chemistry notes on particle theory and bonding
The Particulate Nature of Matter
Kinetic Particle Theory
Solid
Liquid
Gas
Strong intermolecular forces
Weaker intermolecular forces
than solids
Almost no intermolecular
forces
Fixed lattice arrangement
No fixed arrangement; particles
can move and slide over each
other
Particles far apart and
move quickly
Particles vibrate in fixed
position; fixed shape and
volume
Particles slide; fixed volume
Random movement; no
fixed shape or volume
•
When a solid is heated, the particles gain sufficient energy to overcome the strong
intermolecular forces. The particles eventually can slide over each other in a more random
motion- solid expands until the structure is broken at m,p.
•
When a liquid is heated to its b.p, the particles overcome the relatively weaker
intermolecular force to escape the liquids surface and move around in continuous rapid
motion – the liquid has boiled
•
In the vapor, the particles move in rapid random motion. This movement is due to the
collision of vapor particles with air particles.
•
When gaseous particles are heated in a closed environment, the increase in kinetic energy
causes increased collisions with other particles as well as the walls of the containerpressure increases.
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States of Matter
Process
Change
Heat Energy
Exo/endothermic
Melting
S -> L
Gained
Endothermic
Boiling
L -> G
Gained
Endothermic
Condensing
G -> L
Lost
Exothermic
Freezing
L -> S
Lost
Exothermic
Sublimation
S -> G
Gained
Endothermic
Reverse sublimation
G -> S
Lost
Exothermic
Heating Curve
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Brownian motion and Diffusion
1. Brownian motion:
•
It is the random movement of particles in a liquid or a gas caused due to collision with
smaller, invisible particles
•
Evidence:
In liquid- Pollen grains in water
In gases- Smoke in air
1. Diffusion
•
It is the spreading of one substance (liquid or gas) through another from a region of high
concentration to a region of low concentration due to the continuous random motion of
particles.
•
Evidence for diffusion:
•
In liquids: potassium manganate (VII) in a beaker of water
•
In gases: a gas jar of air and a gas jar of bromine connected
•
Factors that affect the rate of diffusion:
•
Temperature increases → rate of diffusion increases
•
Lower relative molecular mass→ rate of diffusion is higher
Experimental Techniques
Measurement
Variable
Apparatus
Time
Stopwatch or Clock
Temperature
Thermomemeter (liquid in glass, thermistor or thermocouple)
Mass
Balance
Measuring Volume:
Beaker
Burette
Pippette
Measuring Cylinder
Gas Syringe
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Critertia of Purity
•
Paper chromatography:
•
Drop substance to center of filter paper and allow it to dry
•
Drop water on substance, one drop at a time
•
Paper + rings = chromatogram.
•
Principle: Difference in solubility separates different pigments
•
Substances travel across paper at different rates which is why they separate into
rings
•
Method works because different substances travel at different levels of attraction to
it
•
Stationary phase is material on which separation takes place
•
Mobile phase consists of the mixture you want to separate, dissolved in a solvent.
•
Interpreting simple chromatograms:
•
Number of rings/dots = number of substances
•
If two dots travel the same distance up the paper they are the same substance.
•
You can calculate the Rf value to identify a substance, given by the formula:
Rf Value= Distance moved by solvent DIVIDE BY Distance moved by solute
•
•
To make colourless substances visible, use a locating agent:
•
Dry paper in oven
•
Spray it with locating agent
•
Heat it for 10 minutes in oven
Assesing purity from m.p./b.p:
•
Pure substances have a definite, sharp m.p./b.p.
•
Substance+impurity has lower m.p. and higher b.p.
•
More impurity means bigger change
Filtration
•
Mixture goes in a funnel with filter paper, into a flask.
•
Residue is insoluble and stays at top.
•
Filtrate goes through
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Crystallization
•
Some water in the solution is evaporated so solution becomes more concentrated.
•
A drop is placed on a slide to check if crystals are forming.
•
Solution is left to cool and crystallise.
•
Crystals are filtered to remove solvent.
Simple Distillation
•
Impure liquid is heated
•
It boils, and steam rises into the condenser
•
Impurities are left behind
•
Condenser is cold so steam condenses to the pure liquid and it drops into the beaker
Fractional Distillation
•
Removes a liquid from a mixture of liquids, because liquids have different b.p.s
•
Mixture is heated to evaporate substance with lowest b.p.
•
some of the other liquid(s) will evaporate too.
•
A mixture of gases condense on the beads in the fractional column.
•
So the beads are heated to the boiling point of the lowest substance, so that substance
being removed cannot condense on the beads.
•
The other substances continue to condense and will drip back into the flask.
•
The beaker can be changed after every fraction
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Seperating Mixture of Two Solids
•
Can be done by dissolving one in an appropriate solvent
•
Then filter one and extract other from solution by evaporation
•
If one solid is magnetic, can use a magnet e.g. sand and iron fillings
Solvent
It dissolves…
Water
Some salts, sugar
White spirit
Gloss paint
Solvent
It dissolves…
Propanone
Grease, nail polish
Ethanol
Glues, printing inks, scented substances
Choosing a Suitable Method
Method of separation
Used to separate
Filtration
A solid from a liquid
Evaporation
A solid from a solution
Crystallization
A solid from a solution
Simple Distillation
A solvent from a solution
Fractional Distillation
Liquids from each other
Chromatography
Different substances from a solution
Atoms, Elements and Compounds
Atomic Structure and the Periodic Table
Particle
Relative charge
Mass (atomic mass)
Proton
+1
1
Neutron
0
1
Electron
-1
\frac{1}{1837}18371
•
Proton number: number of protons in an atom (and number of electrons in an atom)
•
Nucleon number: number of protons + neutrons in an atom.
•
In the periodic table
•
•
The proton number increases by 1 when you go to the right
•
When you go one element down, you increase proton number by 8 in the first 3
periods (transition elements not included)
Isotopes: atoms of the same elements which have the same protons number, but different
nucleon number
•
E.g. Carbon 12 and Carbon 14.
•
Two types: non-radioactive isotopes and radioactive-isotopes which are unstable
atoms that break down giving radiations
•
Medical use: cancer treatment (radiotherapy) – rays kill cancer cells using cobalt-60
•
Industrial use: to check for leaks – radioisotopes (tracers) added to oil/gas. At leaks
radiation is detected using a Geiger counter.
•
Electrons are arranged in electron shells.
•
Atoms want to have full outer shells (full set of valency electrons), this is why they react.
•
Noble gases have full outer shells so they have no need to react.
•
Electron shell structure: 2, 8, 8, 18.
•
More reactive elements have a greater desire to have a full outer shell, so also form more
stable compounds.
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Bonding: the Structure of Matter
•
Element: substance that cannot be split into anything simpler, in a chemical reaction. Each
element has a unique proton number.
•
Mixture: two or more elements mixed together but not chemically combined
•
Compound: substance in which two or more different elements are chemically combined
Metals
Non-metals
Strong
Brittle
Good conductors of heat & electricity
Poor conductors of heat & electricity (except graphite)
High m.p. and b.p.
Lower m.p. and b.p. than metals
High density
Low density
Forms basic oxides
Forms acidic oxides
Forms cations in reactions
Forms anions in reactions
Malleable and ductile
Sonorous
Some are magnetic
•
Alloy: Mixture of two or more metals or mixture of one or more metal with a non-metal, to
improve its properties
Ions and Ionic Bonds
•
Chemical bond formed by transfer of \overline{e}es from one atom to another
•
Metals lose \overline{e}es to form cations, non-metals gain \overline{e}es to form anions
•
Positive cations & negative anions attract to each other
•
Strong electrostatic force of attraction between positive cations and negative anions is
called ionic bonding
Property
Reason
Form giant lattice
Cations and anions attract
High m.p. and b.p.
Strong bonds between ions
Don’t conduct electricity when solid
Ions can’t move
Conduct electricity when molten/aqueous
Ions can move
Usually soluble in water
Not required
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Molecules and Covalent Bonds
•
When atoms share \overline{e}es to obtain a noble gas electron structure
•
Covalent bonding takes place between non-metals only
Single Bond
Double Bond
Triple Bond
2ē shared
4ēs shared
6ēs shared
(1 from each atom)
(2 from each atom)
(3 from each atom)
png)
Macromolecules
Diamond
Graphite
Silicon Dioxide
Four bonds
Three bonds
Makes up sand
High m.p.
Made of flat sheets
Each Si is bonded to 4 oxygen
atoms, and each oxygen is
bonded to 2 silicon atoms
Doesn’t
conduct
Held together by weak forces so is soft ∴
used as a lubricant
∴ it has a high m.p. and is
hard, like diamond
Used for
cutting as is
srongest
known
substance
Conducts electricity as it has one free e-
•
Melting point: high – structure made up of strong covalent bonds
•
Electrical: don’t conduct electricity – have no mobile ions or electrons, except for graphite
•
Strength: hard – exists in tetrahedral structure but graphite is soft
Metallic Bonding
Positive ions held together by electrons – acts like glu
…
