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Classification of Elements
Advanced Concepts & Practice for JEE/NEET
3.4 IUPAC Nomenclature of Elements with Atomic Numbers > 100
For newly discovered elements with very high atomic numbers, IUPAC (International Union of Pure and Applied Chemistry) has established a systematic nomenclature. This is to avoid controversies over naming rights, as these elements are often highly unstable and produced in minute quantities.
The temporary name is derived directly from the atomic number using numerical roots for 0 and numbers 1-9. These roots are put together in order of digits of the atomic number, and “ium” is added at the end. The symbol consists of three letters derived from the abbreviations of these roots.
IUPAC Numerical Roots
| Digit | Name | Abbreviation |
|---|---|---|
| 0 | nil | n |
| 1 | un | u |
| 2 | bi | b |
| 3 | tri | t |
| 4 | quad | q |
| 5 | pent | p |
| 6 | hex | h |
| 7 | sept | s |
| 8 | oct | o |
| 9 | enn | e |
Examples: Elements with Atomic Number Above 100
| Atomic Number | IUPAC Nomenclature | Symbol |
|---|---|---|
| 101 | Unnilunium | Unu |
| 104 | Unnilquadium | Unq |
| 118 | Ununoctium | Uuo |
Later, permanent names and symbols are assigned by IUPAC, often honoring the discoverer or location of discovery.
NEET/JEE Practice Question:
What would be the IUPAC name and symbol for the element with atomic number 120?
- (a) Ununbium, Uub
- (b) Unbinilium, Ubn
- (c) Unnilbium, Unb
- (d) Unnilunium, Unu
Correct Answer: (b) Unbinilium, Ubn
Explanation: Using the roots: 1 (un), 2 (bi), 0 (nil). Combining them and adding ‘ium’ gives Unbinilium. The abbreviation is ‘u’ + ‘b’ + ‘n’ = Ubn.
3.5 Electronic Configurations and Periodicity
Electronic Configurations in Periods
The period number in the Periodic Table directly corresponds to the principal quantum number (n) of the outermost or valence shell. As you move across a period, electrons are successively added to orbitals within the same principal energy level.
- Period 1 (n=1): Filling of 1s orbital. Contains 2 elements (H, He).
- Period 2 (n=2): Filling of 2s and 2p orbitals. Contains 8 elements (Li to Ne).
- Period 3 (n=3): Filling of 3s and 3p orbitals. Contains 8 elements (Na to Ar).
- Period 4 (n=4): Filling of 4s, then 3d (transition series), then 4p orbitals. Contains 18 elements (K to Kr). The 3d transition series starts at Scandium (Z=21, 3d¹4s²) and ends at Zinc (Z=30, 3d¹⁰4s²).
- Period 5 (n=5): Similar to Period 4, filling 5s, then 4d (transition series), then 5p orbitals. Contains 18 elements (Rb to Xe). The 4d transition series starts at Yttrium (Z=39).
- Period 6 (n=6): Filling 6s, then 4f (lanthanoids), then 5d, then 6p orbitals. Contains 32 elements (Cs to Rn). The 4f-inner transition series (lanthanoids) starts at Cerium (Z=58) and ends at Lutetium (Z=71).
- Period 7 (n=7): Incomplete, filling 7s, then 5f (actinoids), then 6d, then 7p orbitals. Includes most man-made radioactive elements. The 5f-inner transition series (actinoids) starts after Actinium (Z=89).
NEET/JEE Practice Question:
How would you justify the presence of 18 elements in the 5th period of the Periodic Table?
Explanation:
For $n=5$, the available orbitals are 5s, 5p, 5d, and 4f. However, based on the Aufbau principle and increasing energy, the order of filling is 5s, 4d, and 5p. The 5s orbital can hold 2 electrons. The 4d orbitals can hold 10 electrons. The 5p orbitals can hold 6 electrons. Total electrons = 2 (from 5s) + 10 (from 4d) + 6 (from 5p) = 18 electrons. Therefore, there are 18 elements in the 5th period.
Groupwise Electronic Configurations
Elements in the same vertical column (group) exhibit similar valence shell electronic configurations. This means they have the same number and distribution of electrons in their outermost orbitals, which is why they display similar chemical behaviors.
Example: Group 1 elements (alkali metals) all have $ns^1$ valence electronic configuration.
Li: $[He]2s^1$
Na: $[Ne]3s^1$
K: $[Ar]4s^1$
Rb: $[Kr]5s^1$
Cs: $[Xe]6s^1$
Fr: $[Rn]7s^1$
3.6 Types of Elements: S-, P-, D-, F- Blocks
Elements are classified into four blocks based on the type of atomic orbital that is being filled with the last electron (the differentiating electron).
3.6.1 The s-Block Elements
- Groups: Group 1 (Alkali Metals, $ns^1$) and Group 2 (Alkaline Earth Metals, $ns^2$).
- Nature: All are reactive metals.
- Properties: Low ionization enthalpies, readily lose outermost electron(s) to form +1 or +2 ions. Highly reactive, thus not found pure in nature. Compounds are predominantly ionic (except Li and Be).
3.6.2 The p-Block Elements
- Groups: Group 13 to 18 ($ns^2np^1$ to $ns^2np^6$).
- Classification: Along with s-block elements, they are called Representative Elements or Main Group Elements.
- Noble Gases (Group 18): Have a completely filled valence shell ($ns^2np^6$), making them very stable and chemically unreactive.
- Halogens (Group 17) & Chalcogens (Group 16): Have highly negative electron gain enthalpies, readily gaining one or two electrons respectively to achieve stable noble gas configuration.
- Trends: Non-metallic character increases from left to right across a period. Metallic character increases down a group.
3.6.3 The d-Block Elements (Transition Elements)
- Groups: Group 3 to 12, located in the center of the Periodic Table.
- Characteristic: Filling of inner d-orbitals. General outer electronic configuration is $(n-1)d^{1-10}ns^{0-2}$ (exception: Pd has $4d^{10}5s^0$).
- Nature: All are metals.
- Properties: Mostly form colored ions, exhibit variable valency (oxidation states), show paramagnetism, and are often used as catalysts.
- Exceptions: Zn, Cd, Hg (with $(n-1)d^{10}ns^2$ configuration) do not show most typical transition element properties.
- Role: Act as a bridge between the chemically active s-block metals and the less active p-block elements.
3.6.4 The f-Block Elements (Inner-Transition Elements)
- Location: Two rows at the bottom of the Periodic Table.
- Types:
- Lanthanoids: Ce (Z=58) – Lu (Z=71), filling 4f-orbitals.
- Actinoids: Th (Z=90) – Lr (Z=103), filling 5f-orbitals.
- Characteristic: Last electron added to f-orbital. General outer electronic configuration is $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$.
- Nature: All are metals.
- Properties: Properties within each series are quite similar. Actinoids exhibit more complicated chemistry due to a large number of possible oxidation states and are radioactive. Many actinoid elements are man-made.
NEET/JEE Practice Question:
The elements Z=117 and 120 have not yet been discovered. In which family/group would you place these elements and also give the electronic configuration in each case?
Explanation:
For Z=117: This element would be in Period 7, completing the p-block. It would have 7 valence electrons ($7s^27p^5$) and thus belong to Group 17 (Halogen Family). Its electronic configuration would be $[Rn]5f^{14}6d^{10}7s^27p^5$.
For Z=120: This element would start a new period, Period 8. It would have 2 valence electrons ($8s^2$) and thus belong to Group 2 (Alkaline Earth Metals). Its electronic configuration would be $[Uuo]8s^2$.
3.6.5 Metals, Non-metals and Metalloids
Elements can also be broadly classified based on their properties into Metals, Non-metals, and Metalloids.
- Metals:
- Comprise >78% of all known elements, located on the left side of the Periodic Table.
- Usually solids at room temperature (except Mercury; Ga, Cs also have low melting points).
- High melting and boiling points.
- Good conductors of heat and electricity.
- Malleable (can be flattened into thin sheets) and Ductile (can be drawn into wires).
- Non-metals:
- Located at the top right-hand side of the Periodic Table.
- Usually solids or gases at room temperature (except Bromine which is liquid) with low melting and boiling points (Boron and Carbon are exceptions).
- Poor conductors of heat and electricity.
- Most non-metallic solids are brittle, neither malleable nor ductile.
- Metalloids (Semi-metals):
- Elements bordering the zig-zag line separating metals and non-metals (e.g., Silicon, Germanium, Arsenic, Antimony, Tellurium).
- Show properties characteristic of both metals and non-metals.
Periodic Trends:
- Metallic character increases as we go down a group.
- Non-metallic character increases as one goes from left to right across a period.
NEET/JEE Practice Question:
Considering the atomic number and position in the periodic table, arrange the following elements in the increasing order of metallic character: Si, Be, Mg, Na, P.
- (a) P < Si < Be < Mg < Na
- (b) Si < P < Be < Mg < Na
- (c) Na < Mg < Be < Si < P
- (d) Be < Mg < Na < P < Si
Correct Answer: (a) P < Si < Be < Mg < Na
Explanation: Metallic character increases down a group and decreases across a period from left to right. P (Group 15, Period 3) is a non-metal. Si (Group 14, Period 3) is a metalloid. Be (Group 2, Period 2) and Mg (Group 2, Period 3) are metals; Mg is below Be, so more metallic. Na (Group 1, Period 3) is an alkali metal, highly metallic. Ordering from least to most metallic: P (non-metal) < Si (metalloid) < Be (metal) < Mg (more metallic metal, below Be) < Na (most metallic, Group 1).
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