C2 - Elements, compounds and mixtures Flashcards
What is in the periodic table?
Group number: columns + the number of electrons in the outer most shell
Period number: Rows + the number of shells the atom has
Left = metals
Right = Non metal
Group 0 = Noble gases (outer shells are full)
What is the electron distributions?
1st shell - 2 electrons
2nd shell - 8 electrons
3rd shell - 8 electrons
What is the Relative atomic mass (R.A.M)?
The relative abundance –> To find out how much of an element there is from its isotopes.
(percentage / 100 x mass number) + (percentage / 100 x mass number)
Eg: Chlorine has two naturally forming isotopes (Cl-35 and Cl-37). 75% of the chlorine atoms are Cl-35. Find the relative atomic mass of chlorine?
(75/100 x 35) + (25/100 x 37) = 35.5
What is Relative formula mass (R.F.M)?
Relative formula mass is all the mass numbers of the compound’s elements added up.
Eg: What is the Relative formula mass of H2SO4? H = 1 S = 32 0 = 16 (1 x 2) + 32 + (16 x 4) = 98
What is ionic bonding?
Ionic bonding is bonding between a metal and a non metal.
Metals lose electrons to form positive ions and non metals gain electrons to form negative ions.
Ionic compounds
They have a giant ionic lattice structure
PROPERTIES:
- High melting and boiling point : lots of energy is required to break the strong electrostatic forces of attraction between oppositely charged ions.
- They don’t conduct electricity in the solid state but they do in the liquid state: in the solid state the ions are restricted in the giant ionic lattice and cannot conduct electricity. In the liquid state the ions are mobile are can conduct electricity.
Simple covalent molecules
This has bonding with two non metal elements and bond by sharing electrons.
PROPERTIES
- Low melting and boiling points: Although there are strong covalent bonds between the non metals, there is weak intermolecular bonds between molecules which can break easily at low temperatures.
- Don’t conduct electricity as there are no delocalised electrons
Diamond:
Hard and lustrous
- -> Doesn’t conduct electricity as each carbon atom bonds to 4 other carbon atoms leaving no delocalised electrons
- -> High melting and boiling points as a lot of energy is required to break the strong covalent bonds
Graphite and graphene:
Slippery and conducts electricity
–> Slippery: Weak intermolecular bonds between layers allow layers to slip over each other
–> conducts electricity as each carbon atom bonds to 3 other carbon atoms leaving one delocalised electron per carbon atom.
Graphene is one layer of graphite
What are fullerenes?
Covalent structure
- shaped like a hollow ball
- Conducts electricity as each carbon atom bonds to 3 other carbon atoms leaving one mobile electron per carbon atom.
What is a nanoparticle? + uses
- It is between 1 -100 nanometers
- Has high surface area to volume ratio
Lubricants
Sun creams
deodorants
What is metallic bonding?
- Positive metal cations within a sea of delocalised electrons
Properties of metals:
1) Malleable - they have layers of cations which can slide over each other.
2) Conducts electricity - sea of delocalised electrons can conduct
3) high melting/boiling points as lots of energy is required to break the strong electrostatic force of attraction between metal ions and delocalised electrons.
Structures and melting/ boiling points:
Simple covalent bonding - low melting/ boiling points. Although they have strong covalent bonds the intermolecular bonds are weak and break easily
Giant covalent structures: High melting and boiling points as high amounts of energy required to break strong covalent bonds.
Ionic lattice structure: High melting / boiling points as large amounts of energy required to break strong forces of attraction between positive and negative ions.
Metallic: High melting and boiling points as high amounts of energy required to break electrostatic forces of attraction between metal cations and sea of delocalised electrons.
What is a pure and impure substance?
Pure: contains one element or molecule
Impure: Contains more than one element or molecule
How do you know if a substance is pure/impure?
Pure: melt over specific temperature
Impure: melt over range of temperatures and melting point is lower than pure substance and boiling point is higher than pure substance.
What is distillation?
Distillation is to separate a soluble substances - when we want to collect liquid as well
or separate mixture of liquids with very different boiling points
Distillation method:
1) Pour sample into distillation flask
2) Run cold water in condenser to keep it cool
3) Increase temperature and part with the lowest boiling point evaporates first and begins to rise.
4) The gas will run down condenser and cool forming back into its liquid state and collected in beaker
5) The liquid is now separated
What is fractional distillation?
Fractional distillation separates mixtures of liquids
Fractional distillation method:
1) Put mixture in beaker and increase temperature
2) The liquid with the lowest boiling point begins to evaporate
3) When temperature reaches boiling point on thermometer, the gas has reached the top of the column.
4) The other liquid will start to evaporate however it is cooler up the column so it will condense back down the column
5) The gas at top of column will condense in condenser and collected in another beaker.
6) Raise temperature for next liquid to evaporate.
What is filtration?
Filtration separates a insoluble from a liquid
What is crystallisation?
Crystallisation separates a soluble from a liquid - we don’t mind loss of liquid
Crystallisation method:
1) pour sample into evaporation dish and gently heat using bunsen burner.
2) The liquid will start to evaporate making the solution more concentrated
3) When crystals begin to form (point of crystalisation) remove from heat and leave at room temperature.
What are the two phases in chromatography?
Mobile –> The molecules that move (gas or a liquid)
Stationary–> The molecules that don’t move (thick liquid or solid)
Chromatography method:
1) Draw line near bottom of plate and add mixture to line
2) Put solvent in beaker and dip bottom of plate in solvent (not spot)
3) Put glass over beaker to avoid evaporation of solvent
4) As solvent goes up plate the ink moves up as well.
5) Different chemicals separate out forming spots at different places.
5) Remove plate from beaker before solvent hits top and draw solvent front
What determines the amount of time spent in mobile phase?
- How soluble the substance is in solvent
- How attracted the substance is to stationary phase
What are the two phases in gas chromatography?
Stationary phase –> Thick liquid coated in tube
mobile phase –> inert gas
What is the Rf value:
Rf value = distance travelled by solute / distance travelled the solvent
What are the two phases in paper chromatography?
Stationary phase –> Chromatography paper
Mobile phase –> solvent like water or ethanol
What is a chromatogram?
Graph for chromatography
1 - each peak is a different chemical
2- The distance of x axis from peak to y axis is the retention time ( can be used to identify substance)
3 - The area under graph is the amount of substance there is
What is an empirical formula?
It is the simplest ratio form of the atoms (eg C6H1206 = CH20)
How did Mendeleev arrange elements in the periodic table?
- In increasing atomic mass
- Grouped similar CHEMICAL properties
Why are metals malleable?
They have layers of cations which can slide over each other.
