Oxides, Hydroxides, Halides — Revision Notes

⚡ 30-Second Revision

Oxides: — Binary compounds with oxygen.

- Acidic: Non-metal oxides ($CO_2$, $SO_2$). - Basic: Metal oxides ($Na_2O$, $CaO$). - Amphoteric: $Al_2O_3$, $ZnO$. - Neutral: $CO$, $NO$, $N_2O$. - Peroxides: $O_2^{2-}$ (O.S. -1), diamagnetic ($Na_2O_2$). - Superoxides: $O_2^-$ (O.S. -1/2), paramagnetic ($KO_2$).

Hydroxides: — Contain $OH^-$.

- Basicity: Increases down a group, decreases across a period. - Amphoteric: $Al(OH)_3$, $Zn(OH)_2$.

Halides: — Compounds with halogens.

- Ionic: Large electronegativity difference (e.g., $NaCl$). High MP/BP, soluble in water, no hydrolysis. - Covalent: Small electronegativity difference (e.g., $CCl_4$). Low MP/BP, may hydrolyze. - Hydrolysis: Occurs if central atom has vacant d-orbitals (e.g., $SiCl_4$, $PCl_5$). $CCl_4$ does not hydrolyze. - Fajan's Rules: Covalent character $\propto$ (cation charge / cation size).

2-Minute Revision

Oxides are compounds of oxygen with another element, categorized by their chemical behavior. Acidic oxides (non-metal oxides like $CO_2$) react with bases, while basic oxides (metal oxides like $Na_2O$) react with acids.

Amphoteric oxides ($Al_2O_3$) exhibit both behaviors, and neutral oxides ($CO$, $NO$) are unreactive. Remember the specific oxidation states of oxygen in peroxides ($O_2^{2-}$, -1) and superoxides ($O_2^-$, -1/2), noting that superoxides are paramagnetic.

Hydroxides are compounds with the $OH^-$ group. Metal hydroxides are generally basic, with basicity increasing down a group and decreasing across a period. Amphoteric hydroxides like $Al(OH)_3$ are important exceptions.

Halides are compounds with halogens. Their bonding can be ionic (e.g., $NaCl$) or covalent (e.g., $CCl_4$), determined by electronegativity differences. Ionic halides are typically high-melting solids, while covalent halides are often liquids or gases.

A key concept is the hydrolysis of covalent halides, which occurs if the central atom has vacant d-orbitals (e.g., $SiCl_4$ hydrolyzes, $CCl_4$ does not). Fajan's rules explain the degree of covalent character: smaller, more charged cations and larger, more polarizable anions lead to increased covalent character.

5-Minute Revision

Let's consolidate the key aspects of oxides, hydroxides, and halides for NEET. Oxides are binary compounds of oxygen. Their classification is crucial: acidic oxides (e.g., $SO_2$, $N_2O_5$) are non-metal oxides that form acids with water and react with bases.

Basic oxides (e.g., $CaO$, $Na_2O$) are metal oxides that form bases with water and react with acids. Amphoteric oxides (e.g., $Al_2O_3$, $ZnO$) react with both acids and bases. Neutral oxides (e.g., $CO$, $NO$, $N_2O$) are unreactive.

Beyond these, remember peroxides ($O_2^{2-}$, oxygen O.S. -1, diamagnetic) and superoxides ($O_2^-$, oxygen O.S. -1/2, paramagnetic). For example, $Na_2O_2$ is a peroxide, while $KO_2$ is a superoxide.

Hydroxides contain the $OH^-$ group. Metal hydroxides are typically basic. Their basicity follows clear periodic trends: it increases as you go down a group (e.g., $LiOH < NaOH < KOH$) because the M-O bond becomes weaker and more ionic, allowing easier release of $OH^-$.

Basicity decreases across a period (e.g., $NaOH > Mg(OH)_2 > Al(OH)_3$) as metallic character decreases. Amphoteric hydroxides like $Al(OH)_3$ can react as both acids and bases, for instance: $Al(OH)_3 + 3HCl \rightarrow AlCl_3 + 3H_2O$ and $Al(OH)_3 + NaOH \rightarrow Na[Al(OH)_4]$.

Halides are compounds of elements with halogens. The nature of their bonding is key: ionic halides (e.g., $NaCl$, $CaF_2$) are formed between highly electropositive metals and halogens, characterized by high melting points and solubility in water without hydrolysis.

Covalent halides (e.g., $CCl_4$, $PCl_5$) are formed between non-metals or metals in high oxidation states, typically having lower melting points and often hydrolyzing in water. The ability to hydrolyze depends on the presence of vacant d-orbitals on the central atom; for example, $SiCl_4$ hydrolyzes readily ($SiCl_4 + 4H_2O \rightarrow Si(OH)_4 + 4HCl$), but $CCl_4$ does not due to the absence of d-orbitals on carbon.

Fajan's rules are crucial for understanding the degree of covalent character: a smaller, more highly charged cation and a larger, more polarizable anion lead to increased covalent character. For example, $AlCl_3$ is more covalent than $AlF_3$ due to the larger $Cl^-$ ion.

Prelims Revision Notes

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Oxides Classification:

* Acidic Oxides: Non-metal oxides ($CO_2$, $SO_2$, $N_2O_5$, $P_4O_{10}$) and high O.S. metal oxides ($CrO_3$, $Mn_2O_7$). React with water to form acids, react with bases to form salts. Acidity $\uparrow$ across period, $\downarrow$ down group (for non-metals).

* Basic Oxides: Metal oxides ($Na_2O$, $CaO$, $BaO$, $FeO$). React with water to form bases, react with acids to form salts. Basicity $\downarrow$ across period, $\uparrow$ down group. * Amphoteric Oxides: $Al_2O_3$, $ZnO$, $PbO$, $SnO_2$, $BeO$, $Ga_2O_3$.

React with both acids and bases. * Neutral Oxides: $CO$, $NO$, $N_2O$. Do not react with acids or bases. * Peroxides: Contain $O_2^{2-}$ ion (O.S. of O = -1). E.g., $H_2O_2$, $Na_2O_2$, $BaO_2$.

Diamagnetic. * Superoxides: Contain $O_2^-$ ion (O.S. of O = -1/2). E.g., $KO_2$, $RbO_2$, $CsO_2$. Paramagnetic (one unpaired electron). * Mixed Oxides: E.g., $Pb_3O_4 (2PbO cdot PbO_2)$, $Fe_3O_4 (FeO cdot Fe_2O_3)$.

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Hydroxides:

* Metal Hydroxides: Generally basic. Basicity $\uparrow$ down group ($LiOH < CsOH$), $\downarrow$ across period ($NaOH > Mg(OH)_2 > Al(OH)_3$). * Amphoteric Hydroxides: $Al(OH)_3$, $Zn(OH)_2$, $Pb(OH)_2$, $Be(OH)_2$. React with acids and strong bases. * Non-metal Hydroxides: Often oxyacids (e.g., $H_2SO_4$, $HNO_3$), acidic in nature.

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Halides: — Binary compounds of elements with halogens.

* Ionic Halides: Formed by highly electropositive metals (s-block, some p-block) with halogens. High MP/BP, solid, soluble in polar solvents, conduct electricity in molten/aqueous state. Generally do not hydrolyze (e.

g., $NaCl$). * Covalent Halides: Formed by non-metals or metals in high oxidation states. Low MP/BP, often liquid/gas, soluble in non-polar solvents, non-conductors. Many hydrolyze. * Hydrolysis: Covalent halides hydrolyze if the central atom has vacant d-orbitals to accept lone pairs from water.

E.g., $SiCl_4 + 4H_2O \rightarrow Si(OH)_4 + 4HCl$. $PCl_5 + 4H_2O \rightarrow H_3PO_4 + 5HCl$. $CCl_4$ does NOT hydrolyze due to absence of vacant d-orbitals on carbon. * Fajan's Rules: Predict covalent character in ionic compounds.

* Covalent character $\uparrow$ with: smaller cation size, higher cation charge, larger anion size, higher anion charge. * Example: $AlF_3$ (ionic) vs. $AlCl_3$ (more covalent, dimerizes to $Al_2Cl_6$).

$LiCl$ is more covalent than $NaCl$. * Trends: Covalent character $\uparrow$ across a period, $\uparrow$ from fluoride to iodide for a given element.

Vyyuha Quick Recall

For Amphoteric oxides, remember Aluminum, Zinc, Lead, Sn (tin), Beryllium, Gallium: 'Always Zebras Look So Beautifully Gray'.