Unit 2 Final Flashcards
The Lewis dot formula fails
To explain the formation of chemical bonds and gives no idea about the shapes of polyatomic molecules
VSEPR theory fails in what way
It gives the geometry of simple molecules but theoretically it doesn’t explain them and it has limited application
Covalent bonds are more clearly represented using
- the valance bond theory
- molecular orbital
What is the basic principle of valance bond theory
Covalent bond forms when orbitals of Two atoms overlap
______bond the electron density lies along the nuclear axis between the bonded nuclei
Sigma
In_________bond electron density is found in lobes above and below nuclear axis
Pi
_____ bond is stronger than______bond
Sigma
Pi
Hybridisation explains
Molecular structure specifically bond angle
Even though it provides a useful and convenient method for predicting the shapes of moléculas but it doesn’t explain the reason for the shape
Some possible hybridisation are
3s➡️ 3p➡️ 3d
3d➡️ 4s ➡️ 4p
They are all possible because they have comparable energies
What is diagonal hybridisation
Is when the central atom is hybridised -sp and is linked to Two other central atoms
2 electron pair
Linear -180
Sp
3 electron pair
Trigonal planar- 120
AB2E1- bent ,angular or v shape -104.5
Sp2
4 electron pair
Tetrahedral- 109.5
AB2E2- bent, angular or v shape- 104.5
AB3E - Trigonal pyramid - 107
Sp3
5 electron pair
Trigonal bipyramid- 90&120
AB3E2- t shape - 90
AB4E - see saw - 90
AB2E3- linear - 180
Sp3d
6 electron pair
Octahedral- 90&180
AB5E- square pyramid - 90
AB4E2 - square planar- 90
Sp3d2
Paramagnetic
Unpaired electrons - attracted by a magnetic field
Diamagnetic
All electrons are paired
Is not attracted by magnetic field and is slightly repelled
In diatomic molecules when the total electron is 14 or less the order is
σ1s σ1s* σ2s σ2s* ( π2py= π2pz) σ2px ( π2py * = π2pz * ) σ2px *
In diatomic molecules when the total electron is greater than 14 the order is
σ1s σ1s* σ2s σ2s* σ2px ( π2py= π2pz) ( π2py * = π2pz * ) σ2px *
Examples of crystalline structure
NACl and table sugar( sucrose)
Ionic bonds conduct electricity when
Molten or dissolved
For molecular crystals among polar molecules what intermolecular forces dominates? Among non polar what intermolecular forces dominates?
- dipole- dipole forces and whenever possible hydrogen bonding dominates
- London dispersion forces are the principal force
The most important network covalent solids are
Silicates
The two common crystalline forms of elemental carbon _____________and___________are examples of network covalent solids
graphite and diamond