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CHEMISTRY > bonding > Flashcards

bonding Flashcards

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1
Q

what is ionic bonding?

A
  • strong electrostatic forces of attraction between oppositely charged ions held in a lattice .
  • electrons transferred from metal to non metal to achieve full other shells
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2
Q

give an example of an ionic ally bonded substance .

A
  • NaCl (sodium chloride - salt)
  • sodium loses an electron and chlorine gains electron to produce ions will full other electron shell
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3
Q

how high are ionically bonded substances bp and mp? why?

A
  • high —> takes lots of energy to break strong electrostatic forces of attraction between oppositely charged ions.
  • thus, makes ionic compounds solid at room temp
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4
Q

do ionic compounds conduct electricity ? why?

A
  • yes, when molten/ in (aq) solution as ions are free to move and carry charge (don’t when solid)
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5
Q

what is simple molecular covalent bonding?

A
  • string covalent bonds between atoms, weak van der waals forces of attraction between molecules .
  • H2O, CO2 and NH3
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6
Q

what is covalent bonding?

A
  • a bond in which high two atoms share one or more pairs of electrons .
  • multiple electron pairs can be shared to produce multiple covalent bonds . + represented using dot and cross diagram
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7
Q

are there any lone electrons in simple covalent bonding ?

A
  • no- all involved in bonding
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8
Q

can simple molecular covalent molecules conduct electricity ? why?

A
  • no - all electrons used in bonding and aren’t free to move
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9
Q

do. simple molecular substances have low/high mpt and bpt? why?

A
  • low = weak van der waals forces of attraction between molecules that don’t take much energy to overcome (these are overcome rather than covalent bonds)
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10
Q

describe macromolecular covalent bonding.

A
  • lattice of many atoms held together by strong covalent bonds .
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11
Q

do substances with macromolecular covalent bonds have high/low mpt and bpts? why?

A
  • high, as it takes lots of energy to overcome many strong covalent bonds .
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12
Q

do substances with macromolecular covalent bonds conduct electricity ?

A
  • most don’t as all electrons are used in bonding .
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13
Q

what’s meant by metallic bonding ?

A
  • consisted of a lattice of positively charged bed ions surrounded by a “sea” of delocalised electrons.
  • produces very strong electrostatic force of attraction between these oppositely charged ions.
  • layers slide over each other = malleable
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14
Q

do metallic compounds have high/low bpt and mpts? why?

A
  • high = strong forces of attraction between positive metal ions + negatively charged sea of delocalised electrons
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15
Q

do metallic compounds conduct electricity? why?

A
  • yes as delocalised electrons can move throughout the metal to carry charge
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16
Q

how does the strength of metallic bonds change across the periodic table ? why ?

A
  • increases —> higher melting and boiling points , stronger
  • higher charge on metal ions
  • more delocalised electrons per ion
  • stronger force of attraction between them
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17
Q

define electronegativity.

A
  • the ability of an atom to attract the pair of electrons (electron density) in a covalent bond
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18
Q

what affects electronegativity ?

A
  • nuclear charge
  • atomic radius
  • electron shielding

—> increases along period as atomic r decreases and decreases down group as shielding increases

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19
Q

what is the most electronegative element ?

A
  • fluorine (4.0 on Pauling’s scale) = largest nuclear charge for its electron shielding, small atomic radius
20
Q

how do you get a nonpolar bond?

A
  • both bonding elements have the same electronegativities
  • if it has a symmetrical geometry - polar bonds will cancel each other out
21
Q

when do you get a polar bond?

A
  • bonding atoms have different electronegativities .
22
Q

what’s the strongest type of inter-molecular force ?

A
  • hydrogen bonding
23
Q

explain what’s meant by hydrogen bonding .

A
  • type of permanent dipole-dipole interaction.
  • attraction between hydrogen on one molecule with an electronegative atom (O2, nitrogen / fluorine) on another molecule
  • anything with -OH can form hydrogen bonds
24
Q

what conditions are needed for hydrogen bonding to occur?

A
  • O-H, N-H, F-H bond, lone pair of electrons on O, F, B as O, H and D are highly electronegative , H nucleus is left exposed
  • strong force of attraction between H nucleus and Lone pair of electrons on O, N, F
25
Q

why is ice less dense than liquid water ?

A
  • in liquid water, hydrogen bonds constantly break and reform as molecules move about
  • in ice, hydrogen bonds hold molecules in fixed positions ; makes them slightly further apart than in liquid water .
26
Q

what’s the weakest type of inter-molecular force ?

A
  • van der waals forces
27
Q

describe van der waals forces of attraction.

A
  • temporarily dipoles area created by random movements of electrons —> induced dipole in neighbouring molecules —> temporary induced dipole-dipole attraction aka van der waals forces of attraction
  • larger Mr of molecule, stronger intermolecular forces , straight chain molecule have stronger VDWF than branched chain molecule as they line up and pack close together
    —> reduced distance over which force acts so stronger
28
Q

are van der waals stronger in smaller or larger molecules ?

A
  • larger = more electrons
29
Q

describe permanent dipole-dipole attraction / interaction

A
  • forces of attraction between those dipoles and those neighbouring molecules .
  • always slight charge difference in bond polarity resulting from presence of electronegative atom
  • slightly positive region on one atom attracted to slightly negative region on another atom of diff molecule .
30
Q

describe induced dipole-dipole interactions .

A
  • random and uneven distribution of electrons within a molecule .
  • uneven distribution of electrons temporarily creates regions that’s slightly positive + other regions slightly negative = instantaneous dipole .
  • temp creates a dipole in that second molecule = induced dipole
31
Q

what are the two main categories of intermolecular forces ?

A
  • forces of attraction between different molecules = when simple covalent substance changes state -> the weak intermolecular forces that need to break not covalent bonds within molecule .

1) permanent dipole-dipole interactions (hydrogen bonding )
2) induced dipole dipole interactions/London dispersion forces ( Van der waals)

32
Q

what is a dative/ co-ordinate covalent bond? when is it formed?

A
  • formed when both electrons come from same species
  • formed when electron deficient atom/ion accepts a lone pair of electrons from an atom/ion with a lone pair of electrons (not used in bonding )
33
Q

explain average bond enthpies .

A
  • measure the strength of a covalent bond
  • average amount of energy required to break the bond
34
Q

what does the shape of molecules depend on?

A
  • number of electrons in the valence shell of the central atom.
  • number of these electrons which are in bonded or lone pairs
35
Q

what does the electron pair repulsion theory state ?

A
  • that electron pairs will take up position as far away from each other as possible , to minimise the repulsive forces between them.
36
Q

describe the lone pair repulsion.

A
  • any line pairs present around central atom provide additional repulsive forces—> changed the bond angle
  • for every line pair present - bond angle between covalent bonds is reduced by 2.5 degrees
37
Q

which experience the most repulsion?

A
  • LP-LP repulsion strongest
  • LP-BP repulsion middle
  • BP-BP repulsion weakest
  • lone repels more than bonding pairs so lone pair-lone angles largest as lone pairs in orbitals which shorter + rounder the orbitals that bonding pairs occupy (take more space)
38
Q

what is the shape, diagram and bond angle in a shape with 2 bonded pairs and 0 lone pairs?

A
  • linear
  • 180 degrees
39
Q

what’s the shape, diagram and bond angle in shape with 3 bonded pairs and 0 lone pairs ?

A
  • trigonal planar
  • 120 degrees
40
Q

what’s the shape, diagram and bond angle in shape with 4 bonded pairs and 0 lone pairs ?

A
  • tetrahedral
  • 109.5 degrees
41
Q

what’s the shape, diagram and bond angle in shape with 5 bonded pairs and 0 lone pairs ?

A
  • trigonal bipyramid
  • 90 and 120 degrees
42
Q

what’s the shape , diagram and bond angle in a shape with 6 bonded pairs and 0 lone pairs ?

A
  • octahedral
  • 90 degrees
43
Q

describe the structure of diamond .

A
  • 3D tetrahedral structure of C atoms , with each C atom bonded to 4 others
44
Q

describe the structure of graphite .

A
  • similar to diamond - macromolecular covalent - but each C atom is only bonded to 3 others, so it is in layers
  • weak van der waals forces of attraction between layers mean they slide over each other - soft, slippery
  • one electron from each carbon is delocalised = and carry charge - conducts electricity .
45
Q

explain how to determine the shape of molecule.

A

1) find the number of electron pairs

2) determine how many of the pairs are bonding pairs and how many are lone pairs

3) bonding pairs indicate basic shape and lone pairs indicate any additional repulsion.

46
Q

what does an instantaneous dipole mean?

A
  • a dipole (molecule/ion with positive charge in one part + negative charge in another) that’s lasts for only an instant .

CHEMISTRY (12 decks)

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