Classification of Elements and Periodicity in Properties
Class 11 · Chemistry
4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.
Genesis of the Periodic Table
Part of: Table and Sizes
Triads grouped lookalikes in threes; octaves repeated every eighth by weight. Mendeleev sorted by mass into property columns, leaving gaps he predicted. Moseley reordered by atomic number, which rules today with groups, periods and blocks.
Why it matters. Each fix shows science self-correcting. The table's shape now predicts behaviour before testing.
Formulas
- Modern law: properties repeat with atomic number.
- Same valence shell pattern sits in one group.
Key words
- Dobereiner's triads
- : Groups of three with the middle resembling the other two.
- Newlands' octaves
- : Every eighth element repeating by weight, like music.
- Mendeleev's table
- : Sorted by mass into property columns, with gaps predicted.
- Moseley's law
- : Atomic number, not mass, orders the table.
- Modern periodic law
- : Properties repeat with atomic number.
Try it in two minutes
- Sort coins by size, then by year.
- Find the gaps in an old table.
- Place three elements by properties.
Try at home. Arrange family items into property columns.
Atomic and Ionic Radii
Part of: Table and Sizes
Half a bond length sets covalent size; half a metal spacing sets metallic. Sizes shrink across periods under rising pull and grow down groups with new shells. Cations shrink below parents; anions swell above; equal-electron sets shrink with charge.
Why it matters. Size orders packing, bonds and reactivity. One trend explains why fluorine is tiny and caesium huge.
Formulas
- Covalent radius = bond length / 2
- Sizes shrink across periods and grow down groups.
- For equal electrons: more protons means smaller.
Key words
- Covalent radius
- : Half a bond length.
- Metallic radius
- : Half a metal spacing.
- van der Waals radius
- : Half the gap between touching unbonded atoms.
- Cation
- : A shrunken positive ion with fewer electrons.
- Anion
- : A swollen negative ion with an extra electron.
- Isoelectronic series
- : Equal-electron sets shrinking with charge.
Try it in two minutes
- Rank period two by size from memory.
- Rank group one top to bottom.
- Shrink a cation and swell an anion.
Try at home. Plot group sizes on paper strips.
Ionization Enthalpy and Electron Gain
Part of: Energy Trends and Behaviour
Ionization enthalpy prices electron removal from a gaseous atom, rising across periods and falling down groups with famous dips at boron and oxygen. Electron gain pays for adding one; halogens pay most with chlorine topping fluorine, while noble gases charge instead.
Why it matters. These prices decide who donates and who grabs in every bond. Dips reveal shells and stability.
Formulas
- Second ionization always exceeds first.
- Trends rise across periods and fall down groups, with dips at B and O.
Key words
- Ionization enthalpy
- : Energy pricing electron removal from a gaseous atom.
- Successive ionization
- : Second removal costs more from the positive ion.
- Electron gain enthalpy
- : Energy paid for adding one electron.
- Boron dip
- : Lower cost from a higher shielded p orbital.
- Oxygen dip
- : Lower cost against nitrogen's half-filled shell.
- Halogen order
- : Chlorine tops fluorine in energy released.
Try it in two minutes
- Rank period two IEs spotting the dips.
- Rank halogen gains with chlorine first.
- Price removing two electrons versus one.
Try at home. Chart IE dips and explain each.
Electronegativity and Chemical Behaviour
Part of: Energy Trends and Behaviour
Electronegativity scores an atom's pull in a bond, peaking at fluorine and fading down groups. Metals give electrons cheaply and grow more metallic down and left; non-metals grab right and up. Borderline metalloids split the difference with mixed behaviour.
Why it matters. Pull gaps sort bonds into ionic, polar and covalent. Metallic order predicts oxides, reactions and uses.
Formulas
- Electronegativity rises across periods and falls down groups.
- Fluorine tops the scale at 4.0.
Key words
- Electronegativity
- : An atom's pull scored in a bond, peaking at fluorine 4.0.
- Metallic character
- : Giving electrons cheaply, growing down and left.
- Non-metallic character
- : Grabbing electrons, growing right and up.
- Metalloids
- : Borderline elements with mixed behaviour on the zig-zag.
- Alkali metals
- : Group 1, whose oxides dissolve to strong alkalis.
Try it in two minutes
- Rank bonds by pull gaps.
- Order five elements by metallic feel.
- Spot metalloids on the zig-zag.
Try at home. Sort home metals by bend and shine.
What your child will practise
- Atomic and Ionic Radii: Candy Puzzle (Clue Puzzle)
- Atomic and Ionic Radii: Candy Quick Fire (Quick Fire)
- Electronegativity and Chemical Behaviour: Desert Puzzle (Clue Puzzle)
- Genesis of the Periodic Table: Ocean Quest (Flip and Match)
- Ionization Enthalpy and Electron Gain: Ocean Quick Fire (Quick Fire)
- Quiz: Atomic and Ionic Radii (8 questions)
- Quiz: Electronegativity and Chemical Behaviour (8 questions)
- Quiz: Genesis of the Periodic Table (8 questions)
- Quiz: Ionization Enthalpy and Electron Gain (8 questions)