Hydrogen Bond Examples in Chemistry

Hydrogen Bond Examples in Chemistry Hydrogen bonds occur when a hydrogen atom undergoes dipole-dipole attraction to an electronegative atom. Usually, hydrogen bonds occur between hydrogen and fluorine, oxygen, or nitrogen. Sometimes the bonding is intramolecular, or between atoms of a molecule, rather than between atoms of separate molecules (intermolecular).   Examples of Hydrogen Bonds Here is a list of molecules that exhibit hydrogen bonding: water  (H2O): Water is  an excellent example of hydrogen bonding. The bond is between the hydrogen of one water molecule and the oxygen atoms of another water molecule, not between the two hydrogen atoms (a common misconception). How this works is that the polar nature of the water molecule means each hydrogen atom experiences attraction to both the oxygen its bound to and to the non-hydrogen side of the oxygen atoms of other water molecules. Hydrogen bonding in water results in the crystal structure of ice, making it less dense than water and able to float.chloroform  (CHCl3): Hydrogen bonding occurs between hydrogen of one molecule  and carbon of another molecule.ammonia (NH3): Hydrogen bonds form between hydrogen of one molecule and nitrogen of another. In the case of ammonia, the bond that forms is very weak because each nitrogen has one lone electron pair. This type of hydrogen bonding with nitrogen also occurs in methylamine.acetylacetone  (C5H8O2): Intramolecular   hydrogen bonding occurs between hydrogen and oxygen. DNA:  Hydrogen bonds form between base pairs. This gives DNA its double helix shape and makes replication of the strands possible, as they unzip along the hydrogen bonds.nylon:  Hydrogen bonds are found between the repeating units of the polymer.hydrofluoric acid (HF): Hydrofluoric acid forms what is called a symmetric hydrogen bond, which is stronger than the regular hydrogen bond. This type of bond also forms in formic acid.proteins:  Hydrogen bonds result in protein folding, which helps the molecule maintain stability and assume a functional configuration.polymers:  Polymers that contain carbonyl or amide groups can form hydrogen bonds. Examples include urea and polyurethane and the natural polymer cellulose. Hydrogen bonding in these molecules increases their tensile strength and melting point.alcohol:  Ethanol  and other alcohols contain hydrogen bonds between hydrogen and oxygen.

Differences in Spanish and English Spelling

Differences in Spanish and English Spelling If you can spell in English, you have a head start with spelling in Spanish. After all, thousands of words are English-Spanish cognates, words in both languages that are spelled identically or similarly because they share common origins. For the English speaker learning Spanish as a second language, most of these words pose little problem in spelling, as the differences between the two languages usually follow regular patterns. Below are listed the most common regular differences in spelling as well as a selection of words whose differences dont fit these patterns. The emphasis here is on words that are likely to cause spelling problems, not ordinary differences in the languages such as radio for the English radium and dentista for dentist. Differences in Prefixes and Suffixes English -tion as the equivalent of Spanish -cià ³n: Hundreds of words fit this pattern. The English nation is nacià ³n in Spanish, and perception is percepcià ³n. Use of inms include inmadurez (immaturity), inmaterial, and inmigracià ³n. Use of trass include trasplantar and trascender. However, there are many Spanish words where both tras- and trans- are acceptable. Thus both trasferir and transferir (transfer) are used, as are both trasfusià ³n and transfusià ³n. Differences in Specific Letters Avoidance of k in Spanish: Except for a few Greek words (such as kilà ³metro and some words of other foreign origin such as kamikaze and various place names), Spanish cognates of English words with a k usually use a c or qu. Examples include quimioterapia (chemotherapy) and Corea. Some words are spelled both ways: caqui and kaki are both used for khaki, and both bikini and biquini are used. Lack of th in Spanish: Cognates of English words with a th usually use a t in Spanish. Examples are tema (theme), metano (methane), ritmo (rhythm) and metodista (Methodist). Avoidance of y as a vowel: Except for some recently imported words such as byte and sexy, Spanish usually doesnt use y as a vowel except in diphthongs, so i is used instead. Examples include hidrà ³geno (hydrogen), dislexia , and gimnasta (gymnast). Use of cua and cuo instead of qua and quo: Examples include ecuador (equator) and cuota. Dropping of Englishs silent letters: Commonly, the h in English words is dropped in the Spanish equivalents, as in ritmo (rhythm) and gonorrea (gonorrhea). Also, it is common in modern Spanish to not use ps- to start words. Thus sicolà ³gico is used for psychologist, although the older forms such as  psicolà ³gico are still used. (The cognate of psalm is always salmo.) Use of ess include especial, està ©reo, escaldar (scald), escuela (school), and esnobismo (snobbery). Use of f for the English ph: Examples include elefante, foto, and Filadelfia. Other Common Differences Avoidance of double letters in Spanish: Except for recent words of foreign origin (such as express), the use of rr and, less commonly, the use of cc (where the second c is followed by i or e), Spanish generally doesnt use double letters in English cognates. Thus the English libretto is libreto in Spanish, possible is posible, and illegal is ilegal. Examples of rr or cc in cognates include accià ³n, acceso, and irrigacià ³n. One Spanish word that doesnt fit this pattern is perenne (perennial). Avoidance of hyphenation in Spanish: Hyphens arent used as much in Spanish as they are in English. An example is that while some styles of English uses hyphens in words such as re-edit and re-encounter, Spanish does not in the equivalents: reeditar and reencontrar (the latter of which can also be spelled as rencontrar). Simplification in Spanish: A number of words, particularly ones whose English spellings come from French, have more phonetic spellings in Spanish. For example, bureau is burà ³ and chauffeur is chà ³fer or chofer, depending on the region. B and V: B and V have identical sounds in Spanish, and there are a few words where the English and Spanish cognates use opposite letters. Examples include govern and gobernar, and Basque and vasco. Words that dont fit other patterns: Following are some other easy-to-misspell words that dont fit any of the above patterns. The Spanish word is in boldface followed by the English word in parentheses. Note that in a few cases the Spanish word doesnt have the same meaning, or has other meanings, than the English word listed. abril (April)adjetivo (adjective)asamblea (assembly)automà ³vil (automobile)billà ³n (billion)caà ±on (canyon)carrera (career)circunstancia (circumstance)confort (comfort)coraje (courage)coronel (colonel)diciembre (December)à ©nfasis (emphasis)erradicar (eradicate)espionaje (espionage)etcà ©tera (et cetera)femenino (feminine)garaje (garage)glaciar (glacier)gorila (gorilla)gravedad (gravity)huracn (hurricane)Irak (Iraq)jamà ³n (ham)jeroglà ­ficos (hieroglyphics)jirafa  (giraffe)jonrà ³n (home run)lenguaje (language)mensaje (message)millà ³n (million)(canyon)mà ³vil (mobile)noviembre (November)objeto, objetivo (object, objective)octubre (October)pasaje (passage)proyecto (project)septiembre or setiembre (September)siniestro (sinister)subjuntivo (subjunctive)tamal (tamale)trayectoria (trajectory)vagabundo (vagabond)vainilla  (vanilla)yogur or yogurt (yogurt)