Periodicity
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Transcript of Periodicity
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Periodicity
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Atomic Radius = half the distance between two nuclei of a diatomic molecule.
}Radius
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Influenced by three factors. Energy Level
› Higher energy level is further away. Charge on nucleus
› More charge pulls electrons in closer. Shielding
› Layers of electrons shield from nuclear pull.
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The electron on the outside energy level has to look through all the other energy levels to see the nucleus
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The electron on the outside energy level has to look through all the other energy levels to see the nucleus.
A second electron has the same shielding.
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As we go down a group
Each atom has another energy level,
So the atoms get bigger.
HLi
Na
K
Rb
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As you go across a period the radius gets smaller.
Same energy level. More nuclear charge. Outermost electrons are closer.
Na Mg Al Si P S Cl Ar
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Table of Table of
Atomic Atomic RadiiRadii
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Cations form by losing electrons. Cations are smaller that the atom they
come from. Metals form cations. Cations of representative elements have
noble gas configuration.
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Anions form by gaining electrons. Anions are bigger that the atom they
come from. Nonmetals form anions. Anions of representative elements have
noble gas configuration.
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Atomic Number
Ato
mic
Radiu
s (n
m)
H
Li
Ne
Ar
10
Na
K
Kr
Rb
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The amount of energy required to completely remove an electron from a gaseous atom.
Removing one electron makes a +1 ion. The energy required is called the first
ionization energy.
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The second ionization energy is the energy required to remove the second electron.
Always greater than first IE. The third IE is the energy required to
remove a third electron. Greater than 1st of 2nd IE.
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Symbol First Second ThirdH
HeLiBeBCNOF Ne
1312 2731 520 900 800 1086 1402 1314 1681 2080
5247 7297 1757 2430 2352 2857 3391 3375 3963
11810 14840 3569 4619 4577 5301 6045 6276
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The greater the nuclear charge the greater IE.
Distance from nucleus increases IE Filled and half filled orbitals have lower
energy, so achieving them is easier, lower IE.
Shielding
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As you go down a group first IE decreases because
The electron is further away. More shielding.
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All the atoms in the same period have the same energy level.
Same shielding. Increasing nuclear charge So IE generally increases from left to
right. Exceptions at full and 1/2 fill orbitals.
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
He He has a greater IE
than H. same shielding greater nuclear
charge H
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He Li has lower IE than H more shielding further away outweighs greater nuclear
charge
Li
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He Be has higher IE than Li same shielding greater nuclear charge
Li
Be
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He B has lower IE than Be same shielding greater nuclear charge By removing an electron we
make s orbital half filled
Li
Be
B
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
N
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
N
O
Breaks the pattern because removing an electron gets to 1/2 filled p orbital
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
N
O
F
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne Ne has a lower IE
than He Both are full, Ne has more
shielding Greater distance
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne Na has a lower
IE than Li Both are s1
Na has more shielding
Greater distance
Na
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Firs
t Io
niz
ati
on e
nerg
y
Atomic number
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Full Energy Levels are very low energy. Noble Gases have full orbitals. Atoms behave in ways to achieve noble
gas configuration.
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Affinity tends to increase across a period
Affinity tends to decrease as you go down in a period
Electrons farther from the nucleus experience less nuclear attraction
Some irregularities due to repulsive forces in the relatively small p orbitals
Electron AffinityElectron Affinity - the energy change - the energy change associated with the addition of an electronassociated with the addition of an electron
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Table of Electron AffinitiesTable of Electron Affinities
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The tendency for an atom to attract electrons to itself when it is chemically combined with another element.
How fair it shares. Big electronegativity means it pulls the
electron toward it. Atoms with large negative electron
affinity have larger electronegativity.
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The further down a group the farther the electron is away and the more electrons an atom has.
More willing to share. Low electronegativity.
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Metals are at the left end. They let their electrons go easily Low electronegativity At the right end are the nonmetals. They want more electrons. Try to take them away. High electronegativity.
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Ionization energy, electronegativityElectron affinity INCREASE
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Atomic size increases, shielding constant
Ionic size increases
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Another Way to Look at Ionization Energy
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Summary of Periodic Summary of Periodic TrendsTrends