UNDERSTANDING

-BY FURQAAN

WHAT IS AN ELEMENT? An element is a substance that is

made entirely from one type of atom. For example, the element hydrogen is made from atoms containing a single proton and a single electron. If you change the number of protons an atom has, you change the type of element it is.

Its CLASSIFICATIONELEMENTS

THEY ARE FURTHER CLASSIFIED INTO

METALS NON-METALS METALLOIDS

WHAT ARE COMPOUNDS? Compounds are pure substances and not mixtures.

For example, table salt is not a compound because it is a mixture of sodium chloride, dextrose and calcium silicate (to keep it from clumping in high humidity) and potassium iodide (an important nutrient necessary for proper thyroid function). But if these components are separated physically, each can be obtained in pure form and each meets all the criteria for compounds.

Compounds are made of atoms of two or more elements. For example, O2 and O3are considered forms of the element oxygen, and not compounds of oxygen.

Atoms of elements combine in fixed ratios to form

compounds. Carbon dioxide is always composed of molecules with two atoms of oxygen for every one atom of carbon. Carbon monoxide has only one oxygen atom per atom of carbon- and it is a completely different substance than carbon monoxide.

Compounds are chemically combined elements. Mixing 2.0 grams of H2 with 70.9 g of Cl2 in the dark results in a homogenous mixture of H2 and Cl2. Mix the gases in the exact same proportions in the light and there is a violent explosion. The gas is now 72.9 g of HCl, a compound. Components in a homogenous mixture may influence each other's chemical behavior slightly, but there is not radical alteration in chemical and physical properties. Compounds are completely different chemically and physically from the elements that form them.

WHAT ARE MIXTURES? A Mixture is a substance which is obtained by

mixing two or more substances in any proportion.There are an infinite number of mixtures. Anything you can combine is a mixture. Think of everything you eat. Just think about how many cakes there are. Each of those cakes is made up of a different mixture of ingredients. Even the wood in your pencil is considered a mixture. There is the basic cellulose of the wood, but there are also thousands of other compounds in that pencil. Solutions are also mixtures, but all of the molecules are evenly spread out through the system. They are called homogenous mixtures.

The constituents of a mixture retain their original properties.The mixture can be further subdivided into simpler substances by simple physical processes like holding the magnet,hand picking etc.In a mixture, the constituents are not in a fixed proportion.When two or more metals or a metal and a non-metal are fused together then,it is an alloy.

Stainless Steel is an alloy of iron,carbon,chromium and nickel. Carbon gives hardness to the mixture. Chromium and Nickel give a silvery look to the mixture.

TYPES OF MIXTURES The two types of mixtures are homogeneous and heterogeneous.

• Homogeneous Mixture : A homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions. Particle size distinguishes homogeneous solutions from other heterogeneous mixtures. Solutions have particles which are the size of atoms or molecules - too small to be seen.

• Heterogeneous Mixture: A heterogeneous mixture consists of visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid.

WHAT IS A SOLUTION? A Solution is a homogeneous mixture of two or

more substances.Lemonade, soda water are some examples of solutions.

Lemonade or sodas taste the same throughout.It indicates that there is homogeneity at the particle level.The particles of sugar or salt are spread uniformly in the solutions.

There are solid solutions (alloys) and gaseous solutions (air) also.The particles in a solution are of very small size, they do not scatter a beam of light passing through it.

Here are types of solutions and some of their examples:-

WHAT IS A SUSPENSION? A Suspension is a

heterogeneous mixture in which the solute particles do

not dissolve but remain suspended in it.These particles

are visible to the naked eye.

WHAT IS A COLLOID? Science has special names for everything.

There are names for the different types of homogenous mixtures. Solutions refer to these mixtures when the particles are very small. You may hear about colloids. Colloids are just solutions with much bigger particles.It is a mixture in which the size of particles is less than the size of particles in a suspension.

Colloids are usually foggy or milky when you look at them. In fact, milk is an emulsified colloid. You may also hear about colloids if you study soil. Milk is an organic colloid, while soils can be made up of inorganic colloids, such as clay.

EMULSIFIED: To make into or form an any colloidal suspension of a liquid in another liquid.

These particles are spread uniformly throughout the solution and due to the relatively smaller size of these particles,as compared to that of a suspension,this mixture appears to be homogeneous.But a colloid solution is a heterogeneous mixture.

TWO COMPONENTS OF COLLOIDSThe Dispersed Phase and Dispersion Medium are the components.For eg: milk (Here milk is the Dispersed Phase and water is the Dispersion Medium) here both the Dispersed Phase and Dispersion Medium are liquids.We cannot see colloidal particles with the naked eyes.These small particles can easily scatter the beam of light.Take a look at this:

THE TYNDALL EFFECTThe Tyndall effect, also known as Tyndall

scattering, is light scattering by particles in a colloid or particles in a fine suspension. It is named after the 19th century physicist John Tyndall. It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth power of the frequency, so blue light is scattered much more strongly than red light. An example in everyday life is the blue colour sometimes seen in the smoke emitted by motorcycles.

Some examples of Tyndall Effect:

The Tyndall Effect was discovered by John Tyndall:

SEPERATING COMPONENTS OF A MIXTURE

Heterogeneous mixtures can be easily separated by simple means like hand picking, filtration and other physical means. Evaporation is another technique used for separating mixtures. For some mixtures, one needs techniques like distillation and crystallization to separate them. Fractional Distillation is another method where a mixture of liquids is separated into components according to their different boiling points. This method is used to separate components of Air.

ALWAYS REMEMBER