The Periodic Table — Question 17

(a) Alkali metals —

1. The elements of group 1 [IA] from ³Li [Lithium] to ⁸⁷Fr [Francium] are called alkali metals as they react with water forming strong alkalis.
2. They are light metals and are univalent with one valence electron in outer shell. This makes them strong reducing agents as they readily donate the one electron to achieve stable electronic configuration.
3. They are highly reactive electropositive metals, which are soft and can be cut with a knife.
4. They are good conductors of heat & electricity.
5. They form electrovalent compounds with non-metals. e.g. KCl, NaBr.

(b) Alkaline earth metals —

1. The elements of group 2 [IIA] from ⁴Be [Beryllium] to ⁸⁸Ra [Radium] are called Alkaline earth metals.
2. They are light metals and are divalent with two valence electrons in their outer shell. They are reducing agents as they can donate the two electrons to achieve stable electronic configuration.
3. They have properties similar to alkali metals but are slightly less reactive than alkali metals.
4. They are good conductors of heat & electricity.
5. They form electrovalent compounds with non-metals. e.g. CaCl₂, MgO.

(c) Halogens —

1. The elements of group 17 [VIIA] from ⁹F [Fluorine] to ⁵³I [Iodine] are called Halogens. They are called Halogens as Halogens means salt producer and these elements react with metals to form salts.
2. They are non-metals and are univalent with seven valence electrons in their outer shell. This makes them strong oxidising agents as they readily accept one electron to achieve stable electronic configuration.
3. They are highly reactive, electronegative non-metals.
4. They are bad conductors of heat & electricity.
5. They form covalent compounds with non-metals. e.g. HCl, PCl₃.

(d) Noble gases —

1. The elements of group 18 [0] from ⁹He [Helium] to ⁵³Rn [Radon] are called Noble gases.
2. They are non-metals and have eight valence elections in outer shell [except Helium (He) which has only two]. They have stable electronic configuration hence their valency or combining capacity is Zero.
3. Noble gases do not react with other elements & are therefore inert or unreactive. They are all monatomic gases.

(e) Transition and inner transition elements —

Transition elements —

1. The elements of group 3 to 12 [IB to VIIB & VIII] are called Transition elements.
2. They are all metals.
3. They lie at the centre of the periodic table between metals [highly electropositive] on the left and non-metals [highly electronegative] on the right.

Inner transition elements —

1. Lathanide [Rare earths] and Actinides series are called inner transition elements.
2. They lie at the bottom of the periodic table in two horizontal rows [14 elements each].
3. Lanthanide series : from Cerium ⁵⁸Ce to Lutetium ⁷¹Lu : [Period - 6]
4. Actinide series : from Thorium ⁹⁰Th to Lawrencium ¹⁰³Lr: [Period - 7]
5. They are all metals and chemically very reactive [actinides are radioactive elements].

(f) Normal elements —

1. Elements of groups 1, 2, 13, 14, 15, 16, 17 are called normal elements.
2. Atoms of these elements have all inner shells complete except outermost shell.
3. They consist of metals, metalloids and non-metals.
4. The number of electrons in their outermost shell signifies the group to which they belong.