InterviewSolution
Saved Bookmarks
InterviewSolution
| 1. |
Characteristics of groups and periods |
| Answer» General Characteristics of a Group1. Metallic Character: In a group, on moving downwards, the metallic character gradually increases. For example, in the halogen family (group VIIA), fluorine, chlorine and bromine are typical non-metals but iodine, though a non-metal has a metallic lustre. This property is more marked in the elements of groups IVA and VA. These groups begin with a non-metal and end with metals.2. Valency: In a group, all the elements have the same valency. The group number is, in fact, the valency with respect to oxygen.3. Atomic Size: It is the distance between the centre of the nucleus and the outermost shell of an isolated atom. The atomic radius of hydrogen atom is 37pm. On moving downwards, in a group the size of the atom increases. This is because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so that the atomic size increases in spite of the increase in nuclear charge.4. Chemical Reactivity: There is a regular gradation in their physical properties like melting point, boiling point density, etc in a group. For example, in alkali metals (group IA), the melting point decreases on moving down the group.General Characteristics of a Period1. Valence Electrons: In a period, from left to right, the number of valence electron increases from 1 to 8.2. Atomic Size: The atomic radius decreases while moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electron closer to the nucleus and reduces the size of the atom.3. Valency with respect to Oxygen: From left to right in a period, valency with respect to oxygen increases from 1 to 7.\xa0 | |