Basic chemistry
The key to success is to know the basic chemistry building building blocks of the pyramid
The understanding of chemistry involves a progression in the sequences of certain chemical concepts.
The basic building blocks start with the junior high school years and develop into the senior years.
While high school chemistry students study a much larger range of topics the key to success is to be firmly established in the each of the above chemical building blocks.
Acids and bases
Acids, bases and indicators
Acids and bases were first thought as follows. An acid is a substance that tastes sour and a base is a substance that tastes bitter. Most acids and bases however, are NOT SAFE to taste.
A strong base is soluble in water and is called an alkali. Alkali solutions are caustic and can cause severe burns. Alkali solutions dissolve fats and are used as cleaning agents. Examples include cleaning products containing cloudy ammonia and oven cleaners which contain caustic soda or sodium hydroxide.
| Alkali (strong bases - soluble) | Bases (low solubility) | ||
| Name | Chemical formula | Name | Chemical formula |
| Sodium hydroxide | NaOH | Magnesium hydroxide | Mg(OH)2 |
| Potoassium hydroxide | KOH | Calcium hydroxide | Ca(OH)2 |
| Ammonia | NH3 | Aluminum hydroxide | Al(OH)3 |
The oxides of the Group I elements or alkali metals all dissolve in water to produce alkali solutions.
Eg. Sodium oxide + water → sodium hydroxide
Na2O + H2O → 2NaOH
Strong acids are corrosive in nature and dissolve active metals like magnesium, zinc and iron. examples of strong acids include sulfuric acid, hydrochloric acid and nitric acid.
| Name of acid |
Chemical formula |
| Hydrochloric acid | HCl |
| Nitric acid | HNO3 |
| Nitrous acid | HNO2 |
| Acetic acid | CH3COOH |
| Sulfuric acid | H2SO4 |
| Sulfurous acid | H2SO3 |
| Carbonic acid | H2CO3 |
| Phosphoric acid | H3PO4 |
Soluble non-metallic oxides dissolve in water to produce acidic solutions.
Eg. Water + carbon dioxide → carbonic acid
H2O + CO2 →H2CO3
Chemical indicators are substances that change color in the presence of an acid or base. They can be used to safely to help us determine if a substance is acidic or basic.
Examples of chemical indicators include litmus paper, phenolphthalein, bromothymol blue, methyl red and methyl orange. Litmus is pink in acidic solutions and blue is basic solutions.
Atoms
Atoms
An atom is the smallest particle of an element that has the properties of that element.
There have been various models that have been proposed to describe the structure of the atom.
- Billiard ball model - John Dalton
- Plum pudding model - J.J. Thomson
- Nuclear model - E. Rutherford
- Shell model of the atom - N. Bohr
- The quantum model of the atom - various scientists.
The atom consists of three subatomic particles. The proton, the neutron and the electron.
In a chemical reaction all the action takes place in the outer or valence shell of electrons.
Molecules
What is a molecule? A molecule is a group of atoms that joined together by a covalent bond.
Models of the atom
MODELS OF THE ATOM - SUMMARY
| Scientists |
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Description |
Evidence |
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The atom is the smallest particle of an element. The atom is a solid, indestructible unit. Atoms of different elements have different masses. |
Law of Constant Proportions. (% mass composition) Law of Multiple Proportions. E.g. Two compounds of nitrogen oxide. The ratio of oxygen between both compounds is 2:3. |
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J. Dalton |
The Billiard Ball model (1808) |
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The ‘pudding’ is the positive material of an atom. The embedded ‘raisins’ are negative electrons. |
Cathode rays (negative particles or electrons) Canal rays (positive particles with large masses) |
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J. J. Thomson |
The Plum Pudding model (1903) |
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The mass and positive charge of an atom is concentrated in a small core called the nucleus. Negative electrons orbit the nucleus. The atom is mostly made up of empty space. |
The scattering of alpha particles through thin gold foil. A small percentage of particles were deflected at large angles, some even returning. ‘it is like a cannonball rebounding off a piece of paper’ |
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Ernest Rutherford |
The Nuclear model (1911) |
Protons & later neutrons are identified. |
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Electrons are arranged around the nucleus in discrete energy levels or shells. |
Explains emission spectra (flame test) Explains patterns in the successive ionisation energies of an element. |
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Neils Bohr |
The Shell model (1923) |
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s-orbital |
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Electrons exist in orbitals. i.e. an area surrounding the nucleus that has a 90% probability of containing an electron. |
Better explains anomalies in successive ionisation energies and emission spectra. |
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Orbitals differ in shape(s, p, d, & f orbitals) and size(dependent upon energy level). No orbital may contain more than two electrons. |
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Various Scientists |
The Quantum model (1935) |
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Balancing chemical equations
Balancing chemical equations
In a chemical reaction mass is always conserved. This means that matter is not created nor destroyed. You can turn atoms of lead into atoms of gold in a chemical reaction. The same atoms are simply rearranged as old chemical bonds are broken and new bonds formed.
When a chemical equation is balanced the number and type of reactant atoms must be the same as the number and type of product atoms.
- 2Mg + O2 → 2MgO
- 4Al + 3O2 → 2Al2O3
- 2HCl + Zn → ZnCl2 + H2
- H2SO4 + Zn → ZnSO4 + H2
- 2H2 + O2 → 2H2O
- N2 + 3H2 → 2NH3
- CH4 + 2O2 → CO2 + 2H2O
- 2Na + 2H2O → 2NaOH + H2
- CuO + CO → Cu + CO2
- H2 + I2 → 2HI
Chemical formula
Help with Chemical formula
The use of chemical formula is a shorthand way of showing
- the number and type atoms in a compound and
- the number of atoms in a molecular element.
| Compound | Molecular element | ||
| Water | H2O | Hydrogen | H2 |
| Carbon dioxide | CO2 | Oxygen | O2 |
| Glucose | C6H12O6 | Ozone | O3 |
| Sodium chloride | NaCl | Chlorine | Cl2 |
| Magnesium sulfate | MgSO4 | Sulfur | S8 |
The chemical symbols of the elements are shown in the Periodic table. For example the element hydrogen is given the chemical symbol H and the element oxygen the chemical symbol O.
In a chemical formula the chemical symbol of each element is shown with subscript numbers which tell us the numbers or ratio of atoms in the compound or molecular element.
For example the compound water has the chemical formula H2O. This tells us water is made up of two elements, hydrogen and oxygen. The subscript 2 in H2O tells us there are two parts hydrogen to one part oxygen. Note: The subscript 1 is never but taken for granted. That is why water has the formula H2O and not H2O1
Some elements also exist as molecules. Molecules are groups of atoms joined together by chemical bonds. Molecular elements like compounds also have a chemical formula. Examples of molecular elements include hydrogen, H2 and ozygen O2.
Hydrogen atoms are too unstable to exist by themseleves as free atoms. They pair up to with other hydrogen atoms to form hydrogen molecules which are much more stable. The chemical formula of the hydrogen molecule is therefore H2. This means two hydrogen atoms are joined together. The molecule O2 is also much more stable than single oxygen atoms.
The combining power or valency of an element determines the ratio that atoms will combine with one another. A knowledge of valencies can help us predict the chemical formula of a substance. Atoms achieve a stable outer shell of electrons by transferring or sharing electrons. They always combine with one another n simple whle number ratios.
Writing chemical formula
Writing Chemical Formula
How do you write chemical formula?
When writing chemical formula for compounds it is important to know the combining powers or valencies of the elements. This allows you to determine the ratio the elements combine in. All compunds are made of of elements that are chemically combined in whole number ratios. eg. Water is made up of 2 parts hydrogen to 1 part water. Its chemical formula is therefore H2O
The elements in the periodic table are grouped together in columns with similar combining powers. These valencies also contain a charge. Eg. Mg is in group 2. It has a valency of 2+, O is in group 6 and has a valency of 2-
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Valency |
1+ |
2+ |
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3+ |
4 |
3- |
2- |
1- |
0 |
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Periodic table |
H |
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Li |
Be |
Transition block |
B |
C |
N |
O |
F |
Ne |
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First 20 elements |
Na |
Mg |
variable |
Al |
Si |
P |
S |
Cl |
Ar |
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K |
Ca |
valencies |
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A metal combines with a non-metal to produce an ionic compound. During the reaction ions or charge particles are formed. Refer to the valencies in the table above to help you determine the ionic charge. Eg. The sodium ion Na+ has a charge of +1, the calcium ion, Ca2+ is +2, the oxide ion, O2- is -2 and the chloride ion, Cl- is -1. Note: The 1 is ignored when determining the ionic charge in group I and group 7 elements.
When writing chemical formula determine the simplest ratio of positive and negative ions that are needed to produce a neutral compound. These numbers are written as subscripts. Eg. Al2O3
Look at the following worked examples on how to determine the chemical formula of compunds.
Chemical compound |
Make the simplest neutral compound from the ions |
Chemical formula (ignore ions) |
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Sodium chloride |
Na+ Cl- Check: + 1 + -1 = 0 |
NaCl |
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Magnesium chloride |
Mg2+ Cl- Check: 2+ + 2- = 0 |
MgCl2 |
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Aluminum chloride |
Al3+ Cl- Check: 3+ + 3- = 0 |
AlCl3 |
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Calcium oxide |
Ca2+ O2- Check: 2+ + 2- = 0 |
CaO |
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Sodium oxide |
Na+ O2- Check: 2+ + 2- = 0 |
Na2O |
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Lithium phosphide |
Li+ P3- Check: 3+ + 3- = 0 |
Li3P |
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Aluminum oxide |
Al3+ O2- Check: 6+ + 6- = 0 |
Al2O3 |
Chemical reactions
Chemical reactions
Assumed perquisite knowledge:
Students understand the difference between a physical change and a chemical change
Introduction
- A chemical reaction occurs when substances combine or breakdown to produce something NEW.
- A chemical reaction is accompanied by a chemical change. eg. permanment change in color or the production of a gas.
Chemical changes indicate that something new has been produced. eg. the permanent color change produced as bread is toasted in a toaster or the smoke from a burning match.
- Chemical reactions are generally difficult to reverse. eg. turning a slice of toast into a slice of fresh bread.
The chemicals that react are called the reactants. The new materials that are produced are called the products.
A chemical reaction can be shown by the use of a word equation. The ==> means 'give or produce'
| Reactants | ==> | Products |
| chemicals that react | ==>
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chemicals that are produced |
| hydrogen + oxygen | ==> | water |
| hydrogen peroxide | ==> | water + oxygen |
| magnesium + oxygen | ==> | magnesium oxide |
| sodium chloride | ==> | sodium + chlorine |
Types of chemical reactions.
- There are many different types of reactions which include
- Corrosion of metals. Eg. The rusting of iron
- Combustion: Eg. The burning of fossil fuels
- Acid and base : Eg. Hydrochloric acid and sodium hydroxide.
- Acid and carbonate: Eg. Vinegar and bicarb of soda
- Acid and active metal: This type of reaction is also called a single displacement reaction. Eg. The dissolving of magnesium ribbon in hydrochloric acid.
- Precipitation: This type of reaction is also called a double displacement reaction. Eg. Mixing colorless lead nitrate and potassium iodide to yellow produce lead iodide.
- Decomposition: Eg. Hydrogen peroxide being broken down into water and oxygen
- Synthesis: Eg. The burning of magnesium in air to produce magnesium oxide.
- Displacement:. Eg. The production of copper wool by from steel wool being placed into a solution of copper sulphate.
- Redox (Reduction/ Oxidation): Eg. Making a battery.
- Condensation: Eg. Glucose and Fructose producing sucrose
- Dehydration: Eg. Adding concentrated sulphuric acid to sugar
- Substituion: Eg. Bromine reacting with octane in the presence of UV light.
- Addition: Eg. Adding bromine to cyclohexene
- Polymerisation: Eg. making Nylon, polyethylene
- Fermentation: Eg. The making of wine
- Exothermic: Eg. The thermite reaction is used to weld rail tracks together. The reaction is so hot molten iron is produced!
- Endothermic: Eg. An ice pack. Mix the contents inside the packet and the mixture becomes cold
Chemical change
Chemical change
A chemical change is a sign that indicates that a chemical reaction has occurred.
Chemical changes include
- The production of a gas. Eg. Fizz from sherbet
- A permanent color change. Eg. A red solution changing to a colorless solution
- The production of light. Eg. Glow in the dark light sticks which is an example of chemiluminesce
- The production of a flame. Eg. A Bunsen burner
- The dissolving of an insoluble solid. Eg. Magnesium dissolving in acid.
- The production of an insoluble solid. Eg. The production of a precipitate
These changes indicate that something new has been produced.
Physical changes on the other hand are easy to reverse and don't produce anything new. They only involve a change in the physical states (solid. liquid and gas). eg. the melting of an ice cube and steam being produced from a kettle.
Corrosion
Corrosion reactions
Corrosion is the loss of metallic properties of a metal as the metal reacts with the atmosphere or water. e.g. strength, lustre or shine and electrical conductivity.
Rust is brownish red in color and is formed from the corrosion of iron. Other metals like copper and aluminium also corrode or weaken.
For corrosion to occur both water and oxygen need to be present.
Examining the corrosion of iron using nails:
| Oxygenated water (shaken) |
Humid air |
Dry air (anhydrous CaCl2) |
Deoxygenated water (Boiled water/ oil layer) |
Salt water |
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Rust |
Rust |
No rust |
No rust |
Extensive rust |
If a nail is placed in deoxygenated water it will not rust. If a nail is placed in dry air it will not rust. For rust to occur both oxygen and water need to be present. The presence of salt accelerates or speeds up the rate of corrosion.
The chemical formula of rust is Fe2O3.nH2O
The process of rust formation is due to a series of chemical reactions. Points of stress acts in the nail allow the iron to be easily oxidised. Carbon impurities in the nail allow water to be reduced. An internal battery or galvanic cell is set up.
Oxidation of iron at points of stress in the crystal lattice: 2Fe(s) ==> 2Fe2+(aq) + 4e-
Reduction of water at the site of carbon impurities: O2(g) + H2O(l) + 4e- ==>4OH-(aq)
Overall equation: 2Fe(s) + O2(g) + H2O(l) ==>Fe(OH)2
The iron(II) hydroxide is converted to rust through a serious of reactions.
The ion(II) hydroixde firstly oxides to iron(III) oxide.
1. Fe(OH)2(s) =oxidation-=> Fe(OH)3
The iron(III) oxide then changes to rust through a dehydration reaction.
2. Fe(OH)3(s) =dehydration=> Fe2O3.nH2O(s) or rust
Rust does adheres loosely to the surface of the metal. This exposes the metal to more and more water and oxygen allowing rust to continue to proceed.
Compounds
Compounds
Introduction
Compounds are pure substances that are made up of two or more elements that are chemically combined in fixed mass ratios.The elements in the compound are joined together by chemical bonds.
The properties of a compound are unique are greatly differ from the elements that make make up the compound.
How do you name compounds?
When compounds are named the name of the second element is changed to an “ide” suffix to indicate that the elements are chemically combined and are not just mixtures. Also by convention the metals are named first. Eg. The reaction of magnesium metal and oxygen produces the compound magnesium oxide. The reaction of iron and sulfur produces the compound iron sulfide.
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Element 1 |
Element 2 |
Compound ("ide" suffix) |
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Sodium |
Chlorine |
Sodium chloride |
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Barium |
Sulfur |
Barium sulfide |
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Aluminum |
Oxygen |
Aluminum oxide |
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Magnesium |
Nitrogen |
Magnesium nitride |
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Potassium |
Fluorine |
Potassium fluoride |
What is a chemical formula?
All compounds have a chemical formula which tell us
- the elements that are present in the compound and
- the ratio of these elements in the compound.
For example
- the chemical formula for water is H2O. This means that there are two parts hydrogen to one part oxygen.
- the chemical formula for salt is NaCl. This means that the ratio of sodium to chlorine parts is 1:1
Ionic or covalent?
Compounds may be divided into two main groups, ionic compounds or covalent compounds.
As a general rule it is helpful to know the following
| Ionic Compounds | Covalent compounds |
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Made of a metal + non-metal Eg. Sodium chloride, NaCl |
Made of non-metal + non-metal Eg. Water, H2O |
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Composed of positive and negative ions Eg. Na+ and Cl- Are good electrolytes |
Composed of neutral or unchanged molecules. Eg. H2O Are poor electrolytes |
An electrolyte is a liquid that conducts an electic current. The liquid may be molten or aqueous which means dissolved in water.
Ionic substances are made up of charged particles called ions. eg. Na+ and Cl-
Postive ions are called cations and negative ions anions. A helpful way of remembering cations are positives is that the t in cations looks like a + sign!
The positive sodium ion, Na+ is an example of a cation and the negative chlorine ion, Cl- is an example of anion.
When an ionic compound is dissolved in water the postive and negative ions are surrounded by the water molecules. The symbol aq means aqueous or surrounded by water molecules.
The dissolving of sodium chloride or common table salt, chemical formula NaCl is gven by the following chemcial equation.
NaCl(s) → Na+(aq) + Cl-(aq)
(s) = solid
(aq) = aqueous
Ionic substances are good electrolytes or conductors of electricity when dissolved in water because the charged ions are able to move in an electric field.
The covalent compound water on the otherhand is a relatively poor conductor of electricity. It is made up mostly of neutral water particles which are not affected by an electric field.
Please note that water always contains a small amount of H+ and OH- ions and is able to conduct electricity at high voltages, so always be careful. Only test the conductivity of water at school under the directions of a science teacher. A low voltage power pack will be used.
Matter
What is matter?
Matter is anything that has mass and volume (takes up space).
There are three physical states of matter. Solid, liquid and gas.
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| Solid ice | Liquid water | Iodine gas |
Solids retain their shape. They have a fixed volume.
Liquids take up the shape of their container. They have a fixed volume.
Gases fill their container. They have a variable volume. This means the volume changes. It depends upon the volume of the container.
Experiments - physical changes
Experiments and ideas: Physical changes
- Can the three states of water exist together in a test tube?
- Is steam different from water vapour?
- How do clouds form?
- Water passing through a beaker?
- Examine your breath!
- Boil water in a paper cup.
- How to pick up an ice cube with string and salt?
- To sublime or not to sublime! That is the question.
- Does water boil past 100ºC?
- Observe a candle burn
- How to make a heat pack. (Sodium acetate)
Physical change
Physical changes
Matter exists in one of three physical states - solid, liquid or gas.
In a physical change matter changes state from one physical state to another.
For example when an ice cube melts it changes from the solid state to the liquid state.
Physical changes are easily reversible. In the melted ice cube is put back into the freezer it will change back into a solid.
Key points:
- Matter exists in three physical states - solid, liquid and gas.
- Matter can change from one physical state to another.
- The physical changes of state are easily reversible
- Energy is absorbed or given off during physical changes of state.
What are the physical changes of matter?
- A solid changing to a liquid it is called melting or fusion.
- A liquid changing to a gas is called evaporation.
- A gas changing to a liquid is called condensation.
- A liquid changing to a solid is called solidification or freezing.
- A solid changing to a gas is called sublimation.
Examples of physical changes.
| Physical change | Example |
| Sublimation | Dry ice change from a solid to a liquid |
| Melting or fusion | An ice cube melting |
| Condensation | The formation of dew on grass in the morning |
| Evaporation | A puddle disappearing on a hot day |
| Solidification or freezing | The formation of hail stones |
The particle theory
The particle theory of matter
The particle theory states
- All matter is made up of particles.
- All particles are attracted to one another.
- All particles are constantly moving.
- Temperature is a measure of the average speed of the particles.
This theory can be used to help explain some of the properties of matter.
The Properties of Solids, Liquids and Gases and the Particle Theory
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variable shape variable volume can be compressed rapid diffusion* |
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Conical |
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Particle |
The particles are close together and are vibrating in fixed positions. |
The particles are close together and are moving slowly over one another. | The particles are far apart and are moving quickly past one another. |
* Diffusion is the random movement of particles from an area of high concentration to an area of low concentration.
Mole Chemistry
The mole concept
The mole concept is in chemistry used to calculate the quantity or amount of chemical substances that are used and produced in a chemical reaction.
There are various words in English that are associated with various quantities as show by the table below.
Terms and quantities
| Term | Dozen | Century | Gross | Ream | Millenium |
| Quantity | 12 | 100 | 144 | 500 | 1 000 |
In Chemistry the quantities of a dozen, a century, a gross, ream and millenium are far too small.
Even a million is too small. One million atoms of iron weighs 0.0000000000000000928 grams!
Chemist’s measure atomic particles using a large QUANTITY called the mole.
One mole is equal to 602214179000000000000000 or 6.022 x 1023 particles.
Scientists have defined a mole as the number of carbon atoms in exactly 12 grams of carbon-12.
This number is called AVOGADRO’S NUMBER.
Amedeo Avogadro was an Italian physicist whose work lead to the development of the mole.
One mole is 6.022 x 1023 particles
The symbol for the number of moles is n. The unit used in measurement is the mol.
A description of the particle should be included. In Chemistry the particles may be atoms, ions, molecules or sub-atomic particles like the electron.
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Shorthand notation |
n(Fe) = 1 mol |
n(H2O) = 1.5 mol |
n(OH-) = 0.25 mol |
n(e-) = 0.1 mol |
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Means |
1 mole of iron atoms |
1.5 moles of water molecules |
0.25 moles of hydroxide ions |
0.1 moles of electrons |
Periodic table of elements
The Periodic table of elements
Elements are
- pure substances which cannot be broken down into simpler substances by thermal (heat), chemical, or electrical means.
- composed of the same type of atoms. i.e. small particles that have identical chemical and physical properties.
For example oxygen gas cannot be broken down into anything simpler so it is called an element.
Water on the other hand can be broken down into the simpler substances, hydrogen and oxygen. Water is not an element.
Elements are the building blocks of matter and combine with one another in chemical reactions to form new substances called compounds. eg. water, H2O
B. SYMBOLS OF ELEMENTS
There are about 90 naturally occurring elements.
Each element is given a name and a symbol. eg. Hydrogen, symbol H and Oxygen, symbol, O
Chemical symbols are used as a means of chemical shorthand for the elements.
- They are listed in the Periodic table.
- The first letter is ALWAYS a CAPITOL letter. eg. O for oxygen
- If the element has two letters the second letter is always lower case.
eg. The symbol for the element Cobalt is Co and not CO which is chemical formula for carbon monoxide.
eg. The symbol for the element Nobellium is No and not NO which is chemical formula for nitrogen monoxide.
All of the elements that we know and their chemical symbols are listed in the periodic table of the elements.
- The symbols of some elements are also based upon their Latin names.
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SYMBOLS FOR ELEMENTS |
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Al |
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Au |
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Ar |
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Am |
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B |
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Be |
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Bi |
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Br |
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C |
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Ca |
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Cu |
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Cr |
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Co |
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F |
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Fe |
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N |
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Ni |
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Nd |
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P |
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Pt |
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Pb |
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Separating mixtures
Separating mixtures into pure substances.
There are a variety of techniques that can be used to separate mixtures into pure substances. Eaxh method uses differences in the physical properties of the materials in the mixture to achieve separation.
| Method of separation | Used to separate ... |
| Filtration | an insoluble solid from a liquid based upon differences in size. eg. clay from water |
| Evaporation | a soluble solid from a liquid based upon differences in boiling points. eg. salt from sea water |
| Crystallisation | two or more soluble solids from one another based upon differences in solubilities |
| Distillation | a solvent from a soluble soild based upon differences in boiling point. eg. water from sea water |
| Fractional distillation | miscible liquids from one another based upon differences in boiling point. eg. water and ethanol (alcohol) |
| Separating funnel |
immiscible liquids from one another based upon differences in miscibility. eg. oil and water. |
| Magnetism | solids from one another based upon differences in their ferromagnetic properties. eg. aluminum and iron. |
| Paper chromatography | soluble substances from one another based upon differences in retention rates as a solvent moves over paper. |
| Decanting | an insoluble solid from a liquid by carefully pouring off the liquid. Based upon differences in density. |
Mixtures
Mixtures
Mixtures are made up of many different types of particles. eg. conglomerate rock is a good example of a mixture. Dirt is also a mixture of different things. You can easily see the different types of particles.
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Examples of chemical mixtures are solutions, suspensions, solids. The following picture is a mixture of copper sulfate and water.
Mixtures are defined as impure substances that can be separated into pure substances by physical process such as distillation, froth flotation, decanting, centrifuging, crystallization, fractional distillation, evaporation, filtration and chromatography.
Mixtures may be classified as homogeneous or heterogenous in nature.