Periodic Table Family Spectacular
Group I: The Alkali Metals
These elements show a strong family resemblance. All are soft, light metals
(some are less dense than water) with low melting and boiling points. They are
all very chemically reactive and will react violently with air or water. Cesium
melts in your hand but don’t try it or it will burn right through everything.
http://www.youtube.com/watch?v=HY7mTCMvpEM
This reactivity is because of the single electron in the outer
shell, which is easily lost and makes possible the
corresponding +1 ion, (the only type of ion ). Sodium is the most common group I
element and is found in compounds like common salt (NaCl) and sodium bicarbonate
(NaHCO3). Lithium metal is used in hi-tech rechargeable batteries, where its low density
(0.5g/cm3) makes it a good choice. Potassium compounds are important in body
chemistry. It is critical that the right concentration of potassium ions be maintained in
the blood stream.
The name “alkali metals” stems from the fact that the hydroxides of all group I elements are highly
alkaline (basic).
Hydrogen is sometimes placed in group I, but it is not a very good fit. It forms +1 ions and is fairly
reactive, but it is not a metal, it is a gas at room temperature and can even form a -1 ion on occasions.
Hydrogen is like the “red-headed stepchild” of the group I family.
All group I elements have distinct and easily visible flame colors: it’s easy to kick out the 1 electron from
the outer shell. In technical terms, group I elements have a low ionization energy.
Group II: Alkaline Earth Metals
These elements also bear many similarities to each other. They are a little
harder, denser and less reactive than group I. Beryllium and magnesium
metals are stable enough in air to be used as structural metals, although
magnesium can be persuaded to burn if heated. Calcium compounds are
abundant in rocks and minerals, the most common being calcium carbonate
(CaCO3), or limestone.
All of these elements have two electrons in the outer shell,
which are easily lost, to form the 2+ ion. Group II elements only ever form +2 ions.
The calcium ion is also important in body chemistry.
Beryllium and barium compounds are both quite poisonous. Strangely, barium
sulfate is used in X-ray procedures. It is opaque to X-rays and so when people drink a
suspension of barium sulfate, X-rays of the stomach and digestive tract may be taken.
The compound is not soluble in water, so it cannot enter the bloodstream.
Radium is a famous member of the family. It was discovered by Marie Curie and is
dangerously radioactive; Marie died from aplastic anemia, caused by the radium.
Group III Metals
Boron is the odd man out in group III because it is usually considered
to be a metalloid. Group 3 elements have 3 electrons in their outer
shell. Except for boron, the elements in group 3 can form a +3 ion, but
a few elements (ex. Tl) can also form a +1 ion. The best known element
from this group is aluminum and it is used extensively for building
strong, lightweight and corrosion resistant structures. (like soda cans)
The reactivity of group 3 elements is variable
but aluminum can be made to burn – powdered
aluminum is the main fuel in the solid rocket boosters for the space shuttle.
Gallium is unusual because it has a very low melting point, and will actually melt
in your hand. (and it will not poison or burn you).
Group IV
This group is a “non-traditional” family with properties ranging from non-metal
(carbon) at the top to metal (tin and lead) at the bottom with silicon and germanium
in the middle (metalloids). The element carbon has 2 main allotropes, graphite and
diamond with dramatically contrasting properties. Compounds of carbon far outnumber all compounds of the other 100 or so elements. Carbon chemistry is organic
chemistry (excepting carbonates) which means the chemistry of life.
Group IV does not have a good pattern of ion charges. Carbon rarely forms a -4 ion, but usually prefers to
bond covalently, or by sharing electrons. Tin and lead may form +2 or a +4 ion.
The metalloids are semi-conductors, which makes them useful in the electronics industry. Most
computer circuitry is manufactured on thin disks of ultra-pure silicon.
Tin and lead are metals which have been used for 1,000’s of years - they are easy
to refine and work. Pewter is an alloy which is mainly tin, and tin cans are made of
steel with a thin layer of tin to prevent corrosion.
Historians suggest that lead poisoning contributed to the fall of Rome and it
almost contributed to the fall of ours till we took lead tetraethyl out of gasoline.
http://en.wikipedia.org/wiki/Tetra-ethyl_lead
Group V: Pnictogens (which I agree is a silly name)
The family resemblances in group V are harder to find although nitrogen and
phosporus are both important components of fertilizers, or to be exact, their
compounds, nitrates and phosphates.
80% of the air is nitrogen gas, which hestitates to react with other elements. Liquid
nitrogen boils at about -200°C and is a common refridgerant.
Elemental phosphorus is white waxy solid (melting point 44°C) which is poisonous and
dangerously flammable. It was used in WW II as the critical component of incendary bombs.
Arsenic is a metalloid and has been used as a poison for centuries, but now there are compounds which
are more toxic with less mess. The first drug that ever killed a bacteria was an arsenic compound
(Salvarsan, 1909). It was used to treat syphillis which was a scourge at that time.
http://www.pbs.org/wgbh/aso/databank/entries/dm09sy.html
Antimony, Utah is of course, the site of an old mine which produced this element.
It has a variety of minor uses but it is about as toxic as arsenic. It is also considered
a metalloid.
Bismuth is a heavy metal with some unusual properties.
It is non-toxic and the compound bismuth subsalicylate is
the active ingredient in Peptobismol. Crystals of metallic bismuth are a
common curiosity.
All group V elements form a trioxide with formula X2O3, and a hydride with
formula XH3. They all may have oxidation numbers of +3 and +5, which is not
quite the same as ion charges.
Group VI: Chalcogens
This family has also a wide range of properties from oxygen (non-metal, gas) to
polonium (radioactive metal, exquisitely toxic).
All have compounds with similar formulas ex. H2O, H2S, H2Se, H2Te, H2Po,
although the properties of these compounds have a few similarities and many
differences. Water is very unusual if compared with related compounds. It has a
boiling point about 100°C higher than expected and expands when it freezes
(most elements and compounds do not). Water is a wonderful solvent for many types of materials and is
definitely one of the great strategic minerals of civilization.
Sulfur is “brimstone” as alluded to in ancient scriptures. Elemental sulfur had been associated with
volcanos and this was a good way to present images of torment and
punishment. Ironically, pure elemental sulfur is both non-toxic and odorless,
but some of its compounds are smelly and really poisonous. Oil well drillers
are always in danger of hydrogen sulfide poisoning. One lungful of hydrogen
sulfide is a fatal dose.
Selenium and tellurium are metalloids which have some uses but none are
very famous. Polonium hit the limelight in 2006 . The murder of Alexander Litvinenko, a Russian
dissident, was announced as due to 210Po poisoning. According to Prof. Nick Priest, Litvinenko was
probably the first person ever to die of the acute α-radiation effects of 210Po. This isotope has an LD50 of
about 1 microgram for an 80 kg person. Experts agree that the Russian government probably did it, as
210Po is essentially unavailable, even to most leading universities.
Group VII: Halogens
This family has many physical and chemical similarities. All are
colorful and reactive non-metals which like to form -1 ions.
The chemical reactivity falls predictably as you go down the
group. All elements exist as diatomic
molecules in the vapor phase. The term
halides refers to salts which contain fluoride,
chloride, bromide or iodide ions.
Fluorine, a pale yellow gas, will react with
almost every other element (except He &
Ne) and even glass and asbestos. A famous debate raged in
recent years over whether or not fluoride compounds should be added to our water. The
pros and cons of this argument continue, but fluoridated toothpaste is still a great idea.
Chlorine is a greenish gas with a long list of uses. Chlorine gas is used to purify water in
culinary water systems and keep swimming pools safe. Although this use is not without
challenges, the benefit to public health is obvious.
Bromine is a fuming brown-red liquid at room temperature and has fewer uses. Organic bromides were
once used to kill insects in large scale farming operations, but the ozone layer is very susceptible to
photodegraded by-products of these compounds and so this use has been discontinued.
Iodine is a purple-black solid which easily gives a dense purple vapor when heated. Iodine is a vital
nutrient as it is in the hormone thyroxine which is produce by the thyroid gland. Radioactive iodine is a
nasty part of nuclear fall-out, because the body tends to concentrate it in the thyroid gland. Potassium
iodide pills were handed out after the Chernobyl disaster, so that body would be over-dosed on iodine
and not absorb any porentially radioactive iodine from the environment. The high levels of potassium
also protected from radioactive cesium.
Astatine has never been produced in sufficient quantity to be looked at and its longest-lived isotope has
a half life of 56 seconds.
Group VIII: Noble gases
The noble gas family get its name because all these elements dislike forming compounds. A few
compounds of krypton and xenon have been prepared, usually with the help of the very aggressive
element fluorine, and at very low temperatures, but few are stable enough to have any practical use.
There are some exotic life saving uses for xenon and some
of its compounds.
http://en.wikzipedia.org/wiki/Xenon
All have a stable outer shell, usually of 8 electrons, although
helium is happy with 2. All are gases at room temperature
and all except radon are used in a variety of discharge
tubes, the most common being neon. The term “neon light”
may be used to describe many colors of lights, but a true
neon tube is the familiar red color. The color is generated
when high voltage first knocks an electron loose, then when
it jumps back to its original energy level, a specific wavelength of light is released. These lights run off
about 100 volts (1st i.e. for Ar = 15.8 volts)
Argon is present in the atmosphere (0.93%) and it is extracted by fractional distillation and used as a
inert atmosphere for welding . Bountiful Air Products in Centerville does just this.
Transition Metals
The transistion metals have variable valencies. Iron for instance, may lose the 2
electrons in its outer shell (4s) and form the Fe++ ion. It may also lose another
electron, this time from the 3d shell and form the Fe+++ ion. Vanadium may lose
2, 3, 4 or 5 electrons and the corresponding compounds have wonderful colors.
Here are V2+, V3+, V4+ and V5+. This is typical of many transition elements.
Transition metals have a long list of uses. Hundreds of types of (stainless) steel
are made with iron mixed with lesser quantities of chromium, nickel, cobalt,
manganese, vanadium, molybdenum, niobium to name a few.
Other famous metals from this family: gold, silver and copper,
coinage metals; tungsten, high meting point (3422°C), used for
light bulb filaments; mercury, liquid at room temperature; titanium, lightweight and
stronger than steel; platinum, coinage metal, but also a catalyst; zinc, coated onto steel
to prevent rust (galvanising). There are some similarities within the mini families
(vertical groups) and also some with main group families. ex. Silver, gold and copper
are a little like group I.
Lanthanides: 14 elements with properties very like lanthanum. Subtle differences give rise to a few
specialty uses. Neodymium alloy magnets are great fun and very powerful.
Actinides: 14 elements which are chemically very like the lanthanides, but they are all radioactive, some
slightly, others fiercely. Nuclear reactors use various actinides, mainly uranium. Atomic bombs use a few
kilograms of uranium or plutonium to release energy and more radioactive material.
Properties across period three
Na
electrons
Metal?
State
M. Point
Oxide
… + H2O
pH
1
Metal
Solid
98°C
Na2O
NaOH
14
Simple ion
+1
At. radius 190 pm
Electroneg 0.9
1st i. e.
5.1 volts
Ox. #’s
+1
Mg
2
Metal
Solid
650°C
MgO
Mg(OH)2
10
+2
143
1.3
7.6
+2
Al
3
Metal
Solid
660°C
Al2O3
Al(OH)3
8
+3
115
1.6
6.0
+3
Si
4
Metalloid
Solid
1410°C
SiO2
SiO2.H2O
7
-108
1.9
8.2
±4
P
5
Non-M
Solid
44°C
P2O5
H3PO4
3
-3
96
2.2
10.5
-5, -3
S
6
Non-M
Solid
114°C
SO3
H2SO4
0
-2
85
2.5
10.4
±2,+4,+6
Cl
7
Non-M
Gas
-102°C
Cl2O7
HClO4
-1
-1
77
3.0
13.0
Ar
8
Non-M
Gas
-189°C
69
15.8
±1,+3,+5,+7 -
Atomic radius: size of the atom in pm, picometers, 10¯12 meter
Electronegativity: a relative scale which gives a measure of how much the atom attracts electrons.
1st ionization energy: the energy needed to remove one electron from the atom
Ox. #’s: Oxidation numbers.