Lewis Structures Lecture Flashcards

Compendium of 100 flashcards based on lecture notes covering Lewis symbols, bonding rules, formal charges, exceptions to the octet rule, and resonance.

How many valence electrons do noble gases have?

$$8$$

What tool is used to keep track of the valence electron configurations of atoms and monoatomic ions?

Lewis dot symbols

What is the electron configuration for oxygen as stated in the notes?

$$1s^22s^22p^4$$

How many valence electrons does oxygen have?

$$6$$

How are valence electrons added to a Lewis symbol?

One at a time in the four cardinal directions

Which atoms are listed in the notes for drawing Lewis symbols after oxygen?

Boron, carbon, fluorine, and neon

What is one example of an ionic compound shown with Lewis symbols?

$$CaS$$

What do Lewis symbols illustrate the formation of in species like calcium and sulfur?

Cations and anions

What is the primary use of Lewis dot structures?

To show how atoms in covalent compounds share electrons

What is the octet rule?

The desire for most atoms in a covalent molecule to have $8$ valence electrons

What is the duet rule?

The desire for certain atoms, like hydrogen, to have only $2$ valence electrons

What is a shared pair of electrons in a covalent molecule called?

A bonding pair

How is a bonding pair usually represented in a structure?

By a line (dash)

What is a pair of electrons associated with only one atom called?

A lone pair

What diatomic halogens are mentioned as examples for Lewis structures?

Chlorine

What type of bond does oxygen ($O_2$) utilize?

A double bond

How many bonding pairs are shared in a double bond?

Two bonding pairs

How do double bonds compare to single bonds in terms of length?

They are shorter

How do double bonds compare to single bonds in terms of strength?

They are stronger

What type of bond does nitrogen ($N_2$) utilize?

A triple bond

How many bonding pairs are shared in a triple bond?

Three bonding pairs

How do triple bonds compare to double bonds?

They are even shorter and stronger

When determining total valence electrons, what must be done for cations?

Subtract one electron for each positive charge

According to the transcript, what must be done for anions when calculating valence electrons?

Add one electron for each positive charge

What is the first step in drawing a more complicated Lewis structure?

Determine the total number of valence electrons

In a skeletal structure, where are hydrogens always placed?

Terminal positions

Where are the most electronegative atoms usually placed in a skeletal structure?

Terminal positions

Where are the least electronegative atoms usually placed in a skeletal structure?

Center positions

How many electrons are subtracted from the total valence count for every single bond used to connect atoms?

$2$ electrons

In what order should remaining valence electrons be distributed as lone pairs?

Starting with the most electronegative atoms first

If valence electrons remain after filling octets for terminal atoms, where are they placed?

On the central atom

What is step 6 if an atom does not have an octet after all electrons are distributed?

Rearrange the electrons of the outer atoms to make double/triple bonds with the central atom

How many valence electrons are in $SiH_4$?

$$4 + 4(1) = 8$$

How many valence electrons are in $CO$?

$$4 + 6 = 10$$

How many valence electrons are in $OF_2$?

$$6 + 2(7) = 20$$

What is significant about how $CH_3CH_2NH_2$ is written?

It is written with atoms separated on purpose to give clues about the skeletal structure

What is the valence electron total for $CH_3CH_2NH_2$?

$$5 + 2(4) + 7(1) = 20$$

How many valence electrons are in $NH_4^+$?

$$5 + 4(1) - 1 = 8$$

How many valence electrons are in $CO_3^{2-}$?

$$4 + 3(6) + 2 = 24$$

In an oxyacid like $H_2CO_3$, where are the hydrogens attached?

The hydrogens are attached to the oxygens

What is formal charge?

The hypothetical charge an atom would have if bond electrons were redistributed evenly between the two atoms

What is the required sum of all formal charges in a neutral compound?

Zero ($0$)

What should the sum of all formal charges in an ion equal?

The charge of the ion

What is the formal charge of Carbon in Carbon Monoxide ($CO$)?

$$4 - (2 + 3) = -1$$

What is the formal charge of Oxygen in Carbon Monoxide ($CO$)?

$$6 - (2 + 3) = 1$$

What is the formal charge of Iodine in $ICl_4^-$?

$$7 - (4 + 4) = -1$$

What is the formal charge of Chlorine in $ICl_4^-$?

$$7 - (6 + 1) = 0$$

What is the most useful application of formal charge?

To determine the best possible Lewis structure

Which formal charge distribution is most preferable in a molecular structure?

A structure with all zero formal charge

If nonzero formal charges are necessary, which arrangement is better?

The one with the fewest nonzero formal charges

What relationship between adjacent formal charges is preferable?

When adjacent formal charges are zero or the opposite sign

When choosing between similar formal charge distributions, where should negative charges be placed?

On the most electronegative atoms

How many valence electrons are used to draw the Lewis structure of $CO_2$?

$16$ valence electrons

How many valence electrons are used to draw the Lewis structure of $SCN^-$?

$16$ valence electrons

Between Sulfur ($S$) and Nitrogen ($N$), which is more electronegative?

Nitrogen ($N$)

What is the term for molecules that contain an odd number of electrons?

Free radicals

What example of an odd-electron species is provided in the notes?

Nitrogen monoxide ($NO$)

Why are free radicals typically unstable and reactive?

They would prefer to have complete octets

What are electron-deficient molecules?

Molecules containing central atoms that do not have a filled valence shell

How many valence electrons does Boron typically have in stable compounds?

Six ($6$) valence electrons

Which metal follows the same electron-deficient trend as Boron?

Aluminum

What choice must be made when drawing $BCl_3$ regarding the octet?

Whether to leave $B$ without an octet or give $Cl$ a positive charge

How many electrons does Beryllium have around it in compounds?

Four ($4$) electrons

Why are no more electrons given to the central atom in $BeH_2$?

There are no more electrons to give away

What is another name for expanded octet molecules?

Hypervalent molecules

Why do first period elements only seek duets?

They only have a $1s$ orbital

What orbitals allow second period elements to accommodate 8 electrons?

$2s$ and $2p$ orbitals

What orbitals allow third period elements and beyond to expand their octets?

$d$ orbitals

How many valence electrons are in $XeF_2$?

$22$ electrons

How many valence electrons are in $XeF_6$?

$50$ electrons

Why do chemists expand the octet of a central atom from the third row or beyond?

To lower the total number of formal charges

How many valence electrons are in sulfuric acid ($H_2SO_4$)?

$32$ electrons

What is the general practice for third-row elements regarding formal charge?

Expand all octets due to formal charge

What are resonance structures?

Two or more Lewis structures with the same arrangement of atoms that can be written for a molecule

What characterizes energetically equivalent resonance structures?

Same formal charges and same bonds between atoms

What does experimental evidence show about the bonds in the carbonate ion ($CO_3^{2-}$)?

All three $C-O$ bonds have the same strength and length and are identical

What is the resonance hybrid?

The actual electronic structure of a molecule, which is the average of its resonance structures

How does the Lewis model simplify electron placement?

It treats electrons as being localized on one atom or between atoms

What is delocalization?

When electrons are spread over several atoms or bonds rather than being localized

What is the physical effect of delocalization on a molecule?

It lowers the electron's energies and stabilizes the molecule

In a the nitrate ion resonance hybrid, where are the extra electrons of the double bond?

Delocalized over the entire molecule

Which species is the first practice problem for drawing the best Lewis structure?

$$HClO_3$$

Which species is the second practice problem?

$$NO_2^-$$

Which species is the third practice problem?

$$BrF_5$$

Which species is the fourth practice problem?

$$BF_3$$

Which species is the fifth practice problem?

$$NO_2$$

Which species is the sixth practice problem?

$$BeF_2$$

Which species is the seventh practice problem?

$$CCl_4$$

Which species is the eighth practice problem?

$$PBr_5$$

Which species is the ninth practice problem?

$$SF_6$$

Which species is the tenth practice problem?

$$BH_2^-$$

Which species is the eleventh practice problem?

$$ClF_4^+$$

Which species is the twelfth practice problem?

$$SF_5^-$$

Which ion is the thirteenth practice problem focusing on resonance?

Cyanate ion ($CNO^-$)

Which ion is the fourteenth practice problem focusing on resonance?

Formate ion ($CHO_2^-$)

Which ion is the fifteenth practice problem focusing on resonance?

Sulfite ion ($SO_3^{2-}$)

What was the lecture title on the first page?

Lewis Structures - filled

What was the date listed on most pages of the lecture notes?

Tuesday, October 17, 2023

What is the purpose of step 5 in the Lewis structure rules?

To check that every atom has an octet (or a duet if $H$)

In $BCl_3$, what rule governs whether to complete the octet using double bonds?

Formal charge