Draw a Lewis structure for each of the following:
b. CO₃²⁻

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Step 1: Count the total number of valence electrons in the molecule. Carbon (C) has 4 valence electrons, each oxygen (O) has 6 valence electrons, and the 2− charge adds 2 extra electrons. Add these together to determine the total number of valence electrons.

Step 2: Place the least electronegative atom (carbon) in the center and arrange the three oxygen atoms around it. Connect each oxygen atom to the central carbon atom with a single bond.

Step 3: Distribute the remaining valence electrons as lone pairs around the oxygen atoms to satisfy the octet rule for each oxygen. Start with the outer atoms (oxygen) and then move to the central atom (carbon) if needed.

Step 4: Check if the central atom (carbon) has a complete octet. If not, form double bonds by converting lone pairs from oxygen atoms into bonding pairs with carbon. Ensure that the total number of valence electrons remains consistent with the count from Step 1.

Step 5: Assign formal charges to each atom to ensure the most stable structure. The formal charge is calculated using the formula: Formal Charge = (Valence Electrons) − (Non-Bonding Electrons) − (1/2 × Bonding Electrons). Adjust the structure if necessary to minimize formal charges, ensuring the overall charge of the ion is −2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They use dots to represent electrons and lines to represent bonds, allowing chemists to visualize the arrangement of atoms and the distribution of electrons. Understanding how to draw Lewis structures is essential for predicting molecular geometry and reactivity.

Formal Charge

Formal charge is a concept used to determine the distribution of electrons in a molecule. It is calculated by taking the number of valence electrons in an atom, subtracting the number of non-bonding electrons, and half the number of bonding electrons. This helps in assessing the most stable Lewis structure, as structures with formal charges closest to zero are generally more favorable.

Resonance Structures

Resonance structures are different Lewis structures that represent the same molecule, differing only in the arrangement of electrons. They are used when a single Lewis structure cannot adequately depict the actual electron distribution. For polyatomic ions like CO3^2−, resonance helps illustrate the delocalization of electrons, contributing to the stability and reactivity of the ion.

Draw a Lewis structure for each of the following:b. CO32−