Understanding Chemical Bonds: Types, Properties, and Examples
Understanding Chemical Bonds
Link: Union of two or more atoms to form larger entities such as molecules or elements.
Types of Chemical Bonds
Ionic Bond: Union between ions of different signs.
- Occurs when the electronegativity difference is greater than 1.7.
- Typically between a metal and a nonmetal.
- Example: Group IIA + O
Covalent Bond: Forms when the electronegativity difference is not sufficient to transfer electrons from atoms. Atoms share one or more pairs of electrons in an orbital.
Metallic Bond: A chemical bond that holds the atoms of metals together.
Key Concepts in Chemical Bonding
Octet Rule: A rule to explain bonding between atoms, stating that when forming a chemical bond, atoms acquire, assign, or share electrons to have the same number of electrons in their last layer.
Exceptions to the Octet Rule: In some compounds, the number of electrons surrounding the central atom in a stable molecule is less than 8.
Molecules with an Odd Number of Electrons: Some molecules with an odd number of valence electrons are known as free radicals due to unpaired electrons.
Expanded Octet: Atoms of the third period and beyond may be surrounded by more than 4 pairs of electrons in certain compounds that have orbitals with an energy low enough to accommodate extra electrons.
Metallic Bonds in Detail
Metallic Bond: Characterized by having few valence electrons, which cannot form covalent bonds. By sharing their electrons, they cannot achieve a noble gas structure.
Characteristics of Metals:
- Exhibit shine (luster).
- Are ductile and malleable.
- Emit electrons.
- Are poorly soluble in solvents.
Classification of Metal Links:
- Conductors: Electrons tightly packed (e.g., Au, Cu, Pt).
- Semiconductors: Electrons spaced 6 to 8.
- Insulators: Separated electrons hardly appear.
Coordinate Covalent Bond: A bond that occurs when two atoms share a pair of electrons, but this pair is provided by only one of the combined atoms. Also called dative covalent bond.
Van der Waals Forces: Forces between bodies that are electrical dipoles, either instantaneous or permanent (e.g., F, Cl, Br, I).
Hydrogen Bonding: Occurs when hydrogen is bonded to a highly electronegative element, generating a permanent dipole.
Example: Alcohols, acids, ketones.
Glass, Ceramic, and Polymers
Structures and crystal properties are determined by the type of force that holds particles together.
Types of Glass:
- Ionic: Electrostatic attraction, brittle, non-conductor.
- Covalent: Covalent bonds, high melting point, poor conductor.
- Molecular: Dispersion forces, soft, low melting point, poor thermal and electrical conductor.
- Metallic: Hard link, soft metal, melting point high or low, good conductor.
Examples: Birth, Cf, CaCO3, MgO.
Polymers: From the Greek poly (many) and meros (parts), a substance whose molecule can be multiples of its molecular weight.
Natural Polymers: Fibers composed of cellulose found in wood are used to make candles and paper.
Ceramics: Substances made from feedstock that is burnt clay, such as lead, water, etc.
Uses: Hollow bricks, bricks, and porcelain tiles.
Lattice Energy and Related Concepts
Lattice Energy: Energy required to completely separate one mole of a solid ionic compound into its gaseous ions.
Coulomb’s Law: The potential energy between two ions is directly proportional to the product of their charges and inversely proportional to the distance that separates them.
Born-Haber Cycle: This procedure relates the lattice energy of ionic compounds with ionization energies, electron affinity, and other properties.
Sublimation: Solid lithium converting to steam.
Hybridization: Used to explain the mixture of atomic orbitals to generate a set of hybrid orbitals. Hybridization occurs when an atom’s orbitals are mixed.
Molecular Geometry
Molecular Geometry: Refers to the three-dimensional arrangement of atoms in a molecule, which affects their physical and chemical properties.