What is chemistry?

Chemistry is a science that studies the properties of substances and how substances react with each other.
Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.
Chemistry has the task of investigating the materials of which our universe is made.
Chemistry investigates chemical changes, conditions under which chemical changes occur.
Chemistry also deals with the way in which similar changes can be brought about in laboratory and on a large scale in industries.

Who uses chemistry?
Many people use chemistry as part of their work.
Cooks use chemistry all the time. They may not have studied chemistry like you, but they learn by experience how to control the changes that happen when food is cooked.
Doctors use chemistry, because everything that goes on in the human body involves chemistry
Engineers use chemistry, when they decide what materials to make things from.

Where do the chemists work?
People who have trained as chemists work in hospital laboratories, in breweries, in oil refineries, in food laboratories and in factories making everything from plastics to poppadums.
Chemists do a particularly important job in protecting the environment from the effects of human activities

MATTER and states of matter
Matter is anything that has mass and takes up a space. Matter can be recognized by its properties of mass and volume.

States of matter
Matter exists in three different states: solid, liquid and gas. If the whole space is considered we should talk about a fourth state – plasma. Almost all objects found in the space consist of plasma. At extremely high temperatures, all matters can not confine at liquid, solid, and gaseous states and dissociate into their ions and atoms.
Flames, magma layer, sparkles passing in higher-voltage cables, stars and the sun can be given as example of plasma.

States of matter

‘substances’
Scientist also use the word ‘substances’. This means a particular type of matter, which you can put a name to.
Salt is a substance, and so is water.
Light is not a substance, because it has no mass and volume and it is not matter.

ELEMENTS
An element is one of a group of fundamental substances that cannot be broken down into simpler substances.
All of the elements have names but each element has been also assigned its own unique symbols, which we will find useful for writing chemical formulas and chemical equations.
The names of chemical elements change a little from one language to another, but symbols do not.
Until the 16th century some elements were named as follow.
Element Name
Gold Sun
Copper Venus
Tin Jupiter
Mercury Mercury
Silver Moon
Iron Mars
Lead Saturn

Symbolic representations
Later on symbols were used because of the difficulty for finding names to excessive number of newly found elements.
By the beginning of the nineteenth century, there were about 26 known elements, but by the beginning of the twentieth century, there were more than 81. As more elements were discovered, the need for symbolic representations for these elements became more evident.
All symbols for elements are placed on a special table called the periodic table.
Today, 116 elements are known; 92 of which are called natural elements

THE MODERN PERIODIC TABLE
The modern periodic table appeared as a function of the physical and chemical properties of elements.

USAGE OF SOME ELEMENTS
Hydrogen:
A rocket fuel
Production of hydrogen bomb
Being the lightest of all gases hydrogen was used to inflate ballons, but its high inflammability led to a number of explosions and its eventual replacement with helium
Refining of the petroleum
Reduction of oxide ores to metals

Sodium:
Production of electricity in nuclear reactors by transferring excess heat to the vapor turbines
Its salt are used in medical industry
Production of soap, baking soda, glass and pigment

Barium:
Gas absorbent in vacuum tubes
Green light in fireworks
BaSO4 is used to take the photos of stomach and intestine

Physical and chemical changes
When we look around, in the world we live, we see some changes. For instance, evaporation of water, rain and snow, spoil of a fruit, drying up of paint on the wall, solidification of cement, fires, dissolving of sugar in tea and rusting iron.
There are some events where the changes occur in the chemical structure, but in some events matter changes only physically. Therefore, changes in matter may be considered as physical and chemical changes.

Physical and chemical changes

chemical changes
Changes in the molecular structure of substances are called chemical changes.
baking of cake
rusting of iron
Another example in daily life is the souring of milk. It spoils at hot places after a while. That is, there are some changes in its chemical properties. In this event, bonds that hold the molecules and atoms are broken down, whereas, some new bonds form at the same time. This means that new substances with new properties form.

physical changes
Evaporation of water, melting ice, dissolving of sugar in water, powdering marble, breaking of glass are not chemical changes and such events do not include changes in chemical properties but some of their physical properties change.
Those kinds of changes are physical changes