section 4.6 periodic trends of the elementshomework.sdmesa.edu/.../ch4_periodic_trends_ppt.pdf ·...
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Section 4.6 Periodic Trends of the Elements
Section 4.6 Periodic Trends of the Elements
acidityionization energyelectronegativity,ENatomic sizePeriodic Trends increasing trends
Supplemental packet page 58
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Lewis Electron-dot Symbols - A Periodic Trend G.N. Lewis, at the University of California at Berkeley devised a simple way to understand the nature ofthe chemical bond in both ionic and molecular compounds. His method rests upon focusing on thevalence electrons of the elements. He represents these valence electrons as "dots" around the four sidesof the elemental symbol.
It is the valence electrons (outermost electrons) that are involved in most chemical reactions. Therefore, theseLewis electron-dot symbols should help us understand the chemical properties of these elements. Recall, forthese representative elements, group number equals the number of valence electrons, except of helium.
Supplemental packet page 29
Lewis Dot Structures
••
NB C O F NeiL BeaN Mg lA Ar
H eH
iS CSP l
Group 1 2 3 4 65 7 8
•
P SSi
H
Na
Li C•
•
Be
Mg
• •
••
B
lA
• •
•
•
• • •
•
•
•
•
•
•
•
••
••
•
••
••
• •
••
••
• •
O F••
• •
•
•
••
• •
••
••
eH
Ne
••
••
• •
••
••
•• ••rA
••
lC
N• •
••
•
Electron Dot Structure = Group Number = Valence Electron (outermost)
Outermost valence electrons provide chemical reactivity
4VE3VE 6VE 7VE
8VE1VE
2VE 5VE
Supplemental packet page 29
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Atomic Number: 11
Name:
Symbol:
mass # 23
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 17
Name:
Symbol:
mass # 35
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 12
Name:
Symbol:
mass # 24
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 8
Name:
Symbol:
mass # 16
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
• •
• •
sodium-23
Na11
23
soft metal, conducts e-
reacts w/ H2O111211
•
•• •
• •
•• •• •
Na•
magnesium-24
Mg12
24
ductile metal, conducts e-
burns in O2121212
•
•• •
• •
•• ••
• Mg•
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2
••
Atomic StructureSupplemental packet page 49
Atomic Number: 11
Name:
Symbol:
mass # 23
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 17
Name:
Symbol:
mass # 35
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 12
Name:
Symbol:
mass # 24
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 8
Name:
Symbol:
mass # 16
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
• •
• •
sodium-23
Na11
23
soft metal, conducts e-
reacts w/ H2O111211
•
•• •
• •
•• •• •
Na•
magnesium-24
Mg12
24
ductile metal, conducts e-
burns in O2121212
•
•• •
• •
•• ••
• Mg •
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2
••
chlorine-35
Cl17
35
yellow gas, nonconductor
reacts w/ Na(s)171817
•
•• •
• •
•• ••
oxygen-16
O 8
16
colorless gas, nonconductor
supportscombustion
888
•
•• •
• •
• •
1s2 2s2 2p6 3s2 3p5
1s2 2s2 2p4
••• •
• •Cl•
•
• •
• •
••
•• •
• • O•
Atomic StructureSupplemental packet page 49
4
Below is a diagram showing the relative size of atoms. the atoms sizes are in picometers (1 pm = 1EE-12 m).
• Two factors must be taken into consideration in explaining this periodic trend(1) Increasing nuclear charge, Z, which is related to the number of increasing protons with a nucleus.
• Along a period (left to right) the the atomic number increases while the valence electrons remain inthe same shell. Thus due to the increasing nuclear charge (pulling electrons closer to the nucleus) theradii of the atoms decrease left to right.
(2) Increasing number of shells, which is related to increasing principal quantum number n, where anelement’s row number equals its total number of electrons shells.• Top to bottom along a group the atomic number continues to increase. However the shell increasesfrom shell 1 to shell 2 etc.. The atomic orbitals for each successive shell get larger and larger - morethan compensating for the increased nuclear charge. The result is atomic radii increase top to bottomalong a group.
Atomic Radii Supplemental packet page 59
Atomic Radius Variation in the Periodic TableZ=nuclear chargeZ increases fromleft to right within a row
Note: atomic sizedecreases within arow as Z increasessee graph
Supplemental packet page 59
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Atomic Number: 11
Name:
Symbol:
mass # 23
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 17
Name:
Symbol:
mass # 35
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 12
Name:
Symbol:
mass # 24
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 8
Name:
Symbol:
mass # 16
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
• •
• •
sodium-23 ion
Na11
23 1+metal cationpositive ion1+ charge
combines w/ anions
111210
•
•• •
• •
•• ••
[Na]1+
magnesium-24 ion
Mg12
24 2+
metal cationpositive ion2+ charge
combines w/ anions
121210
•
•• •
• •
•• ••
[Mg]2+
1s2 2s2 2p6 3s0
1s2 2s2 2p6 3s0
Ionic Structure
More protons than electrons
More protons than electrons
Supplemental packet page 50
Atomic Number: 11
Name:
Symbol:
mass # 23
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 17
Name:
Symbol:
mass # 35
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 12
Name:
Symbol:
mass # 24
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
Atomic Number: 8
Name:
Symbol:
mass # 16
# p ______
# n ______
# e ______
Electronic
Configuration:
Physical Properties:
Chemical
Properties:
Lewis Dot:
• •
• •
sodium-23 ion
Na11
23 1+metal cationpositive ion1+ charge
combines w/ anions
111210
•
•• •
• •
•• ••
[Na]1+
magnesium-24 ion
Mg12
24 2+
metal cationpositive ion2+ charge
combines w/ anions
121210
•
•• •
• •
•• ••
[Mg]2+
1s2 2s2 2p6 3s0
1s2 2s2 2p6 3s2
Ionic Structure
chloride-35 ion
Cl17
35 1-
nonmetal anionnegative ion1- charge
combines w/ cations17
1818
•
•• •
• •
•• ••
oxygen-16 ion
O8
16 2-
nonmetal anionnegative ion2- charge
combines w/ cations
8 810
•
•• •
• •
•• ••
1s2 2s2 2p6 3s2 3p6
1s2 2s2 2p6 3s0
•
• •
• •
•••
••• •
• •Cl••[ ]1-
••• •
• • O ••[ ]2-
More protons than electrons
More protons than electrons
More electrons than protons
More electrons than protons
Supplemental packet page 50
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Atomic Radii
Cations: In a qualitative sense, if an electron is removed thereare fewer electrons for the same nuclear charge, Zeff, to attract.As a result when a neutral atom loses an electron the remainingelectrons are more strongly attracted and are pulled closer to thenucleus. As a result the radii of positive ions are smaller than thecorresponding atom. The more electrons that are removed informing ions the smaller the radius becomes.
Anions: The reverse occurs when a negative ion is formed bygaining an electron. The electron added is in the same energylevel as the other valence electrons but the effective nuclearcharge, Zeff, is lower in comparison to the number of valenceelectrons. The attraction of the nucleus for each electron is lessthan before and the negative ion has a larger radius than theneutral atom. Forming -2 and -3 ions increases the size of theion even more.
Compare the atomic and ionic radii for these selected atoms.
Ionic Radii Very closely linked to the atomic radius is the radius of ions formed from the atoms.
Supplemental packet page 60
Ionic Radius Variation in the Periodic Table - Relative Size Trends
Cations Anions
Anions are larger than cationsFamiliarize yourself with these ion trends
cations < anions
Al3+
Mg2+ Na
+ F- O
2- N
3-
Li+
Na+
K+
O2-
S2-
Se2-
multiple charge
family trend
< < < < < < Same Row Elements Multiple Charge
< < < < < < Elements of the same family
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released+ energy
Ionization Energy (IE)
+absorbedenergy
1X (g) + 11X(g)
Electron Affinity (EA)
1X(g) + 1 1X (g)
HOT gaseous ions (making plasmas)
Oxidation(OIL)
Reduction (RIG) e
- loss
1M+ + 1
e- gain
1M 1X–
1X + 1
X-
> M+
anions are larger than cations
ions
cation
negative positive
anion⊕
⊕
Plasmas (hot gaseous ions) - The Fourth State of Matter
⊕endothermic
•IE energies are always postive in numerical value
1X(g) 1X (g) + 1
energyabsorbed +
⊕Cl
⊕
Li ClO
energy
+
-
endothermic
exothermic
Li
•He has the highest IE
•direction of increasing IE•francium has the lowest IE
•the smaller the IE, the more easily an electron can be removed•IE is a measure of how strongly the electrons are held by the nucleus
Ionization energy is the energy required (absorbed) to remove an electron from an atom in the gaseous state
Ionization Energy (IE)
+absorbedenergy
1X+(g) + 11X(g)
Ionization Energy
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Ionization EnergyIonization energy is how much energy it takes to pull an electron away from each atom in the gaseous phase,
If we plot these ionization energies versus atomic number the resulting graph below emerges.
1X(g) 1X+(g) + 1
energyabsorbed +
Ionization Energy (IE)
Mg
Cl
ClO
energy
+
-
endothermic
exothermic
Mg
0 0
1X–(g)1X(g) + 1
energy+ releasedexothermic
1X–(g)1X(g) + 1
Electron Affinity (EA)
energy+ released
•EA measures the tendency to gain or retain electrons•EA for nonmetals are generally negative in numerical value•EA for metals are generally more positive in numerical value
Electron affinity is the amount of energy released whenan electron is accepted by an atom in the gaseous state
Electron Affinity
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Electron AffinityElectron affinity is, essentially the opposite of the ionization energy: Instead of removing anelectron from the element we add an electron to the element to create an anion.
Note that the noble gases, alkali metals and alkali earth metals have E.A. close to zero - indicating that thesegroups of elements do not particularly like to become anions. However, the nonmetals and especially thehalogens are highly negative and thus readily become anions. A periodic trend is evident, as was the case forthe ionization energy. This periodic trend can be understood as a reflection of the underlying periodicity inthe electronic configuration of the elements
1X–(g)1X(g) + 1
Electron Affinity (EA)
energy+ released
Generally, the energy that results from this process (the electron affinity) is negative or close to zero. Themore negative this energy the more this process is favored. In the figure below we see the trends in theelectron affinity for many of the elements.
Li
exothermic
endothermic
-
+
energy
O ClLi
⊕Cl
⊕
+absorbedenergy
1X (g) + 11X(g)
endothermic
⊕
Mg
Cl
ClO
energy
+
-
endothermic
exothermic
Mg
1X (g)1X(g) + 1 energy+ released
exothermic
Ionization energy is the energy required (absorbed) to remove an electron from an atom in the gaseous state
•the smaller the IE, the more easily an electron can be removed•IE is a measure of how strongly the electrons are held by the nucleus•direction of increasing IE•francium has the lowest IE
•He has the highest IE
•IE energies are always postive in numerical value
⊕
⊕anion
positivenegative
cation
ions
anions are larger than cations
X-
> M+
1X + 1 1X–
1M e- gain
1M+ + 1
e- loss
Reduction (RIG)
Oxidation(OIL)
HOT gaseous ions (making plasmas)
1X (g)1X(g) + 1
Electron Affinity (EA)
1X(g) 1X (g) + 1
energyabsorbed +
Ionization Energy (IE)
energy+ released
•EA measures the tendency to gain or retain electrons•EA for nonmetals are generally negative in numerical value•EA for metals are generally more positive in numerical value
energy released in a chemical process is exothermic energy (negative in numerical value)
energy absorbed in a chemical process is endothermic energy (positive in numerical value)
Electron affinity is the amount of energy released whenan electron is accepted by an atom in the gaseous state
Reduction is the gain of electrons
Oxidation is the loss of electrons
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Electronegativity, EN, is an index that tells the relative attraction an element has for electrons ina bond. Electronegativity has a high value of 4.0 for F, fluorine. The lowest electronegativityvalue is about 0.7 for Cs, cesium. The table below shows the nonmetals have relatively highelectronegativities. The metals have relatively low electronegativities. The electronegativitiesfollow the same trends as ionization energies. The rare gases generally are not tabulated for ENvalues. The takehome messages is that do not need to remember electonegativity values onlythis trend for increasing EN for these nonmetals.
F > O > N > Cl > Br > I > S > C > H
Electronegativity FONClBrISCH
electronegativity,EN ionization energy
metals
Electronegativity
A graph of Electronegativity, EN, indexes
nonmetals (FONCl BrISCH) A small difference in electronegativity indexes affords covalent bonding (nonmetal & nonmetal)
A large difference in electronegativity indexes affords ionic bonding (metal & nonmetal)
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Section 6.2 - Covalent Bonds & Electron-Dot Formulas1) Covalent compounds consist of nonmetals (e.g., F O N Cl Br I S C H)2) Unlike ionic salts, covalent compounds share electrons between atoms
to achieve extra stability associated with 8 valence electrons.
Bohr Models
Lewis dot structures
mutual sharing of electrons
Section 6.2 - Covalent Bonds & Electron-Dot Formulas
Note: Hydrogen wants a duet and the other nonmetals want an “octet.”
12
Bond Polarity is all about UNEQUAL SHARING of electrons in acovalent bond. Our analysis of bond polarity will be based upon anelectronegativity trend. The definition of electronegativity is, “theability for atom to pull electrons toward itself in a covalent bond.”This may cause an UNEQUAL SHARING of the electrons betweenatoms. An electronegativity trend, F O N Cl Br I S C H, can be usedfor determining bond polarity between two nonmetal atoms. Fluorinehas been experimentally determine to be the most electronegativeelement of all the elements. It is small, has only two electron shellsand has high effective nuclear charge. Memorize the trend and on thenext slide will we see how to apply it in determining bond polarity.
F O N Cl Br I S C H
Section 6.6 - Bond of Polarity
1. The elements of F O N Cl Br I S C H are all nonmetals.2. F is the most electronegative element, hydrogen is the least in this trend
F O N Cl Br I S C H
Large difference in electronegativity between H—F most polar bond
F is more electronegative than H
The large difference in electronegativity between H—F requires that we draw in an arrow called a dipole.
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F O N Cl Br I S C H between C—F very polar bond
Little difference in electronegativity values produces a less polar bond
Equal Sharing between identical atoms, H-H, C-C, F-F
Equal sharing of electrons between two atoms produces a nonpolar bond
Na
When EN differences are great, then electrons are transferred; not shared. This transferof electrons produces ions that are involved in ionic bonding; bonds between cationsand anions held together by electrostatics.
Na+
Cl-
Recall, our graph of electonegativities showed
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Electronegativity increases within a row
Electronegativity increases within a row
ACIDS
H2S
H-F
H-Cl
H-Br
H-I
acidity increases
acidity increases
CH4 NH3 H2O
PH3
Periodic Trend
F > O > N > Cl > Br > I > S > C > H
Electronegativity Trend
Foncl Brisch
The more electronegative atom produces a more polar H-X bond
H F
H IAtom size increases going down a family with in “n” shells.A larger atoms afford longer H–X bond.Longer covalent bonds are more easily broken.
ACIDS
H2S
H-F
H-Cl
H-Br
H-I
acidity increases
acidity increases
CH4 NH3 H2O
PH3
Periodic Trend
Acidity IncreasesDown a family
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acidityionization energyelectronegativity,ENatomic sizePeriodic Trends increasing trends
Family
Period
General Periodic TrendsEvidence to Support Wave Mechanical Atomic Orbital Theory
Atomic Size: (distance r between the nucleus and the outer most valence electrons)
PeriodFamily
increase
Ionic Size: (positive ions, negative ions, ions w/ multiple charge)
family trend
multiple charge
Li+
Na+
K+
O2-
S2-
Se2-
Al3+
Mg2+ Na
+ F- O
2- N
3-
cations < anionsPeriodF
amily
smaller larger
Ionization Energy: A(g) ----> A+(g) + 1e-
PeriodFamily
more e- shellslarge atom size
less e- shells high nuclear charge,Zhigh ionization energy
less e- shells high nuclear charge,Zhigh electronegativity
less e- more e-
smaller cation larger anion
Ionization Energy:Ionizing atoms in the gas phase (making plasmas) an endothermic (absorbed) energy process to remove an electron from an atom in the gas phase.
Eletronegativity:The ability for an atom to attract electronstoward itself in a chemical bond FONCl BrISCH
less e- shellslow nuclear charge,Z, (Z=number of protons+) high nuclear charge,Z
small atom sizeZatomic size
ionic size
ionization energy
electronegativity
Why are these FOUR increasingtrends observed???
< < < < < Same Row Elements Multiple Charge
< < < < < Elements of the same familymore e- shellslarge ion size
less e- shellsIon Charges
Supplemental packet page 58