Periodicity •  Periodic Trends –  Size –  Ioniza0on energy and Electron affinity –  electronega0vity •  Metallic Character –  Trends in Acid/base proper0es –  Trends in oxida0on states MJ Bojan Chem 112 1 Review from Chem 110: Review trends in Sizes of Atom How are trends related to structure? Atomic radii increase with
increasing electron
shielding.
Atomic radii decrease
with increasing effective
nuclear charge.
MJ Bojan Chem 112 2 Review trends in sizes of ions •  Ionic size Ca0ons are ____________ their parent atoms. Anions are _____________ their parent atoms. MJ Bojan Chem 112 3 Sizes of atoms and ions
Even though cations have smaller radii and anions
have larger radii than neutral atoms, the periodic
trends in size are still valid for both atoms and ions.
MJ Bojan Chem 112 4 IONIZATION ENERGY: (IE)
is the energy necessary to remove an electron
from an atom, molecule or ion. Example of ioniza8on process: Na(g) è Na+(g) + e−
Ionization energy is always:
What are the trends?
Moving down a group, _______________
(increased electron shielding)
Moving across a row ________________
from left to right,
(increased effective nuclear charge)
MJ Bojan Chem 112 5 The trends in ionization energy for the main group elements is
illustrated below. Groups II and V have anomalous behavior.
It is easier to remove an
electron from a 2p orbital
than it is to remove one
from a filled 2s orbital.
It is easier to remove an electron if it is un-paired than if it is paired.
MJ Bojan Chem 112 6 ELECTRON AFFINITY: is the energy change when
a gaseous atom gains an electron to form a
gaseous ion
Cl(g) + e− è Cl−(g)
Electron affinity can either be exothermic (as the above example) or
endothermic:
Mg(g) + e− è Mg−(g)
MJ Bojan Chem 112 7 Electron Affinity
alkaline earths: EA is close to 0, WHY:
Halogens have the highest EA of any elements:
Other Trends:
MJ Bojan Chem 112 8 Electronegativity: describes the ability of an atom
to attract additional electron density to itself.
TRENDS
·  moving up a group on the periodic
table electronegativity _________.
(Due to decreasing atomic radius)
•  moving across a period from left to
right electronegativity _________
(Due to increasing nuclear charge)
MJ Bojan Chem 112 9 Summarize the periodic trends in Electronegativity
Right – electro________________
(gain electrons to become negatively charged)
Note: A more electronegative central atom attracts electrons
(HNO3 à NO3– + H+)
Left – electro________________
(lose electrons to become positively charged)
NaCl à Na+ + Cl–
MgO à Mg2+ + O2–
Note: A more electropositive central atom gives off electrons
(NaOH à Na+ + OH–)
Recall trends in oxyacid strength
that are related to electronegativity:
HClO4
HBrO4
HIO4
(What is the reason for this?)
MJ Bojan Chem 112 10 Example – the halogens
The properties of the halogens (F, Cl, Br, I) follow the
trends nicely, except for X−X bond energy
(F−F is anomalous)
Property
Atomic radius (Å)
Ionic radius, X!
MJ Bojan F
0.72
1.33
Cl
1.00
1.81
Br
1.15
1.96
I
. 1.40
2.17
First ionization
energy (kJ/mol)
1680
1250 1140
1010
Electron affinity
(kJ/mol)
−332
−349 −325
−295
Electronegativity
4.0
3.2
3.0
2.7
X!X bond energy
(kJ/mol)
155
242
193
151
Reduction potential
X2 + 2e− = 2X−(aq)
2.87
1.36
1.07
0.54
Chem 112 11 Metals and nonmetals
going down a group (column), metallic character
_______________________
going across a period (row), metallic character
______________________
MJ Bojan Chem 112 12 OXIDES: binary compounds of Oxygen What happens when we put an oxide in water?
Oxide + water = Hydroxide
MgO
P2O5
Al2O3
MJ Bojan Chem 112 13 Periodic trends in reactivity
of oxides and hydroxides
When oxides react with water, they become hydroxides
Oxides
Na
Mg
Al
Na2O
MgO
Al2O3
Si
SiO2
P
S
Cl
P2O5
SO3
Cl2O7
+ H 2O
Hydroxides
Acid strength increases
Metal hydroxides are ______________
Nonmetal hydroxides are ______________
MJ Bojan Chem 112 14 AMPHOTERISM: is the ability of a molecule to
act both as an acid and as a base.
This results in metal hydroxides which are soluble in both acids and bases.
Hydration: Al3+(aq) è Al(H2O)63+
Al(OH)3(s) + 3H2O
Al(OH)3(H2O)3(s)
In acid: Al(OH)3(H2O)3 + H+ Al(OH)2(H2O)4+ (aq) Solubility increases. In base: Al(OH)3(H2O)3 + OH− Al(OH)4(H2O)2− (aq) + H2O solubility increases. MJ Bojan Chem 112 15 ALUMINUM SOLUBILITY DEMO Al(NO3)3(s) + H2O è Al3+(aq) + 3NO3−(aq) 1. Hydra0on: Al3+(aq) è Al(H2O)63+ Add Base: Al(H2O)63+ + 3OH− ! Al(OH)3(H2O)3(s) 2. Add acid: Al(OH)3(H2O)3 + H+ è)2(H2O)4+(aq) Solubility increases. 3. Add Base Al(OH)3(H2O)3 +OH−è Al(OH)4(H2O)2−(aq) + H2O Solubility increases. MJ Bojan Chem 112 16 Properties of Metals and nonmetals
Metals
Nonmetals
Almost all solids
Gases, liquids, & solids
Shiny or lustrous
Nonlustrous, often colored
Malleable and ductile
Brittle
Good conductors of heat and electricity
Poor conductors of heat and electricity
Oxides and hydroxides
are basic (soluble in acids)*
Oxides and hydroxides
are acids (soluble in base)*
Form aqueous cations
(lose electrons)
Form aqueous anions or
oxyanions (gain electrons)
Tend to lose electrons when forming
compounds
Tend to gain electrons when forming compounds
Have lower ionization energies
Have higher ionization energies
Reactivity increases downwards in group
Reactivity increases upwards in group
* Metalloid oxides and hydroxides are amphoteric MJ Bojan Chem 112 17 Active metals (Groups 1 and 2) can be used to illustrate
metal properties
Not found in nature as pure metals, always combined
with other elements (e.g. salts in the ocean, minerals)
Reactive with H2O, O2, and H2 (alkaline earth metals more
stable than alkali metals – higher ionization energies)
Group I
Family
MJ Bojan Alkali Metals
Group II
Alkaline Earths
Electronic
Config
ns1
ns2
Oxidation State
+1
+2
Melting Point
Low
Higher
Bonding
Ionic
Ionic (except Be)
Oxides and
Hydroxides
Basic
Basic (except Be)
amphoteric
Electropositive
Most
Yes
Very Reactive
React with Air, Water
Harder/Stronger
18 Periodic trends in oxidation states
Driving force: atoms tend to lose or gain electrons
to achieve an inert gas configuration
Common Oxidation states
For main group elements (s and p block)
The highest possible positive oxidation state
Added stability in ns2 subshell as you go down a family: inert pair
effect
MJ Bojan Chem 112 19 Periodic Trends in Bonding
Trends in Bonding Nonmetals: covalent bonding, Oxides and hydroxides = acidic
Metals: metallic bonding
Metal/nonmetals: ionic, Metal oxides and hydroxides = basic
MJ Bojan Chem 112 20 DIAGONAL RELATIONSHIPS
In many compounds, Li+ resembles Mg2+ rather than Na+.
Examples:
Li2CO3 and MgCO3 are virtually insoluble in water, while
Na2CO3 is very soluble.
Ionic Radii:
Li+
0.60Å
Na+
0.95Å
Be
Mg2+
0.65Å
Al
Be compounds are covalent and the hydroxide is amphoteric
Similar to Al (example of a diagonal relationship)
MJ Bojan Chem 112 21 Oxides and hydroxides When oxides react with water, they become hydroxides
Oxides
Na
Mg
Al
Si
P
S
Cl
Na2O
MgO
Al2O3
SiO2
P2O5
SO3
Cl2O7
+ H 2O
Hydroxides
Si(OH)4 PO(OH)3 SO2(OH)2 ClO3(OH)
NaOH Mg(OH)2 Al(OH)3
ê
ê
ê
ê
H4SiO4
H3PO4
H2SO4
HClO4
Acid strength increases
Take home message: Metal hydroxides are basic, Nonmetal hydroxides are
acidic
MJ Bojan Chem 112 22