WHY?

Same as IE


Re, Bi, Ba

1 = Ba

2 = Re

3 = Bi

Largest = Bi


S, O, Se

1 = Se

2 = S

3 = O

Largest = O

ELECTRONEGATIVITY

Highest Electronegative Element =

Fluorine (F)

E.N. = 4.0

Lowest Electronegative Element =

Francium (Fr)

E.N. = 0.7

Ionic Radius: Trends Within Groups

Definition:Distance from nucleus to outer energy level of an ion(charged particle)

Trend: Generally increases as you move down a group

WHY?

More energy levelsare present

Order in Increasing Ionic Radius

Cl-, I-, F-

1 = F-

2 = Cl-

3 = I-

Largest = I-


Rb+, Li+, Cs+

1 = Li+

2 = Rb+

3 = Cs+

Largest = CS+

Ionic Radius: Trends Within Periods

Trend: Generally decreases moving left-to-right across a period

WHY?More protons

present so nucleus can pull outer electrons in tighter

Special Ionic Radius Scenarios

Metals get smaller moving left-to-right across a period

Then gets bigger as you cross over metalloidstaircase into nonmetals section

Then the trend repeats again, or starts over for nonmetals, and therefore getting smaller again

Scenario #1: Comparing two cations

(+) within same period

Follow regular trend

Scenario #2: Comparing two anions

(-) within same period

Follow regular trend

Scenario #3: Cation (+) and anion

(-) within same period

Cation (+) will always be smaller

Special Ionic Radius Scenarios

Scenario #4: Comparing

isoelectronic elements, atomic number dictates size

Ex: Ca2+ vs S2- vs Ar:

Cation and anion will both attain electron configuration of Argon

But, Ca2+ has atomic # 20, Argon has atomic # 18, and S2- has atomic # 16

According to Zeff effect, Ca2+ will be smallest since it has most protons to pull valence electrons closer to nucleus

Therefore, S2- will be largest in ionic radius

Special Ionic Scenarios


B3+, Be2+, F-

1 = B3+

2 = Be2+

3 = F-

Largest = F-


As3-, Se2-, Br-

1 = Br-

2 = Se2-

3 = As3-

Largest = As3-

METALS = Cations(positive)

NONMETALS = Anions(negative)

Which has the larger radius?K vs K+1

Answer = K

WHY? More energy levels

Which has the larger radius?O vs O2-

Answer = O2-

WHY? More electrons for

nucleus to pull in

Comparing Radius of Atoms(neutral) to Ions(charged)

PERIODIC TRENDS - Honors Chemistry€¦ · PERIODIC TRENDS Author: Ythol Arul Created Date:...

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