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7 years ago
What sorts of bonds are commonly used in living system to combine atoms into molecules? How does each form?
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3 Replies
7 years ago
Well there is ionic bonds, covalent bonds, hydrophobic bonds...

In ionic bonding, electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond.
For example, during the reaction of sodium with chlorine, sodium (on the left) loses its one valence electron to chlorine (on the right), resulting in a positively charged sodium ion (left) and a negatively charged chlorine ion (right) [See attachment]...

Notice that when sodium loses its one valence electron it gets smaller in size, while chlorine grows larger when it gains an additional valence electron. This is typical of the relative sizes of ions to atoms. Positive ions tend to be smaller than their parent atoms while negative ions tend to be larger than their parent. After the reaction takes place, the charged Na+ and Cl- ions are held together by electrostatic forces, thus forming an ionic bond. Ionic compounds share many features in common:

- Ionic bonds form between metals and nonmetals.
- In naming simple ionic compounds, the metal is always first, the nonmetal second (e.g., sodium chloride).
- Ionic compounds dissolve easily in water and other polar solvents.
- In solution, ionic compounds easily conduct electricity.
- Ionic compounds tend to form crystalline solids with high melting temperatures.

This last feature, the fact that ionic compounds are solids, results from the intermolecular forces (forces between molecules) in ionic solids. If we consider a solid crystal of sodium chloride, the solid is made up of many positively charged sodium ions (pictured below as small gray spheres) and an equal number of negatively charged chlorine ions (green spheres). Due to the interaction of the charged ions, the sodium and chlorine ions are arranged in an alternating fashion as demonstrated in the schematic. Each sodium ion is attracted equally to all of its neighboring chlorine ions, and likewise for the chlorine to sodium attraction. The concept of a single molecule does not apply to ionic crystals because the solid exists as one continuous system. Ionic solids form crystals with high melting points because of the strong forces between neighboring ions.

Activity: http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/bo/m1/s1/index.htm

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Covalent bonding occurs when non-metals react with non-metals (notice the difference); thus, atoms share electrons and form a covalent bond. Covalent means sharing.

There are two subtypes of covalent bonds. The H2 molecule is a good example of the first type of covalent bond, the nonpolar bond. Because both atoms in the H2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are equally shared by the two atoms, and a nonpolar covalent bond is formed. Whenever two atoms of the same element bond together, a nonpolar bond is formed.

A polar bond is formed when electrons are unequally shared between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other (yet not enough to pull the electrons away completely and form an ion). In a polar covalent bond, the bonding electrons will spend a greater amount of time around the atom that has the stronger affinity for electrons. A good example of a polar covalent bond is the hydrogen-oxygen bond in the water molecule.

Activity: http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/bo/m1/s2/index.htm

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Hydrophobic Bonds

Hydrophobic bonds occur between nonpolar molecules, such as hydrocarbons (oils), in an aqueous (polar) environment such as water. For instance if you were to put oil into water, the water would separate from the oil and oil would come together. Hence, hydrophobic bonds result not due to any attraction, but only due to a tendency of water (or any polar solution) to exclude or repel the nonpolar groups.
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7 years ago
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7 years ago
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