Question

Using Lewis symbols and Lewis structures, diagram the formation of \(\mathrm{SiCl}_{4}\) from \(\mathrm{Si}\) and \(\mathrm{Cl}\) atoms, showing valence-shell electrons. (a) How many valence electrons does \(\mathrm{Si}\) have initially? (b) How many valence electrons does each \(\mathrm{Cl}\) have initially? (c) How many valence electrons surround the Si in the \(\mathrm{SiCl}_{4}\) molecule? (d) How many valence electrons surround each \(\mathrm{Cl}\) in the \(\mathrm{SiCl}_{4}\) molecule? (e) How many bonding pairs of electrons are in the \(\mathrm{SiCl}_{4}\) molecule?

Short answer

(a) Si has \(4\) valence electrons initially. (b) Each Cl has \(7\) valence electrons initially. The Lewis structure of \(\mathrm{SiCl}_{4}\) is: ``` Si :[.] - Cl :[:] -: | | Cl :[:] - Si :[:]- Cl :[:] | | Cl :[:] ``` (c) \(8\) valence electrons surround Si in the \(\mathrm{SiCl}_{4}\) molecule. (d) \(8\) valence electrons surround each Cl in the \(\mathrm{SiCl}_{4}\) molecule. (e) There are \(4\) bonding pairs of electrons in the \(\mathrm{SiCl}_{4}\) molecule.

Step-by-step solution

Identify the number of valence electrons of individual atoms

To answer the questions about the number of valence electrons in each atom, we need to know their group numbers in the periodic table. Silicon (Si) is in Group 14, and Chlorine (Cl) is in Group 17. (a) Silicon (Si) has 4 valence electrons initially, as it is in Group 14. (b) Each Chlorine (Cl) atom has 7 valence electrons initially, as it is in Group 17.

Formation of the \(\mathrm{SiCl}_{4}\) molecule

Silicon (Si) will share its 4 valence electrons with 4 Chlorine (Cl) atoms, each contributing one electron to form a single covalent bond with Silicon. This results in 4 single, covalent bonds between Silicon and the 4 Chlorine atoms.

Draw the Lewis structure

In the Lewis structure, we represent valence electrons as dots and share them between the atoms involved in bonding. Si :[.] - Cl :[:] -: | | Cl :[:] - Si :[:]- Cl :[:] | | Cl :[:] - Here, each horizontal or vertical line represents a covalent bond (pair of shared electrons) between the Silicon atom and a Chlorine atom. - The remaining electrons that are not taking part in the bond formation are shown as pairs of dots, representing the valence electrons in the outer electron shells.

Answer the specific questions about shared electrons

(c) The number of valence electrons surrounding Si in the \(\mathrm{SiCl}_{4}\) molecule is 8. This is because, after forming 4 single covalent bonds, it has 4 pairs of shared electrons with each Chlorine atom. (d) The number of valence electrons surrounding each Chlorine (Cl) atom in the \(\mathrm{SiCl}_{4}\) molecule is also 8. This is because each Chlorine atom has shared one electron with Silicon to form a single covalent bond, and the remaining 6 valence electrons are unshared pairs, still belonging to the Chlorine atom. (e) There are 4 bonding pairs of electrons in the \(\mathrm{SiCl}_{4}\) molecule, as there are 4 single covalent bonds between the central Silicon atom and the 4 Chlorine atoms.

Key concepts

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. They are crucial because they determine how atoms interact and bond with each other. In the context of Lewis structures, we often represent these electrons as dots around the chemical symbol of the element.
For elements like Silicon (Si), which belongs to Group 14 on the periodic table, there are 4 valence electrons. This means that Silicon has 4 electrons in its outer shell available for bonding. In contrast, Chlorine (Cl), located in Group 17, has 7 valence electrons, just one short of a full shell, making it very eager to form bonds to gain that one additional electron.
Understanding the number of valence electrons an atom has allows us to predict how it will bond with other atoms. This is the foundation of drawing accurate Lewis structures and predicting molecular geometry.

Covalent Bonds

Covalent bonds occur when atoms share electrons to achieve a full outer electron shell, leading them to greater stability. Unlike ionic bonds, which involve the transfer of electrons, covalent bonds involve sharing. This kind of bond typically happens between non-metal atoms, and it's essential in forming molecules.
In the molecule \(\text{SiCl}_{4}\), Silicon shares its 4 valence electrons, one with each Chlorine atom. Each Chlorine atom, in turn, shares one of its valence electrons with Silicon. This sharing creates a shared pair of electrons, or covalent bond, between each Si and Cl.

• Each covalent bond in \(\text{SiCl}_{4}\) is a single bond, involving one pair of shared electrons.
• The formation of these bonds results in a stable molecule, with Silicon achieving the octet rule by having 8 electrons around it, thanks to the shared electrons from Chlorine atoms.
• Similarly, each Chlorine atom also achieves the octet configuration, having 3 lone pairs and one bonding pair totaling 8 electrons around it.

Periodic Table Groups

The periodic table groups are vertical columns (called groups or families) that classify elements based on shared properties and valence electron configuration. Elements in the same group have the same number of valence electrons and thus similar chemical properties.
Silicon (Si) is in Group 14, which contains elements that typically have four valence electrons. This group is sometimes referred to as the carbon group. Such elements can form up to four covalent bonds with other atoms, a critical property when considering organic molecules and many types of compounds.
Chlorine (Cl), found in Group 17, is part of the halogens. These elements have seven valence electrons and are known for forming one covalent bond, typically with hydrogen or a metal. However, in \(\text{SiCl}_{4}\), each chlorine forms a covalent bond by sharing an electron with silicon.

• Understanding the group of an element helps us predict its behavior in bond formation and chemical reactions.
• Groups indicate how many electrons are in the outer shell of an atom, which directly impacts how molecules like \(\text{SiCl}_{4}\) form.

The structure and organization of the periodic table, therefore, are key tools for chemists in predicting and understanding the behavior of elements and their compounds.