Structure of Periodic Table - NEET Notes, Formula & Common Mistakes
Structure of Periodic TablePeriods and groupsClassification of ElementsNEET ChemistryNEET 2025Periodic Table BlocksModern Periodic Table
Structure of Periodic Table - NEET Notes, Formula & Common Mistakes
Classification of Elements and Periodicity in Properties·2 min read·NEET 2026
What NEET Asks
Direct questions on the number of periods/groups and their significance are common.
Identification of period and group for elements based on atomic number.
Understanding the general characteristics associated with elements in specific periods or groups.
Key Points
The Modern Periodic Table is arranged in increasing order of atomic number.
are the 7 horizontal rows, representing the principal energy shells (n). The period number corresponds to the highest principal quantum number (n) of the valence shell.
Periods
Groups are the 18 vertical columns, containing elements with similar valence shell electronic configurations and thus similar chemical properties.
Number of elements per period:
1st period (n=1): 2 elements (H, He)
2nd period (n=2): 8 elements
3rd period (n=3): 8 elements
4th period (n=4): 18 elements
5th period (n=5): 18 elements
6th period (n=6): 32 elements (including Lanthanoids)
7th period (n=7): 32 elements (incomplete, including Actinoids)
Group numbering: Groups 1, 2, and 13-18 are main group (representative) elements. Groups 3-12 are transition elements.
Must-Know Formula / Reaction
Relation between Period Number and Electronic Shell:Period Number = Principal Quantum Number (n) of the valence shellExplanation: This directly tells you the highest energy shell being filled in an element from that period.
Common Mistakes
Students often confuse periods (horizontal rows) with groups (vertical columns).
Don't confuse the total number of elements in a period with the number of d-block or f-block elements within it.
Students often forget that the modern periodic table is based on atomic number, not atomic mass.
Rapid Revision
The Modern Periodic Table organizes elements by increasing atomic number into 7 periods (energy shells) and 18 groups (similar valence electrons/properties). Periods define the principal quantum number 'n', while groups define similar chemical behavior. Remember the element counts per period and their significance.
Frequently Asked Questions
What are periods in the modern periodic table?▾
Periods are the horizontal rows in the modern periodic table. There are seven periods, and each period corresponds to the principal quantum number (n) of the valence shell where electrons are being filled.
What are groups in the modern periodic table?▾
Groups are the vertical columns in the modern periodic table. There are eighteen groups, and elements within the same group generally have similar valence shell electronic configurations and thus exhibit similar chemical properties.
How many periods and groups are there in the modern periodic table?▾
The modern periodic table consists of 7 periods (horizontal rows) and 18 groups (vertical columns). The elements are systematically arranged based on their increasing atomic numbers.
Practice MCQs on this topic
Interactive questions with instant AI explanations