Week 6 Flashcards
In polyatomic molecules, the centre atom…
is the one that needs to share the greatest number of electrons
Resonance structures
Sometimes the Lewis model allows several valid structures
* e.g. O3
double headed arrow
used for resonance
Formal charge =
Valence electrons of free atom - Lone pairs of electron - 1/2(Shared electrons)
Octet rule
Atoms can have a maximum of 4 electron pairs (8 e-) surrounding them (H can only have 1 electron pair, 2 e-)
Lewis structures
- Full bonds are represented by solid lines.
- Partial bond can be represented by dashed lines.
- Lone pairs are represented by dots.
VSEPR theory allows us to find
→ 3D arrangement of electron groups
→ 3D arrangement of atoms (ie. when lone pairs are ignored)
= the SHAPE of the molecule
3D arrangement for 2 electron groups
Linear
* 180°
3D arrangement for 3 electron groups
Trigonal
* 120°
3D arrangement for 4 electron groups
Tetrahedral
* 109.5°
3D arrangement for 5 electron groups
Trigonal Bipyramidal
* Angle between E and A 90°
* Angle between E and E 120°
3D arrangement for 6 electron groups
Octahedral
* 90°
The shapes of molecules with four electron groups (tetrahedral arrangement) may be:
- Tetrahedral (4 bonds, no lone pairs)
- Trigonal pyramidal (3 bonds, 1 lone pair)
- Bent
T-shaped
This molecule is planar but has bond angles a little below 90°. The atoms are “squeezed together” by the “lone pairs”
* e.g. CIF3
If the two atoms forming a bond have different electronegativities, the electrons will be more strongly attracted to the ____ atom
more electronegative
In polyatomic molecules, the bond dipoles add together to determine
the overall polarity of the molecule
If the molecule is symmetric, the bond dipoles will…
cancel out and the molecular dipole will be 0
In asymmetric molecules, the bond dipoles will…
NOT completely cancel out and the molecule will have a finite dipole
C can bond to…
- itself
- metals
- heteroatoms
C-C and C-H bonds
are strong and unreactive
⇒ provides solid scaffolds
If a covalent bond is formed between two atoms with limited differences in electronegativity
Then that bond is said to be “non-polar”.
In asymmetric polyatomic molecules with polar bonds the overall dipole “will not cancel out”
If a covalent bond is formed between two atoms with large differences in electronegativity
Then that bond is said to be “polar”.
In symmetric polyatomic molecules the net molecular dipole will be “zero”
An easy way to figure out what hybridization an atom has
Count the number of atoms bonded to it and the number of lone pairs.
* Double and triple bonds still count as being only bonded to one atom.
More nodes
⇒ shorter wavelength, more momentum and more energy
presence of OH groups will lead to…
H-bonding interactions
delocalised pi electron density will lead to…
dispersion interactions
a charged group with N-H bonds will lead to…
interactions with ion and polar groups
