Intermolecular forces and hydrogen boding Flashcards
What is a non polar covalent bond
give an example
No difference between electronegativity
H-H and Cl-Cl
electronegativity
measure of tendency of an atom to attract a bonding pair of electrons in a covalent bond.
polar covalent bond
give an example
difference in electronegativity H-Cl
H-H and H-F
For each molecule above state whether they are polar or non polar and explain why.
H-H non polar. No difference in electronegativity as they are the same element.
H-F polar. Difference in electrongeativity
What are the 3 common types of intermolecular forces
- London forces
- Induced dipole-dipole forces
- Hydrogen bonds
Would H2 molecules have permanent dipole-dipole interactions between them
Would HCl molecules have permanent dipole-dipole interactions between them?
Why or why not?
No. They have no permanent dipole as there is no difference in electronegativity. (non-polar)
Yes. They have permanent dipoles because there is a difference in electronegativity.(polar)
lone pairs
pair of electrons occupying in an orbital (the electrons in the lewis structure)
which intermolecular forces are these elements :
CO2
SF4
CH3NH3
explain why?
- CO2 has a london dispersion force because
how do you know whether a compound is non-polar:
- central atom has no lone pairs
- all atoms around central atom is the same
Melting and boiling points of water
- Water a higher melting and boiling point compared to other simple molecular substances
- Therefore at room temperature it is a liquid( while other tend to be gases)
- This is because water contains hydrogen bonding which is the strongest intermolecular force
Explain why compounds with hydrogen of group 6 (O, F and N) have higher boiling points than expected.
Contain hydrogen bonds which are the strongest intermolecular force and require the most energy to over come
Temporary (induced) force
- weakest force
- temporary uneven electron distribution in one molecule
- induces a dipole in neighbouring molecule
- causes weak electrostatic between them
- ## low melting and boiling as little energy is needed to break intermolecular forces
What increases the strength of induced forces
- increases surface area of molecule
- increases with larger atoms with grater electron density (electrons)
(e.g chlorine has more electrons than fluorine so higher electron density)
permanent dipole-dipole
- second strongest intermolecular force
- only acts on polar molecules
- arises from a difference in electronegativity between two atoms bonded
- the greater the difference between the two atoms, greater the strength of permanent dipole
hydrogen bond
- strongest intermolecular force
- ## only occurs with N-H, O-H, F-H
In period 3, P4, S6 , Cl2 rank them from highest to lowest boiling points and explain in terms of intermolecular forces
- all 3 molecules are non- polar molecules
- They only experience the temporary dipole-dipole intermolecular forve
- The sulphur has the largest surface area so will experience strongest intermolecular force
- This means sulphurs boiling point will be the highest as more energy is needed to break the intermolecular forces apart
- The chlorine molecule has the smallest surface area and weakest intermolecular forces, so lowest boiling point
HF, HCl, O2 , CH4, rank them from highest to lowest boiling points and explain why in terms of intermolecular forces
- O2 and CH4 are non polar molecules, so will only experience temporary dipole-dipole intermolecular force which are the weakest, Little energy is needed to break these forces, therefore having the lowest boiling points
- CH4 has a larger surface area so will have stronger temporary dipole-dipole so will have a slightly stronger boiling point that O2
- HCL is a polar molecule because of the large difference in electrongeativity between H and Cl. Hal experiences both termporary and permenant dipole , meaning higher boiling point.
- HF experiences hydrogen bonds, as well as 2 other intermolecular forces. this is the strongest intermolecular forces, so large amount of energy is needed to separate molecular apart. Meaning HF has the highest boiling point
