Last Minute Flashcards
Forces, bonds, attraction, periodicity, etc
What are the trends as you go down a group?
1st ionisation decreases
Number of shells increase
》the distance from nucleus
》weaker attractive force
Shielding increases
Ionic radius increases
What is the trend across a period?
Atomic radius decreases
No change in shielding (same number of shells)
Increased nuclear charge
》increased nuclear attraction
Protons increase
》General increase of 1st ionisation energy
Define isotope.
Isotopes are atoms of the same element that have different neutrons.
What is the atomic number?
Number of protons
Define relative atomic mass.
The weighted mean mass if an atom compared to 1/12 of the mass of carbon-12.
In period 3 explain the melting points of Na to Al.
Electrons in outer shell increase
》More electrons in delocalised sea
Charge on cations increases (+1 to +3)
Ionic radius decreases
》Delocalised elections are closer to nucleus
Explain the melting point of Silicon in the trend of period 3.
It is Giant Covalent
》Large increased melting point
Explain the trend in melting point in period 3 from P to Ar.
Simple covalent
》lower melting points
Weak intermolecular london forces
Larger the molecule the great the london forces
》Hense P4, S8, Cl2, Ar
What state is S8 at room temperature?
Solid
Compare the strength of intermolecular forces
HBond > permanent > London
Key point of London Forces.
They induce dipoles in neighbouring molecules (like bumpercars) that attact eachother.
No polar bonds
Very weak and short lived
The bigger the molecule the greater the forces
eg C3H6 -89C , C4H8 -43C
The more points of contact, the greater the attraction
Key points on permanent dipole-dipole forces.
Polar bonds with overall dipole
Asymmetrical
》polar
Attractions between these and neighbouring molecules eg. H-Cl molecules
Key points of Hydrogen bonding.
H atom bonded to a very electronegative element (F, O, N)
Bond between H and lone pair on F, O, N
Stronger that London or permanent dipole-dipole forces.
Define electronegativity.
Measure of attraction of an atom in a covalent molecule for the bondinh pair of electrons.
What makes a molecule polar or non-polar?
Polar = Asymmetric
Non-Polar = Symmetric
What are the effects of hydrogen bonds in ice?
Ice is less dense than water due to hydrogen bonding because of large areas of empty space.
Ice has ‘diamond-like’ structure.
Permifrost traps methane in empty space.
Does ammonia or water have a higher boiling point?
Water because it has 2 hydrogen bonds per molecule, whereas ammonia only has 1.
Why do boiling points decrease down a group generally?
Increased electrons means increased london forces between molecules.
What is the bond angle of trigonal planner?
120
What is the bond angle of linear?
180
What is the bond angle of non-linear / bent?
104.5
What is the bond angle of tetrahedral?
109.5
What is the bond angle of trigonal planer?
107
What is the bond angle of square planar and octahedral?
90
What is the temperature used for the habor process and why?
450C
Compromise on yield and rate as:
Lower temp gives higher yield of NH3 and forward reaction is exothermic.
High temp gives faster rate.
What is the pressure used in the habor process and why?
200atm
Compromise on yield and cost as:
High pressure gives higher yield of NH3 as less gass molecules on the right of the equation.
High pressure is very expensive.
What is the catalyst for the haber process?
Iron
Increases rate but has no effect on yield or position.
State Le Châtelier’s principle.
If conditions of a system at equilibrium changes then the position of equilibrium moves to oppose the change.
What effect does pressure have on Kc?
No effect.
What is meant by dynamic equilibrium?
Both forward and backward reactions occur at the same time and rate.
Concentration for reactants and products is constant.
What is the difference between homogeneous and heterogeneous equilibrium?
Homogeneous: All reactants and products are in the same state.
Heterogeneous: All the reactants and products aren’t in the same state.
