Anonymous asked in Science & MathematicsChemistry · 1 decade ago

Questions about hydrogen bonding?

can someone explain to me the principles of hydrogen bonding that keep water molecules close together. in a water molecule (H2O)

3 Answers

  • 1 decade ago
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    Hydrogen bonding is a special case of intramolecular attraction (attraction between two or more distinct molecules) that occurs when hydrogen is bonded to a highly electronegative atom, usually O, N or F. Bond polarity refers to the difference in electronegativity between bonded atoms. Electronegativity is a measure of the ability of an atom to attract negatively charged electrons.

    A chemical bond is an region of space occupied by two electrons, located between two atomic nuclei. The electrons are in constant motion, and the bond is an area where there is a very high probability of finding an electron, however, when a highly electronegative atom is bonded to an electropositive, the distribution of electrons throughout the bond is not even. The electrons spend more time near the nucleus of the electronegative atom, causing a build up of negative charge around that atom, and a build up of positive charge on the now electron-deficient electropositive atom. The partially positive charge on the electropositive atom will be attracted to the partially negative regions on other polar molecules, or to the "full" negative charge on ions. Similarly, the electronegative atom will be attracted to positive charges. As a result of this attraction, polar molecules will tend to orient themselves in space so that positive regions are pointing toward negative regions on other molecules or ions, and vice versa. Because of the attraction, the molecules pack closely together and are more difficult to separate from one another than non-polar molecules, which are much less strongly attracted to one another.

    What's so special about hydrogen bonding? Recall that a hydrogen atom is composed of a single positively charged nucleus surrounded by a single negatively charged electron. It can donate this electron into a bond with another atom, which must donate the other electron. Hydrogen is much more electropositive than oxygen, nitrogen and fluorine and as a result forms highly polar bonds with these elements. The electronegative atom holds both electrons close to its nucleus. The hydrogen is essentially a "naked" proton sticking out in space, and is strongly attracted to anions and partially negative groups on other polar molecules.

    A hydrogen bond is the electrostatic attraction between a hydrogen atom bonded to O, N, or F and a lone pair of electrons on another atom in a molecule or ion. Water molecules stick together because of the attraction between the slightly negative oxygen atom in one molecule of H2O and a partially positive hydrogen on a neighboring water molecule. Hydrogen bonds are not "true" bonds, like the covalent bonds between hydrogen and oxygen in a single water molecule. In other words, the formation of a hydrogen bond does not result in the formation of a new molecule, but rather in the formation of aggregates or groups of molecules "stuck" to one another thanks to their mutual attraction. Hydrogen bonding causes water molecules to stick together, and also makes water an excellent solvent for most salts (hydrogen bonding with the free ions) and many other substances.

  • 1 decade ago

    It is a polar molecule meaning that there are partial charges on the atoms.

    The oxygen has a partial neg while the hydrogens have a partial plus.

    These partial charges are attracted to each other just as a regular +/- would be.

    You get two different outcomes of this. While the oxygen of one molecule is attracted to the hydrogen of the other keeping them together, the polar forces are also repelling. This is why when you freeze water, it takes up more space than in liquid form while most liquids would take up less when frozen.

  • Anonymous
    1 decade ago

    I suppose by "hydrogen bonding" you mean adhesion and cohesion.

    Cohesion is the force by which water molecules are attracted to each other. This is why water beads up on the surface and makes a sort of skin.

    Adhesion is the force by which water molecules are attracted to other things, such as glass.

    The reason for these forces is the polarity of water molecules. Water molecules have a partial positive and a partial negative end, meaning they can still bond with other atoms. In the case of cohesion (which I believe is what you're asking about) the oxygens bond to other oxygens in the water molecules. With adhesion, if they cling to glass (SiO2, or silicon dioxide) they are attaching themselves to the oxygen atoms in the glass.

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