The Periodic Table is a systematic arrangement of all known elements based on their atomic numbers. In RRB Group D exams, this topic appears in almost every paper with 2-3 questions guaranteed. Understanding the periodic table helps solve questions on element properties, chemical behavior, and atomic structure. Core Concept: Elements are arranged in horizontal rows called PERIODS and vertical columns called GROUPS. The position of an element tells us its properties. There are 18 groups and 7 periods in the modern periodic table.
Atomic size DECREASES from left to right in a period
Atomic size INCREASES from top to bottom in a group
Metallic character DECREASES from left to right
Non-metallic character INCREASES from left to right
Ionization energy INCREASES from left to right
Electronegativity INCREASES from left to right
Questions focus on element positions, group properties, periodic trends, and identifying elements from given data. Common question types include finding group/period of elements, comparing atomic sizes, and predicting chemical behavior.
- Noble Gas Rule: Elements in Group 18 are noble gases with complete outer shells. They have 8 electrons in outer shell (except Helium with 2). Any element trying to achieve noble gas configuration will gain/lose electrons accordingly.
Write electronic configuration: 2, 8, 7
Count electron shells = 3 shells = Period 3
Count valence electrons = 7 electrons = Group 17 Answer: Chlorine is in Group 17, Period 3 Worked Example 2: Compare atomic sizes of Sodium (Na, Group 1) and Chlorine (Cl, Group 17) in Period 3.
Both are in same period (Period 3)
Apply periodic trend - atomic size decreases left to right
Sodium is on left, Chlorine is on right Answer: Sodium has larger atomic size than Chlorine Shortcut for Valency: Group 1 = valency 1, Group 2 = valency 2, Group 13 = valency 3, Group 14 = valency 4, Group 15 = valency 3, Group 16 = valency 2, Group 17 = valency 1, Group 18 = valency 0 Most
Students confuse GROUP NUMBER with VALENCY for groups 15, 16, 17. Remember - Group 15 has 5 valence electrons but valency is 3 (8-5=3). Group 16 has 6 valence electrons but valency is 2 (8-6=2).
Group 17 has 7 valence electrons but valency is 1 (8-7=1). Always subtract from 8 for these groups to find valency.
Trick: 'LION' - Lithium is in group 1, period 1 (Li-1-1). This helps remember that period = number of shells, group = valence electrons. The modern periodic table was given by Henry Moseley based on atomic numbers, not atomic masses like Mendeleev's table.
12graded MCQs · easy to hard · full solution & trap analysis