Write Lewis structures that obey the octet rule for the following species. Assign the formal cha

Write Lewis structures that obey the octet rule for the...

Key Concepts

Formal Charge Calculation

Formal charge is a bookkeeping tool used to estimate the distribution of electrons in a molecule. It is calculated by comparing the number of valence electrons in an isolated atom to the number assigned to the atom in the molecule (taking into account bonding and lone pair electrons). Minimizing formal charges across a molecule often leads to more stable and representative structures.

Valence Electrons

Counting valence electrons is a crucial step in drawing Lewis structures. The total number of valence electrons available in a molecule or ion is determined by summing the valence electrons of each atom, adjusted for any positive or negative charges present. This count guides the placement of electrons as bonding pairs or lone pairs in order to satisfy the octet rule.

Resonance Structures

Resonance structures are multiple valid Lewis structures for a single molecule that differ only in the distribution of electrons rather than the arrangement of atoms. These structures contribute to the overall hybrid, providing a better representation of the electron delocalization within the molecule. Recognizing resonance helps in understanding the stability and reactivity of the species.

Lewis Structures

A Lewis structure is a diagram that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist. It represents the arrangement of valence electrons and helps in predicting the molecule’s geometry and reactivity. The structure is drawn by linking atoms with chemical bonds and placing the remaining electrons as lone pairs on the appropriate atoms.

Octet Rule

The octet rule states that atoms tend to form structures in which each atom has eight electrons in its valence shell, similar to the electron configuration of a noble gas. This rule is used as a guideline for predicting the structure of molecules and ions, particularly for main-group elements, although there are important exceptions.

Transcript

00:01 Problem 105 says to draw the lewis structure that obeys the octet rule for each of the following.

00:06 So the first is a central phosphorus bound to an oxygen, a chlorine on each of the remaining sides.

00:26 So because the central phosphorus already has its octet rule to obeyed, meaning that it has eight surrounding electrons, the remaining electrons of the 32 here, five from phosphorus, six from oxygen, making 11, and then an additional 21 from these seven each from chlorine.

00:51 Each of those remaining electrons has to go around the oxygen and chlorines.

01:01 So in total here we have eight electrons surrounding each of these atoms.

01:07 Atoms, meaning that each of the atoms obeys the octet rule, and this is the appropriate structure.

01:15 The problem also says to tell the formal charges of each of the central atoms.

01:19 And so in this case, because phosphorus in its atomic form has five valence electrons, and we only have four valence electrons here, the central atom has a positive one charge.

01:34 So next we have the sulfate ion, which is a central sulfur.

01:39 Surrounded by four oxygens.

01:48 And so because, again, this central sulfur here already obeys the octet rule, the remaining of the 32 electrons here has to surround each of these oxygens.

02:19 So in this case, because, like i said, the central, i don't think i said it, sorry, the central sulfur, typically like oxygen, has six valence electrons.

02:31 It's essentially too short here, meaning that has a positive two formal charge.

02:39 Now, the negative to ionic charge here comes from the fact that each of these oxygens, having seven valence electrons instead of six, has sort of one extra, making each of the surrounding oxygens have a negative one formal charge.

02:55 And so it's interesting about the remaining molecules that you see on this screen, or ions and molecules that you see on this screen, are that the general structures that each of them is the same.

03:18 So for the perchlorate ion here, you have essential chlorine surrounded by four oxygens, the valence around each of the oxygens is three lone pairs...

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