Understanding chemistry

Ionic Bond

chetastrophy — Wed, 30 Jun 2010 18:15:22 +0000

Introduction:

Every element wants to achieve noble gas configuration. Hydrogen wants to be like Helium. Sodium likes to be like Argon. To achieve this atoms have to either gain electrons or lose them or share them.

Defintion:

When an atom having excess of electrons give them to an atom in need of electrons, they form oppositely charged ions. The bond which holds these oppositely charged ions together is known as Ionic bond or Electrovalent bond.

Explanation:

This bond is usually formed between metals and non-metals. The positively charged ion is called Cation and negatively charged ion is called as Anion. Ionic bond is best illustrated by an example:

Sodium Chloride (NaCl): Sodium has 1 extra electron and chlrorine needs 1 electron to achieve stable configuration (Noble Gas configuration). When one atom of Sodium collides with one atom of Chlorine, the extra electron of Sodium gets transferred to the Chlrine atom. Now Sodium has one less electron so it becomes positively charged ion (Na +). Chlorine on the other hand has gained one electron so it becomes negatively charged ion (Cl -).We know that opposite charges attract each other. That is why positively charged sodium ions and negatively charged chlorine atoms attract each other to form a shape in which there is maximum attraction. In this shape each Sodium is surrounded by 6 Chlorine atoms.

Structure of Sodium Chloride

This is why we never refer to ionic compounds as just one “molecule”. Because in reality they are several ions of opposite charges arranged in a certain shape.

Properties:

This type of bond is very tight.
Ionic compounds are hard and brittle.
They have high melting and boiling points.
They are crystalline usually.
When dissolved in water, they dissociate into ions again.
They conduct electricity in molten state and when dissolved in water.

Origins of Organic Chemistry

chetastrophy — Wed, 30 Jun 2010 17:45:22 +0000

Vital Force Theory:

Jons Jacob Berzelius introduced Organic Chemistry in 1907. He defined it as the study of materials present in all nature. He believed that all living beings had a force called “Vital Force”. Because of this force humans, plants and animals were able to produce certain substances which could not be created without it. This was termed as Vitalism. Hence nobody even bothered to create any organic substance in lab.

Downfall of Vital Force Theory:

As nobody tried creating Organic Substances, it was bound to be created accidentally. In the year 1828 Friedrich Wohler did an experiment which changed the very ground of Organic Chemistry. He boiled Ammonium Cyanate in water, and found that it yielded long crystals. These crystals were not of Ammonium Cyanate. They were of Urea (An Organic substance).

Reaction:

NH4OCN = OC(NH2)2

NH4OCN= Ammonium Cyanate (Inorganic Compound)

OC(NH2)2=Urea (Organic Compound)

This was first time someone had ever produced organic substance in lab. This destroyed Vitalism but it took a while to completely replace Vitalism.

This experiment led to more experimentation and finally Organic Chemistry came to be a proper science.

Origins of Chemistry

chetastrophy — Wed, 30 Jun 2010 10:34:46 +0000

Before considering Chemistry as a science, let us look back in time when it was merely an art or craft. The difference being in science we study “Why does it work?” and in art or craft we study “Does it work“.

Six thousand years ago many arts and crafts were established. Earliest metals were Gold, Silver and Copper. People discovered them and started to use them Gold and Silver in royal vessels and ornaments. Whereas copper was used for both ornaments and practical purpose. Bronze was later discovered and was used specifically for weapons of war.

In 1200 B.C. people started producing Iron by heating one of its Ores with charcoal in a furnace. Iron thus produced was not good in quality. But in 1340 A.D. blast furnace came into use, melting the Iron and thus giving a better quality. This Iron then replaced copper for weapons.

In 500-200 B.C Greeks were famous for thinking. It was not futile. They developed Logic, mathematics, curiosity for nature, and gave the concept for Atom. Aristotle said everything is made of small indivisible particles called Atoms. They developed the idea for elements : Earth, fire, air and water.

At the same time Egyptians excelled in handicraft. In working of metals and glass.

Then came Alchemists in the early Christian Era. The primary objective of alchemists was to find a way to convert any metals into Gold. Also called as Transmutation of Metals. They of course failed. Some alchemists later believed that they needed a substance called “Philosopher’s Stone”. This precious stone would convert anything with mere touch and can even give perpetual youth. That’s why it is sometimes called “Elixir of Life”. Note: Transmutation is now possible but the methods are much more complex than what Alchemists imagined.

Alchemists also discovered Antimony and Zinc metals. And non-metals Arsenic and Phosphorous. They also improved industries as metallurgy, glass-making and dyeing. They also developed modern processes such as distilling, filtering, and grinding, and the beginnings of modem chemistry laboratory.

18th Century was all about burning things. The burning question was what makes a thing burn? Alchemists were replaced by Physicians, druggists and teachers at this point. A German writer Stahl said that a chemical fluid called Phlogiston existed in things that burn and didn’t exist in the one’s that don’t. Burning causes Phlogiston to escape. But this theory could not explain why when Iron is burnt its ashes weighed more. The idea of Phlogiston died.

Discovery of Chemistry:
In 1774 Joseph Priestly and Englishman discovered Oxygen. It then became possible not only to explain burning but to lay foundations of the chemistry as we have it today.