CBSE Class 11 · Chemistry
Classification of Elements and Periodicity in Properties
Official NCERT chapter from Chemistry Part I–II (book code kech1). ExamMaster notes are original teaching at CBSE Class 11 depth.
This lesson follows the official chapter “Classification of Elements and Periodicity in Properties” in Chemistry Part I–II. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 11
- Medium level
- 8 concepts
1Why do we Need to Classify Elements ?
We classify elements so a new one inherits a family-job: alkali, halogen, noble-gas as taught. A classify is a test-grid, not a pretty poster. Without it, 118 names are a mute list.
Sorting only by “shiny” is not this need.
Figure. Classification is a family test, not a pile. Li, Na, K share one valence story; He, Ne, Ar share another. A mixed heap hides both.
How it works
- Name a family-job you want to predictThe need.
- Say a table-slot should inherit that jobThe classify.
- Refuse a colour-sort as the scienceHonest.
2Genesis of Periodic Classification
Genesis: triads, octaves, Mendeleev’s mass-order with gaps — as the lesson named the tries. A leftover (tellurium–iodine as taught) pushed atomic-number order. Genesis is a why-the-table-changed story, not a biography dump.
Calling Mendeleev wrong and done skips the gap-success.
Figure. Dobereiner's triad: the middle atomic mass is the mean of the two ends. (7+39)/2 = 23, so Na sits between Li and K. One triad is a hint, not the modern table.
How it works
- Name an older tryTriad, octave, or mass-table.
- Name a leftover it could not holdThe push.
- Land on Z-order as the modern fixGenesis done.
3Modern Periodic Law and the Present Form of the Periodic Table
Modern law: properties repeat when Z is the order, not mass. The present table is periods (rows) and groups (columns) as taught. A period-number tracks the outer shell being filled in the school story.
Putting K after Ar by mass instead of Z is the old leftover.
Figure. Modern law: properties repeat when elements are written in atomic-number order. A period is a left-to-right Z walk. A group is a down-the-column family (Li–Na–K; B–Al–Ga).
How it works
- Order by ZThe law.
- Read period as a row, group as a familyThe present form.
- Keep a gap as a prediction-slot if the lesson used oneThe table-job.
4Nomenclature of Elements with Atomic Numbers > 100
Names for Z>100 follow a systematic school-code (as taught): digits → roots → -ium. Ununbium-style names are temporary handles until a proper name lands. The heading is the code, not a news-name quiz.
Inventing a pretty Latin name is not the systematic write.
Figure. Z > 100 uses digit roots: 0 nil, 1 un, 2 bi, 3 tri, 4 quad, 5 pent, 6 hex, 7 sept, 8 oct, 9 enn, then ium. 107 is un-nil-sept-ium (Uns), not a trivial name from the book.
How it works
- Write Z as digitsThe given.
- Map each digit to the taught root and add -iumThe temporary name.
- Keep it a handle until the proper name is givenHonest.
5Electronic Configurations of Elements and the Periodic Table
Electronic configuration and the table: Z tells the fill; the outer-shell write tells the group-family as taught. Na (Z=11) as 2,8,1 sits in the alkali column. A config is the reason the slot was earned, not a second table.
Parking Na as 2,8,8 “to look noble” is a Z-skip.
Figure. The period number is the outer principal shell n. Period 2 fills 2s then 2p. Li is 2s1; B is the first 2p electron. Group is the valence count, not the digit in the symbol.
How it works
- Copy ZThe given.
- Fill shells as taughtThe config.
- Read the outer write as the familyTable-link.
6Electronic Configurations and Types of Elements: s-, p-, d- and f-Blocks
Blocks: s (outer s filling), p, d, f as taught. A block is a fill-region, not a colour on a wall-chart. Transition and inner-transition sit in d and f as the lesson placed them. Block plus period plus group is the three-word address.
Calling every metal “d-block” skips s-block metals.
Figure. A block is the subshell being filled: s (groups 1–2), p (13–18), d (3–12), f the inner lanthanoid/actinoid strip. Widths here are schematic, not a cell count.
How it works
- Name the subshell being filledThe block.
- Place the element in s, p, d, or fThe type.
- Keep alkali in s, noble gas in p as taughtThe map.
7Periodic Trends in Properties of Elements
Trends (school): atomic radius, ionisation enthalpy, electron gain, electronegativity — as named, along a period or down a group. A trend is a direction plus a reason-shell, not a memorised number-dump. Li to F: radius falls as taught; down a group it grows.
Saying “everything increases down” without naming the property is a mute trend.
Figure. First IE generally rises Li → F as Z rises in the same shell. Be > B and N > O are the filled-2s / half-filled-2p dips, not a broken law. Values are kJ/mol.
How it works
- Name the property and the direction (period or group)The trend.
- Give the school reason (shell or Z-pull)The why.
- Refuse a single number as the whole trendA direction-story.
8A definition is a test you can run
Periodicity is a test: Z-order, a family-job, a block, or a named trend. If you only say “table”, you have furniture.
A wall-chart glow is not the test.
Figure. A family is a test you can run: same outer configuration (ns1 for alkali). A tidy table that only looks nearby is not the test. K would pass; a neighbour that is only pretty would not.
How it works
- Name Z, a group-job, a block, or a trendThe object.
- Give the school sentenceThe test.
- Then the word has contentThe definition ran.
Modern periodic order is by
- Atomic number Z — not mass
- Alphabetical names
- Density only
Z-order is the law.
Notes
- Mapped to the official NCERT chapter “Classification of Elements and Periodicity in Properties”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Formulas
- order by Z
- block = subshell being filled
Recap
Hold these pegs from the official chapter “Classification of Elements and Periodicity in Properties”. The wording is ExamMaster’s teaching, not a textbook recap.
- Why do we Need to Classify Elements ?
- We classify elements so a new one inherits a family-job: alkali, halogen, noble-gas as taught.
- Genesis of Periodic Classification
- Genesis: triads, octaves, Mendeleev’s mass-order with gaps — as the lesson named the tries.
- Modern Periodic Law and the Present Form of the Periodic Table
- Modern law: properties repeat when Z is the order, not mass.
- Nomenclature of Elements with Atomic Numbers > 100
- Names for Z>100 follow a systematic school-code (as taught): digits → roots → -ium.
- Electronic Configurations of Elements and the Periodic Table
- Electronic configuration and the table: Z tells the fill; the outer-shell write tells the group-family as taught.
- Electronic Configurations and Types of Elements: s-, p-, d- and f-Blocks
- Blocks: s (outer s filling), p, d, f as taught.
Practise Classification of Elements and Periodicity in Properties
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- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device