Revision Flashcards
Relative atomic mass
Average mass of all the isotopes of an element compared to 1/12th the mass of an atom of Carbon-12
Steps of mass spectrometry
Electrospray ionisation, acceleration, ion drift, ion detector, data analysis
Describe electrospray ionisation
A sample is dissolved in a volatile solvent (water/methanol) and injected through a fine needle attached to high voltage power supply. The particle gains a proton, forming 1+ ion
Acceleration
The ion accelerated towards a negatively charged plate
Ion drift
Travel through flight tube with different velocities (because of different masses)
Ion detection
When the ion hit the plate, it gains an electron, producing a current, which is detected by the detector
Data analysis
Showing relative abundance and mass to charge ratio (m/z)
Why Cr has an unusual electron configuration?
Half-filled 3d subshells to be more stable
Why Fe has an unusual electron configuration?
Fully-filled 3d subshells to be more stable
Definition of isoelectronic
Particles with same electron configuration
Plum pudding model
- positive pudding (not empty spaced)
- negative electron
- no energy shell
Covert m^3 to dm^3 and cm^3
1 m^3 = 1000 dm^3 = 1000000 cm^3
Ideal gas equation with units
pV= nRT
(Pa)(m^3) = (mol) (JK^-1mol^-1)(K)
Percentage yield
(Actual yield/ theoretical yield) x 100
Atom economy
(Molecular mass of desired production/ total mass of reactants) x 100
Why is percentage yield not 100%?
- lost in transfer
- not all reactants have fully reacted
Why conical flask does not have to be fully dry?
Doesn’t affect the number of moles of the solute
Why using conical flask?
Easier to swirl
Prevent spitting out
Why placing a white tile?
To view the indicator colour more clearly
Why the funnel needed to be removed?
To ensure any drops remained in it do not interfere with the titre
Percentage error (uncertainty)
(number of times used x uncertainty) /
Amount measured
Ionic bond
Strong electrostatic attraction between oppositely charged ions held in a lattice
Explain how Na and Cl react
Na atom loses its 3s electron, forming Na+ ion
Cl atom gains that electron, forming Cl- ion
Forming NaCl
Bp and mp for ionic compounds
High
Because strong electrostatic attraction between oppositely charged ions
Can ionic compounds conduct electricity?
Yes when molten or in aq
Ions are free to move and carry charge
Are ionic compounds soluble in water?
Yes
Water molecules break the lattice and surround the ions
What is simple covalent bonding?
Strong covalent bonds between atoms and weak VDW between molecules
Are there any lone pair in simple covalent bonding?
No - they are all bonded
Can simple covalent molecules conduct electricity?
No - no free electron
So simple covalent molecules have a high/ low bp and mp?
Low - small amount of energy is needed to break the weak VDW between molecules
Example of molecular covalent substances
Crystalline: Water (ice), iodine
Chlorine, oxygen
Macromolecules
-high mp and bp: breaking lots of strong covalent bond
- don’t conduct electricity (except graphite)
Example of macromolecules
Diamond, Graphite
Properties of diamond
Hard- each C atom is bonded with 4 others (strong covalent bond)
High mp
Tetrahedral 109.5
Can’t conduct electricity
Properties of graphite
Each C atom is bonded with 3 others
VDW between Layers - slide over
High mp
Hexagonal 120
Conduct electricity - delocalised electron
Coordinate bond
Share two electrons from the same atom
Example of coordinate bond
NH4+ , H3O+, BF4-
Electronegativity
The ability to attract an electron in a covalent bond
Electronegativity ______ across the period
Increases - the atomic radius decreases, so stronger attraction between the nucleus and electrons
Electronegativity _____ decreases down the group
Decreases - the atomic radius increases as there are more shielding, so the attraction between the nucleus and the electrons in the covalent bond decreases
Example of non - polar covalent bond
Cl-Cl
H-H
C-H
Example of polar covalent bond
H-Cl
C-Cl
Be-Cl
Why B-F is polar but BF3 is non - polar?
Because the shape is trigonal planar (symmetrical) , the polarities of the bond cancel each other out
What other shape is non polar?
Linear, tetrahedral, octahedral
Induced dipole - dipole forces
(VDW)
Larger atoms
More electrons
Greater VDW between atoms
Permanent d-d forces
Polar molecules
Stronger than VDW
Hydrogen bond
H atom and the lone pair of O/N/F
Strongest intermolecular forces
Hess’s law
The enthalpy change for a chemical reaction is independent of the route taken
Mean bond enthalpy
The measure of energy required to break one mole of a covalent bond In the gaseous state
