Bonding and structure part 2 Flashcards
Define electronegativity (2)
The ability of an atom to attract the bonding electrons towards itself to form a covalent bond
Describe and explain how a covalent bond is formed in Br2 (3)
- Both same atom so both have some pulling power (electronegativity)
- So the bonding electrons are shared equally between the bonding atoms
- Therefore the bonds in bromine are non-polar
Describe and explain how a covalent bond is formed in HCl (4)
- Cl is far more electronegative than H
- The bonding electrons are held closer to the Cl atom
- The electron cloud is denser over the Cl atom so there is a permanent dipole across the bond
- Therefore HCl has polar molecules
How would the bonding in HI be represented?
H———————————————————I
delta positive delta negative
xo
(bond shown slightly closer to I due to a difference in electronegativity)
On what scale are the electronegativities of different atoms shown?
The Pauling Scale
Does CH4 have polar molecules? Explain why. (2)
No- carbon and hydrogen have very similar electronegativities so the electron pair isn’t held closer to any of the atoms.
Compare the charges in NaBr and HBr (2)
NaBr=ionic, so full charges
HBr=polar covalent, so only partial charges
Which element is the most electronegative? Explain why (4)
- Fluorine
- Has the least number of shells in group 7, so lower shielding effect and smaller atomic radius
- So stronger nuclear attraction with oncoming electron
- Has the highest nuclear charge in period 2, so strongest nuclear attraction between nucleus and oncoming electrons
So fluorine gains an electron most easily
Non-polar or polar:
CF4
explain why (3)
Non-polar- although there is a difference in electronegativity, the bond pairs are repelled equally meaning symmetry cancels the dipoles out- no net dipole across the molecule.
Non-polar or polar:
NH3
explain why (3)
Polar-there is a difference in electronegativity, and a lone pair of electrons around the central atom making the molecule unsymmetrical, so the dipoles do not cancel
Non-polar or polar:
CO2
explain why (3)
Non-polar- although there is a significant difference in electronegativity between the two atoms, the linear shape mean it is symmetrical which cancels out the dipoles
Non-polar or polar:
OCl2
explain why (3)
Polar- O is more electronegative than Cl, and there is two pairs of lone electrons around the oxygen (central) atom, meaning the molecule is bent, as the bonds are not cancelled out.
Non-polar or polar:
SF6
explain why (3)
Non-polar- although there is a difference in electronegativity in a single bond, the symmetry of 90 degrees cancels out the dipoles.
Non-polar or polar:
CH3Cl
explain why (3)
Polar- the molecule is unsymmetrical because Cl is more electronegative than C, so an outward dipole moment is produced (as the charge flows from + to -)
Describe what intermolecular forces are (3)
- Attractive forces between molecules
- Much weaker than ionic or covalent bonds
- Only found in covalent structures
Name the 3 types of intermolecular forces
- Induced dipole-dipole interactions (London forces)
- Permanent dipole-dipole interactions
- Hydrogen bonds
In which molecules are London forces found?
Between all molecules, whether polar or non-polar (as long as there is 2+ atoms)
Explain how London forces arise between molecules (3)
- There is an uneven distribution of electrons in a molecule
- This causes an induced dipole at either ends of the molecule
- This dipole causes another dipole in a neighbouring molecule (delta + on one molecule attracts to delta - on another molecule)
Therefore, they can be found between 2+ atoms bonded together
In what molecules are permanent dipole-dipole interactions found?
Found between polar molecules
What intermolecular force(s) are found in hydrochloric acid? Explain why. (3)
- London forces and permanent dipole-dipole interactions
- LF’s because there may be an imbalance of electrons between the 2 atoms at any point
- PDDI’s because of a polar bond- difference in electronegativity and no symmetry so the dipoles do not cancel
Explain how permanent dipole-dipole interactions arise between molecules (3)
- Due to a permanent polar bond (no symmetry between the dipoles)
- The delta + on one molecule attracts to the delta - on a neighbouring molecule
- This produces a permanent dipole-dipole interaction between the molecules
Compare the strength of the three types of intermolecular forces
- Both London forces and permanent dipole-dipole interactions are weak, however London forces are weaker
- Hydrogen bonds are the strongest
What is a hydrogen bond?
A strong dipole-dipole interaction between molecules containing O-H, N-H or F-H bonds
Describe how a hydrogen bond is formed (2)
- A hydrogen atom attracts to the lone pair on a O, N or F atom on a neighbouring molecule (highly electronegative)
- This forms a delta positive hydrogen atom and a delta negative O, N or F atom
