Transcript Document

PERIODIC TABLE
Periods go across:
1st period H  He
2nd period Li  Ne
3rd period Na  Ar
Groups go down:
1st group Alkali Metals
2nd goup Alkaline Earth Metals
…
Last group Noble/Inert Gases
Li  Fr
Be  Ra
He  Rn
RELATIVE ELECTRONEGATIVITIES
Up and to the right: electronegativity increases.
(same trend for ionization energy & electron affinity)
Smallest size
Highest EN
IE
EA
Largest size
Lowest EN
IE
EA
RELATIVE SIZES
Down and to the left: size increases.
Metallic Character
Most elements in the periodic table are metals
- metals lose electrons
- good thermal and electrical conductors
- malleable and lustrous
- non-metals gain electrons
- gas, liquid, or brittle solid
- poor conductors
increasing metallic character
OXIDATION STATES
Atoms tend to lose or gain electrons to achieve an inert gas
configuration.
Elements to the right (e.g., O, F) are electronegative
gain electrons to become negatively charged (anions).
Elements to the left (e.g., Cs, Sr, Al) are electropositive
lose electrons to become positively charged (cations).
NaCl  Na+Cl
MgO  Mg2+O2
For main group (s- and p-block) elements:
The highest possible positive oxidation state is equal to the
Group Number
AQUEOUS SOLUTIONS
Metals lose electrons to form cations in aqueous
solutions (e.g, Ba2+)
Non-metals gain electrons when forming anions in
solution (e.g., Br-).
Non-metals can also lose electrons to more
electronegative elements, as in oxyanions:
e.g., in SO42-, oxidation states are S6+, O2-
OXIDES
Metal Oxides and Hydroxides are basic
more soluble in acidic solutions.
More electropositive central atom gives off electrons
(Na+ OH-)
Non-Metal Oxides and Hydroxides are acidic
more soluble in basic solutions.
More electronegative central atom attracts electrons
(HNO3  NO3- + H+)
Metalloid Oxides and Hydroxides are amphoteric
More soluble in both acidic and basic solutions
compared to pure water.
2nd row (Li,Be…F) vs. 3rd, 4th, 5th rows
Period II:
Small atoms
The only valence orbitals are 2s and 2p
No 2d orbitals
Maximum number of bonds = 4.
CF4, NH3.
Small size  a greater tendency to form  bonds because
there is better sideways overlap of p-orbitals.
Period III:
Bigger size.
Valence orbitals: 3s, 3p, and 3d.
Maximum number of bonds > 4.
SiF4, SiF62-, PCl3, and PCl5.
Bigger size  less tendency to form  bonds because
there is less overlap of p-orbitals.
2nd row (Li,Be…F) vs. 3rd, 4th, 5th rows
Hydrogen
Properties
diatomic gas
colorless,
odorless
tasteless
most abundant element in the universe
rare in its elemental state on earth
(it escapes from the atmosphere).
Common Oxidation States
0, +1, -1
Hydrogen - Sources
Steam reforming (current method of H2 production)
CH4(g) + 2 H2O(g)  CO2(g) + 4 H2(g)
(natural gas)
Uses Ni catalyst at 800oC
Carbon monoxide (CO) is made as a byproduct.
water gas shift (converts CO at 300oC using Cu catalyst)
CO(g) +H2O(g)  CO2(g) + H2(g)
Other methods
electrolysis of water
(clean but uses too much energy)
2 H2O(l)  2 H2(g) + O2(g)
reactions of active metals (lab scale method)
H2SO4(aq) + Fe(s)  H2(g) + FeSO4(aq)
steam reforming of carbon
C(s) + 2 H2O(g)  CO2(g) + 2 H2(g)
high temperature catalytic process, coal is the source of carbon.
Hydrogen Isotopes
1H
protium
most abundant isotope, nucleus consists of a single proton
2H
deuterium
one neutron and often given the symbol “D”.
forms the hydrogen component of heavy water (D2O).
3H
tritium
radioactive isotope: half-life of 12.3 y, not found in nature.
Isotope effects
Deuterium and hydrogen exhibit isotopic
differences in their reaction rates and properties.
E.g., boiling points of heavy water and conventional water are slightly
different allowing them to be separated by fractional distillation.
Hydrogen - Commercial applications
Main use of H2 in US
Haber-Bosch process
N2(g) + 3H2(g)  2 NH3(g)
synthetic fertilizers: (NH3)
can also be further reacted to produce nitrate (–NO3) compounds.
Other Uses:
Production of methanol
CO(g) + 2H2(g)  CH3OH(l)
Hydrogenation
CH2  CH2
 CH3  CH3
converts double bonds into single bonds: unsaturated
compounds like oils into saturated fats.
Hydrogen Compounds
Molecular hydrides
hydrogen bonded covalently to another element.
Examples: HCl, HBr, NH3,CH4, Al2H6…
exist as molecules (in gas, liq., solid)
acid strength increases from left to right
PH3 < H2S < HCl
bond strength decreases going down family
H2O < H2S < H2Se < H2Te (least stable)
Ionic Hydrides:
hydrogen and an alkali metal such as lithium
Examples: NaH (=Na+H-), CaH2
strong bases, strong reducing agents
react with water or acids to make H2
Molecular Hydrides:
hydrogen and a non-metal
Examples: NH3, H2O, HCl
covalent bonding
Metallic hydrides
hydrogen and a transition metal.
retain their metallic characteristics
hydrogen atoms are absorbed into the
interstices of the metal atomic lattice.
ACTIVE METALS - GROUPS I AND II
Group I
Family
Alkali Metals
Group II
Alkaline Earths
Electronic config.
ns1
ns2
Oxidation State
+1
+2
Melting Point
Low
Higher
Bonding
Ionic
Ionic (except Be)
Oxides, hydroxides
Basic
Electropositive
Most
Very Reactive
Basic (exc. amphoteric Be)
Yes
React with Air, Water
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
Mg2+ 0.65Å
CHEMICALS FROM NaCl
Na metal is obtained by molten salt electrolysis of
a 40:60 mixture of Na/Cl/CaCl2.
This mixture melts at 580°C vs. 800°C for
pure NaCl.
Cathode: 2Na+ + 2e-  2Na (l)
Anode:
2Cl-  Cl2(g) + 2e-
2Na+ + 2Cl-  2Na (l) + Cl2(g)
NaOH (caustic soda).
>20,000,000,000 pounds made anually by
electrolysis of aqueous NaCl (chlor-alkali process).
Cathode:
Anode:
2H2O + 2e-  H2(g) + 2OH2Cl-  Cl2(g) + 2e-
2H2O + 2Cl-  H2(g) + Cl2(g) + 2OH2Na+ + 2OH- (=2 NaOH) is left behind.
NaOH dissolves hair and skin (e.g., Drano).
Uses: Soap, Rayon, Cellophane, Paper, Dyes.
ALKALINE EARTHS
Mg, Ca, Sr, Ba compounds are ionic; hydroxides are basic.
Metals are obtained by high temperature electrolysis of their
molten chlorides.
Mg metal is made in three steps from sea water:
1) Add base to sea water:
2) Dissolve in HCl:
3) Electrolysis:
Mg2+ + 2OH-  Mg(OH)2(s)
Mg(OH)2(s) + 2HCl  MgCl2(aq) + 2H2O
MgCl2(l)  Mg(l) + Cl2(g)
Principal Uses of Mg: Light structural alloys (lighter than Al or Fe,
but strong). Light alloys with Zn, Al, or Mn for aircraft wheels,
space vehicles, portable tools, and cameras
BERYLLIUM
Rare element - 0.0005% of the earth’s crust is Be
Source: The mineral beryl is Be3Al2Si6O18 has different
colors due to trace impurities
if light blue-green = aquamarine
if deep green = emerald
Uses:
Nuclear reactor parts – strong but transparent to neutrons
X-ray tubes have Be windows
Be is strong and relatively light and is transparent to X-rays.
Be compounds are covalent
Be(OH)2 is amphoteric
Similar to Al (diagonal relationship)
The twelve most abundant elements in
the lithosphere:
Element
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
Hydrogen
Titanium
Chlorine
Phosphorus
Percent by weight
50
26
7.5
4.7
3.4
2.6
2.4
1.9
0.9
0.6
0.2
0.1
CALCIUM
Fifth most abundant element on earth.
CaCO3
Depending on form is limestone, marble, chalk.
Bones and teeth are largely CaCO3 and Ca3(PO4)2
Tooth Enamel = Ca10(PO4)6(OH)2 = Hydroxyapatite
Cavities: Ca10(PO4)6(OH)2 + 8H+  10Ca2+ + 6HPO42- + H2O
Fluoride replaces OH- with F-.
F- is a weaker base, so it reacts less with acid.
CaCO3(s) + Heat  CaO(s) + CO2(g)
(Lime)
Very important industrial chemical (steelmaking, concrete).
CALCIUM (cont’d)
CaSO4 . (H2O)2 (Gypsum) is used to make cement and plaster wallboard.
2 CaSO4. (H2O)2 + Heat  3H2O + (CaSO4)2 . (H2O)
(Plaster of Paris)
Reverse reaction by adding water.
BARIUM
Barium is very dense.
BaSO4 is a dense, very insoluble material used as an additive to concrete
in nuclear reactors.
This makes the walls more dense.
This also makes the walls absorb neutrons.
BaSO4 also absorbs X-rays - used by radiologists for stomach X-rays.
WATER SOFTENING
Hard water contains dissolved Ca2+ and Mg2+.
These form precipitates with soap – bath tub rings.
Most detergents do not work well to remove this.
Also forms deposits in water pipes.
Ca2+(aq) + 2HCO3-(aq)  CaCO3(s) + CO2(g) + H2O
from dissolved CO2
scale
Scale forms on the bottom of teapots, in faucets, on the
walls of hot water pipes and boilers, etc.
Can be removed with acid (e.g., vinegar)