Building Blocks

1
Unit 1
Building Blocks
2
Menu

• To work through a topic click on the title.
• Substances
• Reactions Rates
• The structure of the atom
• Bonding structure and properties
• Chemical symbolism
• The mole
• Click here to End.

3
Substances
4
Elements

• Everything in the world is made from about 100
  elements.
• Each element has a name and a symbol.
• The symbol is usually one capital letter and one
  small letter e.g. Ca
• Chemists have arranged elements in the Periodic
  Table.

5
The Periodic Table

• Chemists have arranged elements in the Periodic
  Table.
• The vertical columns are called groups.
• The horizontal rows are called periods.
• Elements in the same group of the Periodic Table
  show similar chemical properties.

6
The Periodic Table

• The elements in group 1 of the Periodic table
  are called the alkali metals. They are very
  reactive metals.

7
The Periodic Table

• The elements in group 7 of the Periodic table
  are called the halogens. They are reactive
  non-metals.

8
The Periodic Table

• The elements in group 0 (8) of the Periodic
  table are called the noble gases. These are very
  unreactive gases.

9
The Periodic Table

• The elements between groups 2 and 3 are the
  transition metals.

10
Elements

• Most elements are solid at room temperature.
• Mercury and bromine are liquid at room
  temperature.
• 11 elements hydrogen, nitrogen, oxygen,
  fluorine, chlorine, helium, neon, argon, krypton,
  xenon, radon - are gases at room temperature.

11
Elements

• Elements can be classified as metals or
  non-metals.
• There are more metals than non-metals.

12
Elements

• Many elements have everyday uses.
• Aluminium is used as kitchen foil.
• Carbon is used in pencil leads.
• Gold, silver and platinum are used in jewellery.
• Copper is used in electrical wiring.

13
Elements

• Some elements, including gold, silver and copper,
  have been known for a long time.
• The most recently discovered elements have been
  made by scientists.

14
Compounds

• Compounds are formed when elements react together.

15
Mixtures

• Mixtures occur when two or more substances come
  together without reacting.

16
Compounds

• Compounds with a name ending in ide contain
  the two elements named.
• Copper chloride contains copper and chlorine.
• Sodium oxide contains sodium and oxygen.

17
Compounds

• Compounds with a name ending in -ite or
  -ate contain the two elements named and the
  element oxygen.
• Copper carbonate contains copper, carbon and
  oxygen.
• Sodium sulphite contains sodium, sulphur and
  oxygen.

18
Chemical Reactions

• When a chemical reaction takes place one or more
  new substances are made.
• Burning a match is a chemical reaction because
  new substances are made.
• Melting ice is not a chemical reaction since ice
  is solid water.

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Chemical Reactions

• How do we know that a chemical reaction has taken
  place?
• There is a change in appearance
• A precipitate is formed
• A gas is given off
• Energy is released or taken in

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Chemical Reactions

• In an exothermic reaction energy is released.
• In an endothermic reaction energy is taken in.

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Air

• Air is a mixture of gases.
• Air is approximately 80 nitrogen and 20 oxygen.
• The test for oxygen is that it relights a glowing
  splint.
• The splint will not relight in air because there
  is not enough oxygen.

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Solutions

• A solution is formed when a substance dissolves
  in a liquid.
• A substance which dissolves in a liquid is
  soluble.
• A substance which does not dissolve in a liquid
  is insoluble.

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Solutions

• If we only dissolve a small amount of substance
  we make a dilute solution.
• If we dissolve a large amount of substance we
  make a concentrated solution.
• A solution is diluted by adding more liquid.

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Solutions

• A saturated solution is one in which no more
  substance can be dissolved.

25
Substances

• Click here to repeat Substances.
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26
Reaction Rates
27
Following the course of a reaction

• Reactions can be followed by measuring how some
  quantity we can measure changes with time.
• Reactions can be followed by measuring changes in
  concentration, mass or volume of either the
  reactants or products

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Following the course of a reaction

• The average rate of a reaction, or stage in a
  reaction, can be calculated by dividing the
  difference between the initial and final
  quantities by the time interval.
• Rate Dchange
• Dtime

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Following the course of a reaction
Volume of gas released (ml)
Time (s)
30
Following the course of a reaction
Volume of gas released (ml)
V1
t1
Time (s)
31
Following the course of a reaction
V2
Volume of gas released (ml)
V1
t1
t2
Time (s)
32
Following the course of a reaction
V2
Volume change (DV) DV V2 V1
Volume of gas released (ml)
V1
t1
t2
Time (s)
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Following the course of a reaction
V2
Time change (Dt) Dt t2 t1
Volume of gas released (ml)
V1
t1
t2
Time (s)
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Following the course of a reaction
V2
Average reaction rate between t1 and t2. Rate
DV/Dt
Volume of gas released (ml)
V1
t1
t2
Time (s)
35
Following the course of a reaction

• The rate of a reaction, or stage in a reaction,
  is proportional to the reciprocal of the time
  taken.
• Rate proportional to 1/t

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Factors affecting rate

• The rates of reactions are affected by changes in
  
• Concentration
• Particle size
• Temperature.

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Collision Theory

• Reactions will only take place when the reacting
  particles collide.

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Collision Theory

• Reactions will only take place when the reacting
  particles collide.

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Collision Theory

• The particles need to collide at the correct
  angle.

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Collision Theory

• The particles need to collide at the correct
  angle.

41
Collision Theory

• The particles need to collide at the correct
  angle.

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Activation energy
Two molecules approach each other
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Activation energy
If they dont have the required activation
energy nothing happens.
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Activation energy
Two molecules approach each other
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Activation energy
If they have the required activation energy the
molecules form the Activated complex
46
Activation energy
If they have the required activation energy the
molecules form the Activated complex
47
Activation energy
The activated complex splits apart To form the
products.
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Collision Theory

• Collision theory explains the effect of
  concentration on reaction rates.
• The more particles there are in a given volume,
  the greater the chance of collision.

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Concentration
50
Collision Theory

• Collision theory explains the effect surface area
  on reaction rates.
• Collisions can only take place on the surface.
• The larger the surface the more collisions.

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Surface Area
52
Temperature

• Each molecule has a kinetic energy.
• Not all molecules in a material have the same
  kinetic energy.
• Temperature is a measure of the average kinetic
  energy of the molecules.

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Temperature

• The higher the temperature the more energy
  molecules have.
• Molecules at a higher temperature move more
  quickly.
• This means that there are more collisions each
  second and so a faster reaction.

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Catalysts

• Catalysts speed up reactions, without being
  changed by the reaction.
• Catalysts are used in many industrial processes.
• They reduce the temperature needed, so reducing
  energy costs.

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Catalysts

• Heterogeneous catalysts are in a different state
  from the reactants they catalyse.
• Homogeneous catalysts are in the same state as
  the reactants they catalyse.

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Catalysts

• Heterogeneous catalysts work by the adsorption of
  reactant molecules.
• The adsorption of the molecules loosens bonds and
  makes it easier for the substance to react.

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Catalysts

• The surface activity of a catalyst can be reduced
  by poisoning, when surface sites are taken over
  by other substances, preventing reactants being
  adsorbed.
• Impurities in the reactants result in the
  industrial catalysts having to be regenerated or
  renewed.

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Catalytic converters

• Catalytic convertors are fitted to cars to
  catalyse the conversion of poisonous carbon
  monoxide and oxides of nitrogen to carbon dioxide
  and nitrogen.

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Catalytic converters

• Cars with catalytic converters only use
  lead-free petrol to prevent poisoning of the
  catalyst.

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Enzymes

• Enzymes catalyse the chemical reactions which
  take place in the living cells of plants and
  animals.
• Enzymes are used in many industrial processes.

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Enzymes

• Enzymes are catalysts which affect living things.
• Enzymes are used to make
• Yoghurt
• Cheese
• Medicines
• Beer

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Reaction Rates

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• Click here to End.

63
The structure of the atom
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The Periodic Table

• The elements are classified by arranging
  them in the Periodic Table.
• The atoms in the Periodic Table are listed in
  order of their Atomic Number.

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Rutherfords Atom

• Elements are made of small particles called atoms
• In the centre of the atom is the nucleus,
  containing protons and neutrons.
• Electrons orbit around the nucleus, like planets
  around the Sun.

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Atoms

• Most of the mass of the atom is found in the
  nucleus
• The nucleus contains positively charged protons.

• The nucleus also contains neutrons, which have no
  charge.
• Negatively charged electrons orbit around the
  nucleus.

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Atoms

• For each atom the Atomic Number is equal to the
  number of protons.
• The Mass Number is the number of protons
  neutrons.
• The number of neutrons is Mass Number minus
  Atomic Number.

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Atoms

• The atom is neutral because the positive charge
  of the nucleus is balanced by the negative charge
  of the electrons.
• Thus the number of electrons is the same as the
  number of protons. 

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Representing Atoms

• We represent atoms using nuclide notation

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Electrons

• The first shell holds 2 electrons.

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Electrons

• The first shell holds 2 electrons.
• The second shell holds 8 electrons

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Electrons

• The first shell holds 2 electrons.
• The second shell holds 8 electron
• The third shell holds 8 electrons

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Electrons

• The number of outer electrons in an atom is the
  same as the number of its group in the Periodic
  Table.
• Atoms with the same number of outer electrons
  will have similar chemical properties.

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Electrons

• Since electrons are impossible to track down can
  also show them pear-shaped in electron pair
  clouds
• Each cloud can hold two electrons

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Sub-Atomic Particles
Particle Charge Mass Location
Proton positive 1 a.m.u. nucleus
Neutron none 1 a.m.u. nucleus
Electron negative negligible In orbit around the nucleus
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Isotopes

• Not all atoms of the same element have the same
  mass. Most elements are mixtures of isotopes.
• Isotopes are atoms with the same number of
  protons but different numbers of neutrons.

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Isotopes

• Relative Atomic Mass is the average mass number
  of an atom.
• It is not whole number because most elements
  consist of a mixture of isotopes.
• Different isotopes have different abundances.

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The Structure of the Atom

• Click here to repeat The Structure of the Atom.
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Bonding, structure and properties
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Elements and compounds.

• All the elements in the Periodic Table, except
  the Noble Gases, form compounds.
• All the elements in the Periodic Table, except
  the Noble Gases, do not have completely filled
  outer electron energy levels.

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Elements and compounds.

• When atoms form compounds they do so in order to
  achieve a completely full outside electron energy
  level.
• To do this they must share, gain or lose
  electrons.

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Bonds

• The forces involved in sharing, gaining or losing
  electrons are called bonds.
• Bonds are the forces of attraction which hold
  compounds together.
• Some of these forces are strong, and some are
  weak.

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Bonding

• The bonds formed when atoms share electrons are
  called covalent bonds.
• The bonds formed when atoms gain or lose
  electrons are called ionic bonds.
• Metallic bonds are found in metal elements.

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Covalent bonds

• Whenever bonds are formed, the atoms must collide
  with each other.
• When some atoms collide with each other, the
  electrons in the outer shell can be shared
  between the atoms.

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Covalent bonds

• When a collision takes place between atoms it
  must have sufficient energy to form a compound
• The outer energy levels overlap and the atoms
  share the electrons.

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The Covalent Bond

• As two atoms come together the half-filled
  electron pair clouds overlap to form a new cloud.

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The Covalent Bond

• As two atoms come together the half-filled
  electron pair clouds overlap to form a new cloud.
  The covalent bond

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The Covalent Bond

• The overlap area has an increase in negative
  charge, which is strongly attracted by the
  positive nuclei of both atoms.

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Covalent bonds

• This draws the atoms close together.
• The force of attraction between the nuclei and
  the shared electrons forms a strong covalent
  bond.

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Polar covalent bonds

• Sometimes one atom has a greater force of
  attraction than the other.
• This leads to polar covalent bonding, where there
  are slight charges (shown by d and d-) on the
  atoms.

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• The bonds in water are very polar because oxygen
  attracts electrons more strongly than hydrogen.

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Ionic Bonds

• Some substances are made up of ions.
• Ions can be positively or negatively charged.
• They are formed when an atom, or group of atoms
  lose or gain electrons.

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• Examples
• Na ? Na e
• sodium atom sodium ion
• Cl2 ? 2Cl-
  2e
• chlorine molecule chloride ions

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• In ionic bonding, electrons are transferred from
  one atom to another allowing both atoms to
  achieve a stable electron arrangement.
• Ionic bonds are very strong.

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• For example, sodium and chlorine atoms would form
  an ionic bond making the compound sodium chloride
  as shown below

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Metallic bonds

• Metals lose their outer shell electrons to gain a
  stable electron arrangement, forming positive
  ions.
• These electrons are delocalised moving freely
  between these ions.

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• The attraction between the positive ions and
  delocalised electrons forms a metallic bond which
  is very strong.

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Molecules
99
Molecules

• Some substances are made up of discrete
  molecules.
• Molecules are made up of two or more atoms held
  together by strong covalent bonds.

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Diatomic molecules

• A diatomic molecule is made up of two atoms.
• Hydrogen, nitrogen, oxygen, the halogens and
  carbon monoxide exist as diatomic molecules.

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Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

102
Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

H H
103
Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

H H ? H2
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Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

105
Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

106
Diatomic molecules

• We can draw diagrams to show the formation of
  diatomic molecules.

Cl Cl ? Cl2
107
Diatomic molecules

• Some diatomic molecules involve more than one
  covalent bond.

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Covalent molecules

• We can draw similar diagrams of discrete covalent
  molecules.

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Covalent substances

• The bonds between the molecules are weaker than
  the covalent bonds within molecules.
• A covalent network structure consists of a giant
  lattice of covalently bonded atoms.

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Formulae of discrete molecules

• For discrete covalent molecules the chemical
  formula uses atomic symbols to show the number
  and type of atom present.
• For example C3H8 means that the molecule of this
  compound contains 3 carbon atoms and 8 hydrogen
  atoms.

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Other formulae

• The empirical formula shows the simplest ratio of
  particles present.
• For example C4H8 has an empirical formula of CH2.

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Other formulae

• The structural formula shows the relative
  position of atoms.
• For example C4H8 (butene)has the following
  structural formula.

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• We can write formulae by counting the atoms in a
  model or picture.

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• We can write formulae by counting the atoms in a
  model or picture.

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• We can write formulae by counting the atoms in a
  model or picture.

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• We can write formulae by counting the atoms in a
  model or picture.

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• We can write formulae by counting the atoms in a
  model or picture.

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Formulae of covalent networks

• Covalent network structures do not contain
  discrete molecules.
• Their chemical formulae are empirical formulae,
  showing the simplest ratio of the types of atom
  present.

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• SiO2 means that silicon dioxide contains two
  oxygen atoms for each silicon atom.
• SiC means that silicon carbide contains one
  carbon atom for each silicon atom.

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Formulae of ionic lattices

• An ionic structure consists of a giant lattice of
  oppositely charged ions.
• The formula for an ionic compound gives the
  simplest ratio of positive ions to negative ions.

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• NaCl means that sodium chloride contains one
  sodium ion (Na) for each chloride ion (Cl-).

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Conductivity

• An electric current is a flow of electrons.
• Conductors are materials which allow an electric
  current to pass through.
• Insulators are materials which do not allow an
  electric current to pass through.

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Conductivity

• CONDUCTORS
• Metals
• Graphite (a form of carbon - the only
  non-metallic conductor)
• Solutions of ionic metal compounds
• Molten ionic compounds

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Conductivity

• Electrons move through solids.
• Metal elements (solids) and carbon (graphite) are
  conductors of electricity because they contain
  free (delocalised) electrons.
• Metals in the liquid state will also conduct for
  the same reasons.

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Conductivity

• Covalent substances (solids, liquids, solutions)
  do not conduct electricity since they are made up
  of molecules which are uncharged.

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Ions and Conductivity

• Ions move through liquids.
• Positive ions are formed when atoms lose
  electrons.
• Negative ions are formed when at atoms gain
  electrons.

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• An ionic solution or a melt will conduct because
  its ions are free to move to the electrode of
  opposite sign.
• An ionic solid does not conduct because its ions
  are unable to move.

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Liquid or Gas

• At room temperature
• A liquid or gaseous compound will be covalent.
• A liquid or gas contains small discrete
  molecules between which there are fairly small
  forces of attraction.

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Solids

• At room temperature
• A solid compound can be ionic or covalent
• Solids are a result of very strong forces
  holding the particles together.

130
Types of Solid

• In an ionic solid these forces are the ionic
  bonds i.e. the forces of attraction between the
  oppositely charged ions.
• These forces are very strong so the melting point
  of this type of solid is very high.

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• A covalent network solid consists of a huge
  number of atoms held together by a network of
  covalent bonds.
• These covalent bonds are very strong so the
  melting point of this solid is very high.

132

• A covalent molecular solid consists of molecules
  held together by a network of van der Waals
  forces.
• These van der Waals forces are weak so the
  melting point of this solid is low.

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Soluble in water?

• Most ionic substances are soluble in water, the
  lattice breaking, to free the ions  
• Most covalent substances are insoluble in water
  but can dissolve in other solvents. 

134
Electrolysis

• Electrolysis occurs when d.c. (direct current) is
  passed through a melt, or an ionic solution.
  This changes the compound, releasing new
  substances at the electrodes.

135

• An electrolyte is a substance which conducts when
  molten or in solution.
• While most ions are colourless, some are
  coloured. e.g.
• cobalt - pink/purple copper - blue
  dichromate - orange nickel - green
  permanganate - purple

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Electrolysis

• At the positive electrode Chlorine, bromine,
  iodine or oxygen (from water) are released.
• At the negative electrode Copper, silver or
  hydrogen (from water) are released.

137
Electrolysis of copper(II) chloride

• The negative chloride ion moves to the positive
  electrode where
• 2Cl- ? Cl2 2e-

138
Electrolysis of copper(II) chloride

• The positive copper ion moves to the negative
  electrode where
• Cu2 2e- ? Cu

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Bonding, Structure and Properties

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  Properties
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Chemical Symbolism
141
Formula

• A chemical formula shows the relative number of
  each type of atom present in the compound.

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• The name can tell us how many atoms are there.

• Mono- means 1
• Di- means 2
• Tri - means 3
• Tetra- means 4
• Pent- means 5
• Hex- means 6
• Hept- means 7
• Oct- means 8

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• The name can tell us how many atoms are there.

144

• The name can tell us how many atoms are there.

145

• The name can tell us how many atoms are there.

146

• The name can tell us how many atoms are there.

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Valency

• Valency is a number which helps us work out
  molecular formulae.
• It is the combining power of the atom.

• Valency is
• Group Number
• 8 minus Group Number

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Group 1 2 3 4 5 6 7 0/8
Valency 1 2 3 4 3 2 1 0
149
Chemical Formulae

• Using valency
• Write down symbols
• Write down valencies
• Swap over
• Divide (if possible)
• Formula

150
Using valency

• carbon and oxygen
• Write down symbols C O
• Write down valencies 4 2
• Swap over 2 4
• Divide (if possible) 1 2
• Formula CO2

151
Using valency

• calcium and chlorine
• Write down symbols Ca Cl
• Write down valencies 2 1
• Swap over 1 2
• Divide (if possible)
• Formula CaCl2

152
More Valency

• Valency for ions made from more than one atom are
  found from the size of charge on ion.
• Multiple of these ions are written in brackets.

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More Valency

• OH- has valency 1
• Magnesium hydroxides formula is written Mg(OH)2

154

• copper(II) has a valency of 2
• copper(I) has a valency of 1

• Valency for transition metals (which can have
  different valencies) are given by the number
  after metals name

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Using valency

• copper(II) nitrate
• Write down symbols Cu NO3
• Write down valencies 2 1
• Swap over 1 2
• Divide (if possible)
• Formula Cu(NO3)2

156
Chemical Equations

• Reactants are the materials with which are
  present at the start of the reaction and are
  changed by the reaction.
• Products are the materials produced by the
  chemical change.
• These are separated by an arrow (which means
  gives).
• Reactants ? Products

157

• Whenever we write a chemical equation we need to
  know
• what substances are present at the start
• what are the new substances formed in the
  chemical reaction.

158

• To know the chemical reactants and products means
  we can write a word equation
• Here we are naming the reactants and products.
  e.g.
• propane oxygen ? carbon dioxide water 

159

• We need to convert the word equation into
  symbols 
• C3H8 O2 ? CO2 H2O
• If we look closely at this equation we will
  realise that it is unbalanced there are
  different numbers of atoms on each side
• 3xC 8xH 2xO ? C 2xH 3xO

160

• We must write a balanced chemical equation where
  there are equal numbers of moles of each type of
  atom on both sides.
• We can balance the equation we have been working
  with.

161

• Propane has 3 carbons so
• C3H8 O2 ? 3CO2 H2O
• Propane has 8 hydrogens so
• C3H8 O2 ? 3CO2 4H2O
• To balance out the oxygens
• C3H8 5O2 ? 3CO2 4H2O
• This is a balanced chemical equation.

162
Chemical Symbolism

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The mole
164
Formula Mass

• Formula mass is found by adding together the
  relative atomic masses of all the atoms present
  in the formula, e.g. calcium carbonate CaCO3
• Ca 40
• C 12
• O 16x3 48
• Formula Mass 100

165
The mole

• A mole is the formula mass in grams.
• If we look at the previous example 1 mole of
  calcium carbonate is 100 grams.

166
Moles

• To connect gram formula mass, mass in grams and
  number of moles use the triangle opposite
• gfm mass of 1 mole
• n number of moles
• m mass of substance

m
gfm
n
167
Using Chemical Equations

• The numbers we use to balance an equation are the
  actual numbers of moles which react.
• This gives us the mole relationship in the
  reaction.
• If we look at the example we have been given
• C3H8 5 O2 ? 3CO2 4H2O
• 1 mole 5 moles ? 3moles 4moles

168

• Since one mole is the formula weight in grams we
  can now work out the masses which react.
• C3H8 5 O2 ? 3CO2 4H2O
• 1 mole 5 moles ? 3mole 4moles
• 1x44g 5x32g ? 3x44g 4x72g
• 44g 160g ? 132g 72g
• Now by proportion we can work out any reacting
  quantities.

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Example

• How much oxygen is needed to burn 0.22g of
  propane?
• C3H8 5 O2 ? 3CO2 4H2O
• 1 mole 5 moles 3mole 4moles
•  To burn, 1 mole C3H8 needs 5 moles O2
•  44g C3H8 needs 160g O2
• 0.22g C3H8 needs 0.8g O2

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The Mole

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The End
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