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H2 Chemistry > Chemical Bonding > Flashcards

Chemical Bonding Flashcards

(40 cards)

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1
Q

Define metallic bond

A

electrostatic forces of attraction, between lattice of cations and sea of delocalised electrons in giant metallic substances

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2
Q

Behaviour of valence electrons in metal cation

A

Mobile and delocalised, move randomly throughout metal cations packed closely in a lattice

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3
Q

Why do metal atoms form cations easily in solid state

A

valence elctrons loosely bounded, easily removed

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4
Q

Metallic bonds are <strength> and <direction></direction></strength>

A

strong, non-directional

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5
Q

strength of metallic bond formula [proportional]

A

directly proportional to no. of valence e- available for delocalisation per atom / size of metal atm

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6
Q

Why do transition metals have stronger metallic bond than non-transition metals

A

transition metals have s and d electrons available for delocalisation, smaller cationic radius than s-block elements

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7
Q

define ionic bonds

A

electrostatic forces of attraction between oppositely-charged ions in giant ionic substances

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8
Q

ionic bonds are <direction></direction>

A

non-directional

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9
Q

define lattice energy

A

energy released when 1 mole of solid ionic compound formed from constituent gaseous ions

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10
Q

lattice energy formula [DIRECTLY PROPORTIONAL]

A

absolute of product of charges divide sum of ionic radius

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11
Q

define covalent bonds

A

electrostatic forces of attraction between shared pair of electrons and positively-charged nuclei of 2 atoms in simple and giant molecular structures

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12
Q

why is a sigma bond stronger than pi bond

A

side on overlap less effective than head-on overlap

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13
Q

how many overlapping regions for head-on and side-on overlaps

A

1 and 2 respectively

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14
Q

define dative bonds

A

electrostatic forces of attraction exist between a shared pair of electrons and nuclei of donor and acceptor atoms

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15
Q

define electronegativity

A

ability of an atom to attract shared pair of electrons towards itself in covalent bond

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16
Q

what happens when electronegativity diff between 2 atoms is similar or same [describe bond type and forces]

A

non-polar bond, electrostatic forces of attraction between each atom and shared pair of electron are equal in strength

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17
Q

what happens when electronegativity diff between 2 atoms is significant [describe bond type and forces, dipole (if applicable)]

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A

electrostatic forces of attraction between more electronegative atom and shared electron pair stronger, form permanent dipole, polar

18
Q

why is there some degree of ionic character in a polar covalent bond

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A

unequal sharing of electrons causes partial charges to be formed, dipole moment exists

19
Q

define bond dissociation energy

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A

energy required to break one mole of a particular covalent bond in a specific molecule in the gaseous state to form gaseous atoms

20
Q

how is covalent bond strength related to BDE

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A

stronger; higher

21
Q

what are the factors affecting covalent bond strength and explain

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A

bond order -> more bonds between 2 atoms in the bond, more energy break atoms apart

effectiveness of bond overlap -> covalent bond strength increase with greater orbital overlap. If covalent bonds between 2 large atoms, overlap of valence orbitals more diffused, less effective

Bond Length: dist between 2 atomic nuclei — covalent bond strength increase with decrease in bond length

Bond Polarity: Covalent bond strength increase with bond polarity -> polar bonds stronger than non-polar because of increased electrostatic forces of attraction

22
Q

why can central atoms from period 3 have more than 8 valence electrons but not period 2

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A

availability of low-lying vacant d-orbitals to accommodate electrons for bonding but period 2 max 8 electrons cannot expand octet structure

23
Q

what is vsepr theory used for

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A

predict molecular geometry of molecule or molecular ion

24
Q

what are the 2 main principles of vsepr theory

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A

electron pairs are arranged around central atom in a molecule as far as possible to minimize repulsion between them

lp-lp > lp-bp > bp-bp repulsion

25
how does electronegativity of central atom/surrounding atoms affect bond angle
more electronegative central atom increase bond angle as bond pair electrons drawn to it, increase bp-bp repulsion more electronegative surrounding atoms decrease bond angle as they pull bond pair electrons away from central, reduce bp-bp repulsion
26
why do polar covalent bonds cause partial charges induced on atoms and hence a dipole moment?
covalent bonds with ionic character, electron pair not equally shared between 2 atoms
27
why are polar bonds stronger than non-polar bonds with comparable bond length
There is additional electrostatic attraction between oppositely charged dipole
28
How does a greater extent of ionic character in a covalent bond come about and what does it lead to
greater diff in electronegativity; larger dipole moment formed
29
why are lone pair-lone pair repulsion stronger than bond pair-bond pair repulsion
lone pairs of electrons are closer to central atoms, repulsion between lone pairs stronger than that between bond pairs of electrons
30
how does covalent character in ionic bonds come about
polarisation of anion electron cloud by neighbouring cations in ionic compounds. electron density between oppositely charged ions increase
31
what are the 2 factors affecting extent of covalent character in ionic bonds and explain
polarising power of cation -> ability of cation to distort electron cloud of anion, and is proportional to charge density of cation. higher charge density higher polarizing power polarisability of the anion -> refers to how easily anion e- cloud can be distorted, is proportional to size of anion (larger anion, more polarisable)
32
Why are there discrepancies between theoretical and experimental lattice energies
covalent character in ionic bonds
33
what are id-id interactions and describe them
electrostatic forces of attraction that exist between oppositely charged poles of temporary dipoles in molecules. as molecules are in constant random motion, electron cloud of each molecule is distorted and unsymmetrically distributed, forming instantaneous dipoles. the molecule which has an instantaneous dipole can induce a temporary dipole on neighbouring molecules upon close approach
34
factors affecting id-id strength of id-id interactions
total num of e- in molecule/atom: greater total number of electrons present in molecule/atom, larger size of electron cloud. This leads to greater polarisation of e- cloud, forming stronger id-id interactions. shape of molecule (only applicable to organic compounds) if both molecules have same number of atoms (Mr/e- cloud size), linear molecule have greater surface area than branched molecule, stronger id-id.
35
what are pd-pd and describe them
pd-pd interactions refer to electrostatic forces of attraction that exist between oppositely charged permanent dipoles of polar molecules.
36
what are hydrogen bonds
electrostatic forces of attraction between hydrogen bonded already covalently bonded to a small, highly electronegative atom (F,O,N) and the lone pair of electrons on a second small highly electrongeative atom (F,O,N)
37
Why boiling point of water higher than ammonia (can apply to other)
o-h bond in water more polar than n-h bond in ammonia, as o is more electronegative than n, so hydrogen bonding more extensive than that between ammonia molecules. more energy required to overcome stronger hydrogen bonds...
38
what does hydrogen bond formation do to water [explain why ice less dense than water]
cause water to expand when it freezes as the orientation of water molecules needed to maximise intermolecular hydrogen bonds result ice having an open but rigid structure. in the solid state, 2 lone pairs of e- on O atom and 2 H atoms in each water molecule result in regular tetrahedral arrangement where water molecules are held together by hydrogen bonds. this results in open structure where water molecules are further apart in the solid state, than in liquid state, hence ice less dense than water. when ice melts, some of these hydrogen bonds broken structure less regular, pack more closely together, liquid higher density than ice at 0 degrees celcius
39
why does dimerization not occur when organic acid dissolved in water
dimerization does not occur as hydrogen bonds are formed between acid and more abundant water molecules instead of with the other organic acid molecule
40
when does dimerization take place
when organic acid in gas phase / non-polar organic solvents, hydrogen bonding between 2 organic acid molecules lead to dimerization

H2 Chemistry (5 decks)

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