One type of exception to the octet rule are compounds with central atoms having fewer than eight

One type of exception to the octet rule are compounds with...

Key Concepts

Octet Rule

The octet rule is a chemical guideline stating that atoms tend to bond in such a way that they have eight electrons in their valence shell, mimicking the electron configuration of noble gases. This rule helps predict molecular stability and bonding patterns in many compounds, although there are notable exceptions.

Exceptions to the Octet Rule

Some molecules do not adhere strictly to the octet rule. This includes species where the central atom has fewer than eight electrons, such as in electron-deficient compounds. These exceptions are important because they illustrate that not all stable bonding arrangements require a complete octet, and alternative bonding schemes can exist.

Lewis Structures

Lewis structures are diagrams that depict the bonding between atoms within a molecule and the lone pairs of electrons that may exist. They are constructed by accounting for the valence electrons of the constituent atoms and arranging them to form bonds that ideally satisfy or approximate the octet rule, while also accommodating exceptions where appropriate.

Electron Counting and Valence Electrons

Understanding electron counting is fundamental to drawing Lewis structures. By tallying the total number of valence electrons contributed by all atoms in a molecule, one can distribute these electrons to form bonds and lone pairs. This process is crucial not only for fulfilling the octet rule where possible, but also for identifying compounds that are electron-deficient, meaning they have fewer electrons around the central atom than would be expected from the octet rule.

Transcript

00:02 In this video, let's look at compounds that do not follow as when we're drawing the lewis structure, the octet rule.

00:11 So just a reminder, the octet rule is basically stating that every atom in the compound, in the structure, needs to have eight valence electrons that it kind of has at its disposal.

00:26 Okay.

00:27 So that's the octet rule, but sometimes we can see some exceptions to that, and we're going to look at that right here.

00:32 So let's look at this first one right here.

00:33 So we have beryllium, high, or let's see, how would you say that? but beryllium and two hydrogen.

00:42 And so anyways, when we look at this, we have beryllium, which is over on the left side of the periodic table.

00:50 We always want, we'll just follow the same kind of process when drawing these valence electrons, but we have two valence electrons with beryllium.

00:57 And then we have one valence electron each for each hydrogen, making a total of four balance electrons.

01:03 On this molecule on this compound and so we're going to put brilium in the center we draw our hydrogens and you're going to notice something right here we've already used up all four of those valence electrons just by drawing the bonds to hydrogen and remember hydrogen's going to follow what we call the duet uh duet rule and the duet rule basically states that hide and this only applies to hydrogen but it needs two valence electrons only.

01:36 Okay, but beryllium would follow the octet rule and it needs to have eight to be able to follow this, but you can see right here we don't have any electrons extra to donate to it, and right now it only has four valence electrons.

01:48 And so this is an example.

01:50 This is the correct lewis structure for this molecule, but you can see this exception right there that according to this, it does not have its full eight valence electrons.

02:02 Let's look at another one right here...

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