8 - 1 Main Group Elements Main Group Elements Atomic radius is defined as being one half the distance between identical nuclei bonded in a molecule. Atoms get smaller as you proceed from left to right 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.
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8 - 1 Main Group Elements Atomic radius is defined as being one half the distance between identical nuclei bonded in a molecule. Atoms get smaller as you.
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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.