ap ch 8 periodicity

8/8/2019 AP Ch 8 Periodicity

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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

ap ch 8 periodicity

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