IUPAC Numerical Roots (nil, un, bi...) for Naming Elements
Chemistry · Periodic Classification Of Properties · NEET
For new elements with atomic number (Z) more than 100, IUPAC names them using number roots: nil=0, un=1, bi=2, tri=3, quad=4, pent=5, hex=6, sept=7, oct=8, enn=9. You read each digit of Z, join the roots in order, and add "-ium" at the end. Memory hook: "Nil Un Bi Tri Quad Pent Hex Sept Oct Enn" = 0 to 9 in order, like counting on your fingers.
How to build an IUPAC systematic name: split the atomic number into digits, swap each digit for its root (nil, un, bi...), join them in order, and add -ium. The symbol is the first letter of each root.
Your doubts, answered
What are the IUPAC numerical roots and what number does each stand for?
There are 10 roots, one for each digit 0 to 9: nil=0, un=1, bi=2, tri=3, quad=4, pent=5, hex=6, sept=7, oct=8, enn=9. These are the only building blocks you need. For NEET, memorise them in order: nil, un, bi, tri, quad, pent, hex, sept, oct, enn. Every temporary element name is just these roots joined together.
Why does IUPAC use these roots at all instead of a real name?
When a brand new element with Z greater than 100 is first made, only a few atoms exist and scientists may argue over who discovered it and what to call it. For example, both American and Soviet scientists claimed element 104. To avoid fights, IUPAC gives a temporary systematic name built straight from the atomic number using these roots. Once the discovery is confirmed, a permanent name is given (like Rutherfordium).
How do I build the name step by step from the atomic number?
Take the atomic number and read it digit by digit. Replace each digit with its root. Join the roots in the same order as the digits. Add '-ium' at the end. Example, Z = 105: 1=un, 0=nil, 5=pent, so un + nil + pent + ium = Unnilpentium. The symbol is the first letter of each root, capitalised only at the start: Unp.
How do I write the symbol from the name?
Take the first letter of each root and write them together, first letter capital, rest small. For Z=120: 1=un, 2=bi, 0=nil, so name = Unbinilium and symbol = Ubn. Always three letters for a three-digit Z. This is why these are called three-letter provisional symbols.
When two vowels or letters meet, do I drop any letter?
For NEET, the standard rule taught in NCERT is simple: just join the roots and add -ium. You are not expected to apply the fine spelling rules (like 'bi ium' losing an i). Stick to the plain join-and-add-ium method used in NCERT and past NEET answers, because that is what the exam keys accept.
Do these roots only work for Z greater than 100?
IUPAC systematic naming is used mainly for elements that do not yet have a confirmed permanent name, which in practice are the very heavy man-made elements with Z above 100. Lighter elements already have accepted names, so you never call oxygen 'unnilium'. Focus your practice on Z = 101 up to about 120, the range NEET asks.
⚠️ The NEET trap ✗ Reading 'un' as 0 and 'nil' as 1, or mixing up 'enn' (9) with 'sept' (7), so students name Z=109 as 'unnilseptium' instead of the correct 'unnilennium'. ✓ un = 1, nil = 0, enn = 9, sept = 7. For Z=109: 1=un, 0=nil, 9=enn, so it is Unnilennium. For Z=107 it is Unnilseptium. 🧠 NEET 2022 asked the name of element 119 and the answer was 'ununennium' (un-un-enn-ium). The trap options used 'ennium' for 9 in the wrong place. Always spell the LAST digit carefully; 9 = enn, not sept.
Real NEET questions
NEET 2022
The IUPAC name of an element with atomic number 119 is:
A · ununennium ✓
B · unnilennium
C · unununnium
D · ununoctium
Solution: Read Z=119 digit by digit: 1=un, 1=un, 9=enn. Join and add -ium: un + un + enn + ium = ununennium (symbol Uue). Distractors are wrong because unnilennium would be 109, unununnium is 111, and ununoctium is 118.
NEET 2020
Match the IUPAC provisional names with their official names. (a) Unnilunium (b) Unniltrium (c) Unnilhexium (d) Unununnium with (i) Mendelevium (ii) Lawrencium (iii) Seaborgium (iv) Darmstadtium. Which one is correct?
A · (c)-(iii)
B · (d)-(iv)
C · (a)-(i) ✓
D · (b)-(ii)
Solution: Decode each name with the roots. Unnilunium = un-nil-un = 101 = Mendelevium (Md), so (a)-(i) is correct. Check others: Unniltrium = 103 = Lawrencium, Unnilhexium = 106 = Seaborgium, Unununnium = 111 = Roentgenium (not Darmstadtium 110). Only option (C) pairs correctly.
NEET 2022 / 2026
Identify the incorrect statement (one option states: 'The IUPAC name of the element with atomic number 107 is Unnilseptium').
A · Statement about Mg, Mg2+, Al, Al3+ sizes (this is the incorrect one) ✓
B · IUPAC name of Z=107 is Unnilseptium (correct)
C · Li-Mg similarity is the diagonal relationship (correct)
D · Oxidation state and covalency of Al in [AlCl(H2O)5]2+ are 3 and 6 (correct)
Solution: The IUPAC statement is correct: Z=107 gives 1=un, 0=nil, 7=sept, so Unnilseptium. This confirms the naming rule. The incorrect statement is the one about atomic sizes (largest is neutral Mg, smallest is Al3+), so the answer is option A. This PYQ shows examiners embed the root rule inside mixed statement questions.
Solved Periodic Classification Of Properties NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
How many IUPAC numerical roots do I need to memorise?
Exactly 10, one for each digit 0 to 9: nil, un, bi, tri, quad, pent, hex, sept, oct, enn. Learn them in order and you can name any heavy element.
What is the IUPAC name of element 118?
Read 1=un, 1=un, 8=oct, then add -ium: Ununoctium, symbol Uuo. Its confirmed permanent name is Oganesson (Og), but the systematic name is still Ununoctium.
What suffix is added at the end of every systematic name?
Always '-ium'. You join the digit roots first, then add -ium. Example: un + nil + nil + ium = Unnilnilium for Z=100.
How is the three-letter symbol made?
Take the first letter of each root and write them together, capital first, then small letters. For Ununennium (119) the symbol is Uue.
Why does NEET keep asking this topic?
It is a quick, rule-based question with no calculation, so examiners use it to test if you truly memorised the roots. A tiny slip (like enn vs sept) changes the whole answer, which makes it a favourite trap. Scoring here is fast and free marks if you know the table.
