Chemical Bonding Flashcards
What is chemical bond?
Force which holds atoms ions etc together
What is Electromagnet bond?
Bond formed of electrostatic attraction btw +ve & -ve ions
What is Electrovalence?
No. of unit charges on the ion
Octet rule
Atoms combine either by transfer or sharing of valence e’s to have an octet
Lewis dot structure conditions
Bond is formed due to sharing
Each atom contributes at least 1 e
Atoms attain noble gas configuration due to sharing
What is single bond?
2 atoms share 1 e’ pair
Formal charge formula
F C = Valence e’s(total) - no of lone pairs(total) - ½[no of bonding e’s(total)]
Limitations of octet rule
- Not universal
- In some compounds, there are < 8 valence e’s
- In molecules with odd no of e’s, rule is not satisfied
- Some have > 8 valence e’s(expanded octet)
- Some noble gases also combine to form compounds
- Does not account on shape of molecules
- Doesn’t explain relative stability of molecules and their energy
Ionic/electrovalent bond depends on:
Formation of +ve/-ve ions
Arrangement of them
Formation includes ionization(removal of e’) & addition of e’
Ionization is endo or exo?
Endo
Electron affinity
-ve of energy change for e’ gain
Ionic bonds will form easily if
Ionization enthalpies are low and e’ gain enthalpy is high
Lattice enthalpy
Energy required to completely separate 1 mole of a solid ionic compound to gaseous ions
Bond length
Dist btw nuclei of 2 bonded atoms
Bond angle
Angle btw orbitals having bonding e’ pairs around the central atom
Bond enthalpy
Energy required to break 1 mole of bonds of a type btw 2 atoms on a gaseous state
Unit is KJmol^-1
Bond order
No of bonds btw 2 atoms in a molecule
Which 2 have identical bond orders?
Isoelectronic molecules and ions
Non polar covalent bond
Bond formed as a result of E’ btw 2 identical nuclei
Polar covalent bond
E’ pair btw 2 atoms gets displaced towards more e’ -ve atom
Dipole moment
Product of magnitude of charge & dist btw centers of +ve & -ve charge
1 Debye(dipole)
3.33 × 10^-30C (coulomb) m
Dipole moment for polyatomic molecules
Independent of individual dipole moment of bonds and spatial arrangement of bonds
Why is dipole of BeF2 0?
2 equal bond dipoles in opp directions cancel each other
Fajan’s rules
- Small the cation, larger the anion, greater the covalent character
- Greater charge of cation, more covalent char
- Cation polarises anion, pull e’ charge toward itself increasing electronic charge btw the 2
- Polarizing power of cation, polarisability of anion & extent of polarization of anion are the factors
Postulates of VSEPR
- Shape of molecule depends on no of valence shell e’ pairs
- Pairs of e’s on valance shell repel since e’ cloud are -vely charged
- Pair of e’s occupy positions that minimize repulsion & and maximize distance
- Valence shell is taken as a sphere with e’ pairs on the spherical surface at max dist from 1 another
- Multiple bond is treated as single e’ pair & 2 or 3 e’ pairs as single super pair
- Applicable to 2 or more resonance structures as well
Decreasing order of lone pair & bond pair
Lp-lp>lp-bp>bp-bp
Arrangements of e’ pairs
Linear, trigonal planar, tetrahedral, trigonal-bipiramidal, octahedral
Bond enthalpy
Energy released when bond formed btw 2 H atoms
Overlapping of atomic orbitals
Minimum energy state when 2 H atoms are near & their orbitals go penetration
Strength of overlap
Greater overlap stronger bond
What does VBT explain?
Shape, formation & directional properties in polyatomic molecules and overlap & hybridization of atomic orbitals
Sigma bond
End to end overlap along internuclear axis(head on or axial)
Pi bond
Atomic orbitals axes remain parallel to each other & perpendicular to internuclear axis
Stronger sigma or Pi?
Sigma
Hybrid orbitals
Atomic orbitals that combine to form new set
Hybridization
Intermixing of orbitals of diff energies to redistribute their energies forming new set with equivalent energies
Salient features of hybridization
- No of hybrid orbitals = no of atomic orbitals that get hybridized
- Always equivalent in energy and shape
- Form stable bonds
- Have min repulsion btw e’ pairs & a stable arrangement
Conditions for hybridization
- Orbitals jn valencebshell are hybridized
- They should have almost equal energy
- Promotion of e’ is not necessary
- Even filled orbitals can participate
Types of hybridization
- Sp: 1s 1p- 2 sp orbitals
50% s & p char(diagonal) - Sp²: 1s 2p- 3 sp² orbitals(trigonal planar)(180°)
- Sp³: 1s 3p- 4 sp³ orbitals, 25% s 75% p char(tetrahedron)(109.5°)
Axial bonds
bonds- 1 lying above the other lying below the equatorial plane(90°)
Molecular orbital theory
- E’s are present in various molecular orbitals like that of atoms in atomic orbitals
- Atomic orbitals of comparable energies & proper symmetry combine to form molecular orbitals
- E’ is influenced by 2 or more nuclei
- No of molecular orbitals formed = no of combing atomic orbitals(BMO & ABMO)
- Bmo has greater stability & lower energy than abmo
- E’ distribution around nuclei is given by molecular orbital
- Molecular orbitals are filled based on aufbau, Pauli’s principle and Hund’s rule
Conditions for combining of atomic orbitals
- Same energy
- Same symmetry about the axis
- Must overlap to max extent
Types of molecular orbitals
Sigma are symmetrical & Pi is asymmetrical
Stability of molecules
Molecule is stable if:
Nb > Na, Nb is no of e’s of BMO & Na of ABMO
B.O =
½(Nb - Na)
