Intermolecular Bonds: Types and Characteristics
Intermolecular Bonds
Intermolecular bonds are bonds between atoms that form molecules or ionic compounds.
Types of Intermolecular Bonds
- Ionic Bonds
- Covalent Bonds
- Metallic Bonds
Ionic Bonds
An ionic bond is the electrostatic attraction between two or more ions of opposite charges. The resulting structure must be electrically neutral and have a noble gas configuration. It is a bond between a metal and a non-metal, with a strong bond forming solid ionic compounds. These substances are in the form of ionic crystals.
Covalent Bonds
A covalent bond is a bond between non-metals, where both atoms need to receive electrons to achieve a noble gas configuration. However, since there is no electrostatic attraction between the atoms to donate electrons, they share electrons. This bond is magnetic in nature and weaker than ionic bonds, forming compounds called molecules.
Types of Covalent Bond Formulas
- Electronic Formula: Shows the atoms involved and the electron pairs as dots.
- Structural Formula: Shows the atoms involved, with a single line representing a shared pair of electrons (single covalent bond), two lines for two shared pairs (double covalent bond), and three lines for three shared pairs (triple covalent bond).
- Molecular Formula: Indicates the types and number of atoms that have bonded.
Octet Rule and Lewis Structures
This theory states:
Initially, add the valence electrons from all atoms in the molecule. Valence electrons are the electrons in the outermost shell. Then, place the atom with the most electrons to share in the center. If a bond is between two less electronegative atoms, all ionizable H atoms in an oxyacid must be connected to O, and non-ionizable H atoms in an oxyacid are connected to the central atom. Draw a line for each bond and complete the octet of all participating atoms with electron pairs (except for H, B, and Be). If the sum of the distributed electrons matches the initial sum of valence electrons, the structure is complete. Otherwise, replace one or more single bonds with double or triple bonds until the number of distributed electrons matches the initial sum of valence electrons.
We define a region as a single, double, or triple bond between two atoms, or a lone pair of electrons around an atom. If there are four regions (bonding or non-bonding) around a central atom, the molecule’s geometry will be tetrahedral. The atoms occupy the center of a regular tetrahedron, and the four regions occupy the vertices, forming equal angles of 109°28′.
If there are three bonding regions and one non-bonding region around the central atom, the molecule’s geometry will be tetrahedral pyramidal, with the same angle as the tetrahedral structure. The three bonding regions resemble a pyramid. Note: If the atom in the three bonding regions around the central atom is H, the lone pair of electrons will exert repulsion on the H atoms, and the angle will become 107°.
If there are two bonding regions and two non-bonding regions around the central atom, the molecule’s geometry will be tetrahedral, with an angle of 109°28′. Note: If the atoms in the two bonding regions around the central atom are H, the angle will be 105° due to the repulsion of the lone pairs of electrons.
If there are only three bonding regions around the central atom, the molecule’s geometry will be trigonal planar, with angles of 120°. In this geometry, the central atom usually has one double bond and two single bonds.
If there are only two bonding regions around the central atom, the molecule’s geometry will be linear, forming an angle of 180°. In this geometry, the central atom usually has a triple bond and a single bond or two double covalent bonds.
Metallic Bonds
A metallic bond is a bond between metals and is very strong.
Intermolecular Forces
Intermolecular forces are the attractions between molecules that cause them to remain interconnected, forming substances in solid, liquid, or gaseous states depending on the strength of these forces.
Types of Intermolecular Forces
- Dipole-Dipole Interactions: Occur between polar molecules. When a polar molecule has an H atom connected to F, O, or N, the strong dipole-dipole interaction is called a hydrogen bond. This is a stronger intermolecular force due to the large electronegativity difference between these atoms.
- Van der Waals Forces (London Dispersion Forces or Induced Dipole): Occur only between nonpolar molecules. These are the weakest intermolecular forces. However, molecules with different molecular weights can have both polar and Van der Waals forces. The strength of Van der Waals forces increases with molecular weight; the greater the molar mass of a nonpolar molecule, the stronger the Van der Waals forces.