Chemical bonds are generally categorized into two primary types: ionic and covalent. These bonds determine a substance’s structure and its physical and chemical properties. Determining the specific nature of the bond in a compound like Barium Chloride (\(\text{BaCl}_2\)) requires examining the atoms involved.
Distinguishing Chemical Bonds
Ionic bonds involve the complete transfer of one or more valence electrons from one atom to another. This occurs between atoms with a large difference in electron attraction. The resulting charged atoms, called ions, are held together by a strong electrostatic force. Ionic bonding typically forms between a metal, which readily loses electrons, and a non-metal, which readily gains them.
Covalent bonds, in contrast, form when atoms share one or more pairs of valence electrons. This sharing allows each atom to effectively complete its outer electron shell. Covalent bonds usually occur between two non-metal atoms.
The sharing of electrons is not always equal, leading to a polar covalent bond where electrons are pulled closer to the more attractive atom. The continuous spectrum from purely covalent to purely ionic is defined by the difference in electronegativity between the bonded atoms. This difference is the most reliable tool for bond classification.
Analyzing the Barium Chloride Structure
To classify the bond in \(\text{BaCl}_2\), the elements must be identified. Barium (\(\text{Ba}\)) is an alkaline earth metal, and Chlorine (\(\text{Cl}\)) is a non-metal halogen. The combination of a metal and a non-metal strongly suggests an ionic interaction.
Classification relies on the Pauling electronegativity scale, which measures an atom’s tendency to attract electrons. Barium has a low electronegativity value of \(0.89\), while Chlorine has a high value of \(3.16\). The difference in electronegativity is \(3.16 – 0.89 = 2.27\).
A bond is predominantly ionic if the difference is greater than \(1.7\). Since \(2.27\) significantly exceeds this threshold, the bond in Barium Chloride is confirmed to be overwhelmingly ionic. Barium loses its two valence electrons to form the cation \(\text{Ba}^{2+}\), and the two Chlorine atoms gain one electron each to form \(2\text{Cl}^{-}\).
Physical Manifestations of the Bond Type
The ionic structure of Barium Chloride dictates its physical properties. Ionic compounds form extensive crystal lattices stabilized by strong electrostatic forces, which require a large amount of energy to break. This explains the compound’s high melting point of approximately \(962^\circ\text{C}\).
The high boiling point of \(\text{BaCl}_2\), around \(1560^\circ\text{C}\), is also a consequence of the powerful forces holding the crystal lattice together. Such thermal stability is characteristic of ionic salts, whereas covalently bonded substances typically have much lower melting and boiling points.
Barium Chloride is highly soluble in water, a polar solvent. When placed in water, the polar water molecules surround and separate the individual \(\text{Ba}^{2+}\) and \(\text{Cl}^{-}\) ions from the crystal lattice, a process called dissociation.
The presence of these mobile ions governs the compound’s electrical conductivity behavior. Solid \(\text{BaCl}_2\) is a poor conductor because the ions are fixed in the crystal lattice. However, when melted or dissolved in water, the dissociated ions are free to move, allowing the solution or the molten liquid to conduct an electrical current effectively.