Question

By means of Lewis structures, represent bonding between the following pairs of elements: (a) Cs and \(\mathrm{Br} ;\) (b) \(\mathrm{H}\) and \(\mathrm{Sb} ;\) (c) \(\mathrm{B}\) and \(\mathrm{Cl} ;\) (d) \(\mathrm{Cs}\) and \(\mathrm{Cl}\); (e) Li and O; (f) Cl and L. Your structures should show whether the bonding is essentially ionic or covalent.

Short answer

Here are the Lewis structures and bond types of the given pair of elements. (a) Cs-Br = [Cs]+ [Br]- (Ionic), (b) H-Sb = H:Sb (Covalent), (c) B-Cl = B- (unless the charge is specified, no reasonable Lewis structure can be drawn), (d) Cs-Cl = [Cs]+ [Cl]- (Ionic), (e) Li-O = [Li]+ :O- (Ionic), (f) Cl-L= Cl:L (Covalent).

Step-by-step solution

Understanding Lewis Structures

Lewis structures, also known as electron dot structures, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. The total number of electrons represented in a Lewis structure is equal to the sum of the numbers of valence electrons of each atom in the molecule.

Get Electron Configuration

Determine the electron configuration of each element. This can be found using the periodic table.

Draw Lewis Symbols

The Lewis symbol of an element includes the symbol of the element plus one dot for each valence electron. For instance, the element Cs (Cesium) has one electron in its outer shell, which is represented by one dot, and Bromine (Br) has 7 valence electrons.

Determine Ionic or Covalent bonding

Covalent bonding involves the sharing of electron pairs between atoms. This usually occurs between non-metals. Whereas Ionic bonding involves the complete transfer of valence electrons between atoms and usually involves a metal bonding with a non-metal. For instance, between Cs (a metal) and Br (a non-metal), a CsBr molecule will be formed with one electron transferred from Cs to Br. This is an ionic bond. Repeat this process with each pair of elements.

Key concepts

Ionic Bonding

Ionic bonding is a type of chemical bond where there is a complete transfer of valence electrons from one atom to another.
This transfer forms two oppositely charged ions. The atom that loses electrons becomes a positively charged ion, known as a cation, while the atom that gains these electrons becomes a negatively charged ion, or an anion.
This bond is typically formed between metals and non-metals. For example, in the pair Cs and Br, ionic bonding occurs.

• Cs (cesium) is a metal and readily loses its one valence electron.
• Br (bromine) is a non-metal and needs one electron to complete its valence electron shell.
• The electron from Cs is transferred to Br, forming Cs⁺ and Br⁻ ions.

These oppositely charged ions attract each other, maintaining the ionic bond and resulting in the formation of the ionic compound CsBr.

Covalent Bonding

Covalent bonding is the sharing of electron pairs between atoms. This occurs primarily between non-metallic elements. Unlike ionic bonds, where electrons are transferred, covalent bonds form when atoms share electrons to fill their outer shell, or valence shell.
In the case of H and Sb or B and Cl, covalent bonding is present as follows:

• Hydrogen (H) needs one more electron for a complete outer shell and shares an electron with antimony (Sb).
• Boron (B) shares its three electrons with three chlorine (Cl) atoms, each needing one electron, forming BCl₃.

Through sharing electrons, both atoms achieve a stable electron configuration, resulting in a stronger bond. Covalent bonds can be single, double, or triple, depending on how many pairs of electrons are shared between the atoms.

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. These are the electrons involved in bonding, whether it be ionic or covalent.
Understanding how these electrons interact is crucial for predicting bonding behavior:

• Valence electrons determine the chemical reactivity and bonding behavior of an element.
• In Lewis structures, valence electrons are represented by dots around the element's symbol.
• The goal of bonding is to achieve a stable electron configuration, often resembling that of noble gases.

Take for instance chlorine (Cl), which has seven valence electrons and seeks one more to complete its outer shell. This guides it to form bonds with other elements such as hydrogen, cesium, or lithium, depending on their valence electron availability.