What is the difference between atom, element, molecule and compound? Well, we all know about an atom. It is the smallest unit of matter.
I mean everything in the universe is made up of atoms. For example, plants, animals, food, water etc. Now here is an interesting question. If everything is made up of atoms. then why all these things in the universe are different?
I mean, why not they are the same? Why plants are different from animals? Well, it is because there are 118 different atoms or elements which are present in the universe.
Different combination of atoms produces different substances. For example, consider carbon, hydrogen and oxygen. These are the three different types of atoms. When carbon and oxygen combine together chemically, they form carbon dioxide gas CO2.
When hydrogen and oxygen combine together chemically, they form water H2O. Thus different combination of atoms produces different substances. Now coming to the difference between atom, element, molecule and compound. Dear Altaf, two main type of atomic combinations, homo-atomic combination and hetero-atomic combination.
The word homo means same and atomic means atom. So the word homo-atomic means same type of atoms. Now when an atom or group of atoms exist freely, it forms a molecule.
Let me repeat this important statement. When an atom or group of atoms exist freely, it forms a molecule. For instance, homoatomic combination of atoms form a molecule.
In homoatomic combination of atoms, molecule will be either monoatomic molecules or diatomic molecules. The word mono means one. So, monoatomic molecules are like neon, argon, and xenon. One can say that all noble gases form monoatomic molecules.
because they are made up of only one atom. Now when many monoatomic molecules combine together, they form element. For example, when many atoms of neon combine together, they form neon element.
When many atoms of argon combine together, they form argon element. When many atoms of xenon combine together, they form xenon element. Similarly, When many atoms of metals like iron, zinc, gold etc. combine together, they also form elements. But remember that metals like iron, zinc and gold do not form molecules.
Now the word di means two. So diatomic molecules are H2, O2 and N2. They are made up of two atoms. That's why we call them diatomic molecules. These type of molecules are also called as elemental molecule.
When many elemental molecules combine together, they also form element. For example, when many elemental molecule of H2 combine together, they form hydrogen element. When many elemental molecule of O2 combine together, they form oxygen element. When many elemental molecules of N2 combine together they form nitrogen element. Therefore remember that Neon, Argon and Xenon are monoatomic molecules because they exist freely in the nature while H2, O2 and N2 are diatomic molecules because they can also exist freely in the nature.
But one atom of hydrogen, oxygen and nitrogen do not exist freely in the nature. On the other side, elements are formed due to homoatomic combination of either atoms like neon, iron or gold or it is formed by elemental molecules like H2, O2 and N2. Now coming to the heteroatomic combination of atoms. The word hetero means different. Heteroatomic combination means When different atoms combine together chemically, they also form heteroatomic molecules.
For example, like CO2, H2O, and CH4. CO2 are formed from carbon and oxygen. H2O are formed from hydrogen and oxygen. And CH4 are formed from carbon and hydrogen. That's why we call them heteroatomic molecules.
Now when many heteroatomic molecules combine together, they form a compound. For example, when many heteroatomic molecules of carbon dioxide gas combine together, they form compound of carbon dioxide gas. When many heteroatomic molecules of water combine together, they form a compound.
a compound of water. When many heteroatomic molecules of methane combine together, they form a compound of methane. Thus remember that heteroatomic combination of atoms also form molecules and when many heteroatomic molecules combine together, they form a compound. To summarize my whole lecture in one statement, consider hydrogen, H2, many H2, H2O, H2O, and a glass of water. This hydrogen is an atom.
This H2 is homoatomic molecule or elemental molecule. These combined H2 are hydrogen element. This H2O is a heteroatomic molecule and this glass of water is a compound. I hope that you have learned all about atom, element, molecule and compound.