This comprehensive study guide covers the key concepts of covalent bonding, typically found in Chapter 8 of many chemistry textbooks. We'll explore the fundamental principles, delve into different types of covalent bonds, and examine the properties of covalently bonded substances. Use this guide to prepare for quizzes, tests, and a deeper understanding of this crucial chemical concept.
What is Covalent Bonding?
Covalent bonding is a type of chemical bond where atoms share electrons to achieve a stable electron configuration, usually resembling a noble gas (full outer electron shell). Unlike ionic bonds, which involve the transfer of electrons, covalent bonds result from the mutual attraction between atoms and the shared electron pair(s). This sharing leads to a lower overall energy state for the bonded atoms, making the bond energetically favorable.
Key Characteristics of Covalent Bonds:
- Electron Sharing: The defining feature of a covalent bond is the sharing of valence electrons between atoms.
- Nonmetals: Covalent bonds primarily form between nonmetal atoms.
- Lower Melting and Boiling Points: Compared to ionic compounds, covalently bonded substances generally have lower melting and boiling points.
- Poor Electrical Conductivity: Covalent compounds typically do not conduct electricity in either solid or liquid form because they lack freely moving charged particles (ions).
- Molecular Structure: Covalently bonded atoms form discrete molecules with specific shapes.
Types of Covalent Bonds
Several factors influence the nature of covalent bonds:
1. Single, Double, and Triple Bonds:
- Single Bond: One pair of electrons is shared between two atoms (e.g., H-H in hydrogen gas).
- Double Bond: Two pairs of electrons are shared between two atoms (e.g., O=O in oxygen gas).
- Triple Bond: Three pairs of electrons are shared between two atoms (e.g., N≡N in nitrogen gas). Triple bonds are the strongest type of covalent bond.
The number of shared electron pairs directly impacts the bond strength and length. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds.
2. Polar and Nonpolar Covalent Bonds:
The electronegativity difference between the bonded atoms determines the polarity of a covalent bond. Electronegativity is the ability of an atom to attract electrons in a bond.
- Nonpolar Covalent Bond: Occurs when atoms have similar electronegativities. The electrons are shared equally between the atoms (e.g., H-H).
- Polar Covalent Bond: Occurs when atoms have different electronegativities. The electrons are shared unequally, resulting in a partial positive charge (δ+) on the less electronegative atom and a partial negative charge (δ-) on the more electronegative atom (e.g., H-Cl).
Properties of Covalently Bonded Substances
The properties of covalently bonded substances are directly related to the type and strength of the covalent bonds and the intermolecular forces present.
1. Melting and Boiling Points:
Relatively low melting and boiling points are characteristic of many covalently bonded substances due to the weaker intermolecular forces compared to the strong electrostatic forces in ionic compounds.
2. Solubility:
Solubility varies widely depending on the polarity of the molecule and the solvent. Polar covalent molecules tend to dissolve in polar solvents (like water), while nonpolar covalent molecules dissolve in nonpolar solvents (like oil).
3. Electrical Conductivity:
Generally poor electrical conductors, as there are no freely moving charged particles.
Resonance Structures
Some molecules cannot be represented accurately by a single Lewis structure. These molecules exhibit resonance, where electrons are delocalized across multiple bonds. Resonance structures are different Lewis structures that contribute to the overall structure of the molecule. The actual structure is a hybrid of the resonance structures.
Shapes of Molecules (VSEPR Theory)
The Valence Shell Electron Pair Repulsion (VSEPR) theory helps predict the three-dimensional shapes of molecules based on the repulsion between electron pairs around the central atom. The shape influences the properties of the molecule, including polarity and reactivity.
This study guide provides a solid foundation for understanding covalent bonding. Remember to consult your textbook and class notes for additional details and examples. Good luck with your studies!
