Modern Periodic Table — Revision Notes

⚡ 30-Second Revision

Modern Periodic Law: — Properties are periodic functions of atomic number (Z).
Basis: — Atomic number, not atomic mass.
Periods: — 7 horizontal rows, $n$ = period number.

- Period 1: 2 elements ($1s$) - Period 2: 8 elements ($2s, 2p$) - Period 3: 8 elements ($3s, 3p$) - Period 4: 18 elements ($4s, 3d, 4p$) - Period 5: 18 elements ($5s, 4d, 5p$) - Period 6: 32 elements ($6s, 4f, 5d, 6p$) - Period 7: 32 elements ($7s, 5f, 6d, 7p$)

Groups: — 18 vertical columns, similar valence e- config, similar properties.
Blocks:

- s-block (Gr 1, 2): $ns^{1-2}$ - p-block (Gr 13-18): $ns^2np^{1-6}$ - d-block (Gr 3-12): $(n-1)d^{1-10}ns^{1-2}$ (Transition elements) - f-block (Lanthanoids, Actinoids): $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$ (Inner transition elements)

Group Determination:

- s-block: No. of valence s-electrons. - p-block: $10 + (\text{No. of valence s-electrons} + \text{No. of valence p-electrons})$. - d-block: $(\text{No. of } (n-1)d \text{ electrons} + \text{No. of } ns \text{ electrons})$.

2-Minute Revision

The Modern Periodic Table organizes elements by increasing atomic number, a principle established by Henry Moseley. This arrangement, known as the Modern Periodic Law, states that elemental properties are periodic functions of their atomic numbers.

The table has 7 periods (rows), corresponding to the highest principal quantum number of the valence shell, and 18 groups (columns), where elements share similar valence electron configurations and thus similar chemical properties.

Elements are categorized into s, p, d, and f blocks based on the subshell where the last electron enters. This structure effectively resolves issues like the placement of isotopes and anomalous pairs found in earlier classifications.

Key for NEET is to quickly determine an element's period, group, and block from its atomic number or electronic configuration, and understand the general characteristics associated with each block and group.

5-Minute Revision

The Modern Periodic Table is the definitive classification of elements, based on the Modern Periodic Law: properties are periodic functions of atomic number (Z). This law, proposed by Moseley, rectified the shortcomings of Mendeleev's atomic mass-based table.

The table is structured into 7 periods and 18 groups. Each period number corresponds to the principal quantum number ($n$) of the outermost electron shell, while elements in the same group possess similar valence electron configurations, leading to similar chemical properties.

For instance, Group 1 elements ($ns^1$) are alkali metals, and Group 17 elements ($ns^2np^5$) are halogens.

Elements are further divided into four blocks: s, p, d, and f. S-block elements (Groups 1 & 2) have their last electron in an s-orbital. P-block elements (Groups 13-18) have their last electron in a p-orbital. D-block elements (Groups 3-12), also known as transition elements, fill their d-orbitals. F-block elements (lanthanoids and actinoids), or inner transition elements, fill their f-orbitals and are placed separately for table compactness.

To determine an element's position: write its electronic configuration. The highest 'n' gives the period. The orbital of the last electron gives the block. For group: s-block = valence s-electrons; p-block = 10 + (valence s + p electrons); d-block = (n-1)d + ns electrons.

For example, Z=26 (Iron): $[Ar]4s^23d^6$. Period is 4 (highest n=4). Block is d (last electron in 3d). Group is $2+6=8$. This systematic approach is vital for NEET, as questions frequently test the ability to locate elements and infer their properties.

Prelims Revision Notes

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Modern Periodic Law: — Properties of elements are periodic functions of their atomic numbers (Z). (Moseley, 1913)
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Structure:

* Periods (7): Horizontal rows. Period number = highest principal quantum number ($n$) of valence shell. * Period 1: $1s$ (2 elements: H, He) * Period 2: $2s, 2p$ (8 elements: Li-Ne) * Period 3: $3s, 3p$ (8 elements: Na-Ar) * Period 4: $4s, 3d, 4p$ (18 elements: K-Kr) * Period 5: $5s, 4d, 5p$ (18 elements: Rb-Xe) * Period 6: $6s, 4f, 5d, 6p$ (32 elements: Cs-Rn, including Lanthanoids) * Period 7: $7s, 5f, 6d, 7p$ (32 elements: Fr-Og, including Actinoids) * Groups (18): Vertical columns.

Elements in a group have similar valence shell electronic configurations and thus similar chemical properties.

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Blocks: — Determined by the orbital where the last electron enters.

* s-block (Groups 1 & 2): General config $ns^{1-2}$. Reactive metals. * p-block (Groups 13-18): General config $ns^2np^{1-6}$. Metals, non-metals, metalloids. * d-block (Groups 3-12): Transition elements. General config $(n-1)d^{1-10}ns^{1-2}$. Variable oxidation states, colored compounds. * f-block (Lanthanoids & Actinoids): Inner transition elements. General config $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$. Placed separately.

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Determining Position from Z:

* Electronic Configuration: Write the full configuration. * Period: Highest value of $n$. * Block: Orbital of the last electron. * Group: * s-block: Number of valence s-electrons. * p-block: $10 + (\text{number of valence s-electrons} + \text{number of valence p-electrons})$. * d-block: $(\text{number of } (n-1)d \text{ electrons} + \text{number of } ns \text{ electrons})$.

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Advantages over Mendeleev's Table:

* Correct placement of isotopes (same Z, same position). * Resolution of anomalous pairs (e.g., Ar-K, Co-Ni) based on Z. * Logical placement of noble gases (Group 18). * Theoretical basis for periodicity (electronic configuration). * Separation of lanthanoids and actinoids.

Vyyuha Quick Recall

To remember the order of filling orbitals for period length: Some People Don't Feel. (s, p, d, f blocks). For period lengths: 2, 8, 8, 18, 18, 32, 32 (Remember the 32s for periods 6 and 7 due to f-block).