Chemical compounds
Nature of Chemical Compounds.
Mixtures
Solutions.
Alloys
Chemical bonds.
Ionic bonds.
Covalent bonds.
Molecules.
Compounds with ionic and covalent bonds.
Oxidation.
Functional groups.
Bond chains.
Inorganic and organic compounds.
Mole.
Nature of Chemical Compounds.
There are only 118 known elements.
But, there are more than 10 million chemical compounds.
Elements tend to combine with each other, to form compounds.
Many of the substances we known of, or use, are chemical compounds.
When one or more elements, are chemically bonded to each other,
they are called as a chemical compound.
These bonds involve, donating or sharing, electrons.
A chemical compound, is constituted of more than 1 element.
A chemical compound, is the result of a chemical reaction.
The properties of a chemical compound, is very different,
from the properties of it’s constituent elements.
In most chemical compounds, the properties, of the compound, will be unique,
and no way related to the properties of it’s constituents.
For example, Sodium chloride, or common salt, is a chemical compound.
It’s properties are in no way related, to the properties of sodium or chlorine.
Each of the millions, of the chemical compounds, have unique properties.
This makes chemistry, a much more varied, and interesting subject.
We cannot create new elements with chemical reactions.
But, we can create, many more new compounds.
There are some processes, which are not chemical reactions.
Being aware of this, will help us differentiate, chemical compounds.
Mixtures.
The atmosphere contains oxygen, hydrogen, nitrogen, and other gases.
They are mixed together.
But they do not form chemical compounds, with each other.
The elements retain themselves as elements, in the mixture of atmospheric air.
If we mix salt and pepper, the substances, do not chemically react,
to form a new substance.
When we grind many spices together, in a mixer, they do not chemically react,
to form a new substance.
They are just a mixture of different spices.
Solutions.
Oxygen gas, dissolves in water.
It does not chemically react with water.
It is the dissolved Oxygen, which exists as Oxygen, that fish breathe.
The gills in the fish, separate the Oxygen, from the solution, and breathe it.
Common salt, sodium chloride dissolves in water.
There is no chemical reaction.
When we evaporate the water, the salt remains behind.
When we evaporate salty sea water, the salt remains behind.
Substances in a solution, can be separated by a non chemical process.
Sugar dissolves, in milk.
When a solid dissolves in a liquid, the liquid that dissolves the solid,
is called a solvent.
The substance that dissolves is called as a solute.
Alloys.
Steel is much stronger, than Iron.
Steel is a mixture of Iron, and Carbon.
Such a mixture is called an Alloy.
There is no chemical reaction between the Iron, and the carbon, in steel.
Stainless steel, is an alloy of Iron, carbon and chromium.
Though stainless steel has distinctive properties, it is still not a compound.
It is an alloy, of Iron, carbon, and chromium.
An alloy of two elements, can have some very useful properties.
Early civilisations, realised the usefulness of alloys.
One of the earliest alloys used was bronze.
Bronze is an alloy, of copper and tin.
It had widespread use, from ornaments, to weapons.
It was so strong and durable, bronze artefacts, used thousand of years ago,
are even today excavated, by archaeologists.
The period of time in history, when bronze was widely used,
is called the bronze age.
We can appreciate, that mixtures, solutions, alloys, etc are not chemical compounds.
Chemical bonds.
One of the most distinctive feature, of a chemical compound, is that the elements,
in the compound, are bonded by chemical bonds.
This involves donating or sharing valency electrons, of the elements.
Chemical bonds are formed, broken or reformed in chemical reactions.
Ionic bonds.
When an element, donates an electron, to another element, an ionic bond is formed.
For example, sodium has a valency of 1.
It has 1 electron in the outer most shell.
Chlorine has 7 electrons, in the outer most valency shell.
Sodium and chlorine, combine to form a chemical compound, sodium chloride.
Here, sodium donates an electron, and becomes a positively charged sodium ion.
Sodium ion is represented as N, a, superscript +.
We will represent it as N, a, +.
Chlorine receives an electron, and becomes a negatively charged chlorine ion.
Chlorine ion, is represented as C l minus.
The electro static attraction, between the positively charged sodium ion,
and the negatively charged chlorine ion, forms an ionic bond.
The resultant is the chemical compound, sodium chloride, or common salt.
The positively charged N, a, + ion, is called, as a cation.
The negatively charged C l minus ion, is called as an anion.
In an ionic representation, Sodium chloride, can be represented as N, a, + C l minus.
The chemical bond can be represented as a short line, or dash.
So, sodium chloride, can be represented as N, a, dash C l.
As a condensed chemical formula , it is represented, as just N, a, C l.
Sodium is a highly reactive toxic metal.
Chlorine is a highly reactive gas.
Sodium chloride, is an essential ingredient in our food.
The properties of a compound, is unique, and cannot be derived,
from the properties of it’s constituents.
This is true for all the compounds we discuss.
Most salts form ionic bonds.
Elements in group 1, of the periodic table, typically form single ionic bonds,
with elements in group 7, of the periodic table.
Potassium chloride, is another example of a salt with an ionic bond.
It is represented as K dash C l.
Chemical compounds, with ionic bonds, are also called as ionic compounds.
Some examples of ionic compounds, with a single ionic bond are:
Sodium bromide. N, a, B r.
Potassium bromide. K, B r.
Sodium Fluoride. N, a, F.
Potassium Iodide. K,I.
Magnesium chloride. M g, C l.
Silver chloride. A, g, C l.
Magnesium, belongs to group 2, and has a valency, of 2.
Chlorine, belongs to group 7, and can accept 1 electron.
Magnesium forms a chemical compound, with chlorine, by donating,
1 electron each, to 2 chlorine atoms.
This can be written in the ionic form as M g, 2 +, 2, C l minus.
It can also be represented as C l dash, M g, dash C l.
In this compound, there are 2 ionic bonds.
Some example of compounds, with 2 ionic bonds are:
Calcium chloride. C,a, C l 2.
Potassium oxide. K 2, O.
Magnesium oxide. M g, O.
Magnesium oxide is a raw material, for manufacturing cement.
It is also used, as an antacid, in medicine.
Lead chloride. P b, C l 2.
It is common to find an ionic bond, when a metal combines, with a non metal.
Covalent bonds.
When 2 elements share electrons, to form a chemical compound,
the bond is called as a covalent bond.
Carbon belongs to group 14, and has 4 electrons, in the valency shell.
Oxygen belongs to group 16, and has 6 electrons, in the valency shell.
Carbon shares 2 electrons each, with 2 oxygen atoms, to form covalent bonds.
The resultant chemical compound, is carbon dioxide, or C O 2.
In a covalent bond, the electrons, are attracted by the nuclei, of both the elements.
That is, the shared electrons, behave as if they belong to both, carbon and oxygen.
This binds together, carbon and oxygen, to form carbon dioxide, or C O 2.
When 2 electrons are shared, it is called as a double bond.
So, carbon dioxide, is represented as O, double bond, C, double bond O.
This satisfies oxygen, because, the 2 shared electrons,
complete the octet of 8 electrons, in the valency shell.
This satisfies carbon, because the four shared electrons,
complete the octet of 8 electrons, in the valency shell.
Carbon is a combustible solid.
Oxygen is essential for breathing.
Carbon dioxide is a major pollutant of the atmosphere, resulting from,
emissions from industries, and vehicles.
Hydrogen, has 1 electron in the valency shell.
2 Hydrogen atoms, combine with 1 oxygen atom, to form water.
This is a covalent bond.
The 2 hydrogen atoms, share an electron, with the oxygen atom.
2 covalent bonds, are formed in water, or H 2 O.
This can be represented, as H, dash O, dash H.
Water has unique properties.
The properties of water, has no relationship to the properties of oxygen or hydrogen.
Hydrogen is a light, reactive gas.
Oxygen is an essential gas, for most living organisms.
Water is the most abundant liquid, on earth.
Some examples, of compounds, with covalent bonds, are:
Ammonia. N H 3.
In ammonia, 3 hydrogen atoms, share 1 electron with a nitrogen atom.
Three covalent bonds are formed.
Ammonia is used in the fertiliser, and pharmaceutical industry.
Methane. C H 4.
In methane, 4 hydrogen atoms, share 1 electron with carbon.
Four covalent bonds are formed.
Compounds can be represented, in structural form.
C H 4 can be represented with C at the centre, and 4 hydrogen atoms,
on the four sides of carbon.
This will look like a cross, with carbon in the centre, the left bond hydrogen on the left,
the right bond hydrogen on the right, the top bond hydrogen on the top,
the bottom bond hydrogen in the bottom.
This will be the structural representation for C H 4.
The condensed chemical formula, is just C H 4.
The condensed chemical formula, is more commonly used.
Methane is found in it’s natural form, and is called as natural gas.
It is used as a fuel.
Carbon tetrachloride. C C l 4.
Here carbon has 4 covalent bonds, with chlorine.
Phosphorus trichloride. P C l 3.
Here Phosphorus has 3 covalent bonds, with chlorine.
Potassium trichloride, is used in the manufacture of herbicides, and insecticides.
Covalent bonds can be commonly found,
when a non metal combines with another non metal.
Molecules.
Hydrogen has one electron, in the valency shell.
Hydrogen atoms form a covalent bond, with another Hydrogen atom,
to become the molecule H 2.
It is represented as H, single bond, H.
Hydrogen in it’s natural form, in the atmosphere, is present as H 2.
Though it has a covalent bond,
Hydrogen molecule, is not considered, as a compound,
because it comprises of only a single element.
It is called as a homo nuclear molecule, or just as a molecule.
Oxygen atoms form 2 covalent bonds, with other oxygen atoms.
It is represented as, O, double bond, O.
It exists, in its natural form, as O 2.
Nitrogen forms 3 covalent bonds, with other Nitrogen atoms.
It is represented as N, triple bond, N.
It exists, in it’s natural form as N 2.
Hydrogen, Oxygen, Nitrogen, and other molecules, which have only a single element,
are not considered as chemical compounds.
We will refer to them as molecules
Compounds with ionic and covalent bonds.
Many compounds have more than 2 elements.
For example, Sodium Hydroxide. N,a, O, H.
It has 3 elements, Sodium, Oxygen, and Hydrogen.
The oxygen, and the Hydrogen, have a covalent bond,
by which, they share 1 electron.
They form a sub group, in the compound.
It can be represented as, O, single bond, H.
The Oxygen plus Hydrogen, group, is called as the Hydroxide group.
Hydrogen has a valence of 1.
Oxygen has a valency of 6.
After sharing an electron, this group has seven electrons, in the valency shell.
It is eager to receive, 1 more electron.
Sodium, has 1 electron, in the valency shell.
It is eager to donate it.
Sodium forms an ionic bond, with the hydroxide group,
to form Sodium hydroxide.
Sodium hydroxide, has both a covalent bond, and ionic bond.
It can be represented as N a, +, O H, minus.
In this compound, N a, +, becomes the cation.
O H minus, becomes the anion.
This forms the ionic bond.
The O H group has a covalent bond.
Sodium hydroxide, is also called as caustic soda.
Sodium hydroxide, is a highly corrosive alkali.
It is used for cleaning sinks, drains, etc.
There are many compounds like Sodium hydroxide, with more than 2 elements,
which have both, ionic and covalent bonds.
Oxidation.
Many elements combine, with Oxygen.
This group of chemical compounds, is called as oxides.
The most common oxide, is hydrogen oxide, H 2 O, or water.
70% of the Earth is covered by oceans, with water.
Most of the Earth’s crust, also consists of solid oxides.
Silicon dioxide, is S i O 2.
It is found in sand.
It is one of the most abundant substances, in Earth.
Calcium oxide, is C a, O.
It is called as quick lime.
It is used in making cement.
Copper oxide, is C u 2 O.
Silver oxide, is A g 2 O.
Iron oxide, is F e 3 O 4.
It is also called as rust.
Aluminium oxide, is A l 2 O 3.
The process of an element, combining with Oxygen, is called as Oxidation.
The process of removing Oxygen, from an oxide, is called as reduction.
Oxidation, is a very common form, of chemical reactions.
Earlier, oxidation referred only to combination with Oxygen.
The definition of oxidation, has now been expanded.
When an element can donate an electron, or electrons,
it is deemed to have a positive oxidation state.
For example, Hydrogen is said to have an oxidation state, of + 1.
This implies that, Hydrogen is ready to donate, 1 electron.
When an element can receive an electron, or electrons,
it is said to have a negative oxidation state.
For example, Oxygen, has an oxidation state of minus 2.
This implies that, Oxygen is ready to receive, 2 electrons.
Minus, also implies that Oxygen is electro negative.
The sum of the oxidation states, in a compound, is always zero.
For example, the oxidation state, of H 2 O,
is +2, minus 2, equal to 0.
Oxidation state of sodium is + 1.
Oxidation state of chlorine is minus 1.
Oxidation state of sodium chloride,
is +1 minus 1, = 0.
The same is true, for all other compounds.
Functional groups.
Some elements, combine with each other, to form a group.
The same group, can be found in many compounds.
For example, the hydroxide group, O, single bond H, can be found in many compounds.
The O H group is called as the hydroxyl group.
Potassium hydroxide, K O H, has the same hydroxyl group, as Sodium hydroxide.
Calcium hydroxide is M g, (O H) 2.
Calcium hydroxide is used as plaster, in construction.
Magnesium hydroxide, M g, (O H) 2, also has the same hydroxyl group.
Magnesium hydroxide, is called as, milk of magnesia.
It is used as a antacid.
Commonly occurring groups, are identified, classified, and named in chemistry.
They are called as functional groups.
These functional groups, has similar characteristics.
It is practical and convenient, to know functional groups.
Chemical behaviour of these functional groups, tend to be similar.
Some examples, of functional groups are:
Ammonium, is represented as N H 4 +.
Carbonate, is represented as C O 3, 2 minus.
Ammonium carbonate, has the formula (N H 4) 2, C O 3. H 2 O.
It is also called as smelling salt.
It was used in earlier times, to revive ladies, who had fainted.
Sulphate, is represented as S O 4, 2 minus.
The 2 minus, indicates, that the ion, S O 4, can form 2 ionic bonds.
Hydrogen sulphate, H 2 S O 4, is called as sulphuric acid.
Sulphuric acid, is used in car batteries.
Calcium sulphate dihydrate, C a S O 4. 2H 2 O, is also known as Gypsum.
Gypsum is used as a plaster board, in construction.
Magnesium sulphate, M g, S O 4. 7H 2 O, is called as Epsom salt.
It is used as a home medicine.
Nitrate, is represented as N O 3, minus.
Hypochlorite, is represented as C l O minus.
Sodium hypochlorite, N a, C l O, is also called as bleach.
It is used as a whitener, for clothes.
It is also used as a disinfectant.
Phosphate, is represented as P O 4, 3 minus.
Chromate, is represented as C r O 4, 2 minus.
Permanganate, is represented as M n O 4, minus.
The same functional group, can form different compounds,
with dramatically different properties.
For example,
Sodium carbonate, is N a, 2, C O 3.
Sodium carbonate is called as washing soda.
Potassium carbonate, is K 2, C O 3.
Potassium carbonate, is used in production of soap and glass.
Calcium carbonate, is C a, C O 3.
Calcium carbonate is the main component of shells, in the sea shore.
It is also found in egg shells.
Calcium carbonate, is also found in marble.
Sodium bicarbonate, is N a, H C O 3.
Sodium bicarbonate, known as baking soda, is used in cooking.
All these compounds, have the carbonate functional group.
Bond chains.
An atom of an element, can chemically link, with atoms of the same element.
This process is called as catenation.
Catenation results, in a chain of elements.
This chain of elements, can combine with other elements, to form compounds.
Catenation occurs most readily in carbon, which forms covalent bonds,
with other carbon atoms, to form longer chains, and structures.
Such, bond chains are most common, in carbon compounds.
Carbon has four electrons, in the valency shell.
In ethane, carbon forms a covalent bond, with another carbon atom.
This contributes one electron, to the valency shell.
There are still 3 vacancies in the valency shell, of the carbon atoms.
Each carbon atom, combines with 3 hydrogen atoms, to form C 2 H6, or ethane.
This can be structurally represented.
The two carbon atoms, form a chain.
Each carbon atom, is linked in 3 directions, with hydrogen atoms.
This gives us, the structural representation, of ethane.
The condensed formula, for ethane, is C 2 H6.
Carbon has a propensity, to form longer and longer chains.
A chain of 3 carbon atoms, combine with 8 hydrogen atoms,
to form propane.
The formula for propane is C 3 H8.
A chain of 4 carbon atoms, combine with 10 hydrogen atoms,
to form butane.
The formula for butane is C 4 H10.
A chain of 6 carbon atoms, combine with 14 hydrogen atoms,
to form hexane.
The formula for hexane is C 6 H14.
A chain of 8 carbon atoms, combine with 18 hydrogen atoms,
to form octane.
The formula for octane is C 8 H18.
The group of compounds with carbon and hydrogen, is called as hydrocarbons.
They are good examples of carbon chain compounds.
Hydro carbons, are the key ingredients of fossil fuels.
Petrol, Diesel, kerosine, LPG, etc., are all comprised of various hydrocarbons.
Hydrocarbons are the remnants of organic matter, buried deep in the ground,
for millions of years.
They are also called as fossil fuels.
They are fossils of what once was, living organic matter.
They are extracted from the earth, by drilling for crude oil, and natural gas.
Fossil fuels are the main source of energy, in the industrialised world.
The availability of fossil fuels, which we can exploit, is limited.
We are bound to run out of fossil fuels, in the near future.
We need to look for other sources, to fulfil our energy needs.
Hydrocarbon are readily combustible.
During combustion, they combine with Oxygen, to release energy.
This reaction which releases energy, is called as an exothermic reaction.
This is the energy we harvest, in our vehicles, and all machinery using fossil fuels.
To take an example, octane, undergoes combustion, with the chemical equation,
2C 8, H18, +25, O 2 results in 16, C O 2 + 18, H2 O + energy.
This is a typical combustion reaction, of all hydro carbons.
The by product carbon dioxide, is a major pollutant.
Carbon dioxide, in the atmosphere plays a dominant role in global warming.
The polluting nature of fossil fuels, is another good reason,
to migrate to cleaner renewable sources of energy.
Carbon chains, combine with other elements to form compounds.
We will discuss a few examples:
Acetic acid, is C 2 H4 O2.
It is called as vinegar.
It is commonly used as a preservative.
Ethanol is C 2 H6 O.
It is used in alcoholic beverages.
Glycerol is C 3 H5 (O H) 3.
It is called as glycerine.
It is used in pharmaceutical products, like cough syrups, and skin care creams.
Ascorbic acid, is C 6 H8 O 6.
Ascorbic acid, is also known as vitamin C.
It is found naturally, in citrus fruits.
It is also used as a health supplement.
Naphthalene, is C 6 H4, C l 2.
Naphthalene has a pungent odour.
It is also called as moth balls, and used as a insect repellent.
Acetylsalicylic acid, is C 9 H8 O4.
It is sold with a brand name of Aspirin .
It is commonly used for pain relief.
Glucose, is C 6 H12 O 6.
One of the basic foods for the body, is carbohydrates.
Glucose, is the basic carbohydrate, used by the body, for energy.
Sucrose, is C 12 H22 O 11.
Sucrose, is called as sugar.
Sugar is a common ingredient, in food.
Starch, is a large chain of glucose units.
It is called as a polysaccharide.
It is produced by green plants, as an energy store.
It is the most common carbohydrate, in human diet.
It is contained in staple foods like, potato, corn, wheat and rice.
Many organic compounds, contain long chains, of carbon atoms.
Inorganic and organic compounds.
Inorganic compounds, are traditionally viewed, as being synthesised,
by the agency of geological systems.
Inorganic compounds are found all over Earth, in non living systems.
Soil, rocks, minerals, etc, are comprised of inorganic compounds.
Organic compounds, are those found, in biological systems.
All living organisms, are comprised of inorganic compounds.
There is no strict dividing line, between organic and inorganic compounds.
Some compounds, may overlap, this classification.
However, this classification is very useful, to recognise a large majority,
of chemical compounds.
It is useful to consider, organic chemistry, and inorganic chemistry,
as branches of chemistry.
Mole.
A mole is the number of atoms present, in 12 grams of pure carbon C 12.
The unit of the mole, is m o l.
Scientists have calculated this number, to be 6.022 multiplied by 10, to the power of 23. That is there are 602 sextillion atoms, in 12 grams of carbon.
6.022 multiplied by 10, to the power 23, is called the Avogadro constant.
The beauty of the Avogadro constant, is that it is the same for all elements.
The mass of one mole of a element, expressed in grams,
is equal to the element’s, gram atomic mass.
1 gram of hydrogen will have 602 sextillion atoms, and is called as 1 mole of Hydrogen.
12 gram of Carbon will have 602 sextillion atoms, and is called as 1 mole of Carbon.
16 grams of oxygen will have 602 sextillion atoms, and is called as 1 mole of Oxygen.
1 mole of any substance will always have, 602 sextillion atoms.
The concept of the mole, is applicable, to compounds also.
The gram molecular mass, of a compound, is the sum of the gram atomic mass,
of its constituents.
Calcium carbonate has a formula, C a C O 3.
For convenience we will round off, the gram atomic mass, of the elements.
Calcium, has a gram atomic mass of 40 grams.
Carbon, has a gram atomic mass of 12 grams.
Oxygen, has a gram atomic mass of 16 grams.
The gram molecular mass of calcium carbonate, will be,
40 + 12,
+ 3 multiplied by 16.
This is equal to 52 + 48 = 100 grams.
The gram molecular mass, of calcium carbonate, C a C O 3,
is 100 grams.
1 mole of calcium carbonate, is = 100 grams.
100 grams of calcium carbonate, will contain, the Avogadro’s constant,
number of molecules.
100 grams of calcium carbonate, will contain, 602 sextillion molecules,
of C a C O 3.
This way, we can calculate, gram molecular mass of any compound.
All compounds will have the Avogadro’s number of molecules, in one mole.
Mole, is a commonly used unit in chemical equations.
There are more than 10 million known compounds.
Each of them have distinct properties.
We are synthesising new compounds, in search of new materials, with new properties.
The pharmaceutical industry, is a good example,
where research is continuously going on, to find new and better medicines.
In the future, we can expect to discover, many new exciting chemical compounds.