Periodic Table Mastery

5 min

Master Mendeleev, Modern Law, Groups, Periods and Classification for exams.

Golden Rule

The Modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. Henry Moseley replaced Mendeleev's atomic mass basis with atomic number to correct anomalies.

Exam Relevance

Direct questions on group numbers, periods and valency appear in every shift.
Metals, non-metals and metalloid boundary lines are favorite topics for defence exams.
Noble gases group 18 properties and inertness are tested in state police exams.

Memory Hooks

Mendeleev = Mass (M & M), Moseley = Number (MN rule).
Groups are Vertical (7 letters = 18 groups up-down).
Periods are Horizontal (7 rows across the table).

Periodic Quick Data

Feature	Mendeleev Table	Modern Table
Basis	Atomic Mass	Atomic Number
Total Groups	8 Groups	18 Groups
Total Periods	7 Periods	7 Periods
Noble Gases	Absent originally	Group 18

Classification Map

Metals

(Left Side Solids)

Left Side Solids

Sodium and Iron are reactive metals.

Non-Metals

(Right Side Gases/Solids)

Right Side Gases/Solids

Oxygen and Chlorine are non-metals.

Metalloids

(Zig-zag Borderline)

Zig-zag Borderline

Silicon and Germanium act as semiconductors.

Noble Gases

(Extreme Right Group 18)

Extreme Right Group 18

Helium and Neon have complete octets.

Exam Traps & Pitfalls

Mendeleev used atomic numberMendeleev used atomic mass

Mendeleev arranged elements by atomic mass; Moseley changed it to atomic number.

Hydrogen is an alkali metalHydrogen is a non-metal gas

Though placed above group 1, hydrogen is a reactive non-metal gas.

Metalloids conduct electricity like metalsMetalloids are semiconductors

Metalloids have intermediate properties and act as semiconductors, not pure conductors.

Quick Exam Practice

Q1.Who modified Mendeleev's periodic table by using atomic number instead of atomic mass?

Q2.Which group in the modern periodic table contains noble gases?

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