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IB Chemistry > chem bonding– the covalent model > Flashcards

chem bonding– the covalent model Flashcards

1
Q

define covalent bonding

A

the electrostatic FOA between the nucleus of each of the 2 bonded atoms and their shared pair of e-

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2
Q

what is another name for dative bond

A

coordinate bond

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3
Q

what are dative bonds

A

the covalent bond established by the donation of an e- pair from one atom to another

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4
Q

to form a dative bond,
1. the donor atom must contain ______________________
2. and the acceptor atom must have a _______________

A
  • lone pair of e-
  • vacant orbital
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5
Q

what are the exceptions to the Lewis structure?

A

BCl3 -> only 6 valence e-
BeCl2 -> only 4 valence e-

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6
Q

what type of orbital overlap do sigma bonds have? (letters)

A

s-s, p-p, s-p

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7
Q

pi bonds are the _______ overlap of ______ orbitals

A

side on, p

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8
Q

draw a sigma bond

A

-

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9
Q

draw a pi bond

A

-

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10
Q

is the pi or sigma bond stronger?

A

sigma

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11
Q

why is the sigma bond stronger

A

it has head on overlap of orbitals

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12
Q

does the covalent bond strength decrease or increase down the group?

A

decrease

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13
Q

why does the strength of covalent bonds down the group decrease?

A
  • the atomic radius incr
  • effectiveness of orbital overlap decr
  • thus strength decr
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14
Q

the stronger the bond, the [shorter/longer] the bond length

A

shorter

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15
Q

across the period, electronegativity [incr/decr]
down the group, electronegativity [incr/decr]

A

increases
decreases

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16
Q

why can some central atoms expand their octet?

A

these elements can utilise their energetically accessible vacant 3d orbitals

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17
Q

what is the bond angle of a molecule that is trigonal planar, bent

A

less than 120º

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18
Q

what is the bond angle of a tetrahedral molecule

A

109.5º

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19
Q

the bond angle of a tetrahedral trigonal pyramidal molec is [greater/lesser] than a tetrahedral bent molec

A

greater

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20
Q

if an atom has 5 electron pairs what is its electron domain geometry?

A

trigonal bipyramidal

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21
Q

how many bond pairs on the central atom would lead to a see-saw shape?

A

4

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22
Q

draw the orbitals involved in the hybridisation of a carbon atom in methane

A

-

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23
Q

why does diamond have very high m.p.?

A
  • each C atom is covalently bonded to 4 other C atoms in a tetrahedral shape
  • has strong and extensive C-C covalent bonds throughout giant covalent lattice
    • reqs large amts of energy to break
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24
Q

can diamond conduct electricity and why?

A

no, no mobile ions/e-

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25
Q

does Si or diamond have lower m.p.? (3)

A
  • Si as it is lower than C in periodic table
    • thus larger atomic radius
  • Si-Si bonds poorer extent of orbital overlap than C-C bonds
    • thus cov bonds weaker than diamond
  • less energy needed to break bonds
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26
Q

why can graphite conduct electricity?

A
  • has delocalised e-
  • act as mobile charge carriers
  • can conduct electricity parallel to its layers
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27
Q

why is graphite an effective lubricant?

A
  • layers held by weak LDF
  • thus layers can slide over e/o
28
Q

why can graphene conduct electricity?

A
  • has delocalised e-
  • act as mobile charge carriers
29
Q

is C60 a giant molecule?

A

no

30
Q

why is C60 a poor conductor of electricity

A
  • charge carriers confined within C60 molecule
  • unable to move fr molec to molec to act as charge carriers
31
Q

what is electronegativity

A

the tendency of an atom to attract a shared pair of e- in a covalent bond toward itself

32
Q

why does electronegativity incr across the period

A
  • incr nuclear charge
  • shielding effect remains relatively constant
  • incr ENC
  • thus incr electronegativity
33
Q

why does electronegativity decr down the group

A
  • incr atomic radius
  • incr shielding effect
  • decr ENC
  • thus decr electronegativity
34
Q

IMFOA are responsible for the ___________ properties of simple molecules.

A

physical

35
Q

IMFOA contributes to the _________ of substances, while the extent of orbital overlap contributes to the ___________ of the ______________ in the substance

A

m.p., strength, covalent bonds

36
Q

the weakest IMFOA are…

A

LDF

37
Q

what’s another name for dpdp forces

A

(permanent dipole) pdpd attractions

38
Q

why does LDF increase down the group?

A
  • e- cloud incr
    • more easily polarisable
  • thus stronger LDF
39
Q

what is the criteria for H bonding?

A
  • one molec must have H atom bonded to FON
  • other molec must have lone pair of e- on FON
40
Q

what affects the strength of the hydrogen bond? (2)

A
  1. electronegativity difference
  2. extensiveness of H bonding
41
Q

how does the difference in electronegativity affect the strength of H bonding?

A
  • greater the e- diff -> greater polarity
  • thus stronger H bond
42
Q

the _______ the number of H bonds formed __ molecule, the more ____________ and stronger the H bonds

A

greater, per, extensive

43
Q

why would a covalent compound be less volatile?

A
  • cmpd has stronger IMF
  • thus lower volatility
44
Q

why can ionic solutes dissolve in polar solvents?

A
  • a lot of energy released from strong ion-dipole interactions
  • thus sufficient to overcome energy between solvent molec
45
Q

what is the formula for Rf value?

A

Rf = dist travelled by substance/dist travelled by solvent

46
Q

how do you measure the distances in calculating Rf value in chromatography?

A

from the origin (start line)

47
Q

recap: what is resonance?

A

delocalisation of π e- in a system

48
Q

species that have resonance have identical_______ and ________

A

bond lengths and strengths

49
Q

what is the formula for formal charge?

A

V - 1/2B - L

V=no. valence e- in unbonded atom
B= no. of e- in bonding domains
L= no. of e- in non-bonding domains

50
Q

the most stable structure would be when all formal charges = __

A

0

51
Q

what is lattice energy? (short defin.)

A

the amt of energy needed to break an ionic cmpd into the constituent gaseous ions

52
Q

what affects the strength of the ionic bond?

A

lattice energy

53
Q

what is the formula for lattice energy?

A

-

54
Q

why do ionic compounds have a high melting point?

A
  • strong electrostatic FOA btw oppositely charged ions
  • large amts of energy is req to overcome
55
Q

are ionic compounds good conductors of electricity?

A
  • only in aqueous and molten state
    • mobile ions can act as charge carriers
  • in solid no
    • ions are held in a fixed lattice
56
Q

why would an ionic compound shatter if I drop it?

A
  • brittle
  • ions of the same charges will be forced next to eo -> repel eo
  • causes lattice structure to break
57
Q

why is there covalent character in all ionic compounds

A
  • cation can polarise the e- cloud of the anion
  • results in a degree of e- sharing
  • thus covalent character exists in all ionic cmpds
58
Q

what is metallic bonding?

A

the electrostatic FOA between metal cation and the sea of delocalised e-

59
Q

what is the structure of a metal?

A

giant metallic lattice

60
Q

electrostatic FOA exist in…

A

metals, ionic cmpds, covalent cmpds

61
Q

draw a diagram of the bonding in Al

A

-

62
Q

what is the formula for charge density?

A

-

63
Q

why is the m.p. of Na lower than Mg

A
  • Na has fewer no. of cations that delocalise into the sea of e-
  • thus less metallic bonding
  • lesser energy needed to break
64
Q

why are metals ductile?

A
  • when a large force is applied
  • layers of metal cations slide over eo w/o disrupting e metallic bonds
65
Q

why are metals good conductors of heat?

A
  • delocalised e- and cations are closely packed together
  • efficient transfer of heat

IB Chemistry (7 decks)

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