How to Draw Lewis Structures, The Octet Rule and Exceptions | Study Chemistry With Us

The video begins with an introduction to the topic of drawing Lewis structures, emphasizing the importance of understanding the foundational steps. The instructor mentions creating a free study plan and encourages viewers to download it for additional resources. The focus is on learning how to draw Lewis structures correctly, as it is a fundamental concept in chemistry that affects subsequent topics like molecular geometry and resonance. The instructor reviews valence electrons, highlighting the necessity of memorizing the number of valence electrons for common atoms and differentiating between covalent and ionic compounds.

This paragraph outlines the steps to draw a Lewis structure, starting with calculating the total number of valence electrons. It explains the process of identifying the central atom, which is typically the least electronegative atom or, in the case of this example, carbon due to its presence and ability to form more than one bond. The instructor demonstrates how to place atoms and electrons to form bonds, convert Lewis dot diagrams into structures with single bonds, and verify that the structure has the correct number of electrons, adhering to the octet rule for stability.

The instructor delves into the octet rule, which states that atoms prefer to have eight valence electrons for stability. Examples are given to show how to apply the octet rule when drawing Lewis structures, including how to adjust for atoms that do not follow this rule due to having fewer than four valence electrons, such as hydrogen. The concept of expanded octets and incomplete octets is introduced, with the instructor noting that the latter is common in atoms from groups that do not start with four valence electrons.

The script discusses more complex Lewis structures involving multiple central atoms, such as those found in molecules with carbon and oxygen. The process involves calculating total valence electrons, identifying central atoms, and ensuring that all atoms, especially the central ones, follow the octet rule. The instructor provides an example of a molecule with carbon and oxygen, showing how to form double bonds to satisfy the octet rule and adjust for atoms that do not have a full octet due to their group in the periodic table.

This section covers Lewis structures with exceptions to the octet rule, such as boron and beryllium, which typically have incomplete octets, and atoms in the third row and below the periodic table, which can have expanded octets. The instructor provides examples of how to draw Lewis structures for these exceptions, ensuring that the total number of valence electrons is correct and that the structures are stable, even if they do not adhere strictly to the octet rule.

The script introduces Lewis structures for ions, explaining the need to adjust the total number of valence electrons based on the charge of the ion. For cations, an electron is subtracted, and for anions, an electron is added. The instructor demonstrates how to draw Lewis structures for ions, including placing the structure in brackets and indicating the charge. The importance of ensuring an even number of valence electrons and correctly applying the charge to the structure is emphasized.

The final paragraph encourages viewers to practice drawing Lewis structures and to believe in their ability to learn and apply this skill. The instructor provides a summary of the steps and concepts covered in the video and motivates the audience to continue their studies, especially since they are in the middle of the semester. The goal is to ensure that viewers are well-prepared and can successfully draw Lewis structures for a variety of chemical compounds.