Understanding Chemical Bonds: Covalent, Metallic, and Intermolecular Forces
Chemical Bonds: An In-Depth Look
The density of materials is generally high, especially in transition metals due to their compact structures. Atoms with high atomic numbers and minimal gaps between them exhibit high intensity.
Covalent Bonds
A covalent bond is formed when two atoms share one or more pairs of electrons. The covalent valence of an element is its ability to form covalent bonds. For example, oxygen has a covalency of 2, as seen in water (H2O), where it forms two covalent bonds.
In covalent bonding, bonding electron pairs and lone pairs surrounding a central atom are oriented to maximize distance from each other, minimizing repulsions. This orientation determines the molecular geometry. Repulsive forces are strongest between lone pairs, followed by lone pair-bonding pair interactions, and weakest between bonding pairs.
Valence Bond Theory
According to valence bond theory, a covalent bond is the overlap of two semi-occupied orbitals from different atoms, with paired electrons having antiparallel spins. Greater overlap results in a stronger bonding force. Atomic orbitals not involved in bonding remain unchanged.
The coupling of a pair of electrons in a common orbital forms a single bond, while double and triple bonds involve two or three pairs of electrons, respectively. The covalent valence of an element is determined by the number of covalent bonds it can form, which depends on the number of unpaired electrons.
Intermolecular Forces
Dipole-Dipole Forces
Dipole-dipole forces are attractive forces between polar molecules. The dipole of one molecule orients the dipoles of neighboring molecules (polar-polar interactions).
Dipole-Induced Dipole Forces
Polarized molecules or molecules near nonpolar neutral atoms can induce a shift in electron density, creating induced dipoles. A weak attractive force arises between the permanent dipole and the induced dipole (polar-nonpolar interactions).
Dispersion Forces (London Dispersion Forces)
Dispersion forces occur because, at any given time, a non-polar molecule may experience a slight shift in electron distribution, forming an instantaneous dipole. This dipole can polarize a nearby molecule, forming an induced dipole (nonpolar-nonpolar interactions).
Metallic Bonds
A metallic bond is the union between metal atoms, responsible for the stability and properties of metallic lattices.
Electron Cloud Model
In the electron cloud model, the lattice is formed by metal ions, where atoms have transferred their valence electrons. These electrons are delocalized throughout the crystal and move freely through the gaps between the ions, forming the electron cloud. The stability of the crystal lattice results from the interaction between metal ions and the delocalized electron cloud.
Properties of Metals
- Generally high melting and boiling points, particularly high in transition metals and relatively low in alkali and alkaline earth metals.
- High electrical conductivity in the solid state, making them conductors of the first kind. This is due to the mobility of their valence electrons.
- High thermal conductivity.
- Ability to dissolve in each other, forming molten alloys or solid-state solutions.
- Good mechanical properties such as ductility, malleability, and toughness, in both pure metals and their alloys. These properties lead to varied technical applications.