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CHEM 1000 > Lewis Structures > Flashcards

Lewis Structures Flashcards

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1
Q

What are types of chemical bonds? Explain each briefly.

A

ionic: electron transferred from metal to non-metal

covalent: electron shared between non-metals

metallic: valence electrons delocalized over many metal nuclei

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2
Q

What are the steps to drawing a lewis structure?

A
  1. calculate total number of valence electrons
  2. identify central atom
  3. draw a signle bond between each atom
  4. calculate remaining electrons
  5. distribute remaining electrons in pairs around the terminal atoms, then central atom
  6. if any atoms don’t have octets then make double or triple bonds
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3
Q

How can you identify the central atom?

A

atom with lowest group number

if in same group then atom with higher period is central

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4
Q

How many valence electrons are in each group?

A

group 1: 1 ve
group 2: 2 ve
group 13: 3 ve
group 14: 4 ve
group 15: 5 ve
group 16: 6 ve
group 17: 7 ve

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5
Q

When drawing lewis structures of polyatomic ions what is different?

A

add or subtract electrons to total ve count

draw square bracket to indicate charge

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6
Q

What is the born-haber cycle used for?

A

estimate lattice energy

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7
Q

What are the five reactions used in born haber cycle?

A

1.sublimation reaction of metal (solid to gas)
2. bond energy (breaking bond between diatomic molecule)
3. ionization of gaseous metal (removing electron)
4. electron affinity (adding electron to nonmetal)
5. formation of ionic compound from gaseous ions

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8
Q

How do you solve a born haber cycle?

A

find enthalpy of formation for the compound from solid metal and gas nonmetal

rearrange equation to find lattice energy

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9
Q

What is equation used to solve born haber cycle?

A

enthalpy of formation=(enthalpy of sublimation)+(enthalpy of IE)+(enthalpy of BE)+(enthalpy of EA)+(enthalpy of LE)

rearrange to find LE

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10
Q

What is trend for lattice energy?

A

magnitude decreases going down a column (less exothermic)
as magnitude of charges increases so does lattice energy

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11
Q

What is bond energy?

A

amount of energy required to homolytically break 1 mol of bonds between two atoms in the gas phase

homolytically means electrons in covalent bond are divided equally

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12
Q

Is bond energy positive or negative? Why?

A

positive

takes energy to break a bond

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13
Q

How can you use bond energy to caluclate enthalpy of a reaction?

A

break all bonds in the reactants and find all the values and add them together

break all bonds in products and find values and add them together and then make it negative

add these two values together

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14
Q

What happens when a bond get longer?

A

generally it gets weaker

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15
Q

What causes a polar covalent bond?

A

unequal sharing of electrons (one atom is more electronegative)

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16
Q

What is electronegativity?

A

measure of an atom’s ability to attract
electron towards itself in a chemical bond

17
Q

What is the trend for electronegativity?

A

is decreases down a column and increases from left to right

18
Q

What are the values for a difference in electronegativity for each bond?

A

0-0.4 is covalent
0.4-2.0 is polar covalent
above 2 is ionic

19
Q

What are resonance structures? What are resonance hybrids? How are they drawn?

A

resonance structures are the different possibilities for the compound structure (drawn with arrow pointing between)

resonance hybrid have characteristics of all resonance structures (drawn with dashes to represent the possible bonds)

20
Q

What is electron delocalization?

A

electrons go around the entire molecule

21
Q

How can you calculate formal charge?

A

of ve-# of bonding electrons-1/2 bonded electrons

(take number of ve and count backwards for each electron/bond)

22
Q

What can formal charges be used for?

A

comparing resonance structures to figure out the most dominant one

23
Q

What is the optimal formal charge rules?

A

as many atoms as possible have full octets

magnitudes of formal charges as small as possible

negative formal chrages on most electronegative atom

24
Q

What is a free radical? What does this usually mean?

A

an electron that is unpaired

more reactive

25
Q

Why do some compounds have incomplete octets when resonance structure do not?

A

incomplete octet is more favourable (formal charge)

26
Q

What are hypervalent compounds? What can do this?

A

exceed octet rule

third row or lower

usually large central atom with more electronegative terminal atoms

27
Q

What are ionic resonance strucutes?

A

can be drawn without expanded octet but introduce charges

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