Showing posts with the label Chemistry

What is a Molecule?

A molecule is in general a group of two or more atoms that are chemically bonded together, that is, tightly held together by attractive forces. A molecule can be defined as the smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance. Atoms of the same element or of different elements can join together to form molecules.

How Do Atoms Exist?

Atoms of most elements are not able to exist independently. Atoms form molecules and ions. These molecules or ions aggregate in large numbers to form the matter that we can see, feel, or touch.

Dalton’s atomic theory

According to Dalton’s atomic theory, all matter, whether an element, a compound, or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows: All matter is made of very tiny particles called atoms. Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction. Atoms of a given element are identical in mass and chemical properties. Atoms of different elements have different masses and chemical properties. Atoms combine in the ratio of small whole numbers to form compounds. The relative number and kinds of atoms are constant in a given compound.  You will study in the next chapter that all atoms are made up of still smaller particles.

Properties of non-metal

Non-metals usually show some or all of the following properties: • They display a variety of colours. • They are poor conductors of heat and electricity. • They are not lustrous, sonorous, or malleable. Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc. Some elements have intermediate properties between those of metals and non-metals, they are called metalloids; examples are boron, silicon, germanium, etc.

Properties of metal

Metals usually show some or all of the following properties: • They have a lustre (shine). • They have silvery-grey or golden-yellow colour. • They conduct heat and electricity. • They are ductile (can be drawn into wires). • They are malleable (can be hammered into thin sheets). • They are sonorous (make a ringing sound when hit). Examples of metals are gold, silver, copper, iron, sodium, potassium, etc. Mercury is the only metal that is liquid at room temperature.

What is colloidal solution? Properties of a colloid

Colloidal Solution The particles of a colloid are uniformly spread throughout the solution. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk. Because of the small size of colloidal particles, we cannot see them with naked eyes. Properties of a colloid A colloid is a heterogeneous mixture.  The size of particles of a colloid is too small to be individually seen by naked eyes. Colloids are big enough to scatter a beam of light passing through it and make its path visible. They do not settle down when left undisturbed, that is, a colloid is quite stable. They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation, can be used to separate the colloidal particles. The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute

What is a suspension? Properties of a Suspension

Suspension A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye. Properties of a Suspension The suspension is a heterogeneous mixture. The particles of a suspension can be seen by the naked eye. The particles of a suspension scatter a beam of light passing through it and make its path visible. The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. They can be separated from the mixture by the process of filtration.

What is a Solution? Solvent and Solute, Properties of a solution

Solution A solution is a homogeneous mixture of two or more substances. You come across various types of solutions in your daily life. Lemonade, soda water, etc. are all examples of solutions. Usually, we think of a solution as a liquid that contains either a solid, liquid, or a gas dissolved in it. But, we can also have solid solutions (alloys) and gaseous solutions (air). In a solution, there is homogeneity at the particle level. For example, lemonade tastes the same throughout. This shows that particles of sugar or salt are evenly distributed in the solution. Solvent and Solute A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute. Examples: A solution of sugar in water is solid in a liquid solution. In this solution, su

What is a Mixture?

Mixtures are constituted by more than one kind of pure form of matter, known as a substance. A substance cannot be separated into other kinds of matter by any physical process. We know that dissolved sodium chloride can be separated from water by the physical process of evaporation. However, sodium chloride is itself a substance and cannot be separated by the physical process into its chemical constituents. Similarly, sugar is a substance because it contains only one kind of pure matter and its composition is the same throughout.  Soft drinks and soil are not single substances. Whatever the source of a substance may be, it will always have the same characteristic properties.  Therefore, we can say that a mixture contains more than one substance.

Why do we see water droplets on the outer surface of a glass containing ice-cold water?

Let us take some ice-cold water in a tumbler. Soon we will see water droplets on the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

Why should we wear cotton clothes in summer?

During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into a vapour. The heat energy equal to the latent heat of vaporization is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.


In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surroundings to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold.


The rate of evaporation increases with – An increase in the surface area: We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out. An increase in temperature: With the increase of temperature, more number of particles get enough kinetic energy to go into the vapor state. A decrease in humidity: Humidity is the amount of water vapor present in the air. The air around us cannot hold more than a definite amount of water vapor at a given temperature. If the amount of water in the air is already high, the rate of evaporation decreases. An increase in wind speed: It is a common observation that clothes dry faster on a windy day. With the increase in wind speed, the particles of water vapor move away with the wind, decreasing the amount of water vapor in the surrounding.

What is salt?

Salt is the product of a neutralization reaction between an acid and a base other than water.

What is PVC?

Polyvinyl Chloride or PVC is a polymer plastic that is prepared from vinyl chloride (CH 2 =CHCl). 

Define nylon.

Nylon 6 : 6  is produced when adipic acid is heated with hexamethylene di-amene in presence of titanium oxide. 

What is Coke?

After the emission of different volatile compounds as gases by heating coal, the leftover substance is called coke. 

What is LDPE?

If polymer of ethelen (polyethylene) is produced in presence of little oxygen at 200°C temperature and 1200 atm pressure, its density and melting point low and it is soft in nature. This polyethylene is known as LDPE (Low-Density Polyethylene).

What is called orbital?

The sublevels of an atom are called orbital.

Le Chatelier's Principle.

Le Chatelier's principle states that - if a constraint (such as a change in pressure, temperature, or concentration of a reactant) is applied to a system in equilibrium, the equilibrium will shift so as to tend to counteract the effect of the constraint. 

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