1.3 Bonding Flashcards
What’s dative covalent bonding?
It’s where both shared electrons come from one atom.
Dative covalent bonding shown
in diagrams via arrows (away from donor atom)
Eg, ammonium ion forms when nitrogen atom in NH3
donates a pair of electrons to a proton (H+)
DIAGRAM NO 1
What are charge clouds
Bonding and lone pairs of electrons exist as charge clouds.
It’s an area where you have a large chance of finding an electron pair.
- electrons don’t stay still; they whizz around charge cloud.
How do electron charge clouds repel?
The clouds repel each other, sitting as far apart as possible.
The shape of the charge cloud affects how much it repels other clouds.
Lone pair clouds repel more than bonding pair.
—> greatest angles are between lone pairs of electrons
—> angles between bonding pairs are reduced
as pushed together by lone pair repulsion. (Why all molecules are different shapes)
DIAGRAM NO. 2
What’s the shape of a molecule with just 2 bonding pairs
Linear (180° bond angle)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with just 3 bonding pairs?
Trigonal planar (120° bond angle)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with 2 bonding pairs and 1 lone pair?
Bent (118° bond angle)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with 4 bonding pairs?
Tetrahedral (109.5° bond angle)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with 3 bonding pairs and 1 lone pair?
Trigonal Pyramidal (bond angle 107°)
(NO.3 DIAGRAMJ
What’s the shape of a molecule with 2 bonding and lone pairs
Bent (104.5° bond angle)
(NO.3 DIAGRAM)
What’s the shape of a molecule with 5 bonding pairs
Trigonal bipyramidal (120° bond angle , 90° bond angle from top/bottom)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with 4 bonding and 1 lone pair
seesaw (or trigonal pyramidal)
(119° bond angle between toward and away)
(89° elsewhere)
(NO. 3 DIAGRAM)
What’s the shape of a molecule with 3 bond and 2 lone angles
(Trigonal planar or) T shape
(89° bond angle if up/ down are bond)
(120° if between toward and away if all bond are flat)
NO. 3 DIAGRAM
What’s the shape of a molecule with 6 bonds
Octahedral (90° bond angle)
NO. 3 DIAGRAM
What’s the shape of a molecule with 5 bond and 1 lone pair
Square pyramid (89° bond angle)
NO.3 DIAGRAM
What’s the shape of a molecule with 4 bond and 2 lone pairs
Square planar (90° bond angle)
NO. 3 DIAGRAM
What’s electronegativity and what are H, C, N, Cl, O, and F on the electronegativity/pauling scale
Electronegativity =
An atom’ ability to attract the
Electron pair in a covalent bond
Is called electronegativity.
Fluorine (most electronegative element) = 4.0
Oxygen = 3.4
Chlorine = 3.0
Nitrogen = 3.0
Carbon = 2.5
Hydrogen = 2.2
Some atoms attract bonding electrons more than others..
What happens if covalent bonds are polarised by differences in electronegativity
In a cov. Bond between two atoms at diff electronegativities
The bonding electrons are pulled toward the more electronegative atom
This makes the bond polar
‘’
• A covalent bond between two atoms of same element (H^2 eg)
Is non-polar as atoms have equal electronegativities
—> equal attraction to both nuclei
• some elements (carbon, hydrogen) have very similar electronegativities
• so binds between are non polar
“
• in a polar bond, the diff in electroneg. between atoms
causes a permanent dipole
—> this is a difference in charge between the 2 atoms
- caused by a shift in electron density in the bond
More diff in electroneg. Means bond is more polar
Cl is more electronegative than H, so HCl
Has a permanent dipole (Cl is then δ- - slightly neg - and vice versa)
More negative if more electroneg.
How are whole molecules polar too
If you have a molecule with polar bonds
You end up with an uneven distribution of charge
Across whole molecule
—> this means the molecule is polar
Not all molecules that contain polar bonds are polar..
If polar bonds are arranged symmetrically
The charges cancel out - no permanent dipole
(DIAGRAM No. 4]
To tell if polar or not, is charge evenly distributed?
Is it + just at top and - at bottom ?
What are the three types of intermolecular forces
Intermolecular forces between molecules
Are much weaker than covalent, ionic or metallic bonds.
—> important as intermolecular forces affect physical properties of compounds
- van der waals forces OR induced dipole-dipole
- permanent dipole dipole forces (caused by polar molecules)
- hydrogen bonds (are forces)
Strongest at bottom
How are permanent dipole dipole forces made between polar molecules
In a substance made up of molecules that have perm. dipoles
There will be weak electrostatic forces of attraction
between δ+/- charges on neighbouring molecules
…
Like
- putting charged rod next to polar liquid (water tap)
- liquid will move to rod, as polar liquid molecules have perm dipoles
- Polar molecules in liquid turn around so oppositely charged end faces rod
Eg. Hydrogen chloride gas has polar molecules
The δ- chlorine is attracted to δ+ hydrogen on next molecule
What are van der waals forces
They’re found between all atoms and molecules
—> causing all to be attracted to one another
- Electrons in charge clouds always move quick
- at any moment , electrons are likely to be one side than other.
» at this moment, atoms would have temp. dipole - this dipole can cause a temp dipole in opposite direction on neighbouring atom
- the two dipoles are then attracted to each other
- this can do same on a third atom; and so on
Because electrons move constantly, dipoles are made and destroyed all time
Even though dipoles keep changing, overall effect is for atoms to be attracted to each other
How are molecules arranged with van der waals forces between
I2 is a solid.
It’s the van der waals forces between iodine molecules, which hold them together in a lattice.
- I2 atoms are held in pairs by strong covalent bonds
- but molecules held together in a lattice by weak van der waals forces
It’s why they vibrate
What affects strength of van der waals forces
Larger molecules with larger electron clouds
have stronger van der waals forces.
Shape of molecules affects strength too.
Long straight molecules lie closer together than branched ones
The closer together two molecules get , stronger forces between are.
—> When boiling a liquid, you need to overcome intermolecular forces
>You need more energy to overcome stronger intermolecular forces
>So liquids with stronger van der waals forces have higher bps
(Eg. no.5)
What is hydrogen bonding
—> strongest intermolecular force
It only happens when H is covanlently bonded to F, O or N
AS they are very electronegative
- this means they draw bonding electrons away from hydrogen atom
- the bond is so polarised and H has such a high charge density
(As it’s so small) - that H atoms form weak bonds with
- lone electron pairs on F, O, N atoms of other molecules
..
Molecules wch have hydrogen binding usually contain groups…
-OH
-NH
Like water and ammonia have hydrogen bonding
How does hydrogen bonding have effects on substance properties
• have higher se if extra energy needed to break H bonds
- this is the case with water and hydrogen fluoride
- wch have much higher bps than other hydrogen halides
• as liquid water cools to form ice, molecules make more H bonds
• and arrange themselves into a regular lattice
- ice is less dense than liquid water
- because in regular struc of H2O , molecules are further apart
What to include in intermolecular force drawings
- lone pairs and bonds
- all δ+/-
- sraight force line
What affects whether a substance is soluble or not
How soluble a substance is in water
Depends on the type particles it contains
Water is a polar solvent so substances that are polar or charged will dissolve.
Non-polar and uncharged substances won’t,
