8 - 1

Main Group ElementsMain Group ElementsAtomic radius is defined as being one half thedistance between identical nuclei bonded in amolecule.

Atoms get smaller as you proceed from left toright across a period (series).

The nucleus contains more protons and the electron cloud contains more

electrons.

The increased charge results in a greater attraction making the atom smaller.

8 - 2

Atomic Radius Across A PeriodAtomic Radius Across A Period.

Na Mg Al Si P S Cl Ar

Atomic Radius Decreases

8 - 3

Atomic RadiusAtomic Radius

Atomic Radius vs Atomic Number

0

50

100

150

200

250

0 10 20 30 40 50 60

Atomic Number

Ato

mic

Ra

diu

s (

pm

)

Li

Ne

Na

He

K

ArKr

Rb

Xe

Cs

8 - 4

Main Group ElementsMain Group Elements

Atoms get larger as you proceed from top to

bottom down a group (family).

There is one more principal energy level each time you go down a period.

The valence electrons get further from the nucleus and feel less of an attraction by the positive nucleus.

8 - 5

Atomic Radius Down A GroupAtomic Radius Down A Group.

Li

Na

K

Rb

Cs

Atomic Radius Increases

8 - 6

Atomic RadiusAtomic Radius

Atomic Radius vs Atomic Number

0

50

100

150

200

250

0 10 20 30 40 50 60

Atomic Number

Ato

mic

Ra

diu

s (

pm

)

Li

Ne

Na

He

K

ArKr

Rb

Xe

Cs

8 - 7

Ionic Radius for Cations in a PeriodIonic Radius for Cations in a Period

Cations are smaller than the atoms fromwhich there are formed.

Metals give off their valence electrons, i.e.

Ca → Ca2+ + 2e-

1s22s22p63s23p64s2 → 1s22s22p63s23p6 + 2e-

The entire highest numbered principal energy

is lost (n = 4) which also decreases thenumber of electrons which decreases therepulsion.

8 - 8

Ionic Radius Across A PeriodIonic Radius Across A Period.

Na Mg Al Si P S Cl Ar

Atomic radius decreases for both cations and anions.

8 - 9

Ionic Radii for Anions in a PeriodIonic Radii for Anions in a Period

Anions are larger than the atoms from which

there are formed.

Nonmetals take in valence electrons to form a

complete octet, i.e.

N + 3e- → N3-

1s22s22p3 + 3e- → 1s22s22p6

Adding electrons increases the repulsionbetween electrons residing in the samesublevel.

8 - 10

Ionic Radii for Anions in a PeriodIonic Radii for Anions in a Period

Compare nitrogen to oxygen:

N + 3e- → N3-

1s22s22p3 + 3e- → 1s22s22p6

O + 2e- → O2-

1s22s22p4 + 2e- → 1s22s22p6

N3- and O2- are isoelectronic but O2- has thegreater nuclear charge making it the

smalleranion.

8 - 11

Ionic Radius Across A PeriodIonic Radius Across A Period.

Na Mg Al Si P S Cl Ar

Atomic radius decreases for both cations and anions.

8 - 12

Transition ElementsTransition Elements

.

Cr2+

Cr3+

Mn2+ Fe2+

Fe3+

Ni2+ Cu+

Cu2+

Co2+

Co3+

Transition elements tend to have multiple valence numbers.

Almost all the transition elements of the fourth period form monatomic ions with a charge of +2.

8 - 13

Transition ElementsTransition Elements

Because transition elements in thed-block have 2 electrons in their valenceshell, they tend to react chemically the same.

Both lanthanoids and actinoids are found inthe f-block.

Lanthanoids occur in trace amounts in natureand are called the rare earth elements.

Actinoids usually have large unstable nucleithat undergo spontaneous radioactive decay.

8 - 14

Ionization EnergyIonization Energy

First Ionization EnergyFirst Ionization Energy

Ionization energy or ionization potential is theminimum amount of energy needed to removean electron from the valence shell of a

gaseousatom.

Na(g) + IE1 Na+(g) + e-

IE indicates how easy it is for a metal to form acation.

8 - 15

Ionization EnergyIonization Energy

Generally, IE increases across a period(series) because of an increase in nuclearcharge.

IE increases as the size of the atomdecreases.

Nonmetals easily accept electrons causingthem to have a high IE.

8 - 16

Ionization EnergyIonization Energy

As you move from left to right in a period, the

IE also depends on half-filled andcompletely-filled orbitals.

When an s sublevel is filled with 2 electrons, there is an increase in its stability.

When a p sublevel is half-filled with 3 electrons, there is an increase in its stability.

8 - 17

Ionization EnergyIonization Energy

When a p sublevel is completely filled with 6 electrons, there is an even

greater increase in its stability.

The same is true for a d sublevel except

it is for 5 electrons and 10 electrons.

Remember the two exceptions in Period 4, Cr (3d5) and Cu (3d10) which follows this same tendency.

8 - 18

Ionization EnergyIonization Energy

The highest IE occurs for the noble gasesbecause they have a complete octet.

Generally, IE decreases from the top to thebottom in a group or family because of theaddition of a principal energy level.

IE decreases as the size of the atom increases.

8 - 19

Ionization EnergyIonization Energy

The second IE is larger than the first because

the second electron is being removed from a

cation rather than a neutral atom.

The third IE is larger than the secondbecause the third electron is being removedfrom a cation with a +2 charge.

8 - 20

First Ionization EnergyFirst Ionization Energy

First Ionization Energy vs Atomic Number

0

500

1000

1500

2000

2500

0 20 40 60 80 100

Atomic Number

Fir

st I

on

izat

ion

En

erg

y (k

J/m

ol)

HeNe

ArKr

Xe Rn

8 - 21

ElectronegativityElectronegativity

Electronegativity is a measure of theattraction of an element for a shared pair ofelectrons.

H Cl

Comparing the electronegativity values ofhydrogen and chlorine, chlorine has a valueof 3.2 and that of hydrogen is 2.2.

...... ..δ-δ+

8 - 22

ElectronegativityElectronegativity

The origin of these values is unimportant and

the atom with the higher value is moreelectronegative.

The most electronegative element is 9Fbecause it has the smallest atomic radiuswith very few of it electrons shielding thenucleus.

The least electronegative is 87Fr.

8 - 23

ElectronegativityElectronegativity

Generally, electronegativity increases fromleft to right within a period or series.

Generally, electronegativity decreases fromtop to bottom within a group or family.

Electronegativity values are not assigned tothe noble gases because they are inactive.

The explanation for the trends inelectronegavity is the same as for ionizationenergy.

8 - 24

ElectronegativityElectronegativity

Electronegativity vs Atomic Number

0.00.51.01.52.02.53.03.54.04.5

0 20 40 60 80 100

Atomic Number

Ele

ctr

on

eg

ati

vit

y

F

Cl BrI

At

8 - 25

Electron AffinityElectron Affinity

A measure of an atom’s tendency to gainelectrons in the gas phase.

A(g) + e- A-(g) + thermal energy

Electron affinity is an irregular periodicfunction of atomic number. In general, itincreases from left to right.

Noble gases are not included since they have

little or no tendency to gain electrons.

8 - 26

Periodic Trends in DensityPeriodic Trends in Density

Generally, the density increases as youproceed from top to bottom in a group ofmetals or nonmetals.

The atomic mass increases more rapidly

than the atomic radius.

8 - 27

Density (g/cmDensity (g/cm33))

.

Element Density Element Density

Li 0.53 F 1.31

Na 0.97 Cl 1.56

K 0.86 Br 3.12

Rb 1.53 I 4.92

Cs 1.90

8 - 28

Periodic Trends in DensityPeriodic Trends in Density

Generally, the density increases as youproceed from left to right in a period until

youreach the metalloids.

There is a big drop off in density in the nonmetals (gases) but then starts to increase.

8 - 29

Trends in Boiling and Melting Trends in Boiling and Melting PointsPoints

The boiling and melting points generallydecrease as you proceed from top to

bottomin the metals.

This results from metallic bonding.

The boiling and melting points generallyincrease as you proceed from top to bottomin the nonmetals.

This results from Van der Waals forces.

8 - 30

Boiling and Melting PointsBoiling and Melting Points

. Element BP (°C) MP (°C)

Li 1372 179

Na 892 98

K 774 64

Rb 679 39

Cs 690 28Alk

ali

Alk

ali

Meta

ls

Meta

llic

Bonds

Meta

llic

Bonds

8 - 31

Boiling and Melting PointsBoiling and Melting Points

. Element BP (°C) MP (°C)

F -187 -223

Cl -35 -101

Br 59 -72

I 185 114Halo

gens

Van

der

Waal Fo

rces

8 - 32

Metallic CharacteristicsMetallic Characteristics

Metals are good conductors of heat andelectricity due to their “sea of electrons”.

Metals have shiny surfaces that are bothmalleable and ductile due to their d-

electrons.

Metals are malleable because they can be hammered into a thin foil without breaking.

Metals are ductile because they can bestretched into a thin wire without breaking.

8 - 33

Metallic CharacteristicsMetallic Characteristics

Metals have three or fewer valence electrons

which they donate during chemical reactions.

Generally, metallic character increases asyou go down a group or family.

The valence electrons are further from the nucleus and are more shielded

from the nucleus.

8 - 34

Metallic CharacteristicsMetallic Characteristics

Generally, metallic character decreases asyou proceed from left to right in a period(series).

Metals → Metalloids → Nonmetals

8 - 35

Metallic CharacteristicsMetallic Characteristics

When a metal donates electrons it is said toundergo oxidation.

Metals that are more easily oxidized will react

more readily in the presence of a nonmetal.

Group I and Group II are very active metals.

Because they have such a strong tendency to form compounds they are not found in their elemental or free state.

8 - 36

Alkali MetalsAlkali Metals

The Group IA metals have an outer electronconfiguration of ns1.

The loss of an electron to form a 1+ ion is the

basis of almost all reactions of the alkalimetals.

M → M+ + e-

8 - 37

Alkaline Earth MetalsAlkaline Earth Metals

The Group IIA metals have an outer electron

configuration of ns2.

The Group II metals are not as reactive asthe alkali metals because they need to losetwo electrons from a completely filleds-sublevel in order to achieve a noble gasconfiguration.

M → M2+ + 2e-

8 - 38

Nonmetallic CharacteristicsNonmetallic Characteristics

Nonmetals are poor conductors of heat andelectricity.

Nonmetals have dull surfaces and are brittle.

Nonmetals have 4-7 valence electrons,therefore they gain electrons.

Generally, nonmetallic character decreasesfrom top to bottom within a group or family.

8 - 39

Nonmetallic CharacteristicsNonmetallic Characteristics

The atomic radius is a very important factorin determining the reactivity in nonmetals.

F and Cl are the smallest halogens and willmore readily accept electrons in theirvalence shell.

According to Coulomb’s Law, the positivenucleus will attract valence electrons more

ina smaller atom.

8 - 40

Nonmetallic CharacteristicsNonmetallic Characteristics

Generally, nonmetallic character increasesas you proceed from left to right in a period(series).

Metals → Metalloids → Nonmetals

8 - 41

Nonmetallic CharacteristicsNonmetallic Characteristics

When a nonmetal accepts electrons it is saidto undergo oxidation.

Nonmetals that are more easily oxidized willreact more readily in the presence of anonmetal.

Group VII are very reactive nonmetals.

Because they have such a strong tendency

to form compounds they are not found in their elemental or free state.

8 - 42

HalogensHalogens

The common group VIIA elements are allnonmetals. Each only needs a single electronto achieve a noble gas configuration.

When reacting with metals, they form 1- ions.

2Na(s) + Cl2(g) 2NaCl(s)

When they have no other elements to reactwith, they are found as diatomic molecules.

2F(g) F2(g)

8 - 43

Noble GasesNoble Gases

Each noble gas has filled s and p sublevelsexcept for helium (1s2).

All are very unreactive.

A limited number of compounds have beenproduced using xenon and krypton.

Xe(g) + F2(g) XeF2(g)

8 - 44

The Anomoly of HydrogenThe Anomoly of Hydrogen

Hydrogen is a nonmetallic gas at roomtemperature.

While it may lose an electron to form H+, italso can gain an electron to form H-

(hydride).

2Na(l) + H2(g) 2NaH(s)

Hydrogen is placed in Group IA. Where elsecould it go?

8 - 45

Semimetals (Metalloids)Semimetals (Metalloids)

These elements (B, Si, Ge, As, Sb, Te, and At)

along the “stairway” exhibit properties ofboth metals and nonmetals.

They have some similarities with metalsbecause they are shiny and conductelectricity.

They are similar to nonmetals because theyare brittle.

8 - 46

AllotropesAllotropes

Allotropes are elements having more thanone form because of structural differences(the way in which their atoms or moleculesare arranged).

The element oxygen has 3 forms:

O – monatomic oxygen

O2 – molecular or diatomic oxygen

O3 - ozone