Bonding Flashcards
Define ionic bonding
Electrostatic forces of attraction between oppositely charged ions formed by electron transfer
What is the structure of sodium chloride?
Giant ionic lattice
Why do ionic substances have high mp/bp?
Strong electrostatic forces of attraction between oppositely charged ions require high energy to break
Why is the ionic radii of positive ions smaller?
One less shell of e- so force of nucleus holds them closer
Why is the radii of negative electrons bigger?
More e- but same number of protons, so pull of nucleus is shared over more e-, reducing attraction per e-
What is covalent bonding?
Shared pair of e-
What is dative covalent bonding?
When a shared pair of e- in the covalent bond comes from one of the bonding atoms
What can dative covalent bonding also be called?
Co-ordinate bonding
Give examples of molecules with dative covalent bonding
NH4+
H3O+
NH3BF3
How do you draw a dative covalent bond?
Arrow goes from the atom donating the e- pair to the one that is deficient
If there’s a charge, then add square brackets around it and write the charge outside
What is metallic bonding?
Electrostatic forces of attraction between positive metal ion and delocalised e-
Describe 3 factors affecting the strength of metallic bonding
1) Number of protons / strength of nuclear attraction
- More protons –> stronger bond
2) Number of delocalised e- per atom
- ore delocalised e- –> stronger bond
3) Size of ion
- Smaller ion –> stronger bond
What is a simple molecular structure?
With intermolecular forces between molecules
Eg. Van der Waals / permanent dipoles / hydrogen bonds
Give examples of molecules with a simple molecular structure
CO2
H2O
H4
What is a macromolecular structure?
Giant molecular structures
Give examples of molecules with a macromolecular structure
Diamond
Graphite
Silicon dioxide
Silicon
Describe the difference between the mp / bp of simple molecular vs macromolecular structures
Simple –> low mp sue to weak intermolecular forces between molecules (must specify type if force in answers)
Macro –> high mp due to many strong covalent bonds which take a lot of energy to break
Conductivity of ionic compound when solid VS when molten
Solid –> poor as ions can’t move / fixed in lattice
Molten –> good as ions are free to move
Conductivity of simple molecular substances when solid VS molten
Solid –> poor as no ions to conduct / e- are localised
Molten –> poor as no ions
Why can graphite conduct electricity when solid but not diamond?
Graphite –> free delocalised e- between layers as each carbon atom is only bonded to 3 other carbon atoms
Diamond –> e- can’t move
Conductivity of metallics structures when solid VS molten
Both –> good as there are delocalised e-
How would you explain the shape of a molecule?
1) state number of bonding pairs & lone pairs of e-
2) State that e- pairs repel to get as far away as possible
3) If no lone pairs –> state that e- pairs repel equally
4) If lone pairs –> state that lone pairs repel more than bonding pairs of e-
5) State shape and bond angle
How many degrees does each lone pair reduce the bond angles by?
2.5
What is electronegativity?
Relative tendency of an atom in a covalent bond in a molecule to attract electron pairs to itself
Which atoms are most electronegative
Fluorine
Oxygen
Nitrogen
Chlorine
How is electronegativity measure?
Pauling scale (0-4)
Explain the trend in electronegativity cross a period
Increase –> number of protons increase and atomic radius decreases as e- in same shell are pulled in more
Explain the trend in electronegativity down a group
Decrease –> distance between nucleus and outer e- increases and shielding of inner shell e- increases
How do you know if a compound is purely covalent?
Small difference in electronegativity
What does it tell you if a compound contains elements with large electronegativity difference?
It’s ionic
How do permanent dipoles arise (aka polar covalent bond)?
When bonds have different electronegativities of around 0.3-1.7
Unequal distribution of e- produces charge separation (dipole)
Are symmetric molecules polar or non-polar? Why?
Non-polar as all bonds are identical and no lone pairs
Dipoles cancel out
Is CH3Cl polar or non-polar?
Polar
Where do Van der Waals forces occur?
Between all molecular substances and noble gases (not ionic substances)
How are induced dipole-dipole interactions formed?
1) In molecules, electrons are moving constantly and randomly
2) Causing electron density to fluctuate and parts of the molecule become more / less negative (temporary / transient dipoles)
3) These instantaneous dipoles cause dipoles to form in neighbouring molecules (induced dipoles)
Induced dipole is always opposite to the original
What is the main factor affecting the size of Van der Waals
More e- in a molecule = higher chance of dipole forming –> make vdW stronger between molecules –> greater boiling points
Why does be increase down group 7?
More e- in bigger molecules –> cause increase in size of vdW between molecules
Why does boiling point oof alkane homologous series increase?
More e- in bigger molecules –> increased size of vdW between molecules
How does the shape of a molecule affect the size of vdW?
Longer chain alkanes have larger surface area of contact between molecules for vdW (compared to spherical / branched) –> stronger vdW
What type of molecules do dipole-dipole forces occur between?
Polar
Where do hydrogen bonds occur?
Between hydrogen atom on one molecule and N / O / F on another molecule
Order the intermolecular forces in terms of bp from highest to lowest
Hydrogen
Permanent dipole-dipole
Van der Waals
What must you always show hen drawing hydrogen bonding between 2 molecules?
Lone pairs on O / N / F
And charges of H & O / N / F
