What is Hydrogen Acceptor and Hydrogen Donor?

Explanation:

Hydrogen bonds are formed between a hydrogen atom bound to a small, highly electronegative atom and another small, highly electronegative atom with an unshared electron pair. The elements that usually participate in hydrogen bonds are nitrogen, oxygen, and fluorine. A hydrogen bond is much weaker than a covalent bond (10-40 kJ/mol vs. hundreds of kJ/mol for a covalent bond), but when a lot of hydrogen bonds are added together, they can have a significant influence on the structure of molecules. An example of hydrogen bonding is the lattice formed by water molecules in ice. In biological molecules, the electronegative atoms the hydrogen atom is "shared" by are usually oxygen and nitrogen.

Scientists distinguish between the electronegative atoms in a hydrogen bond based on which atom the hydrogen atom is covalently bonded to. In the diagram at left below, the oxygen atom of the hydroxy group is called the hydrogen bond donor, because it is "donating" its hydrogen to the nitrogen. The nitrogen atom is called the hydrogen bond acceptor, because it is "accepting" the hydrogen from the oxygen. In the picture of two water molecules at lower right, the oxygen of the water molecule B is the hydrogen bond donor. The oxygen of water molecule A is the hydrogen bond acceptor.

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explanation:

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).