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External Exam
Friday 18th November, 9:30am
5 literacy Credits
The following topics will be covered in the first 6 weeks of term 1. The 7th week will be spent revising and bringing everything from this topic together and time permitting we will have a practise exam.
Learn
Learn
Electron Configurations
Electron Configurations
We can actually zoom in on the electron shells and get more detail about how the electrons are arranged in the shells.
The shells can be broken down into sub shells called an s, p or d sub shell. These sub shells have allow for different numbers of electrons:
An s sub shell can hold 2 electrons
A p sub shell can hold 6 electrons
A d sub shell can hold 10.
The first energy level only has an s sub shell.
The second energy level has an s and a p sub shell
The third energy level has an s, p and d sub shell.
Rules for electron configurations
Rules for electron configurations
Pauli's Exclusion Principle
Each orbital holds 2 electrons. These electrons are said to have opposite spin, with the symbol:
Hund's Rule
Every orbital in a sub shell is singularly occupied before one is doubly occupied.
Forming an ion
When removing electrons to form an ion you remove the electrons from the outermost shell. Reminder: the 4s orbital is further away than the 3d so you remove from the 4s before the 3d.
Stability
Having a half filled or completely filled d sub shell is desirable as it creates stability for the atom. Electrons can move from the 4s sub shell to achieve this goal.
Coloured or not
If a substance has a completely filled OR empty d sub shell it will not be coloured (white). If it has 1,2,3,4,5,6,7,8 or 9 electrons in its d sub shell then it will be coloured.
Periodic Trends
Periodic Trends
You need to be able to identify trends going across a period (1st bullet point) and down a group (2nd bullet point).
Atomic Radii
Generally getting smaller as electrons are being added to the same electron shell with added proton power attracting them and the same shielding from inner electrons.
Getting bigger as an extra electron shell is added on.
Ionic Radii
If you are forming a cation it will become smaller as you remove an electron. If you form an anion it will become bigger due to the electron-electron repulsion.
Getting bigger as an extra shell is added.
Ionisation Energy
Generally, as the atom gets smaller it requires more energy to remove the outermost electron as it is more tightly held.
Less energy is required as the atoms gets bigger.
Electronegativity
Generally, as the atom gets smaller it will be able to have a stronger hold on a pair of bonding electrons, so an increase in electronegativity.
As the atom gets bigger its electronegativity will decrease.
Revision and Practise Questions
Revision and Practise Questions
che_90780_ periodictrends_revision.pdfche_91390_collated atomic trends.pdfStructure and Shapes
Structure and Shapes
Much the same as last year but just with a few more shapes to learn as we can now have a maximum of 6 areas of negative around the central atom instead of 4. YAY!
This situation happens if an atom has free d orbitals which we can promote electrons in to from either the 3s or 3p. Thus, making more electrons free to bond.
Explanation of shapes:
Explanation of shapes:
Number of negative regions repel into what shape.
Number of bonding/ non bonding regions.
Name shape and bond angle.
Identify polar/ non-polar bond and which atom is more electronegative.
Identify if it's symmetrical or not symmetrical and effect on bond dipoles.
Identify if it is polar or non-polar. EASY EXCELLENCE QUESTION!!
Names of Shapes.pptxRevision and Practise Questions
Revision and Practise Questions
che_91390_shapes and polarity.pdfche_91390_collated shapes.pdfTypes of Bonding
Types of Bonding
Reminder: Strength of bonds is related to melting and boiling points of substances. The stronger the bond then the higher the M/P and B/P will be.
Temporary Dipoles
Temporary Dipoles
Every substance has temporary dipoles, even non-polar molecules. They are very weak.
The bigger the molecule, the stronger the temporary dipoles.
The more linear the shape is, the stronger the temporary dipoles are.
Permanent Dipoles
Permanent Dipoles
Only found in the bonds of polar molecules. Stronger bonds which require more energy to break.
Hydrogen Bonding
Hydrogen Bonding
The strongest type of intermolecular bonding. Specifically between Hydrogen and either N, O, or F. Due to the large difference in electronegativity these atoms create very strong bonds.
Solubility
Solubility
Polar substance dissolve in polar solvents and likewise for non polar.
Ionic Substances
Ionic Substances
A cation and an anion held together by strong electrostatic forces of attraction. These bonds are very strong and hence require a lot of heat energy to break (high M/P and B/P). Ionic substances are polar so can dissolve in water. They can only conduct in when molten or dissolved in water.
Factors which affect the strength of the ionic bond:
The size of the ions. Larger ions have weaker attractive forces.
Charge of the ions. Larger charges have stronger attractive forces.
Revision and Practise Questions
Revision and Practise Questions
che_91390_collated attractive forces.pdfche_91390_ionicbonding.pdfEnergy Changes Recap
Energy Changes Recap
Exothermic: The release of energy
Endothermic: The absorption of energy.
Breaking of bonds releases energy.
Making of bonds absorbs energy.
Enthalpy= (bonds broken) - (bonds formed)
Latent Heat
Latent Heat
The energy required to convert 1 mole of a substance between states.
Enthalpy of fusion ∆fusH - solid to liquid.
Enthalpy of vaporisation ∆vapH - liquid to gas.
Enthalpy of sublimation ∆subH - solid to gas.
Entropy
Entropy
This is a measure of the amount of disorder in a chemical reaction. If the entropy has increased that means there has been an increase in the amount of disorder in the system. Most systems want to become more disordered (2nd law of thermodynamics).
Factors affecting the change in entropy (∆S):
Moles of reactants vs products.
More moles = more disorder.
States of reactants vs products.
Solid= less disorder, gas = more disorder.
Example of dissolving
Example of dissolving
When dissolving a solid it's entropy will increase as it dissociates into a liquid. The solvent's entropy will also increase as a solid has been dissolved in it.
Gibbs Free Energy
Gibbs Free Energy
A reaction is said to be spontaneous if no intervention is needed and it happens by itself. Two factors will increase the spontaneity of a reaction.
Enthalpy
Enthalpy
When the enthalpy of the products is lower than the reactants (exothermic).
Entropy
Entropy
When there is an increase in the disorder of the system.
A reaction can still be spontaneous when it is endothermic, if the change in entropy is high enough!
Formula you need to remember!
∆G= ∆H- T∆S
If ∆G is negative then the reaction is spontaneous, if ∆G is positive then it is not spontaneous.
Revision and Practise Questions
Revision and Practise Questions
che_91390_entropy basics.pdfche_91390_Collated entropy questions.pdfCalorimetry
Calorimetry
An experimental method to calculate the energy released or absorbed by measuring the effects the system has on a known amount of water. You will need to remember these formulae!
Q= mc∆T
Q= heat energy
m= mass of water
c= constant= 4.18
∆T= Change in temp
The heat energy is being calculated in Joules. You can divide this answer by 1000 to get KJ.
You can then use:
n= m/M
∆H= -Q/n
to calculate the enthalpy for a specific amount of reactant.
Experimental values may differ from theoretical values due to:
Heat will be absorbed by the equipment and the surroundings.
Experiment may not be done in standard conditions (25˚C, 1atm).
Enthalpy- just gotta learn these.....
Enthalpy- just gotta learn these.....
There are different types of enthalpies. All to do with a change in heat energy. Pay particular attention to the subscripts by the H. As you will need to know how to complete an equation purely off the subscript.
Neutralisation, ∆nH
Neutralisation, ∆nH
The standard enthalpy change when solutions of an acid and a base react together to form 1 mole of a water. You need to calculate the number of moles of acid and base and the smallest number is equivalent to the number of moles of water produced.
Combustion , ∆cH
Combustion , ∆cH
The enthalpy change when 1 mole or a substance is reacted with O2 to form H2O and CO2 .You will need to balance the equation. Balance the C's first, then the H's, and finally the O's You may need to include fractions.
Formation, ∆fH
Formation, ∆fH
The enthalpy change when 1 mole of a substance is formed from it's pure elements (eg oxygen exists as O2 not O).
Calculations using ∆fH
Calculations using ∆fH
Enthalpy for a reaction can be calculated using the formation values provided. Found via (products - reactants). Note that elements have a value of 0 and coefficients need to be taken into account in the calculation.
Hess' Law
Hess' Law
Using all of the knowledge from the last couple of sections you will need to create and then rearrange certain equations to combine together to make the equation you want. Really hard to describe and it's best to just do heaps of examples. Once you get it though it is an easy excellence question
Hess’ Law.pptxRevision and Practise Questions
Revision and Practise Questions
che_91390_collated enthalpy calcs.pdfHess' Law exam practice.docxA3 Revision Sheets
A3 Revision Sheets
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