What is The Difference Between Distance And Displacement:

S.No	Distance	Displacement
1.	It is the actual distance travelled by an object in the given time.	It is the shortest distance between the initial and final positions of the object in the given time.
2.	It is a scalar quantity.	It is a vector quantity.
3.	The distance travelled by an object in a given time is never negative or zero, but is always positive.	The displacement of an object in a given time can be positive, zero or negative.
4.	The distance travelled by an object in a given time is either equal or greater than displacement but never less than displacement.	The displacement of an object in a given time can be equal or less than distance travelled but never greater than distance travelled.
5.	The distance covered by an object between two positions can have many values, depending upon the path followed.	The displacement of an object between two positions has a unique value.
6.	The distance travelled by the object between two positions tells the type of path followed.	The displacement of an object between two positions does not tell the type of path followed.

What is an Element?

Elements: An element is defined as the pure substance which is made of only one kind of particles. These particles may be atoms or molecules.

• Carbon sulphur, iron, lead, gold, mercury, hydrogen, oxygen, and nitrogen are some examples of familiar elements.
• Iron, gold, copper etc contain single atoms as constituent particles held together.
• Hydrogen, oxygen, nitrogen etc consists of molecules, comprising of two atoms combined together.
• The no of elements known to-date is 114. Out of these elements known, 92 are occurs in earth’s crust and the left one have been prepared artificially in the laboratory through nuclear reactions.

Types of elements:

Elements are classified as:

Metals: Metals are those elements which possess lustre (shining appearance), reflects light, are good conductors of heat and electricity, are malleable (hammered to thin sheets) and ductile (drawn into wires), exist as solid at room temperature (except mercury), possess high density.

• Example: iron, copper, silver, gold etc.

Non-metals: Non-metals are those elements which does not reflects light, poor conductors of heat and electricity (except graphite), does not possess malleability and ductility, do not have lustre (except iodine), exists in all the three states.

• Example: carbon, hydrogen, oxygen, nitrogen etc.

Metalloids: Metalloids are those elements which exhibits the property of both metals and non-metals.

• Example: Arsenic, antimony and bismuth.

What is Science?

Science is nothing but it is getting the deep knowledge of nature and natural phenomena. In other word the deep and systematic study of whatever happens in this physical world is called science. 

The word science is derived from the Latin verb ‘scientia’ which means ‘to know’. The Sanskrit word vijnana and the Arabic word Ilm convey the similar meaning, namely ‘knowledge’.

The knowledge which humans have collected through their observations and experiments, when organized systematically is called Science.

The different definitions of Science given by various scientists are:

Albert Einstein: Science is not just a collection of laws, a catalogue of unrelated facts. It is a creation of human mind. With its freely invented ideas and concepts.

Bruce Lindsay: Science is a method of describing, creating and understanding human experience.

Neils Bohr: The task of science is both to extend the range of our experience and to reduce it to order.

Gerald Holton: Science is ever unfinished quest to discover all facts, the relationship between things and the laws by which the world runs.

Science is divided into many branches:

Physical Sciences: The Science in which we study about non living things is called physical sciences. For example, Physics, Chemistry, Geology, Astronomy, Geography, Astrology, Oceanology etc.

Biological Sciences: The science in which we study about the living things is called Biological Sciences. For example, Botany, Omithology, Anthropology, Entromology, Zoology, Forensic science etc.

Occurrence of Metals

How do metals occur in nature?

Our earth’s topmost layer which is also known as crust is the main source of metals. Some metals which form soluble salts are found in sea water in the form of their soluble salts.

• The elements or compounds that occur naturally in the earth’s crust are known as minerals.
• These minerals contain high percentage of a particular metal and the metal can be profitable extracted from it.
• The minerals from which metals can be extracted are called ores.
• The most abundant metal on the earth’s crust is aluminium. Whose percentage is about 7%. And the remaining metals are present in very small amount.

Extraction of Metals

According to the activity series the metals are dived into three parts:

1. Metals of low reactivity

• It consists of gold, silver, platinum and copper which are found in free state.
• Copper and silver are also found in combined state as their sulphide or oxide.

2. Metals of middle reactivity

• It consists of metals like Zn, Fe, Pb etc which are moderately reactive.
• They are mainly found in earth’s crust as oxides, sulphides or carbonates. 

3. Metals of high reactivity

• It consists of metals like K, Na, Ca, Mg etc which lie on the top of the activity series and are never found in free state. They are always found in combined state.

What is Metallurgy?

• The various steps involved in the extraction of metals from their ores followed by refining of the metal is called metallurgy.

The various steps that are involved in extraction of metals from their ores are:

Extracting of metals which lie low in the activity series

• The metals that lie low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating them alone. 
• For example, cinnabar (HgS) is an ore of mercury. When it is heated in air. It is first converted into mercury oxide and reduced to mercury on further heating.

2HgS (s) + 3O₂ --^heat---> 2HgO (s) + 2SO₂ (g)

2HgO (s) + O₂ --^heat---> 2Hg (l) + 2O₂ (g)

Metals And Non-metals

Classification of elements

The elements that are present on earth are classified as metals and non-metals on the basis of their properties. And the basis of their classification is based on the physical and chemical properties.

Physical Properties of Metals and Non-metals

Physical properties of metals

1.  Metals are solid and hard.

2.  Malleability:-

• Some metals can be beaten into thin sheets. This property is called malleability.
• Gold and silver are most malleable metals.

3.  Ductility:-

• The ability of metals to be drawn into thin wires is called ductility.
• Gold is the most ductile metal. A wire of about 2 km can be drawn from one gram of gold.

4.  Metallic lustre.

• Metals in their pure state have a shining surface. This property is called metallic lusture.
• Metals can be given different shapes according to our needs because of their malleability and ductility.

5.  Heat conduction:-

• Metals are good conductors of heat and have high melting points.
• Silver and copper are best conductors of heat.
• Lead and mercury are comparatively poor conductors of heat.

6.  Electrical conductivity:-

• Metals are good conductors of electricity.
• Silver is the best conductor of electricity. But copper is commonly used for electrical wiring because silver is much expensive than cooper.

7.  Sonorous:-

• Metal that produces sound when strikes with a hard substance are said to sonorous. Metals are sonorous in nature.

Physical properties of non-metals

1. Non-metals are either solids or gases except bromine which is a liquid.
2. They are non malleable.
3. They are non ductile.
4. They are bad conductors of heat and electricity.
5. They are non sonorous.
6. They are non lustrous.

We can’t group elements according to their physical properties alone, as there are many exceptions. For example:-

1. All metals exist as solids at room temperature except mercury.
2. Metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on your palm.
3. Iodine is a non-metal but it is lustrous.
4. Carbon is a non-metal that can exist in different forms. And each form is called an allotrope.

• Diamond is an allotrope of carbon, which is the hardest natural substance known and has very high melting and boiling points.
• Graphite is another allotrope of carbon, which is conductor of electricity.

    5.  Alkali metals like lithium, sodium and potassium are so soft that they                  can be cut with a sharp knife. They have low densities and low                          melting points.

Most non-metals when dissolved in water give acidic oxides. On the other hand most metals give rise to basic oxides.