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Summary

In this educational video, the host explains deviations from the octet rule in chemistry. The octet rule typically states that atoms strive to achieve 8 electrons in their valence shell, but some compounds, like BF₂, BCl₃, PCl₅, ClF₃, and NO₂, do not follow this rule. The video covers three types of deviations: incomplete octet (where the atom has fewer than 8 valence electrons), expanded octet (where the atom has more than 8 valence electrons), and odd-electron species (with an odd number of electrons). Through clear examples and step-by-step explanations, the host helps viewers understand these complex concepts.

Takeaways

• 😀 The octet rule in chemistry states that atoms bond to achieve 8 valence electrons, similar to the noble gases in group 8A.
• 😀 Some compounds are stable but do not follow the octet rule, which are referred to as deviations from the octet rule.
• 😀 One type of deviation is an incomplete octet, where the central atom is surrounded by fewer than 8 valence electrons.
• 😀 An example of an incomplete octet is BF2, where boron (B) has fewer than 8 valence electrons after bonding with fluorine (F).
• 😀 Another example of incomplete octet is BCl3, where boron (B) also ends up with fewer than 8 electrons after bonding with chlorine (Cl).
• 😀 The second type of deviation is the expanded octet, where the central atom has more than 8 valence electrons, typically for elements in period 3 or higher.
• 😀 An example of an expanded octet is PCl5, where phosphorus (P) forms bonds with 5 chlorine (Cl) atoms, resulting in more than 8 electrons around phosphorus.
• 😀 ClF3 is another example of an expanded octet, where chlorine (Cl) has more than 8 valence electrons after bonding with fluorine (F).
• 😀 The third type of deviation is odd-electron species (radicals), which occurs when the molecule has an odd number of electrons, leaving at least one atom without an octet.
• 😀 NO2 is an example of an odd-electron species, where nitrogen (N) has an unpaired electron, causing a deviation from the octet rule.

Q & A

What is the purpose of atoms forming chemical bonds according to the octet rule?

Atoms form chemical bonds to achieve stability by having a full outer shell of electrons, typically with 8 electrons, known as the octet, or in some cases 2 electrons, called a duplex for atoms like helium.

What is meant by an 'incomplete octet'?

An incomplete octet refers to molecules where the central atom is surrounded by fewer than 8 electrons in its valence shell, making it not satisfy the typical octet rule.

Can you give an example of a molecule that has an incomplete octet?

An example is **BF2** (boron difluoride), where the boron atom only has 6 electrons in its valence shell, which is less than the octet.

Why does **BCl3** violate the octet rule?

**BCl3** violates the octet rule because the boron atom, the central atom, only has 6 electrons in its valence shell, despite sharing electrons with chlorine atoms.

What is an 'expanded octet'?

An expanded octet occurs when the central atom in a molecule has more than 8 electrons in its valence shell, which typically happens for atoms in period 3 or beyond on the periodic table.

Which molecule is an example of an expanded octet?

**PCl5** (phosphorus pentachloride) is an example where the phosphorus atom has 10 electrons in its valence shell, which is more than the standard octet.

How does **ClF3** (chlorine trifluoride) exhibit an expanded octet?

**ClF3** shows an expanded octet because the chlorine atom is surrounded by more than 8 electrons in its valence shell, which exceeds the typical octet rule.

What are 'odd-electron species' in chemistry?

Odd-electron species are molecules where the total number of electrons in the structure is odd, making it impossible to satisfy the octet rule for all atoms in the molecule.

Can you explain why **NO2** (nitrogen dioxide) is an odd-electron species?

**NO2** is an odd-electron species because the total number of electrons is 17, which is odd. As a result, the nitrogen atom cannot have a complete octet, and at least one electron is unpaired.

Why are the deviations from the octet rule significant in understanding molecular structure?

Understanding deviations from the octet rule is important because it helps predict and explain the bonding behavior and stability of molecules that do not follow the standard octet configuration, which is common in many chemical compounds.