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Radioactive Radioactive tracers are extensively used in medicine Radioactive isotopes (or radioisotopes) have been employed for cancer treatment for years, with radioactive iodine being used to treat tumors. Knowledge of complete atomic structure and its concepts will be very helpful to handle such type of advanced techniques.

Learning Objectives

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

  • Describe and draw the basic structure of an atom.
  • Analyze and detect how electrons are configured around a nucleus.
  • Explore the importance of trace elements which play a key role in keeping the body working effectively.
  • Identify the difference between compounds, mixtures and elements.
  • Discover and analyze how elements are combined into compounds and molecules.
  • Use the periodic table to evaluate relationships between atomic number and mass number.
  • Define isotopes and radioisotopes. Investigate how radioisotopes are applicable in different fields like agriculture and medicine.
Different states of matter Different states of matter Matter exists in three different states at room temperature. They are solid, liquid and gaseous states. The three states of the matter are inter-convertible to each other when heat is supplied or removed from molecules. Two other forms of state also exists – plasma state and Bose–Einstein condensate which occur at a very high (105 K) and very low (<10−7 K) temperatures respectively.
What is matter?

All substances around us consist of matter. Matter is anything that occupies space and has mass. The blackboard in the classroom, the chair that you are sitting on, the air you breathe, the food you eat, the plate and spoon, etc., are all made up of matter. All living and non–living objects − everything is made up of matter!

What do you first observe about matter? Our perception and understanding of everything around us is through our five different sense organs − eyes, nose, ears, tongue and skin. We see that matter comes in various colors, smells, textures, temperatures etc. Edible matter comes in various tastes and if you hit various objects, they make many different sounds. The variety of matter is immense.

Besides these properties, matter, as seen in everyday life, comes in three states: solids, liquids and gases. The simplest example is water. Water at ordinary temperature is liquid. But if we cool it, it becomes ice. If we heat water, we get steam. Heat plays a crucial role in transforming matter from one state into another. In addition, in general matter or substances can be either pure or a combination of two or more substances. For example, water may be a pure liquid, but salt solution is a combination of water and salt.

Examples for elements Examples of elements Any element consists of only one kind of atoms. Gold consists of only gold atoms, a flask of gaseous nitrogen consists of only nitrogen atoms, and the lead of a graphite pencil consists of only carbon atoms.
Atoms, elements and molecules

If you take a piece of chalk and go on cutting it into smaller and smaller bits, you will come to a stage where you need a microscope to see the smaller dimensions. As you go further into smaller dimensions, you need very powerful microscopes to see the minuscule bits. There you will see that the chalk piece is made up of molecules. A molecule of chalk is made up of smaller parts − the atoms.

All atoms are made up of protons, neutrons and electrons(only exception: 1H1 doesn't have neutrons). It is the way these subatomic particles are arranged that gives each atom its unique characteristics. The electron arrangement (or configuration) gives each atom or element its chemical and physical characteristics. Thus, the number of protons or the atomic number (Z) identifies a particular element. Since an atom is electrically neutral, its number of electrons is equal to the proton number Z. For example, hydrogen is denoted as H and its atomic number (Z) = 1, and it has 1 electron. Helium is denoted as He and its atomic number (Z) = 2 and it has 2 electrons.

An element is a substance, which cannot be split into two or more simpler substances by the usual methods of applying heat, light, electric energy or even by chemical reactions. Pure gold, for instance, is an element because it consists of only gold atoms. Similarly, the element nitrogen consists solely of nitrogen atoms, and the element carbon solely of carbon atoms. When atoms combine, a molecule is formed. A molecule may be made up of same kind of atoms or different kinds of atoms. When atoms of the same element combine together, they may be monoatomic (Ex: Inert or Noble gases such as He, Ne, Ar etc), diatomic (Ex: H2, N2, O2 etc) or polyatomic molecules (O3, P4, S8 etc).