We will begin with the term matter, and define it as any thing that occupies space and has mass. (We measure the mass of a matter by weighing it). As long as you have some idea what a matter is, it is sufficient for now. Once you know what atoms and molecules are you will most likely have no use for the term matter. Most (not all) matters can be seen, touched, or smelled. Air is a good example of a matter we cannot see.
Tutorial 1
Name something that is not a matter. Answer
ATOMS AND MOLECULES
All matters are made of atoms and molecules, the smallest complete building blocks in the world. You can use them to build all the things you see around you (or matters).
Iron is actually a collection of atoms. If we keep on cutting a piece of iron until it is the last unit, then that it is an atom of iron. Of course an atom of iron can still be broken down into smaller entity (known as subatomic particles), but these entities will not have the property of iron.
Water is actually a collection of molecules. If we keep on dividing a cup of water until it is the last unit, then that is a molecule of water. If you break down a molecule of water into smaller entities, the entities would not have the property of water.
Molecules are matters formed from atoms. So if you take two of more (different or similar) atoms and make a new matter then you have a molecule. Hydrogen (H) and oxygen (O) are atoms. They react with each other to give H2O or water.
Oxygen gas, O2, is made up of two atoms of oxygen. The properties of oxygen atom and oxygen molecule are different. If you have difficulty here do not worry. All you need to know at the moment is a rough idea of atoms and molecules. As we move on this problem will disappear.
Tutorial 2
Why do we have to come up with terms like atoms and molecules? Why not discuss a piece of iron instead of an atom of iron? After all iron is iron. Why not discuss a cup of water instead of a molecule of water? After all water is water. Try giving me your answer. Answer
Tutorial 3
- What is matter?
- Is an atom the smallest matter in the world?
- What is the difference between an atom and a molecule? Answer
WHAT IS AN ATOM?
It was discovered that the atom is made up of protons, neutrons and electrons. So neutrons, protons and electrons are subatomic particles. In science a particle is visualised as something so small that it is represented by a micro point, to signifies that it does occupy a space though you cannot see it. (Discovery of the atom)
The protons and neutrons form the nucleus of the atom with the electrons orbiting around it.
Charges
Neutrons are called neutrons because they are neutral particles. Protons are positively charged particles and electrons are negatively charged. One proton has one unit of positive charge and one electron has one unit of negative charge.
The First Law of Matter states that "All matters in their natural states must be neutral in charge". So every atom must have the same number of protons and electrons.
Mass
Although a neutron has no charge it has the same mass as a proton. An electron is so small that its mass is comparatively insignificant (or negligible). Negligible is very often used in science to say, "The value is not worth bothering about, comparatively". For example, if you stand with ten elephants on a weighing scale, than your weight is negligible.
Unlike charge, atoms need not have the same number of protons and neutrons. Hydrogen has a proton but no neutron. This is one of the mysteries of nature. Most of us know that like charges repel each other, and unlike charges attract each other. But all the positively charged protons are concentrated in the nucleus with the neutrons. It appears that the neutrons somehow are there to keep the protons from flying apart. (Of course the truth is much more complex.) Is it possible that hydrogen with only one proton had no need for a neutron? Nature has its own way of working things out.
Note: The actual content of any material is known as the mass. The weight of the substance is dependent on the gravitational force exerted on substance. The same mass if weighed on the moon may be about six times as light as when it is weighed on earth.
ATOMIC NUMBER
It is the number of protons in an atom. All atoms with the same atomic number will have the same number of electrons; since atoms are neutral in charge. This means that the electronic configuration for these atoms will be the same, and so they should have the same chemistry. So we identify atom by the number of protons, otherwise referred to as the atomic number (usually represented by Z). For example the atomic number of hydrogen is 1 and that of helium (with two protons) is 2.
Atoms can have the same number of protons but different number of neutrons. They are known as isotopes of the same atom. For example there are small fractions of hydrogen atoms that has one neutron or two neutrons. We named the isotopes deuterium and tritium,
and Tritium = 
or H-2 and H-3, according to their atomic mass unit.
The most stable form of the isotopes is that which has the same number of protons and neutrons. The others are formed from radiation activities. Tritium is formed in the upper atmosphere by cosmic ray induced nuclear reactions. It is radioactive and "decays" to normal isotope within 12.4 years.
If we picked up a piece of carbon it is very likely that there is 98.89% of 12C, 1.11% of 13C, and trace amount of 14C. (Interesting reading: Carbon Dating.)
RADIOACTIVE
Atom gets larger with every increase in the number of proton. We started with one proton and we ended up with an atom with as much as 103. As more and more protons squeeze themselves into the nucleus of the atom, the neutrons have difficulty holding them together. The nucleus becomes unstable and breaks up by itself under normal condition, in most cases emitting energy and harmful subatomic particles, commonly referred to as rays. Such atoms are said to be radioactive. Radioactive atoms found use in nuclear plants, also for the nuclear bombs, because it can be easily designed to release a large amount of energy.
ATOMS IN THEIR NATURAL STATE
A major part of science is about how matters behave in day-to-day situations. So it is only to be expected that we are interested in their behaviours under day-to-day (or ambient) conditions. Meaning, the stability of matter in terms of temperature, pressure, and in the presence of moisture, oxygen, carbon dioxide and nitrogen. We must bear in mind that scientists in temperate countries normally consider 25°C as ambient temperature, even though in winter the temperature is much lower. In the tropic the ambient temperature is more like 30°C.
There are only five atoms that are stable enough to exist as atoms in the natural state. They are the gases helium, neon, argon, krypton, and xenon. Because they are not reactive (in our human culture that means not known to lose their temper and go into a rage) they are called noble (or inert)gases.
Tutorial 4
If you visit a laboratory you would notice that some chemicals are kept in the refrigerator while others in dessicators (a closed container with some drying agents in them, like you keep your expensive cameras at home). Why? Answer
