163Compounds
Selected alkaline earth and zinc salts densities,
gꞏcm−3(^) O2− S2− F− Cl− SO2−
4
CO2−
3
O2−
2 H
−
Ca2+[9] 3.34 2.59 3.18 2.15 2.96 2.83 2.9 1.7
Sr2+[10] 5.1 3.7 4.24 3.05 3.96 3.5 4.78 3.26
Ba2+[11] 5.72 4.3 2.1 1.9 4.49 4.29 4.96 4.16
Zn2+[12] 5.6 4.09 4.9 2.09 3.8 4.4 1.57 —Barium salts are typically white when solid and colorless when dissolved, as barium ions provide
no specific coloring. They are also denser than their strontium or calcium analogs, except for the
halides.
Barium hydroxide ("baryta") was known to alchemists who produced it by heating barium
carbonate. Unlike calcium hydroxide, it absorbs very little CO 2 in aqueous solutions and is therefore
insensitive to atmospheric fluctuations. This property is used in calibrating pH equipment.
Volatile barium compounds burn with a green to pale green flame, which is an efficient test to detect
a barium compound. The color results from spectral lines at 455.4, 493.4, 553.6, and 611.1 nm.
Organobarium compounds are a growing class of compounds: for example, dialkylbariums are
known, as are alkylhalobariums.
Isotopes of Barium
Barium occurs naturally on Earth as a mixture of seven primordial nuclides, barium-130, 132, and
134 through 138. The first two are thought to be radioactive: barium-130 should decay to xenon-
130 via double beta plus decay, and barium-132 should similarly decay to xenon-132.
The corresponding half-lives should exceed the age of the Universe by at least thousand times.
Their abundances are ~0.1% relative to that of natural barium. Their radioactivity is so weak that
they pose no danger to life.
Out of the stable isotopes, barium-138 makes up 71.7% of all barium, and the lighter the isotope,
the less it is abundant. In total, barium has about 50 known isotopes, ranging in mass between 114
and 153. The most stable metastable isotope is barium-133, which has a half-life of approximately
10.51 years, and five more isotopes have their half-lives longer than a day. Barium also has 10
meta states, out of which barium-133m1 is the most stable, having a half-live of about 39 hours.
Biological Dangers and Precautions
Because of the high reactivity of the metal toxicological data are available only for compounds.
Water-soluble barium compounds are poisonous. At low doses, barium ions act as a muscle
stimulant, whereas higher doses affect the nervous system, causing cardiac irregularities, tremors,
weakness, anxiety, dyspnea and paralysis. This may be due to the ability of Ba2+ to block potassium
ion channels, which are critical to the proper function of the nervous system.
Other target organs for water-soluble barium compounds (i.e., barium ions) are eyes, immune
system, heart, respiratory system, and skin. They affect the body strongly, causing, for example,
blindness and sensitization.