Periodic Classification of Elements 10 Science — Revision Notes
The periodic table is a systematic arrangement of all known elements based on their atomic number and chemical properties. Understanding periodic trends he
TL;DR: The periodic table is a systematic arrangement of all known elements based on their atomic number and chemical properties. Understanding periodic tren…
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The periodic table is a systematic arrangement of all known elements based on their atomic number and chemical properties. Understanding periodic trends he
Development of Periodic Table
- Mendeleev's periodic table arranged elements by atomic weight
- Mendeleev left gaps for undiscovered elements and predicted their properties
- Modern periodic table arranged by atomic number not atomic weight
- Henry Moseley determined atomic numbers using X-ray spectroscopy
- Current periodic table has 118 confirmed elements
Organization of Periodic Table
- Periods are horizontal rows; there are 7 periods
- Groups are vertical columns; there are 18 groups
- Period number indicates number of electron shells
- Group number related to number of valence electrons
- Each element has unique atomic number
Classification of Elements
- Metals are lustrous, malleable, ductile, and good conductors
- Non-metals are brittle and poor conductors; can be solid, liquid, or gas
- Metalloids have properties of both metals and non-metals
- s-block includes alkali metals and alkaline earth metals
- p-block includes halogens and noble gases
Periodic Trends
- Atomic radius decreases from left to right across a period
- Atomic radius increases down a group
- Ionization energy increases from left to right across a period
- Ionization energy decreases down a group
- Electronegativity increases from left to right and from bottom to top
Chemical Properties and Groups
- Group 1 alkali metals are highly reactive and form positive ions
- Group 2 alkaline earth metals are less reactive than alkali metals
- Group 17 halogens are highly reactive non-metals
- Group 18 noble gases are unreactive with complete electron shells
- Transition metals have variable oxidation states
Key Terms
- Atomic Number: Number of protons in nucleus of an atom
- Valence Electrons: Electrons in the outermost shell that participate in bonding
- Electronegativity: Measure of an atom's tendency to attract electrons in a bond
- Ionization Energy: Energy required to remove an electron from an atom
Frequently Asked Questions
Why are noble gases unreactive?
Noble gases have complete valence electron shells, making them extremely stable and unlikely to form chemical bonds with other elements.
How does atomic radius change in the periodic table?
Atomic radius decreases from left to right across a period due to increasing nuclear charge pulling electrons closer. It increases down a group due to additional electron shells.
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