what else is necessary in order for a hydrogen atom in a molecule to participate in a hydrogen bond?

The Chemic Level of Arrangement

Chemical Bonds

OpenStaxCollege

Learning Objectives

By the end of this section, you lot volition be able to:

• Explicate the relationship between molecules and compounds
• Distinguish between ions, cations, and anions
• Place the key difference betwixt ionic and covalent bonds
• Distinguish between nonpolar and polar covalent bonds
• Explain how water molecules link via hydrogen bonds

Atoms separated past a bully distance cannot link; rather, they must come close enough for the electrons in their valence shells to interact. Only do atoms ever actually touch i some other? Most physicists would say no, because the negatively charged electrons in their valence shells repel one another. No force inside the homo body—or anywhere in the natural globe—is strong enough to overcome this electrical repulsion. So when you read about atoms linking together or colliding, bear in mind that the atoms are not merging in a physical sense.

Instead, atoms link by forming a chemical bail. A bond is a weak or strong electrical attraction that holds atoms in the same vicinity. The new grouping is typically more stable—less probable to react again—than its component atoms were when they were separate. A more than or less stable group of 2 or more atoms held together past chemic bonds is called a molecule. The bonded atoms may exist of the same element, as in the case of H_two, which is called molecular hydrogen or hydrogen gas. When a molecule is fabricated up of ii or more than atoms of different elements, it is called a chemical compound. Thus, a unit of water, or H_iiO, is a compound, equally is a unmarried molecule of the gas marsh gas, or CH₄.

Three types of chemic bonds are important in homo physiology, because they concur together substances that are used by the body for critical aspects of homeostasis, signaling, and energy production, to proper noun just a few important processes. These are ionic bonds, covalent bonds, and hydrogen bonds.

Ions and Ionic Bonds

Recall that an atom typically has the same number of positively charged protons and negatively charged electrons. As long as this situation remains, the atom is electrically neutral. But when an atom participates in a chemical reaction that results in the donation or acceptance of one or more than electrons, the cantlet will and so get positively or negatively charged. This happens frequently for most atoms in club to have a full valence crush, equally described previously. This can happen either by gaining electrons to fill a trounce that is more than one-half-full, or by giving away electrons to empty a shell than is less than one-half-full, thereby leaving the next smaller electron shell as the new, total, valence shell. An atom that has an electric accuse—whether positive or negative—is an ion.

Visit this website to learn near electrical free energy and the attraction/repulsion of charges. What happens to the charged electroscope when a usher is moved between its plastic sheets, and why?

Potassium (K), for instance, is an important chemical element in all trunk cells. Its diminutive number is 19. It has just 1 electron in its valence shell. This characteristic makes potassium highly probable to participate in chemic reactions in which it donates one electron. (It is easier for potassium to donate one electron than to gain vii electrons.) The loss will cause the positive charge of potassium's protons to be more influential than the negative accuse of potassium's electrons. In other words, the resulting potassium ion volition be slightly positive. A potassium ion is written K⁺, indicating that it has lost a single electron. A positively charged ion is known every bit a cation.

Now consider fluorine (F), a component of bones and teeth. Its atomic number is 9, and it has seven electrons in its valence crush. Thus, information technology is highly likely to bond with other atoms in such a way that fluorine accepts one electron (it is easier for fluorine to gain one electron than to donate vii electrons). When it does, its electrons will outnumber its protons by one, and it will take an overall negative charge. The ionized grade of fluorine is called fluoride, and is written as F^–. A negatively charged ion is known as an anion.

Atoms that accept more than ane electron to donate or take volition end up with stronger positive or negative charges. A cation that has donated two electrons has a net charge of +2. Using magnesium (Mg) every bit an case, this tin be written Mg⁺⁺ or Mg²⁺. An anion that has accepted two electrons has a net charge of –2. The ionic form of selenium (Se), for instance, is typically written Se^2–.

The opposite charges of cations and anions exert a moderately strong mutual attraction that keeps the atoms in close proximity forming an ionic bond. An ionic bond is an ongoing, close association between ions of reverse charge. The table common salt you lot sprinkle on your food owes its existence to ionic bonding. Equally shown in [link], sodium ordinarily donates an electron to chlorine, becoming the cation Na⁺. When chlorine accepts the electron, information technology becomes the chloride anion, Cl^–. With their opposing charges, these two ions strongly concenter each other.

Ionic Bonding

(a) Sodium readily donates the solitary electron in its valence vanquish to chlorine, which needs only ane electron to accept a full valence beat out. (b) The opposite electrical charges of the resulting sodium cation and chloride anion consequence in the germination of a bond of attraction chosen an ionic bond. (c) The allure of many sodium and chloride ions results in the formation of large groupings called crystals.

H2o is an essential component of life considering it is able to break the ionic bonds in salts to gratis the ions. In fact, in biological fluids, near individual atoms be as ions. These dissolved ions produce electrical charges within the body. The behavior of these ions produces the tracings of heart and brain function observed as waves on an electrocardiogram (EKG or ECG) or an electroencephalogram (EEG). The electrical action that derives from the interactions of the charged ions is why they are too called electrolytes.

Covalent Bonds

Unlike ionic bonds formed by the attraction between a cation's positive charge and an anion'southward negative charge, molecules formed by a covalent bond share electrons in a mutually stabilizing human relationship. Like next-door neighbors whose kids hang out start at ane home and then at the other, the atoms practice not lose or gain electrons permanently. Instead, the electrons motility back and forth between the elements. Because of the close sharing of pairs of electrons (one electron from each of 2 atoms), covalent bonds are stronger than ionic bonds.

Nonpolar Covalent Bonds

[link] shows several common types of covalent bonds. Detect that the two covalently bonded atoms typically share but one or two electron pairs, though larger sharings are possible. The important concept to take from this is that in covalent bonds, electrons in the outermost valence shell are shared to fill up the valence shells of both atoms, ultimately stabilizing both of the atoms involved. In a single covalent bond, a single electron is shared betwixt two atoms, while in a double covalent bond, two pairs of electrons are shared between ii atoms. There even are triple covalent bonds, where iii atoms are shared.

Covalent Bonding

You lot can meet that the covalent bonds shown in [link] are balanced. The sharing of the negative electrons is relatively equal, equally is the electrical pull of the positive protons in the nucleus of the atoms involved. This is why covalently bonded molecules that are electrically balanced in this manner are described equally nonpolar; that is, no region of the molecule is either more positive or more negative than any other.

Polar Covalent Bonds

Groups of legislators with completely opposite views on a item issue are ofttimes described equally "polarized" by news writers. In chemistry, a polar molecule is a molecule that contains regions that have opposite electrical charges. Polar molecules occur when atoms share electrons unequally, in polar covalent bonds.

The nearly familiar example of a polar molecule is water ([link]). The molecule has three parts: i atom of oxygen, the nucleus of which contains eight protons, and two hydrogen atoms, whose nuclei each comprise merely one proton. Because every proton exerts an identical positive charge, a nucleus that contains eight protons exerts a charge eight times greater than a nucleus that contains one proton. This ways that the negatively charged electrons nowadays in the h2o molecule are more strongly attracted to the oxygen nucleus than to the hydrogen nuclei. Each hydrogen atom's single negative electron therefore migrates toward the oxygen cantlet, making the oxygen end of their bond slightly more negative than the hydrogen end of their bond.

Polar Covalent Bonds in a Water Molecule

What is true for the bonds is true for the water molecule as a whole; that is, the oxygen region has a slightly negative accuse and the regions of the hydrogen atoms have a slightly positive accuse. These charges are often referred to as "partial charges" because the strength of the charge is less than one total electron, as would occur in an ionic bail. As shown in [link], regions of weak polarity are indicated with the Greek letter of the alphabet delta (δ) and a plus (+) or minus (–) sign.

Even though a single water molecule is unimaginably tiny, it has mass, and the opposing electrical charges on the molecule pull that mass in such a way that it creates a shape somewhat similar a triangular tent (see [link]b). This dipole, with the positive charges at ane stop formed by the hydrogen atoms at the "bottom" of the tent and the negative charge at the opposite stop (the oxygen cantlet at the "tiptop" of the tent) makes the charged regions highly likely to interact with charged regions of other polar molecules. For human being physiology, the resulting bond is i of the nigh important formed past water—the hydrogen bail.

Hydrogen Bonds

A hydrogen bond is formed when a weakly positive hydrogen cantlet already bonded to one electronegative atom (for instance, the oxygen in the h2o molecule) is attracted to another electronegative atom from another molecule. In other words, hydrogen bonds ever include hydrogen that is already office of a polar molecule.

The virtually common case of hydrogen bonding in the natural earth occurs between molecules of h2o. It happens earlier your eyes whenever two raindrops merge into a larger dewdrop, or a creek spills into a river. Hydrogen bonding occurs because the weakly negative oxygen atom in 1 water molecule is attracted to the weakly positive hydrogen atoms of two other h2o molecules ([link]).

Hydrogen Bonds betwixt Water Molecules

Discover that the bonds occur between the weakly positive accuse on the hydrogen atoms and the weakly negative charge on the oxygen atoms. Hydrogen bonds are relatively weak, and therefore are indicated with a dotted (rather than a solid) line.

H2o molecules as well strongly attract other types of charged molecules as well as ions. This explains why "tabular array salt," for case, actually is a molecule chosen a "table salt" in chemistry, which consists of equal numbers of positively-charged sodium (Na⁺) and negatively-charged chloride (Cl^–), dissolves so readily in water, in this case forming dipole-ion bonds between the water and the electrically-charged ions (electrolytes). Water molecules also repel molecules with nonpolar covalent bonds, like fats, lipids, and oils. You tin can demonstrate this with a simple kitchen experiment: pour a teaspoon of vegetable oil, a compound formed by nonpolar covalent bonds, into a drinking glass of water. Instead of instantly dissolving in the water, the oil forms a distinct bead because the polar water molecules repel the nonpolar oil.

Chapter Review

Each moment of life, atoms of oxygen, carbon, hydrogen, and the other elements of the homo trunk are making and breaking chemical bonds. Ions are charged atoms that form when an cantlet donates or accepts one or more negatively charged electrons. Cations (ions with a positive charge) are attracted to anions (ions with a negative charge). This attraction is called an ionic bond. In covalent bonds, the participating atoms do not lose or proceeds electrons, just rather share them. Molecules with nonpolar covalent bonds are electrically counterbalanced, and accept a linear three-dimensional shape. Molecules with polar covalent bonds accept "poles"—regions of weakly positive and negative charge—and accept a triangular three-dimensional shape. An cantlet of oxygen and two atoms of hydrogen form water molecules past means of polar covalent bonds. Hydrogen bonds link hydrogen atoms already participating in polar covalent bonds to anions or electronegative regions of other polar molecules. Hydrogen bonds link water molecules, resulting in the properties of water that are of import to living things.

Interactive Link Questions

Visit this website to learn about electrical free energy and the attraction/repulsion of charges. What happens to the charged electroscope when a conductor is moved between its plastic sheets, and why?

The plastic sheets jump to the nail (the usher), because the conductor takes on electrons from the electroscope, reducing the repellant force of the two sheets.

Review Questions

Which of the following is a molecule, but non a chemical compound?

1. H₂O
2. ²H
3. H₂
4. H⁺

C

A molecule of ammonia contains one atom of nitrogen and three atoms of hydrogen. These are linked with ________.

1. ionic bonds
2. nonpolar covalent bonds
3. polar covalent bonds
4. hydrogen bonds

C

When an atom donates an electron to some other cantlet, it becomes

1. an ion
2. an anion
3. nonpolar
4. all of the above

A

A substance formed of crystals of equal numbers of cations and anions held together past ionic bonds is called a(n) ________.

1. noble gas
2. salt
3. electrolyte
4. dipole

B

Which of the following statements well-nigh chemical bonds is truthful?

1. Covalent bonds are stronger than ionic bonds.
2. Hydrogen bonds occur between two atoms of hydrogen.
3. Bonding readily occurs betwixt nonpolar and polar molecules.
4. A molecule of water is unlikely to bond with an ion.

A

Critical Thinking Questions

Explicate why CH_iv is one of the most common molecules found in nature. Are the bonds between the atoms ionic or covalent?

A carbon cantlet has four electrons in its valence shell. Co-ordinate to the octet rule, it will readily participate in chemical reactions that result in its valence shell having 8 electrons. Hydrogen, with one electron, will complete its valence shell with two. Electron sharing between an cantlet of carbon and four atoms of hydrogen meets the requirements of all atoms. The bonds are covalent because the electrons are shared: although hydrogen often participates in ionic bonds, carbon does not because it is highly unlikely to donate or have iv electrons.

In a hurry one day, you only rinse your dejeuner dishes with water. Every bit you lot are drying your salad bowl, you discover that it still has an oily film. Why was the water alone not constructive in cleaning the bowl?

H2o is a polar molecule. It has a region of weakly positive charge and a region of weakly negative charge. These regions are attracted to ions also every bit to other polar molecules. Oils are nonpolar, and are repelled by h2o.

Could two atoms of oxygen engage in ionic bonding? Why or why not?

Identical atoms have identical electronegativity and cannot form ionic bonds. Oxygen, for example, has half-dozen electrons in its valence shell. Neither donating nor accepting the valence shell electrons of the other will consequence in the oxygen atoms completing their valence shells. Ii atoms of the same chemical element ever form covalent bonds.

Glossary

anion

atom with a negative charge

bail

electric force linking atoms

cation

atom with a positive charge

covalent bond

chemical bond in which 2 atoms share electrons, thereby completing their valence shells

hydrogen bond

dipole-dipole bond in which a hydrogen atom covalently bonded to an electronegative atom is weakly attracted to a second electronegative atom

ion

atom with an overall positive or negative charge

ionic bond

attraction between an anion and a cation

molecule

two or more atoms covalently bonded together

polar molecule

molecule with regions that accept reverse charges resulting from uneven numbers of electrons in the nuclei of the atoms participating in the covalent bond

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Source: http://pressbooks-dev.oer.hawaii.edu/anatomyandphysiology/chapter/chemical-bonds/

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