ap ch 8 periodicity
TRANSCRIPT
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Periodic Relationships
Among the ElementsChapter 8
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8.2
ns
1
ns
2
ns
2np
1
ns
2np
2
ns
2np
3
ns
2np
4
ns
2np
5
ns
2np
6
d1
d5
d10
4f
5f
Ground State Electron Configurations of the Elements
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8.2
Classification of the Elements
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General Periodic TrendsGeneral Periodic Trends Atomic and ionic sizeAtomic and ionic size
Ionization energyIonization energy
ElectronegativityElectronegativity
Electron AffinityElectron Affinity
Higher effective nuclear chargeElectrons held more tightly
Larger orbitals.Electrons held lesstightly.
Shielding Effect!
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Effective nuclear charge (Zeff) is the positive charge felt by
an electron.
Na
Mg
Al
Si
11
12
13
14
10
10
10
10
1
2
3
4
186
160
143
132
ZeffCoreZ Radius
Zeff = Z - 0 < < Z ( = shielding constant)
Zeff Z number of inner or core electrons
8.3
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Effective Nuclear Charge (Zeff)
8.3
increasing Zeff
increa
sing
Zeff
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8.3
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8.3
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Atomic Radii
8.3
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Atomic SizeAtomic SizeAtomic SizeAtomic Size
Size goes UPSize goes UP on going down a group.on going down a group.
Because electrons are added further from theBecause electrons are added further from the
nucleus, there is less attraction. This is due tonucleus, there is less attraction. This is due toadditional energy levels and theadditional energy levels and the shieldingshieldingeffecteffect. Each additional energy level. Each additional energy levelshields the electrons from being pulled inshields the electrons from being pulled in
toward the nucleus.toward the nucleus.
Size goes UPSize goes UP on going down a group.on going down a group.
Because electrons are added further from theBecause electrons are added further from the
nucleus, there is less attraction. This is due tonucleus, there is less attraction. This is due toadditional energy levels and theadditional energy levels and the shieldingshieldingeffecteffect. Each additional energy level. Each additional energy levelshields the electrons from being pulled inshields the electrons from being pulled in
toward the nucleus.toward the nucleus.
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Atomic SizeAtomic SizeAtomic SizeAtomic Size
SizeSize decreasesdecreases across a period owing toacross a period owing toincrease in the effective nuclear charge.increase in the effective nuclear charge.
LargeLarge
SmallSmall
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Cation is always smallerthan atom from
which it is formed.Anion is always largerthan atom from
which it is formed.
8.3
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8.3
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8.3
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Ionization energyis the minimum energy (kJ/mol) required
to remove an electron from a gaseous atom in its ground
state.
I1 + X (g) X+
(g) + e-
I2
+ X+(g)
X2+(g)
+ e-
I3 + X2+
(g) X3+
(g) + e-
I1 first ionization energy
I2 second ionization energy
I3 third ionization energy
8.4
I1 < I2 < I3
Updated charges were left off left side of I2 and I3 earlier
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8.4
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Filled n=1 shell
Filled n=2 shell
Filled n=3 shellFilled n=4 shell
Filled n=5 shell
8.4
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General Trend in First Ionization Energies
8.4
Increasing First Ionization Energy
In
creas
ing
First
Ioni z
ation
Ene
rgy
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Electron affinityis the negative of the energy change that
occurs when an electron is accepted by an atom in the
gaseous state to form an anion.
X (g) + e- X-(g)
8.5
F (g) + e-
F-(g)
O (g) + e- O-(g)
H = -328 kJ/mol EA = +328 kJ/mol
H = -141 kJ/mol EA = +141 kJ/mol
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8.5
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8.5
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Group 1A Elements (ns1, n 2)
M M+1 + 1e-
2M(s) + 2H2O(l) 2MOH(aq ) + H2( g)
4M(s) + O2( g) 2M2O(s)
Increas in
g
reac
tivity
8.6
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Group 2A Elements (ns2, n 2)
M M+2 + 2e-
Be(s) + 2H2O(l) No Reaction
Increas
ing
rea
ctivity
8.6
Mg(s) + 2H2O(g) Mg(OH)2( aq ) + H2( g)
M(s) + 2H2O(l) M(OH)2( aq ) + H2( g) M = Ca, Sr, or Ba
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Group 7A Elements (ns2np5, n 2)
X + 1e-
X-1
X2( g) + H2( g) 2HX(g)
Increas
ing
reactivity
8.6
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Group 8A Elements (ns2np6, n 2)
8.6
Completely filled ns and np subshells.Highest ionization energy of all elements.
No tendency to accept extra electrons.
P ti f O id A P i d
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Properties of Oxides Across a Period
basic acidic
8.6
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Electronegativity,Electronegativity,
is a measure of the ability of an atom in a molecule to attractis a measure of the ability of an atom in a molecule to attractelectrons to itself.electrons to itself.
Concept proposed byConcept proposed by
Linus PaulingLinus Pauling
1901-19941901-1994
Concept proposed byConcept proposed by
Linus PaulingLinus Pauling
1901-19941901-1994
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Periodic Trends:Electronegativity
In a group: Atoms with fewer energy
levels can attract electrons better (less
shielding). So, electronegativity increases
UP a group of elements.
In a period: More protons, while the
energy levels are the same, means atoms
can better attract electrons. So,electronegativity increases RIGHT in a
period of elements.
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ElectronegativityElectronegativity