Chemical Bonding Flashcards
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Electrovalent Bond
The bond formed, as a result of the electrostatic attraction between the positive and negative ions
How to write Lewis Dot structure
- Add up the total number of electrons (valence)
- Add / Subtract the charges as well
- Knowing chemical symbols, distirbute total number of electrons
- Least electronegative occupies central position
Formal charges
Total number of valence electrons - Total number of non bonding electrons - 1/2 (total number of bonding electrons)
Lowest energy structure has _ formal charges
Smallest
Examples of incomplete octet
LiCl, BCl3, HBeH
Odd electron molecules
N = O or O = N - O
Expanded octets
PF5, SF6, H2SO4 etc.
Electron Gain Enthalpy
Enthalpy change when a gas phase atom in its ground state gains an electron
Is ionization endo or exo
Always endo (+)
Ease of formation of ionic bonds
- Elements with low ionization enthalpies
- Elements with high electron gain enthalpy
- Higher lattice enthalpy = stronger bonds
Lattice enthalpy
Energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions
Bond length
Equilibrium distance between nuclei of two bonded atoms in a molecule
Covalent Radius
Radius of an atom’s core which is in contact with the core of an adjacent atom in a bonded situation
van Der Waals radius
Represents the overall size of the atom which includes its valence shell in a nonbonded situation
Bond Angle
Angle between the orbitals containing bond electron pairs around the central atom in a molecule
Bond order
Number of bonds between two atoms in a molecule
Bond order in isoelectronic species
Identical
Relation between bond order bond enthalpy and bond length
Bond order increases = Bond enthalpy increases = Bond length decreases
Dipole Moment
- Product of magnitude of charge and distance of separation
- Basically tells how polar it is
Why is dipole more in NH3 compared to NF3
- In NH3 the lone pair has the upward direction
- In NF3, the lone pair faces the bonds of F, and hence has cancelling of dipoles
Factors affecting covalent character in ionic bonds
- Smaller cation & Larger anion = Greater covalent character
- Greater charge on cation = Greater covalent character of ionic bond
- Transition metals generally more polarising than noble gases
Higher ionic character characterized by
- Larger difference in electronegativity
- Higher polarizing power
- Higher polarizability
VSEPR of central atom with no lone pair of electrons
- Linear (180 degrees) (BeCl2, HgCl2)
- Trigonal Planar (120 degrees) (BF3)
- Tetrahedral (109.5 degrees) (CH4, NH4+)
- Trigonal Bipyramidal (120 and 90) (PCl5)
- Octahedral (90 degrees) (SF6)
Repulsive interaction of electron pairs decrease in order of
lp - lp > lp - bp > bp - bp
Bond electrons for with lone pair
-
Why is there a lone pair at equatorial position?
- Minimize repulsion
- Equatorial has 120 degree bond angle with each other
- Better for it to have because only two 90 degree repulsions
Explain VBT
Find the minimum bond enthalpy
Sigma Bonds
- End - to - end (head on) overlap of bonding orbitals
- Axial overlap
- Formed by s-s overlap, s-p overlap, p-p overlap head on
Pi bonding
- Axes remain parallel to each other and perpendicular to internuclear axis
- Saucer type formation
Sigma vs Pi bond strength
- Sigma - Overlapping of orbitals to a larger extent (stronger)
- Pi bond - Overlapping to a smaller extent (weaker)
What is hybridization?
Process of intermixing of the orbitals of slightly different energies so as to redistribute their energies, resulting in the formation of new set of orbitals of equivalent energies and shape
sp hybridization example
- 50 - 50 s and p character
- Linear geometry
- Diagonal hybridization
sp2 hybridization example
- 33 - 66 s and p character
- BCl3
- Trigonal Planar arrangement
- Bond angle 120 degrees
sp3 hybridization example
- 25 - 75 s and p character
- Tetrahedron and bond angle is 109.5
- NH3 and H2O
Explain NH3 and H2O
- NH3 - 3 unpaired electrons in the sp3 hybrid and lone pair of electrons present in fourth. Bond angle now 107
- H2O - Tetrahedral shape (two lone pairs and two electron pairs) - reduced from 109.5 to 104.5
sp3 hybridization in C2H6 molecule
- One of four orbitals overlaps axially with similar orbitals of other atom to form sp3 - sp3 sigma bond
sp hybridization in C2H2
- Both carbon atoms undergo sp - hybridization having two unhybridised orbital
sp2 hybridization in C2H4
- One of the orbitals overlaps axially
- Other two are used for sp2 - s sigma bond with two hydrogen atoms
- Unhybridized overlaps sideways
Name the shapes and orbitals for undergoing sp and d orbital hybridization
-
Bonding vs Antibonding molecular orbital
- Bonding - Bond electrons paired with each other, forming a covalent bond. Have a lower energy and greater stability
- Antibonding - Do not participate in bonding; have a higher energy than component atomic orbitals
MOT for oxygen, flourine
sigma 1s < sigma * 1s < sigma 2s < sigma * 2s < sigma (2pz) < (pi 2px == pi 2py) < (pi * 2px = pi * 2py) < sigma * 2pz
MOT for below oxygen
sigma 1s < sigma * 1s < sigma 2s < sigma * 2s < (pi 2px = pi 2py) < sigma 2pz < (pi * 2px = pi * 2py) < sigma * 2pz
Bond order
One half the difference between the number of electrons present in bonding and antibonding orbitals
= 1/2 (Nb - Na)
Stability through bond order
- Positive bond order means stable molecule
- Negative bond order / zero means an unstable bond order
Relation between bond order and bond length
Inversely proportional
Diamagnetic vs Paramagnetic
Diamagnetic - Molecular orbitals are doubly occupied
Paramagnetic - Molecular orbitals are singly occupied
Hydrogen bond
Attractive force which binds hydrogen atom of one molecule with the electronegative atom of another molecule
Atoms which can go through hydrogen bonding
F , O , N
Intermolecular hydrogen bond
Between two different molecules of the same or different compounds. Eg: HF, alcohol, water, etc.
Intramolecular hydrogen bond
Hydrogen atom is in between two highly electronegative atoms (F , O , N)
Eg: o-nitrophenol molecule
Electronegativity order
F > O > Cl > N > Br > S > C
Which has higher electronegativity difference: ClF3 or SO2
ClF3
