When carbon atoms form covalent bonds with fewer than four hydrogen atoms, extra bonding electrons are left in the carbon atom's outer shell. For example, two carbon atoms that form covalent bonds with three hydrogen atoms can each form a covalent bond with each other, sharing their single remaining bonding electrons. That compound is ethane, C 2 H 6. Similarly, two carbon atoms can bond with two hydrogen atoms each and form a double covalent bond with each other, sharing their four leftover electrons between them.
That compound is ethylene, C 2 H 4. In acetylene, C 2 H 2 , the two carbon atoms form a triple covalent bond and a single bond with each of the two hydrogen atoms. In these cases, only two carbon atoms are involved, but the two carbon atoms can easily maintain only single bonds with each other and use the rest to bond with additional carbon atoms.
Propane, C 3 H 8 , has a chain of three carbon atoms with single covalent bonds between them. The two end carbon atoms have a single bond with the middle carbon atom and three covalent bonds with three hydrogen atoms each. The middle carbon atom has bonds with the other two carbon atoms and two hydrogen atoms.
Such a chain can be much longer and is the basis for many of the complex organic carbon compounds found in nature, all based on the same kind of covalent bond that joins two hydrogen atoms. A hydrogen bond in water occurs between the hydrogen atom of one water molecule and the lone pair of electrons on an oxygen atom of a neighboring water molecule.
A hydrogen bond is an intermolecular attractive force in which a hydrogen atom that is covalently bonded to a small, highly electronegative atom is attracted to a lone pair of electrons on an atom in a neighboring molecule.
Hydrogen bonds are very strong compared to other dipole interactions. Hydrogen bonding occurs only in molecules where hydrogen is covalently bonded to one of three elements: fluorine, oxygen, or nitrogen. These three elements are so electronegative that they withdraw the majority of the electron density in the covalent bond with hydrogen, leaving the H atom very electron-deficient. The H atom nearly acts as a bare proton, leaving it very attracted to lone pair electrons on a nearby atom.
The hydrogen bonding that occurs in water leads to some unusual, but very important properties. Most molecular compounds that have a mass similar to water are gases at room temperature. Because of the strong hydrogen bonds, water molecules are able to stay condensed in the liquid state. The figure below shows how the bent shape and two hydrogen atoms per molecule allows each water molecule to be able to hydrogen bond to two other molecules.
Figure 2. The nucleus is shown as the big sphere in the center of the atom. Types of Chemical Bonds Not all chemical bonds form in the same way as the bonds in water.
Polar Covalent Bonds and Hydrogen Bonds A covalent bond is the force of attraction that holds together two nonmetal atoms that share a pair of electrons. Each oxygen atom has an approximately tetrahedral geometry — two covalent bonds and two hydrogen bonds. Ionic bonds Electrons are transferred between atoms. The animation shows sodium Na losing an electron. This electron is taken by fluorine F. This makes Na positively charged and F negatively charged.
These ions are then attracted to each other. Review How is a covalent bond different from an ionic bond? Why is a hydrogen bond a relatively weak bond? Diagram the polarity of a water molecule. What is a chemical bond? Explain why hydrogen and oxygen atoms are more stable when they form bonds in a water molecule. How many valence electrons does sodium have? How many valence electrons does chlorine have? How does a chlorine atom bonds with sodium? The shape formed is called angular.
More than one bond can be formed between atoms leading to double and triple bonds. Examples of these are diatomic oxygen double bond or nitrogen triple bond. This could also be written as:. Substances that consist of covalent molecules are usually gases or liquids at room temperature because the attractions between molecules are weak and easy to overcome. Covalent substances that are solids with high melting points have much larger molecules.
A covalent network structure consists of a giant 3-dimensional lattice of covalently bonded atoms. Boron, carbon and silicon are all examples of covalent network elements. Diamond and graphite, two forms of carbon and compounds like silicon dioxide and silicon carbide are all covalent networks. Covalent compounds, structures, bonding and properties. Bonding and properties of materials Atoms can be held together by chemical bonds.
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