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Atomic Structure

The molecular gears and naomachines The molecular gears and nanomachines When the Dalton proposed his atomic theory there were no advanced instruments to practice the chemistry at atomic or nano−scale. But now nanochemistry, chemistry at nanometers, is the most advanced and developing science. What is the use of chemistry at atomic or molecular level? Current medical technology cannot get inside the human brain to remove the blood clots responsible for strokes. Just imagine, what if we could manufacture nano machines that could propel themselves through the arteries, navigate to the proper site, and either delicately excise the clot or deliver a nanodose of a clot‐dissolving drug? Recently researchers in Singapore have invented a molecular gear of the size of 1.2nm whose rotation can be deliberately controlled.

Learning Objectives

After completing the topic, the student will be able to:

  • Dfferenciate an atom from element, compound, molecule and ion.
  • Summarize the Dalton's atomic theory.
  • Understand how the fundamental subatomic particles, proton, neutron and electron were discovered.
  • Differentiate the characteristics of fundamental particles.
  • Discuss the earlier models of atom developed by Thomson and Rutherford and their drawbacks.
  • Represent an atom and an element using symbols.
  • Differentiate isotopes, isotones and isobars.
  • Discuss the history of periodic table.
Understanding of an element, molecule and compound Element is a pure substance composed of atoms. Atoms combine to form molecule or compounds. Compound is always made of different atoms while a molecule can be made of either similar or different atoms.
Atoms, Molecules and Ions

An element is composed of extremely small particles called atoms. All the atoms of an element are identical. The atoms of different elements are different and exhibit different properties. Atoms of an element cannot be converted into atoms of another element; nor they can be created or destroyed in normal chemical reactions.

When two or more atoms of the same or different elements combine it is called a molecule. Example: H2, O2 are molecules of same element hydrogen and oxygen respectively while, H2O is a molecule of two different elements: hydrogen and oxygen. Compounds are formed when atoms of different elements combine. Example: H2O, CO2. In other words, compounds are molecules of different elements.

When the particles in the combined atoms gain energy, they break the bonds and form charged species called ions. Negatively charged ions are called anions while positively charged ions are called cations. Their generation is due to unequal sharing of electrons and the process is called ionization.

A French chemist Antoine Lavoisier (1743–1794), known as the 'Father of modern chemistry' laid its foundation. Lavoisier accepted the idea of an element as any material made of only one component. He identified a compound as any material composed of two or more elements.

 Pure metals Pure metals Pure metals (copper, gold, silver ) are examples of elements. Elements combine to form the compounds.
Pure elements

Substances are made up of either one element or a combination of many elements. Elements and combination of elements are also called chemicals. Gold (Au) or silver (Ag), can exist as pure elements and can be found as gold or silver itself. We do have commercial gold jewellery and silverware which, however, is not pure.

On the other hand, we have substances such as water and oxygen − essential for life. They are made up of a combination of elements. Water is a combination of two hydrogen atoms and one oxygen atom. Oxygen we breathe in is made up of two oxygen atoms. Stable combination of elements is known as a molecule.

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