Lewis Structures

What do Lewis dot symbols track?

valence electrons

What do Lewis dot symbols allow prediction of?

covalent bonding

What do the dots represent?

valence electrons

Where are these dots placed?

around the symbol of the element

True or false. The four positions around the symbol (top, bottom, left, right) are equivalent → multiple Lewis symbols are "correct". 

true

What arrangement do dot symbols show? 

ideal bonding arrangement

What are sites w/ single electrons sites for? 

bonding

What are sites w/ two electrons called? 

lone pairs

What are sites w/ no electrons called? 

vacant

True or false. Atoms tend to form ions that have a noble gas electron configuration. 

true

Does the octet rule work well for ? 

nonmetals, Group 1 and 2 metals, and aluminum

What does the octet rule not work very well for? 

transition metals

Explain the octet rule in actuality. 

C,N,O,F will add electrons until their valence shell has 8 and only 8 electrons

What is the first step in visualizing molecules? 

first convert the molecular formula to a lewis structure

What are 3 key details in Lewis structures? 

electron-dot symbols used for atoms

bonding pairs are shown as lines

lone pairs represented as pairs of dots

What rule do we apply to write Lewis structures? 

Octet rule

What do Lewis structures decide on? 

the placement of atoms in a molecule or polyatomic ion

What do Lewis structures distribute total number of valence electrons as? 

bonding pairs and lone pairs

In most cases, the electron placement is guided by what rule? 

octet rule

What does it mean for species to obey the octet rule? 

outer level of atoms contain 8 electrons

What is the 1st step in molecules with single bonds? 

place the atoms relative to each other

What atom gets placed in the center? 

the least electronegative non hydrogen

What is the 2nd step in molecules with single bonds? 

determine total number of valence electrons

What is the 3rd step in molecules with single bonds? 

draw a single bond from each surrounding atom to the central atom

What is the 4th step in molecules with single bonds? 

distribute the remaining valence electrons as lone pairs, complete the octet of each non hydrogen

True or false. For simple Lewis structures, shape matters. 

false, some molecules have multiple correct lewis structures

As long as connectivity/lone pair is the same, Lewis structures are equivalents. 

true

Hydrogen atoms form ____bond. 

1

Carbon atoms form ____bonds. 

4

Nitrogen atoms form ____bonds. 

3

Oxygen atoms form ____bonds. 

2

Surrounding (outside) halogen atoms form ____ bond. 

1

Fluorine is always a ____

a surrounding atom

True or false. Other halogens than Fluorine may be placed as the central atom occasionally. 

true

True or false. For molecules w/ multiple bonds, the 1st 4 steps stay the same and a step is added. 

true

If there are not enough electrons present for the central atom to get an octet, what must be present? 

multiple (double or triple) bond

What is the 5th step for molecules w/ multiple bonds? 

change a lone pair on a surrounding atom into a shared pair, forming a multiple bond to the central atom

Multiple Lewis structures can be written for ? 

molecules or polyatomic ions with double bonds next to single bonds

True or false. One single Lewis structure is sufficient to describe the actual structure. 

False

Some molecules are more correctly represented by two or more that describe a ____

resonance forms that describe a resonance hybrid

What do Ozone (O3 ) and other molecules/polyatomic ions require due to electron-pair delocalization? 

more than one Lewis structure for an accurate depiction

In resonance hybrids _____ are delocalized over multiple atoms (usually?). 

one lone pair and one double or triple bond (usually 3 atoms)

In ozone we have_____ paired with each ____ (bond order 1.5). 

partial bonds, single bond

True or false. for Ozone, Double bond can be placed to the left or right. 

true

Different double or triple bond and lone pair placements result in . 

resonance structures

What is one method of evaluating resonance contributors? 

determining formal charge

Define formal charge. 

charge an atom gains if bonding electrons were shared equally

What makes a resonance structure better? Why? 

resonance structures that minimize formal charges because they contribute more to the hybrid (resemble closer to the actual structure)

What is the formal charge formula? 

valence electrons- (lone pair electrons+bonds)

When assessing resonance contributors: 

1. Less formal charge =  

2. Identical formal charge on adjacent atoms is  

3. More negative formal charges should reside on more  

better

destabilizing (++ or —)

more electronegative atoms