S and P blocks and Lewis structures [ENDORSED]

[Jessica Beroukhim 3K]

Since Lewis structures are based on octets, does this mean we only use them for s and p blocks? Or maybe only for the first few periods? Are they applicable/useful for elements with d orbitals?

[Lourick Bustamante 1B]

The octet rule can be used for the some of the s- and p- block elements (with exception for the lighter elements in these blocks), and only applies to some of the elements in the d- block. General exceptions to the octet rule: (1) molecules whose atoms have fewer than 8 electrons (e.g., boron chloride and lighter s- and p- block elements ); (2) molecules in which atoms have more than 8 electrons (.e.g, sulfur hexafluoride and elements beyond period 3); (3) molecules with an odd number of electrons (e.g., NO). (Helmenstine)

[Angel Gomez 1K]

Lewis structures are used to model the chemical bonds between two or more elements regardless of what block they are in. Lewis models use the valance electrons(v.e-) of elements to visualize the bonds because the v.e- are in the outermost shell, and it wouldn't make sense for elements to bond with each other through their inner shells because it's not physically possible. Group 1A has one outer v.e-, Group 2A has two, and so forth. This continues until Group 8A. No B Level groups are considered because the number of valence electrons will vary for all transition metals, so the group is relatively unimportant in determining v.e- numbers for them. We use Lewis dot structures for all elements, but can only know the number of v. e- for the elements in the s- and p-blocks by their position on the periodic table.
Hope this helps!

[Sarah Brauer]

For Lewis Structures, how do we know when an element is double or triple bonded?

[Vincent Kim 2I]

You know whether a molecule uses a double or triple bond if you use all the available electrons in the covalent bond.

For example, Carbonate (CO₃^2-) has 24 valence electrons in total (4 from Carbon, 18 from three Oxygens, 2 from the 2- charge).
The Carbon atom needs to double bond to one of the Oxygen atoms in order to fulfill octets for all 4 atoms using the 24 electrons available. If you try to use a single bond on all of the atoms and reach octets, you will need to use 26 electrons, which is not the amount we have.