Chemistry Part=3

The six non-metallic elements in Group 17 (or Group VIIA) of the periodic table are called halogens. These six elements are fluorine (F), chlorine (CI), bromine (Br), iodine (Shift-1) and astatine (At). All of them have seven electrons in their outermost shell.

Elements in groups 3 to 12 of the periodic table are called d-block elements or transition clements. The d-orbitals of these elements are incomplete or only partially complete. All transition elements are metals.

Elements found in the middle part of the periodic table are called 'transition elements. They are called d-block elements because the electrons added to this block of elements are added to the d-orbital.

Elements of the same period also have the same number of atomic orbital

Helium is not a rare earth element, but it is an inert element. It is the second most abundant element in the universe. It is used in diving, weather forecasting etc.

When a metal is heated, its atoms gain energy and vibrate more vigorously. This energy is transferred to the electrons present in the atoms. These electrons travel to the metal, they transfer energy to other electrons and atoms of the same element. The thermal conductivity is represented by the sign K. Its unit is Watt per meter-Kelvin (W/m-k). The thermal conductivity of silver is 406, that of copper is 385, that of aluminium is 205 and that of iron is 79.5 watts per m-Kelvin.

Water molecules (H₂O) are polar in nature. That is. both the hydrogen atoms present in a molecule of water have a positive charge and the central oxygen atom has a negative charge. This is due to oxygen's more negatively electronegative nature, which results in higher electron density near the oxygen atom.

The number of atoms in the molecule of an element is called atomicity. The atomicity of argon (Ar) is one. That is, argon is an inert gas found in the monoatomic state.

Those elements whose density is more than 5 grams per cubic centimeter are called 'heavy metals". The density of gold is 19.32, the density of silver is 10.5. the density of iron is 7.87 and that of copper is 8.96. Hence, the heaviest metal among the above is gold.

The symbol for gold is Au. It is a single atomic element. That is, its atoms do not combine with each other to form diatomic, triatomic, or polyatomic molecules.