General Revision - Summer 2017 Flashcards
What is a dative covalent bond?
A bond where one atom gives both the electrons in bond
What is electronegativity?
Power of an atom to attract the electron density in a covalent bond
What are three factors that influence electronegativity?
- Nuclear charge
- Atomic/ionic radius
- Electron shielding
Explain why H20 is polar, but CO2 is non-polar.
- Bonds containing oxygen are polar
- CO2 is symmetrical
- Symmetrical shape of CO2 cancels the dipole
What are the three key factors of the electron repulsion theory?
- Electron pairs repel each other
- Pairs take specific positions in order to repel each other
- Results in specific shapes of molecules and ions
Why is ice less dense than water?
- Water molecules arranged into a fixed pattern
- Open lattice
- Hydrogen molecules hold water molecules apart with H bonds
- Allowing ice to be less dense than water
What are the three types of intermolecular forces?
- Van der Waals/London forces
- Dipole-dipole forces
- Hydrogen bonding
What are Van der Waals forces caused by?
Caused by random movement of electrons
What do Van der Waals forces cause?
- causes temporary dipole
- temporary dipole induces further temporary dipoles to nearby atoms
What do dipole-dipole forces act between?
Act between molecules with permanent dipoles
Explain the trend in boiling points of the hydrogen halides from HCl to HI.
- Van der Waals forces of attraction
- Increase with increasing size of hydrogen halide
- Increase with increasing size of electron cloud
How is a cation formed?
Formed through loss of electron
How is an anion formed?
Formed through gain of electron
Why does the polarising power of a cation depend on the ionic radius of an ion?
- Smaller radius = more polarising cation
- Positive charge of nucleus felt more strongly
Why does the polarising power of a cation depend on charge on an ion?
- Larger charge = more polarising
- Stronger attraction for outer electron
Why does the polarising power of an anion depend on the ionic radius?
-Larger ionic radius = electrons in outer shell held less tightly
What is the key feature of a polar bond?
- Uneven distribution of electrons
- Bond having negative and positive end
Why is water a good solvent for ionic compounds?
- Ionic compound becomes hydrated
- Surrounded by polar water molecules
- Attracted to the charged ions
Why is water a good solvent for short chain alcohols?
- Can form hydrogen bonds with the water molecules
Why are longer alcohol chains less soluble?
- Hydrocarbon chain is long
- Hydrogen bonds between water have to be broken
- Hydrogen bonds between alcohol have to be broken
- More bonds broken than formed
- Hydrogen end can only form weak electrostatic forces of attraction
Why is water a poor solvent for non-polar molecules?
- Halogenoalkanes not polar enough to dissolve in water
- Cannot form hydrogen bonds
- Form weak intermolecular forces of attraction
Why are non-aqueous solvents better for halogenoalkanes?
- Strength of intermolecular forces between solvent and solute similar
