November 24: Group Work and Starting on the Mind Map

Wednesday 24th November Chemistry Class

Group Work:

At the start of class, Mr Carmichael put the class in separate groups of 3. Each group was given 2 sheets, one with many different molecules and another with classification groups.

We were asked to cut the molecules out and place them into the correct categories.

These categories were:

- The number of electron domains:
(1, 2, 3, 4, 5 or 6)

-The shape of the molecule :
(Linear, V-Shaped, Trigonal Planar, Pyramidal, Tetrahedral, Trigonal Bipyramidal, Octahedral)

-The strongest intermolecular force  present:
(London Forces, Dipole-Dipole, Hydrogen Bonding)

The molecules to categorise were:

H₂
CO₂
NO₂
SeCl₂
H₂O
SO₂
F₂O
Cl₂
CO 
NO 
HF
ICl
CO₃²-
NH₃
PH₃
NH₄+
SiI₄
CBr₄
PBr₅
SCl6

Mind Map:
After matching each of the elements to the correct group in the 3 categories, we returned to our seats and were given the final assessment for the bonding unit : a concept map. For this, we were to arrange general to specific concepts on a map, with relationships between boxes related to each other. Mr Carmichael gave some ideas on the board that would need to be included. These were: 
SL:                                                         HL:
-Metallic Bonding                                 -5, 6 shapes
-Ionic Bonding                                      -O₃
-Covalent Bonding                                -Hybridization
-Polarity                                                -Formal Charge
-Electronegativity                                 -Sigma & Pi Bonds
-Shape 
-Electron domains
-Lewis Structures
-IMFs
-Physical Properties
-Carbon allotropes/giant covalent structures
-Lattice
-Length/strength 
-Resonance 

We were allowed to spend the end of class on the concept map, mostly brainstorming a list of concepts we were going to mention. 

November 24: Metallic Bonds & Lab Design Review

November 24: Metallic Bonds & Lab Design Review

In class we finished up on metallic bonds, reviewing what we knew and adding a bit more.

A quick question sheet was handed out, referring to: melting points, ductility, malleability and conductivity (questions below).

Questions:

1. Discuss the melting point of Mg (which is 6500oC) with Na (which is 97oC).
2. Explain why Li has a melting point of 180oC, but K has a melting point of 63oC.
3. Describe why Copper allows to be ductile, malleable and a good conductor.

Additional Information:

Alloy Structure Diagram

Steel: is a mixture of Fe and C. Adding Cr makes stainless steel (used in cutlery), in addition adding Ti (and other metals like V) makes titanium steel (used in armour plating and aircrafts).

Brass: is an alloy of Co and Zi (used in taps and musical instruments). Bronze is an alloy of Co and Sn (used in statues). Cupro-nickel is used in 'silver' coins. All of these are corrosion resistant.

We also covered Metallic Characteristics, meaning the set of chemical properties associated with elements that are metals. These chemical properties result from how readily metals lose their electrons. Metallic characters includes the ability to be reduced, formation of ionic chlorides and basic oxides, and the ability to displace hydrogen from dilute acids.



Relating to metallic characteristics, we covered trends and influences for certain switches between metals and non-metals. 

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Lab Design Review:

In class as well as going over metallic bonds, we also used class to go through the IB1 Chemistry Analysis and Evaluation rubric. We covered systematic errors, conclusions and data.

Systematic Erros:

1. Folding of filter paper/surface area
2. Time
3. Wind draft
4. Room temp.
5. length of run/scales
6. Elastic band coverage

Conclusion:

To understand the conclusion and receive full marks you need to understand the differences between: interpreted conclusion, the actual conclusion and the contextual conclusion. The main difference is what you make your conclusion upon. For example the interpreted conclusion should be done on your general data, where as the actual conclusion should focus on processed data. Finally the Contextual conclusion should be according to the theory of the experiment.

Data:

For the data recordings, the main emphasis was placed on "keeping units and uncertainties" correct and according to their relevant points of interest.

Also you shouldn't forget to include qualitative and quantitative observations.

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November 14: Intermolecular Forces

In  class, we learned about 4.4- Intermolecular Forces 

The Physical Properties of molecular substances result from different types of forces between their molecules

Our key understandings for this topic were:

        Intermolecular forces include London (dispersion) forces, dipole-dipole forces and hydrogen bonding
    The relative strengths of these interactions are London (dispersion) forces < dipole-dipole forces < hydrogen bonds << covalent bond

London (dispersion) forces: 

  These are the weakest form of intermolecular force        
       Arise due to electrons constantly moving around → electrons are unevenly spread
    This produces temporary instantaneous dipoles
      An instantaneous dipole can induce another dipole in a neighboring particle 
    This results in a weak attraction between the two particles
      Their strength increases with increasing molecular mass

Dipole-Dipole Forces:

                   Still relatively weak, but the attraction is stronger than London (dispersion) forces

                     Occurs when polar molecules are attracted to each other by electrostatic forces                         
                     Permanent dipole: when one end of the molecule is electron deficient with a partial positive charge (δ+), while the other end is electron rich with a partial negative charge (δ–) 
                     Dipole-dipole forces occur when the opposite charges on neighboring molecules    attract each other

Hydrogen Bonding:

                  
 Hydrogen bonds are the strongest form of intermolecular attraction 
 Occurs when hydrogen is (covalently) bonded directly to a highly electronegative element, such as fluorine, oxygen or nitrogen

 

This causes boiling points of substances that contain them to be higher than what would be expected from their molar mass

Physical Properties → related to bonding type:

Melting/Boiling Points 
-       The melting & boiling points (of simple covalent molecules) depend on the type of forces of attraction between the molecules:

Hydrogen bonding > Dipole-dipole > London (dispersion) forces

  Solubility
-       ‘Like dissolves like’
-       Polar substances tend to dissolve in polar solvents
-       Non-polar substances tend to dissolve in non-polar solvents

Ex: Water H₂O (which shows hydrogen bonding) will be good for dissolving Ethanol C₂H₅OH (which also shows hydrogen bonding), but it won’t dissolve Hexane (only London forces) → oil & water won’t mix

  Volatility
-       The weaker the intermolecular forces, the more volatile the substance

  Electrical conductivity
-       For conductivity to occur the substance must possess electrons or ions that are free to move