Molecular Nature of Matter | Physics for Grade 12 PDF Download

Molecular Nature of Matter Physics

The matter makes up our entire universe and acts as the essential building block. We can define matter as a substance that occupies space in the form of volume and has some amount of mass. The matter can exist in various states such as solids, liquids, and gases. It only includes particles that have mass and hence, particles such as photons that are massless are not in the category of matter. For example, water can exist in all three states as steam in gaseous form, liquid water in liquid form, and ice in solid form. The matter has a molecular nature. It is made up of small particles called atoms. For a long time, we believed this theory to be complete until even tinier particles were discovered. Today we will look at the definition of molecular nature of matter physics and try to understand the hierarchy in which this concept evolved.

Dalton’s Theory

We shall start with dalton’s atomic theory, the very first of its kind. John dalton was the first scientist to introduce the atomic theory of matter. Although the origin of his theory is still not completely understood. He proposed a set of laws or postulates describing the behaviour of particles in matter. For a long time, dalton’s atomic theory was considered to be concrete until smaller particles such as protons, neutrons etc. were discovered. Let us try to understand his theory of the molecular nature of matter physics. He proposed that all matter whether its a compound, a mixture or a molecule is made up of even smaller particles known as atoms and they can not be separated any further. The critical points in his theory are as follows:-

• All the matter in the universe is made up of small particles called atoms. 
• Atoms can neither be created nor be destroyed during a chemical reaction and thus, they are indivisible particles.
• The mass and chemical properties of all the atoms of a given element are the same or identical. 
• The mass and chemical properties vary for the atoms of different elements. 
• The atoms in a Compound are combined in the ration of tiny whole numbers. 
• For a given element its types of atoms and their relative number are constant.  

This law also states that molecules are formed in the compound by combining a few atoms from every element. Gay Lussac’s theory of gaseous molecules also came up with similar findings as this theory. We can better understand Gay Lussac’s law by combining dalton’s theory and Avogadro’s law. So let us study Avogadro’s law regarding the molecular nature of matter physics.

Avagadro’s Law

It is a law based on gases that relate their volume and total amount present. This law is an experimental gas law. According to Avagadro’s law, the number of gases has an equal number of molecules if they have the same volume at equal pressure and temperature. It also states that for an ideal gas if the pressure and temperature are constant, then its amount and volume are directly proportional to each other. Now let us look at Gay Lussac’s findings on molecular nature of matter physics.

Gay Lussac’s Law

According to Gay Lussac’s law if the volume of a gas is taken as constant, then the pressure of a given amount of gas varies directly to its temperature. This law is also called pressure law as it says pressure is directly proportional to temperature if the volume is constant. In other words, the volumes of gases are in the ratio on small integers when gases go through chemical combination.  He gets credited as the first person to give substantial evidence of the relationship between pressure and temperature of fixed gases.

Evolution to Current Molecular Nature of Matter Physics

These theories were trending until the late 19th century, when many scientists saw flaws in Dalton's atomic theory. It was one of the fundamental laws that states matter is made up of tiny particles called atoms. As we further discovered that atoms are made up of even smaller particles that are categorized as protons, neutrons, and electrons. They are available in different proportions in an atom.
We were able to visualize this theory due to the advancement in technology such as electron scanning microscopes. This discovery proved the fundamental theory wrong making atoms an elementary particle. The atoms consist of electrons and a nucleus that contains both protons and neutrons.
Recent discoveries have also proved that even smaller particles exist inside neutrons and protons called quarks. We can further find smaller units that contain quarks. Our scientists are currently working on string theory that proposes a string-like object as the elementary particle. This theory will prove to be revolutionary in the future.