Grade 11 → Chemical Bonding and Molecular Structure ↓
Bond parameters
In chemistry, it is important to understand how atoms join together to form molecules. This bonding is determined by several factors, known as bond parameters, which help us understand the nature of chemical bonds. These parameters include bond length, bond angle, bond energy, bond order, and polarity. Gaining insight into these parameters helps students predict the molecular structure and properties of substances.
Bond length
Bond length is the distance between the nuclei of two bonded atoms. It is an important indicator of the strength and stability of a bond. Bond length can be affected by the size of the atoms and the bond order. Generally, as the size of the atoms increases, so does the bond length. Conversely, as the bond order increases, the bond length decreases. This is because double bonds are shorter than single bonds, and triple bonds are shorter than double bonds.
Example: The bond length of a single bond CC is approximately 154 pm. The bond length of a double bond C=C is approximately 134 pm. The bond length of a triple bond C≡C is approximately 120 pm.
Looking at bond length
Bond angle
The bond angle is the angle formed between three atoms in at least two bonds. Like bond length, bond angles are also important because they determine the shape of the molecule. VSEPR (valence shell electron pair repulsion) theory helps predict bond angles. According to this theory, electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion forces.
Example: In a water molecule (H2O), the bond angle between HOH is approximately 104.5°. In carbon dioxide (CO2), the bond angle between OCO is 180°, making it linear.
Visualization of bond angles
Bond energy
Bond energy refers to the amount of energy needed to break one mole of bonds in gaseous molecules. It is a direct measure of bond strength: the higher the bond energy, the stronger the bond. Different bonds have different bond energies affected by factors such as bond order and bond length. Stronger bonds with higher bond orders generally have higher bond energies.
Example: The bond energy of a CH bond is about 413 kJ/mol. For a C=O double bond, it is approximately 743 kJ/mol.
Visualization of bond energy
Bond order
Bond order is an indication of the number of chemical bonds between a pair of atoms. Higher bond orders indicate stronger, shorter bonds. It is calculated by dividing the difference between the number of bonding and antibonding electrons by two. In simple diatomic molecules or entities, it can be equal to the number of shared electron pairs.
Example: For a single bond (HH) in H2, the bond order is 1. For a double bond (O=O) in O2, the bond order is 2. For a triple bond (N≡N) in N2, the bond order is 3.
Looking at bond order
Bond polarity
Bond polarity occurs when there is a difference in electronegativities between bonded atoms. In polar covalent bonds, electrons are not shared equally, resulting in a partial charge. Nonpolar bonds involve equal sharing of electrons. The degree of polarity affects the physical properties of compounds, such as their state, boiling point, and solubility.
Example: In an H-Cl bond, the chlorine atom is more electronegative, making it partially negative, while hydrogen is partially positive. In an NH bond in ammonia (NH3), nitrogen is more electronegative than hydrogen, creating a dipole.
Visualization of bond polarity
Conclusion
Understanding bond parameters is the key to understanding how and why substances behave the way they do. By analyzing bond lengths, bond angles, bond energies, bond orders, and polarity, we can predict and explain the structures and properties of various chemical compounds. This insight is fundamental for students as they advance in the study of chemistry and move on to deal with more complex molecular interactions and reactions.