Chem Bonding Flashcards
What are metallic bonds & their strength
Metallic bonds are strong electrostatic forces of attraction between cations & sea of delocalised e- in a giant metallic lattice structure
Strength directly proportional to :
**No. of valence e- **
Charge density of cation
Structure -> Properties of metal
What
What are ionic bonds
Strong electrostatic forces of attraction betw. oppositely charged ions in giant ionic lattice structure
Factors affecting ionic bond strength
**Lattice energy **
(directly proportional to ion charge,
indirectly proportional to ionic radius)
Physical properties of giant ionic structure
- High MP & BP
- Large amt of energy req. to overcome strong electrostatic FOA betw opp. charged ions - Good conductor of elec
- Molten & aqueous free mobile ions present to conduct elec
- ions can only vibrate about fixed positions in solid (no free mobile e-) - Soluble in polar solvents, insoluble in non polar
- Energy released in formation of ION-DIPOLE interactions betw ions & water sufficient to overcome ionic bonding betw cations & anions in crystal lattice
(Insoluble in non polar solvents due to absence of ion dipole interactions (solute-solvent interactions) to overcome strong ionic bonds in crystal lattice)
- Hard & brittle
Hard: opp. Charged ions held by strong electrostatic FOA
Brittle: Stress applied causes sliding of layers thus ions of similar charges come tgt, resultant repulsion shatters ionic structure
What are Covalent bonds (also dative)
Electrostatic attraction betw. Shared pair of e- & positively charged nuclei
Sigma (head-on overlap, e- density of sigma bond conc. Between nuclei of bonding atoms)
Pi (side-on overlap (cannot be s orbital))
When atoms form multiple bonds
Sigma stronger & more stable than pi, more effective orbital overlap
Hence sigma always formed before pi
Factors affecting covalent bond strength (Bond energy)
- Bond order: Triple>double>single
- Bond length: Shorter dist betw nuclei, greater extent of overlap betw orbitals (larger orbitals are more diffused, lower accumulation of e- density)
- Bond polarity (difference in EN pdpd forces)
What are dative bond
Covalent bond where shared pair of e- provided by only 1 of bonded atoms
Donor has at least 1 lone pair
Acceptor must have vacant & energetically accessible orbital (e- deficient)
What are ionic bonds w covalent character
AlCl3 Vs AlF3
BeCl2 Vs BeF2
Caused by distortion/polarisation of anion e- cloud by cation
Small + Highly charged cation Al3+ high charge density strong polarising power
Polarisess large Br- e- cloud to large extent greater polarisability
Polarisation of significant extent -> covalent character
Physical properties of GMS
- High MP & bp
Large ant energy req. Overcome strong & EXTENSIVE covalent bonds in giant 3d molecular structure - Non conductor of elec
- Hard (same as high MP BP)
- Insoluble in polar & non polar
- absence of strong solute-solvent forces that overcome strong covalent bonding of atoms in 3d (solute solute)
What are the VSEPR theory
- e- pairs around central atom arrange themselves as far as possible to minimise repulsion
- Strength of repulsion
1) LPLP > LPBP >BPBP
Shapes of 2 e- pair
2 BP 0LP
Linear 180°
BeCl2
Shapes of 3 e-pair
3 BP 0LP
Trigonal Planar 120°
BF3
2BP 1LP
Bent 119°
SnCl2
Sha
Shapes of 4 e- pair
4BP 0LP
Tetrahedral 109.5°
CH4
3BP 1LP
trigonal pyramidal 107°
NH3
2BP 2LP
Bent 104.5°
H2O
Shapes of 5e-pair
5BP 0LP
Trigonal bipyramidal 120° plane 90° perpendicular
PCl5
4BP 1LP
see-saw 119° plane <90° perpendicular
SF4
3BP 2LP
T shaped <90° on perpenidicular axis
ClF3
2BP 3LP
linear 180°
Shapes of 6e- pair
6BP 0LP
Octahedral 90°
SF6
5BP 1LP
Square pyramidal <90°
IF5
4BP 2LP
Square planar 90°
XeF4
Polarity
How equal e- shared betw atoms:
Difference in EN
- Bonding e- not equally shared
Affects Bond energy
- Permantent partial separation of charges -> difference in EN -> Dipole moment
IDID forces
Weakest, betw non polar
PDPD forces
Betw polar moleq,
For similar e- cloud size, relatively stronger than idid
Factors affecting IDID/PDPD forces
- Size of e- cloud
- Greater size of e- cloud, greater extent of distortion e- cloud more extensive IMF - Type of IMF
H>pdpd>idid - Shape of moleq
Straight chain higher bp than branched
Hydrogen bonds
H bonds to N/O/F (Very EN)
No. of H bonds per moleq based on:
1. no. of LP on EN atom
2. no. of H atoms
How does hydrogen bonding affect physical properties
- Soluble in water
- Dissolve in water by forming intermolecular H bonds w H2O moleq - H2O, NH3, HF higher mp than SMS -> Larger amt of energy req. to overcome stronger intermolecular hydrogen bondsthan weaker idid
(Dowm the group, size of e- cloud increase, extent of distortion e- cloud increases, idid more extensive) - DIMERISATION (carboxylic acids)
- dimers due to formation of intermolecular hydrogen bonding - INTER vs. INTRA molecular bonding
- moleq w inter mp> intra
- inter more solubility in H2O > intra
Physical properties of SMS
Atoms bonded by strong covalent bonds
- held by idid -> Low mp&bp
- No mobile ions/e- cannot conduct elec
- Soluble in nonpolar but not soluble in polar solvents
-> (energy released in formation of idid betw. solute solute sufficient to overcome solvent solvent)
-> (energy released in forming idid solute solute insufficient to overcome H solvent solvent betw. water moleq & idid solute solute)
Structure & property of ice
Intramolecular: Strong covalent
Intermolecular: Strong hydrogen
2H atoms +2 LP -> 3d tetrahedral structure
OPEN cage-like structure
Less dense than water
-> When ice melts, tetrahedral arrangement partially broken up,
-> moleq closer tgt
-> More H2O moleq per unit vol
-> Density water higher
