Chemical structure
Introduction
Chemical structure refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. The chemical structure of a molecule determines many properties such as its reactivity, polarity, phase of matter, color, magnetism, and biological activity. The chemical structure can be represented graphically as a structural formula.
Atomic Structure
The atomic structure of a molecule refers to the arrangement of subatomic particles within an atom. Atoms are composed of protons, neutrons, and electrons. The protons and neutrons form the nucleus of the atom, while the electrons orbit the nucleus in various energy levels, also known as shells. The number of protons in an atom determines its atomic number and identifies the type of element it is. The number of neutrons and electrons can vary, leading to isotopes and ions, respectively.
Chemical Bonds
Chemical bonds are the attractive forces that hold atoms together in molecules. There are three primary types of chemical bonds: ionic, covalent, and metallic.
Ionic Bonds
Ionic bonds occur when electrons are transferred from one atom to another, resulting in the formation of ions. The resulting positive and negative ions are held together by electrostatic forces of attraction. This type of bond typically occurs between a metal and a non-metal.
Covalent Bonds
Covalent bonds occur when two atoms share one or more pairs of electrons. This type of bond typically occurs between two non-metals. Covalent bonds can be further classified into polar and non-polar covalent bonds based on the electronegativity difference between the bonded atoms.
Metallic Bonds
Metallic bonds occur between metal atoms. In metallic bonds, the valence electrons are delocalized and free to move throughout the entire metal lattice, forming a 'sea' of electrons. This delocalization of electrons results in the characteristic properties of metals such as electrical conductivity and malleability.
Structural Formulae
The structural formula of a molecule represents the arrangement of atoms and the bonds between them. There are several types of structural formulae, including the Lewis structure, the line-angle formula, and the condensed formula.
Lewis Structures
Lewis structures, also known as Lewis dot diagrams, represent the valence electrons of an atom. These diagrams can be used to predict the shape of a molecule and are useful in understanding the formation of chemical bonds.
Line-Angle Formulae
Line-angle formulae, also known as skeletal formulae, are a simplified representation of a molecule where each vertex and line terminus represents a carbon atom, and each line represents a chemical bond. Hydrogen atoms attached to carbon are not explicitly drawn in these formulae.
Condensed Formulae
Condensed formulae represent the atoms and bonds in a molecule in a single line of text. This type of formula is useful for representing large molecules where drawing a full structural formula would be impractical.
Molecular Geometry
The shape of a molecule, also known as its molecular geometry, is determined by the arrangement of the atoms in space. The molecular geometry can be determined using the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron pairs around a central atom will arrange themselves in such a way as to minimize repulsion.
See Also
Introduction to Molecular Orbital Theory