Question

Draw the Lewis structure for each molecule or ion. a. SeF \(_{2}\) b. \(C l O_{2}-\) c. \(P O_{3}^{3-}\) d. \(\mathrm{POCl}_{3}\) e. GeF_

Short answer

The following are the Lewis structures for the given molecules and ions: SeF₂: ``` F \ Se - F / \ : : ``` ClO₂⁻: ``` O \ Cl - O / \ : : ``` PO₃³⁻: ``` O \ P / \ O O : : ``` POCl₃: ``` O \ P / | \ Cl Cl Cl : : : ``` GeF₄: ``` F \ Ge / \ F F \ F : ```

Step-by-step solution

Calculate the total number of valence electrons

The total number of valence electrons is the sum of the valence electrons of each atom in the molecule. Selenium (Se) has 6 valence electrons, and each Fluorine (F) atom has 7 valence electrons. So, the total number of valence electrons is 6 + 2 × 7 = 20.

Determine the central atom

Since there is only one Selenium (Se) atom, it is the central atom, and the two Fluorine (F) atoms will be bonded to it.

Distribute the electrons

Start by forming single bonds by distributing 2 electrons between the central atom (Se) and each surrounding atom (F). This will be 4 electrons in total. Distribute the remaining 16 electrons as lone pairs around the atoms to complete their octet. Selenium should have two lone pairs, and each Fluorine atom will have three lone pairs. We can now draw the Lewis structure. SeF₂ Lewis structure: ``` F \ Se - F / \ : : ``` #b. ClO2− #

Calculate the total number of valence electrons

Since this is an ion, the total number of valence electrons includes the extra electron added to the molecule. Chlorine (Cl) has 7 valence electrons, and each Oxygen (O) atom has 6 valence electrons. So, the total number of valence electrons is 7 + 2 × 6 + 1(extra electron) = 20.

Determine the central atom

Chlorine (Cl) is the central atom, and the two Oxygen (O) atoms will be bonded to it.

Distribute the electrons

Start by forming single bonds. Then, distribute the remaining 14 electrons as lone pairs to complete the octet. Chlorine should have two lone pairs, and each Oxygen atom will have three lone pairs. The ion will have a negative charge. We can now draw the Lewis structure. ClO₂⁻ Lewis structure: ``` O \ Cl - O / \ : : ``` #c. PO₃³⁻ #

Calculate the total number of valence electrons

Phosphorus (P) has 5 valence electrons, and each Oxygen (O) atom has 6 valence electrons. For the ion, we need to consider the extra 3 electrons. The total number of valence electrons is 5 + 3 × 6 + 3(extra electrons) = 26.

Determine the central atom

Phosphorus (P) is the central atom, and the three Oxygen (O) atoms will be bonded to it.

Distribute the electrons

Start by forming single bonds. Then, distribute the remaining 20 electrons as lone pairs to complete the octet. Phosphorus should have no lone pairs, and each Oxygen atom will have three lone pairs. The ion will have a 3-negative charge. We can now draw the Lewis structure. PO₃³⁻ Lewis structure: ``` O \ P / \ O O : : ``` #d. POCl3#

Calculate the total number of valence electrons

Phosphorus (P) has 5 valence electrons, Oxygen (O) has 6 valence electrons, and each Chlorine (Cl) atom has 7 valence electrons. The total number of valence electrons is 5 + 6 + 3 × 7 = 32.

Determine the central atom

Phosphorus (P) is the central atom, Oxygen and three Chlorines will be bonded to it.

Distribute the electrons

Start by forming single bonds. Then, allocate the remaining 24 electrons as lone pairs to complete the octet. Phosphorus has no lone pair, and Oxygen and each Chlorine atom will have three lone pairs. We can now draw the Lewis structure. POCl₃ Lewis structure: ``` O \ P / | \ Cl Cl Cl : : : ``` #e. GeF4#

Calculate the total number of valence electrons

Germanium (Ge) has 4 valence electrons, and each Fluorine (F) atom has 7 valence electrons. The total number of valence electrons is 4 + 4 × 7 = 32.

Determine the central atom

Germanium (Ge) is the central atom, and the four Fluorine (F) atoms will be bonded to it.

Distribute the electrons

Start by forming single bonds. Then, allocate the remaining 24 electrons as lone pairs to complete the octet. Germanium has no lone pair, and each Fluorine atom will have three lone pairs. We can now draw the Lewis structure. GeF₄ Lewis structure: ``` F \ Ge / \ F F \ F : ```

Key concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They are essential for bonding as they can be shared between atoms to fill up each atom's outer shell. Valence electrons determine how an atom behaves in chemical reactions. In order to create a Lewis structure, it's important to first calculate the total number of valence electrons in the molecule or ion. To do this:

• Add up the valence electrons of each atom present in the molecule.
• For ions, adjust the total by adding or subtracting electrons to account for the charge.

For example, in SeF₂, selenium (Se) has 6 valence electrons, and each fluorine (F) atom has 7. Totaling them gives you 6 + 2×7 = 20 valence electrons. Calculating the correct number of valence electrons is the first step in accurately drawing the Lewis structure. This foundation allows us to proceed to determine which atom should be the central atom.

Central Atom

The central atom in a Lewis structure is typically the atom that is able to form the most bonds or has the highest capacity to expand its valence shell. It is usually the atom that appears once in the compound. To determine the central atom:

• Choose the atom that can form the most bonds; often this is the least electronegative atom, except hydrogen.
• In molecules with different atoms, atoms like carbon, phosphorus, or sulfur are often central atoms due to their ability to form multiple bonds.

For instance, in the ion ClO₂⁻, chlorine (Cl) is chosen as the central atom, because it can bond with both oxygen atoms. Identifying the correct central atom is crucial, as it dictates how other atoms attach in the molecular structure.

Lone Pairs

Lone pairs are the pairs of valence electrons that are not shared with another atom in a molecule. These pairs do not participate in bonding but are essential for understanding the shape and reactivity of a molecule.

• Lone pairs occupy space around the central atom and can influence molecular geometry due to electron repulsion.
• Accounting for lone pairs ensures that atoms fulfill their octet requirement (or the duet rule in the case of hydrogen) and stabilizes the atom.

When distributing electrons around atoms, after making bonds, assign any remaining electrons as lone pairs. For example, in GeF₄, each fluorine atom has three lone pairs, which complete their octet, maximizing stability.

Octet Rule

The octet rule is a chemical rule of thumb that states atoms tend to bond in such a way that they seek to fulfill an "octet" of electrons in their valence shell, gaining stability like noble gases. This rule is the baseline for predicting the bonding behavior in most molecules.

• Many atoms, like carbon, nitrogen, oxygen, and fluorine, try to surround themselves with 8 electrons.
• Atoms may share, donate, or receive electrons to achieve an ideal configuration.

An example here is POCl₃, where phosphorus bonds with oxygen and chlorine atoms to complete not just its own octet but helps surrounding atoms achieve theirs as well. Exceptions do exist, such as molecules with fewer than or more than eight electrons around central atoms, but understanding this rule and its applications facilitates the creation of correct Lewis structures.