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Chemistry - Periodic Properties and variations of Properties

Grade 10ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Modern Periodic Law: The physical and chemical properties of elements are periodic functions of their atomic numbers (ZZ).

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Groups and Periods: The Modern Periodic Table consists of 1818 vertical columns called groups and 77 horizontal rows called periods.

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Atomic Radius: It is the distance between the center of the nucleus and the outermost shell. It decreases across a period due to increasing effective nuclear charge (ZeffZ_{eff}) and increases down a group due to the addition of new shells (nn).

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Ionisation Potential (I.P.): The energy required to remove the most loosely bound electron from an isolated gaseous atom to form a positive ion. M(g)+I.P.→M+(g)+e−M(g) + I.P. \rightarrow M^+(g) + e^-

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Electron Affinity (E.A.): The amount of energy released when an electron is added to an isolated gaseous atom to form a negative ion. X(g)+e−→X−(g)+E.A.X(g) + e^- \rightarrow X^-(g) + E.A.

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Electronegativity: The tendency of an atom to attract the shared pair of electrons towards itself in a covalent bond. It increases across a period and decreases down a group.

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Metallic and Non-Metallic Character: Metallic character (electropositive nature) decreases across a period and increases down a group. Non-metallic character (electronegative nature) increases across a period and decreases down a group.

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Valency: Across a period, valency with respect to hydrogen increases from 11 to 44 and then decreases to 11 (00 for noble gases).

📐Formulae

Zeff=Z−σZ_{eff} = Z - \sigma (where ZZ is atomic number and σ\sigma is the shielding constant)

M(g)+I.E.1→M+(g)+e−M(g) + I.E._1 \rightarrow M^+(g) + e^-

X(g)+e−→X−(g)+Energy ReleasedX(g) + e^- \rightarrow X^-(g) + \text{Energy Released}

Metallic Character∝1Ionisation Potential\text{Metallic Character} \propto \frac{1}{\text{Ionisation Potential}}

💡Examples

Problem 1:

Arrange the following elements in increasing order of their atomic size: Li,Be,B,NaLi, Be, B, Na.

Solution:

B<Be<Li<NaB < Be < Li < Na

Explanation:

Li,Be,Li, Be, and BB belong to Period 2. Across a period, atomic size decreases, so B<Be<LiB < Be < Li. NaNa belongs to Period 3 and has an additional shell, making it larger than LiLi. Thus, B<Be<Li<NaB < Be < Li < Na.

Problem 2:

Explain why the Ionisation Potential of Noble gases (e.g., He,Ne,ArHe, Ne, Ar) is very high.

Solution:

I.P.Noble Gas≫I.P.HalogensI.P._{\text{Noble Gas}} \gg I.P._{\text{Halogens}}

Explanation:

Noble gases have a stable octet or duplet configuration (ns2np6ns^2 np^6). Their outermost shells are completely filled, making them extremely stable. High energy is required to remove an electron from this stable electronic configuration.

Problem 3:

Between FF (Fluorine) and ClCl (Chlorine), which element has a higher Electron Affinity and why?

Solution:

Cl>FCl > F (in terms of energy magnitude)

Explanation:

Normally, E.A. decreases down a group. However, FF has an exceptionally small size, leading to high inter-electronic repulsion in its 2p2p subshell. This makes it harder to add an incoming electron compared to ClCl, which has more space in its 3p3p subshell. Thus, Chlorine has a higher E.A. than Fluorine.