Molecular formula

What is the significance of a molecular formula? The smallest unit of substance capable of independent existence, and showing all the properties of that substance is called molecule. A molecule contains two or more chemically bonded atoms of the same or different type. Therefore, a molecule can be represented in terms of the symbols, and number of atoms of the elements present in it.

Molecular formula

Then calculate the mass of aluminum Molecular formula a 3. Such a procedure was actually used to determine the empirical and molecular formulas of the first antibiotic to be discovered: Antibiotics are chemical compounds that selectively kill microorganisms, many of which cause diseases.

Although we may take antibiotics for granted today, penicillin was discovered only about 80 years ago.

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The subsequent development of a wide array of other antibiotics for treating many common diseases has contributed greatly to the substantial increase in life expectancy over the past 50 years.

The discovery of penicillin is a historical detective story in which the use of mass percentages to determine empirical formulas played a key role.

InAlexander Fleming, a young microbiologist at the University of London, was working with a common bacterium that causes boils and other infections such as blood poisoning. For laboratory study, bacteria are commonly grown on the surface of a nutrient-containing gel in small, flat culture dishes.

One day Fleming noticed that one of his cultures was contaminated by a bluish-green mold similar to the mold found on spoiled bread or fruit. Such accidents are rather common, and most laboratory workers would have simply thrown the cultures away.

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Fleming noticed, however, that the bacteria were growing everywhere on the gel except near the contaminating mold part a in Figure 3.

To test this hypothesis, he grew the mold in a liquid and then filtered the liquid and added it to various bacteria cultures.

The liquid killed not only the bacteria Fleming had originally been studying but also a wide range of other disease-causing bacteria. Because the mold was a member of the Penicillium family named for their pencil-shaped branches under the microscope part b in Figure 3.

Right In this photomicrograph of Penicillium, its rod- and pencil-shaped branches are visible. Finally, intwo chemists at Oxford University, Howard Florey — and Ernst Chain —were able to isolate an active product, which they called penicillin G.

Within three years, penicillin G was in widespread use for treating pneumonia, gangrene, gonorrhea, and other diseases, and its use greatly increased the survival rate of wounded soldiers in World War II.

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As soon as they had succeeded in isolating pure penicillin G, Florey and Chain subjected the compound to a procedure called combustion analysis described later in this section to determine what elements were present and in what quantities.

The results of such analyses are usually reported as mass percentages. They discovered that a typical sample of penicillin G contains The sum of these numbers is only It could be any other element. If we assume that all the missing mass is due to oxygen, then penicillin G contains From these mass percentages, the empirical formula and eventually the molecular formula of the compound can be determined.

To determine the empirical formula from the mass percentages of the elements in a compound such as penicillin G, we need to convert the mass percentages to relative numbers of atoms.

For convenience, we assume that we are dealing with a This assumption simplifies the arithmetic because a the formula of a molecule of a covalent compound MF = n x empirical formula (n, is a positive non-zero whole number).

Molecular formula

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Biological Magnetic Resonance Data Bank A Repository for Data from NMR Spectroscopy on Proteins, Peptides, Nucleic Acids, and other Biomolecules Molecular Mass Calculator.

Enter the molecular formula of the molecule.

Calculating Molecular Weight

Examples: C6H12O6, PO4H2(CH2)12CH3 Calculate molecular . Molecular formula definition is - a chemical formula that gives the total number of atoms of each element in each molecule of a substance.

How to use molecular formula in a sentence. a chemical formula that gives the total number of atoms of each element in each molecule of a substance. Here is the electron dot diagram and structural formula for another compound that has the same molecular formula, C 2 H 6 O. In each case notice how the structural formula gives you much more information about how the molecule is put together than does the molecular formula.

A chemical formula is a way that chemists describe a molecule. The formula says what atoms, and how many of each type, are in the molecule.

Sometimes the formula shows how the atoms are linked, and sometimes the formula shows how the atoms are arranged in space.

Determining Empirical and Molecular Formulas