When is covalent bonding used

A small molecule contains only a few atoms, so atoms and small molecules have a similar range of sizes. They are very small, typically around 0. Individual atoms and molecules are too small to see even with the most powerful light microscope.

Some electron microscopes can produce images of atoms and simple molecules. A water molecule, H 2 O, is about 0. The chemical formula of a substance with small molecules shows the number of atoms of each element in one molecule of the substance. State the number of atoms of each type in one molecule of methane, CH 4. A methane molecule is made up of one atom of carbon and four atoms of hydrogen. State the number and type of atoms in one molecule of chlorine, Cl 2.

A chlorine molecule is made up of two chlorine atoms. These substances have strong covalent bonds within the molecules between the atoms , but weak intermolecular forces between the molecules. This means that only a small amount of heat energy is required to separate the molecules from each other. The slideshow shows a covalent bond being formed between a hydrogen atom and a chlorine atom, to form hydrogen chloride.

A hydrogen atom with one electron and a chlorine atom with 17 electrons. The hydrogen atom has bonded with the chlorine atom, meaning there is now a shared pair of electrons.

After bonding, the chlorine atom is now in contact with eight electrons in its outer shell, so it is stable. The hydrogen atom is now in contact with two electrons in its outer shell, so it is also stable. A H atom needs one additional electron to fill its valence level, and the halogens need one more electron to fill the octet in their valence levels. Lewis bonding theory states that these atoms will share their valence electrons, effectively allowing each atom to create its own octet.

However, the Lewis theory of covalent bonding does not account for some observations of compounds in nature. The theory predicts that with more shared electrons, the bond between the two atoms should be stronger.

According to the theory, triple bonds are stronger than double bonds, and double bonds are stronger than single bonds. This is true. However, the theory implies that the bond strength of double bonds is twice that of single bonds, which is not true.

Therefore, while the covalent bonding model accounts for many physical observations, it does have its limitations. Privacy Policy. Skip to main content. Basic Concepts of Chemical Bonding.

Search for:. Learning Objectives Identify element pairs which are likely to form ionic or covalent bonds. Key Takeaways Key Points Ionic compounds are formed from strong electrostatic interactions between ions, which result in higher melting points and electrical conductivity compared to covalent compounds.

Covalent compounds have bonds where electrons are shared between atoms. Due to the sharing of electrons, they exhibit characteristic physical properties that include lower melting points and electrical conductivity compared to ionic compounds.

Key Terms valence electrons : Electrons in the outermost principal energy valence level of an atom that can participate in the formation of chemical bonds with other atoms. Hydrogen and helium are exceptions because they can hold a maximum of two valence electrons. Single Covalent Bonds Single covalent bonds are sigma bonds, which occur when one pair of electrons is shared between atoms. Learning Objectives Identify the four orbital types used in covalent bond formation. Key Takeaways Key Points Covalent bonds occur when electrons are shared between two atoms.

A single covalent bond is when only one pair of electrons is shared between atoms. A sigma bond is the strongest type of covalent bond, in which the atomic orbitals directly overlap between the nuclei of two atoms.

Sigma bonds can occur between any kind of atomic orbitals; the only requirement is that the atomic orbital overlap happens directly between the nuclei of atoms. Key Terms sigma bond : A covalent bond whose electron density is concentrated in the region directly between the nuclei. Double and Triple Covalent Bonds Double and triple bonds, comprised of sigma and pi bonds, increase the stability and restrict the geometry of a compound.

Learning Objectives Describe the types of orbital overlap that occur in single, double, and triple bonds. Key Takeaways Key Points Double and triple covalent bonds are stronger than single covalent bonds and they are characterized by the sharing of four or six electrons between atoms, respectively. Double and triple bonds are comprised of sigma bonds between hybridized orbitals, and pi bonds between unhybridized p orbitals. Double and triple bonds offer added stability to compounds, and restrict any rotation around the bond axis.

Bond lengths between atoms with multiple bonds are shorter than in those with single bonds. Key Terms bond strength : Directly related to the amount of energy required to break the bond between two atoms. The more energy required, the stronger the bond is said to be.

It can be experimentally determined. Physical Properties of Covalent Molecules The covalent bonding model helps predict many of the physical properties of compounds. Learning Objectives Discuss the qualitative predictions of covalent bond theory on the boiling and melting points, bond length and strength, and conductivity of molecules. Key Takeaways Key Points The Lewis theory of covalent bonding says that the bond strength of double bonds is twice that of single bonds, which is not true.