Science Makes Sense-Week 37: The alkaline earth metals

My grandmother was very particular that all the grandchildren who came to visit her had milk at night. She would stand with a big warm container of milk and insist that we all had a small glass before we went to bed. My younger sister hated this white liquid and would swallow it with great difficulty. Even now she dislikes the taste of milk but gets her calcium from plenty of yogurt and dietary supplements.
Calcium,Ca, is one of the alkaline-earth metals along with Beryllium,Be, Magnesium,Mg,Strontium,Sr, Barium,Ba and Radium, Ra. (Radium was covered last week) All are metals and form Group 2, next to the Group 1 alkali-metals in the Periodic Table. Like the alkali-metals, they are soft, silvery-white metals, reactive (but not as reactive as the alkali-metals) and never found as an element in the natural state. And again, like them, they glow with characteristic colors and are distinguished by the flame test. Unlike the alkali-metals which have 1 electron in the ‘s’ shell, they have two electrons in the ‘s’ shell.(Ref.1)
Some of the alkaline-earth metals except radium and beryllium were discovered by the English Chemist, Sir Humphrey Davy in the early part of the 19th century. Around this period, Sir Davy also discovered two of the alkali-earth metals, potassium and sodium.(Ref.1)
The alkaline-earth metals react easily with water to release hydrogen gas and form the metal hydroxide. Many of them react with oxygen to form oxides. In nature they are usually found as sulfates and carbonates.(Ref.1)
The most abundant of these metals is calcium, Ca. It is the fifth most abundant element in the earth’s crust as well as in the human body. Magnesium, Mg is the seventh most abundant element in the human body, whereas Ba, Be nor Ra, St are found in the body, since the first two are poisonous while radium is radioactive; meanwhile strontium is only present as 360 ppm on the earth’s crust.(Ref.1)
Beryllium is used in the health-care industry, (besides being found in precious stones)in X-ray tubes as well as in alloys for specialized electrical connections and for high-temperature uses.
Besides magnesium being important as a digestive aid and formerly used for asbestos, today it is used in the manufacture of fertilizers. Because of its property to burn in oxygen with a brilliant flame,in World War 1, magnesium was used as flares, tracer bullets and incendiary bombs. Later in World War 2, it was used to build aircraft and military equipment. Today it is used with other metals to manufacture catcher’s masks, skis, race cars and even horseshoes.(Ref.1)
Calcium has been used in buildings from ancient times. Steel, glass, paper and metallurgical industries use slaked lime(calcium hydroxide, Ca(OH)2). Acetylene used for welding is made by reacting calcium carbide(CaC2) with water. Calcium compounds are also used as a bleach, fertilizer and sometimes to melt ice on roads.
Even though strontium is not as abundantly available it still has several uses. Like magnesium, it is used for flares, tracer bullets and also for fireworks- having a brilliant crimson color. It is also used in color television picture tubes, to refine zinc and combined with iron, strontium is used to make magnets.(Ref.1)
Barium compounds are used extensively in health care applications: in enemas and also to coat inner linings of intestines so doctors can examine the patients’ digestive system.(Ref.1)
The alkaline-earth elements are used in a wide variety of ways; they are not just known for calcium and strong bones.
Activities for Middle School Teachers:
Study the boiling and melting points of the alkaline- earth elements. Is there a correlation between them and their atomic numbers as in the case of alkali-metals?
Helium,, He, has two electrons in its outermost ‘s’ shell, why then does it not behave like an alkaline-earth metal? Let the students discuss this with the teacher.
Nuggets of Information:
Beryllium is found in emeralds and aquamarines as a compound of beryllium and alumino-silicate and is called beryl.(Ref.1)
Magnesium is found as dolomite or magnesite which are carbonates of magnesium, MgCO3. (Ref.1)
Calcium is found mostly as limestone and as dolomite (calcium carbonate, CaCO3) and also as gypsum(calcium sulfate, CaSO4)
Strontium was initially discovered by Adair Crawford, an Irish Chemist in the late 18th century in witherite; it is also found in strontianite(strontium carbonate, SrCO3) and in celestite( strontium sulfate,SrSO4)(Ref.2)
Barium is found as barite(BaSO4,barium sulfate) or witherite(BaCO3,barium carbonate)(Ref.3)
Magnesium sulfate, also known as Epsom salts has been long known for their medicinal value,mainly in Epsom salts springs. It has also been used for the treatment of eclampsia, a condition that causes seizures in pregnant women.(Ref.1)
Salts of magnesium are used as a powerful laxative(Ref.1) but magnesium hydroxide,Mg(OH)2 also known an milk of magnesia is the preferred laxative.(Ref.4)
One of the most controversial uses of magnesium has been in asbestos, as a fire retardant. It is a silicate of magnesium with the formula Mg3Si2O5(OH)4. This had been used for commercial purposes 95% of the time.(Ref.5) For years it was used as a flame-retardant till it was found to be cancer-causing and had to be removed from many buildings. In spite of this, magnesium as an element is important in the health of living organisms.(Ref.1)
Magnesium plays a critical role in chlorophyll, the green pigment in plants that gets its energy from sunlight.(Ref.1)
More than magnesium, calcium is vital for living beings and is present in leaves, teeth, bones, shells and coral.(Ref.1)
We all know that calcium is essential for bone-building but it also plays an integral part in almost every cell in the body especially in the growth of muscles, the nervous system as well as the heart.(Ref.6)
Osteoporosis is caused by a loss in bone density and can be prevented by eating foods high in calcium like green vegetables and dairy products.(Ref.1)
An isotope of strontium, Sr 90, is radioactive and is a by-product of nuclear testing from the ’40’s. Once, during testing, this isotope fell to earth, coated grass and was ingested by cows. The milk from these cows was drunk by many children when the Sr 90 got into their teeth and gums causing many health problems. In the 60’s atmospheric nuclear testing was stopped. Strontium 90 affects production of red blood cells and could lead to death.(Ref.1)
Prior to receiving X-rays, patients drink a chalky barium sulfate,BaSO4 solution which absorbs radiation and adds contrast to the image.(Ref.1)


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