Chemical PeriodicityChemical PeriodicityChapter 5 Chapter 5

Periodic Trends in Atomic SizePeriodic Trends in Atomic SizePeriodic Trends in Ionization Periodic Trends in Ionization

EnergyEnergyPeriodic Trends in Ionic SizePeriodic Trends in Ionic SizePeriodic Trends in Periodic Trends in

ElectronegativityElectronegativity

Periodic Trends in Atomic SizePeriodic Trends in Atomic Size

The boundary of an atom can't The boundary of an atom can't be measured directly be measured directly

Atomic Radius: half the distance Atomic Radius: half the distance between nuclei of two like between nuclei of two like atoms.atoms.

Write the Electron Configuration for Write the Electron Configuration for

Li, K and FLi, K and F

Look at the position of these elements on the Look at the position of these elements on the Periodic Table. Can you detect a Periodic Table. Can you detect a ““trendtrend”” in size in size

as you go down a group?as you go down a group?

What do you think the trend is going What do you think the trend is going across a period?across a period?

Periodic Trends in Atomic SizePeriodic Trends in Atomic Size

Atomic size increases down a groupAtomic size increases down a group– What happens to the energy level as we go What happens to the energy level as we go

down a group? Where are the electrons?down a group? Where are the electrons?

Atomic size decreases from left to rightAtomic size decreases from left to right– Where are the electrons? Where are the electrons? – the nucleus has more attraction to the electronsthe nucleus has more attraction to the electrons

Periodic Trends in Atomic SizePeriodic Trends in Atomic Size

Which would be Which would be bigger?bigger?

a. Sodium or Aluminuma. Sodium or Aluminum

b. Magnesium or Bariumb. Magnesium or Barium

c. Nickel or Brominec. Nickel or Bromine

d. Calcium or Yttriumd. Calcium or Yttrium

e. Describe in your own words why e. Describe in your own words why atoms in the same period decrease in size atoms in the same period decrease in size from left to right.from left to right.

Periodic Trends in Ionization Periodic Trends in Ionization EnergyEnergy

Ionization Energy:Ionization Energy:– Energy required to Energy required to

overcome the attraction of overcome the attraction of the nucleus and remove anthe nucleus and remove an electron.electron.

Draw a Bohr model for Draw a Bohr model for Li, Na and N and FLi, Na and N and F

Ionization energy decreases as you move down Ionization energy decreases as you move down a group because electrons are further away so a group because electrons are further away so they are easier to strip off.they are easier to strip off.

Ionization energy increases as you move left to Ionization energy increases as you move left to right, for representative elements because the right, for representative elements because the attraction by the nucleus is stronger so it is attraction by the nucleus is stronger so it is harder to pull electrons away.harder to pull electrons away.

Ionization Energy GraphIonization Energy Graph

Graph the data listed on the Table of Graph the data listed on the Table of ionization energies.ionization energies.

Graph the Atomic number on the x-axisGraph the Atomic number on the x-axis(1 thru 22)(1 thru 22)

Graph the ionization energy on the y-axisGraph the ionization energy on the y-axis(0 thru 160)(0 thru 160)

What trend do you see?What trend do you see?

Look at theLook at theTable of Ionization EnergiesTable of Ionization Energies

First ionization energy- energy necessary to First ionization energy- energy necessary to remove the 1remove the 1stst electron electron

Second ionization energy- energy necessary Second ionization energy- energy necessary to remove the 2nd electron.to remove the 2nd electron.

Third ionization energy- energy necessary to Third ionization energy- energy necessary to remove the 3remove the 3rdrd electron. electron.

Periodic Trends in Ionization Periodic Trends in Ionization EnergyEnergy

Trends in Electron AffinityTrends in Electron Affinity

The energy change that occurs when an The energy change that occurs when an atom gains an electron.atom gains an electron.

LetLet’’s look at Li and F AGAINs look at Li and F AGAIN

Which one wants to gain an electron?Which one wants to gain an electron?

It would have a high electron affinityIt would have a high electron affinity

Electron Affinity-most atoms release energy Electron Affinity-most atoms release energy when gaining an electron when gaining an electron

(explains the negative sign)(explains the negative sign)

LiLi

-61.8 kJ/mol-61.8 kJ/mol

Have to force the atom Have to force the atom to take the electron.to take the electron.

Energy absorbedEnergy absorbed

Low affinityLow affinity

FF

-340 kJ/mol-340 kJ/mol

Gains electrons easilyGains electrons easily

Energy is releasedEnergy is released

High affinityHigh affinity

Trend in Electron AffinityTrend in Electron Affinity

Periodic Trends in Ionic SizePeriodic Trends in Ionic Size

LetLet’’s look at Li and F again.s look at Li and F again.

If each atom wants to achieve a full outer If each atom wants to achieve a full outer energy level (full octet)…. What has to energy level (full octet)…. What has to happen to the electrons?happen to the electrons?

When they gain or lose electrons, what do When they gain or lose electrons, what do they become? they become?

What happens to the size of the atom?What happens to the size of the atom?

Periodic Trends in Ionic SizePeriodic Trends in Ionic Size

Anions are atoms that have gained electrons Anions are atoms that have gained electrons and have an overall negative charge.and have an overall negative charge.

Anions are larger than the atoms from which Anions are larger than the atoms from which they have formed.they have formed.

Why?Why?

Cations are atoms that have lost an Cations are atoms that have lost an electron and have an overall positive electron and have an overall positive charge.charge.

Cations are smaller than the atom from Cations are smaller than the atom from which they have formed. which they have formed.

Check it out!Check it out!

Periodic Trends in Ionic SizePeriodic Trends in Ionic Size

Cations decrease in the size from left to right.

Anions decrease in size from left to right

As you move down a group the radius increases because of more electrons in higher energy levels

Warm UpWarm Up

Which atom is the largest?Which atom is the largest?

Mg or MgMg or Mg2+2+

O or OO or O2-2-

CuCu2+2+ or Cu or Cu4+4+

Write a rule that will help you get Write a rule that will help you get

these right every time!these right every time!

LetLet’’s go over some homework!s go over some homework!

IsoelectronicIsoelectronic

NaNa1+1+, Ne and F, Ne and F1-1- are said to be are said to be IsoelectronicIsoelectronic..

a. Determine the electron configuration for a. Determine the electron configuration for each of the atomseach of the atoms

b. Db. Define isoelectronicefine isoelectronic

IsoelectronicIsoelectronic

1.1. Write a 2- ion that is isoelectronic with MgWrite a 2- ion that is isoelectronic with Mg2+2+

2.2. Write 3 ions that are isoelectronic with KrWrite 3 ions that are isoelectronic with Kr

3.3. Write 2 ions that are isoelectonic with NiWrite 2 ions that are isoelectonic with Ni

Trends in ElectronegativityTrends in Electronegativity

Electronegativity:Electronegativity:

– The tendency of an element to attract The tendency of an element to attract electrons when in a chemical bond.electrons when in a chemical bond.

LetLet’’s look at Li, Cs and Fs look at Li, Cs and F

Warm Up: In CBWarm Up: In CB

Which is more electronegative? Use the Which is more electronegative? Use the trend, then check them using the table.trend, then check them using the table.

Al or Cl?Al or Cl?

Ca or Ba?Ca or Ba?

Ga or SGa or S

I or Cl?I or Cl?

W or Zn?W or Zn?

Element ReactivityElement Reactivity

What would make an element reactive?What would make an element reactive?Which elements are most reactive?Which elements are most reactive?

What would make an element unreactive?What would make an element unreactive?Which elements would be most Which elements would be most unreactive?unreactive?

LetLet’’s look at your table of s look at your table of electronegativities.electronegativities.

Electronegativity table:Electronegativity table:– Noble gases are left out because they Noble gases are left out because they do do

notnot form compounds. form compounds.– Metals have low electronegativity numbers Metals have low electronegativity numbers

because they want to give electrons away, because they want to give electrons away, not attract them.not attract them.

– Nonmetals have high electronegativity Nonmetals have high electronegativity numbers because they attract electrons to numbers because they attract electrons to make their make their configurations more configurations more stablestable

Trends in ElectronegativityTrends in Electronegativity

Relationship Between Relationship Between Electronegativity and Ionization Electronegativity and Ionization

EnergyEnergy

Moving left to right, the representative Moving left to right, the representative elements, electronegativity increases elements, electronegativity increases because ionization energy increasesbecause ionization energy increases

Moving down a group electronegativity Moving down a group electronegativity decreases because ionization energy decreases because ionization energy decreasesdecreases

Warm Up- Fill in the following table Warm Up- Fill in the following table (p.159 may help)(p.159 may help)

AtomAtom Metal or Metal or nonmetal?nonmetal?

Stable ionStable ion Size relative Size relative to neutral to neutral

atomatom

Larger or Larger or smaller than smaller than

SS2-2-

PP

RbRb

ClCl

BeBe

AlAl

How did you do?How did you do?

AtomAtom Metal or Metal or nonmetal?nonmetal?

Stable ionStable ion Size relative Size relative to neutral to neutral

atomatom

Larger or Larger or smaller than smaller than

SS2-2-

PP nmnm PP3-3- largerlarger largerlarger

RbRb mm RbRb1+1+ smallersmaller smallersmaller

ClCl nmnm ClCl1-1- largerlarger smallersmaller

BeBe mm BeBe2+2+ smallersmaller smallersmaller

AlAl mm AlAl3+3+ smallersmaller smallersmaller

LetLet’’s practice some ECs practice some EC

AlAl3+3+

CC4-4-