General Chemistry
Covalent bonds form between two atoms with similar electronegativities, which means the atoms end up sharing valence electrons in order to fill their outer orbitals. Sigma and pi bonds form the basis of covalent bonds. A sigma bond always forms first and is relatively strong, stable, and low-energy, while pi bonds form around the existing sigma bond and are individually weaker but reinforce the bond overall. Covalent bonds can be single, double, or triple bonds. Bond strength and bond energy increase with bond order, while bond length decreases, resulting in stronger bonds when two atoms are closer together.
Covalent bonds can also be classified as either polar or nonpolar. Polar covalent bonds form between two atoms with significantly different electronegativities, leading to unequal electron sharing, while nonpolar bonds form between atoms whose electronegativities are close enough that the atoms essentially share electrons equally. Diatomic molecules are a special kind of nonpolar molecule that forms between two identical atoms, such as bromine, iodine, nitrogen, and others, remembered using the mnemonic BrINClHOF.
Lesson Outline
<ul> <li>Introuduction to Covalent Bonds</li> <ul> <li>Covalent bonds form between two atoms with similar electronegativities</li> <li>Covalent bonds involve sharing electrons in order to fill outer orbitals</li> </ul> <li>Sigma and pi bonds</li> <ul> <li>Sigma bonds: single, strong, stable, low-energy</li> <li>Pi bonds: weaker, but reinforce overall bond</li> <li>Double bond: one sigma and one pi bond</li> <li>Triple bond: one sigma and two pi bonds</li> </ul> <li>Bond strength, bond energy, and bond order</li> <ul> <li>Higher bond order (single -> double -> triple) leads to stronger bonds and greater bond energy</li> <li>Energy needed to break a bond is called bond dissociation energy</li> </ul> <li>Bond length and strength</li> <ul> <li>Shorter bond length corresponds with stronger bond</li> <li>Distance between atoms & atom size affect bond strength</li> </ul> <li>Polarity in covalent bonds</li> <ul> <li>Form between atoms with different electronegativities</li> <li>Greater electronegativity difference = more polar bond</li> </ul> <li>Nonpolar bonds and diatomic molecules</li> <ul> <li>Nonpolar bonds form between atoms with similar electronegativities</li> <li>Diatomic molecules: special nonpolar covalent bonds between identical atoms (e.g., H2, F2, O2)</li> <li>Mnemonic "BrINClHOF" to remember common diatomic molecules</li> </ul> </ul>
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FAQs
The bond length in covalent bonds is determined by factors such as the size of the bonded atoms and the type of orbital overlap (sigma or pi bonds). Generally, larger atoms have longer bond lengths, while multiple bonds (double or triple bonds) have shorter bond lengths due to the increased electron density between the atoms.
Electronegativity is a measure of an atom's ability to attract bonding electrons towards itself. When two atoms with different electronegativities form a covalent bond, the electrons are more attracted to the atom with higher electronegativity, creating an uneven distribution of charge. This results in a polar covalent bond with a positive and negative end (dipole moment). If the electronegativity difference is relatively small, the bond is considered nonpolar, and the electron distribution is shared more evenly between the atoms.
The bond energy is the amount of energy required to break a covalent bond, while the bond strength refers to the stability of the bond. They are directly related: as the bond energy increases, the bond strength also increases. Bonds with higher bond energies are more stable and more difficult to break, while those with lower bond energies are less stable and more easily broken.
Sigma bonds and pi bonds are types of covalent bonds that differ in the orientation of their electron orbitals. In a sigma bond, the orbitals overlap head-on, with electrons shared directly between the nuclei of the bonded atoms. Sigma bonds are stronger, more stable, and can rotate freely around the bond axis. Pi bonds, on the other hand, involve the side-to-side overlap of p orbitals, creating a region of electron density above and below the bond axis. Pi bonds are weaker, less stable, and restrict rotation around the bond axis. They often accompany sigma bonds in double and triple covalent bonds.
Diatomic molecules consist of two atoms of the same element, such as H2, O2, or N2. In these molecules, both atoms have the same electronegativity, so electrons are shared equally between them, creating a nonpolar covalent bond. Since there is no electronegativity difference, there is no charge separation or dipole moment, and the molecule is considered nonpolar.
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