Class 10 Chemical properties of metals, Reactivity series, How do metals and non-metals react, Properties of ionic compounds

Topics to be covered

`=>` Chemical properties of metals
`=>` Reactivity series
`=>` How do metals and non-metals react
`=>` Properties of ionic compounds

๐‚๐‡๐„๐Œ๐ˆ๐‚๐€๐‹ ๐๐‘๐Ž๐๐„๐‘๐“๐ˆ๐„๐’ ๐Ž๐… ๐Œ๐„๐“๐€๐‹๐’

`color{green}("๐Ÿ ๐‘๐„๐€๐‚๐“๐ˆ๐Ž๐ ๐–๐ˆ๐“๐‡ ๐Ž๐—๐˜๐†๐„๐ :")`

`color{green}(โ˜…)` Almost all metals combine with oxygen to form metal oxides.

`color{red}("๐Œ๐ž๐ญ๐š๐ฅ + ๐Ž๐ฑ๐ฒ๐ ๐ž๐ง โ†’ ๐Œ๐ž๐ญ๐š๐ฅ ๐Ž๐ฑ๐ข๐๐ž")`

`color{green}(โ€ข)` For example, when copper is heated in air, it combines with oxygen to form copper(II) oxide, a black oxide.

`color{red}(underset("(Copper)")(2Cu) + O_2 โ†’ underset("(Copper(II) oxide)")(2CuO))`

`color{green}(โ€ข)` Aluminium forms aluminium oxide.

`color{red}(underset("(Aluminium)")(4Al) + 3O_2 โ†’ underset("(Aluminium oxide)")(2Al_2O_3))`

`color{green}(โ˜…)` Some metal oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as well as basic behaviour. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. For eg:

`color{red}(Al_2O_3 + 6HCl โ†’ 2AlCl_3 + 3 H_2O)`

`color{red}(Al_2O_3 + NaOH โ†’ underset("(Sodium aluminate)")(2NaAlO_2) + H_2O)`

`color{green}(โ˜…)` Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis. Sodium oxide and potassium oxide dissolve in water to produce alkalis as follows โ€“

`color{red}(Na_2O(s) + H_2O(l) โ†’ 2NaOH (aq))`

`color{red}(K_2O(s) + H_2O(l) โ†’ 2KOH (aq)) `

`color{green}(โ˜…)` Different metals show different reactivities towards oxygen.

`color{green}(โ€ข)` Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.

`color{green}(โ€ข)` At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc., are covered with a thin layer of oxide. The protective oxide layer prevents the metal from further oxidation.

`color{green}(โ€ข)` Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner.

`color{green}(โ€ข)` Copper does not burn, but the hot metal is coated with a black coloured layer of copper(II) oxide.

`color{green}(โ€ข)` Silver and gold do not react with oxygen even at high temperatures.

`color{green}(โ€ข)` Sodium is the most reactive of the samples of metals taken here.

`color{green}(โ€ข)` The reaction of magnesium is less vigorous implying that it is not as reactive as sodium.
But burning in oxygen does not help us to decide about the reactivity of zinc, iron, copper or lead.

`color{red}(" ๐‰๐”๐’๐“ ๐…๐Ž๐‘ ๐‚๐”๐‘๐ˆ๐Ž๐”๐’ ")`

`color{green}(โ˜…)` Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.

`color{green}("๐Ÿ ๐‘๐„๐€๐‚๐“๐ˆ๐Ž๐ ๐–๐ˆ๐“๐‡ ๐–๐€๐“๐„๐‘ ")`

`color{green}(โ˜…)` Metals upon reaction with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. But all metals do not react with water.

`color{red}(" ๐Œ๐ž๐ญ๐š๐ฅ + ๐–๐š๐ญ๐ž๐ซ โ†’ ๐Œ๐ž๐ญ๐š๐ฅ ๐จ๐ฑ๐ข๐๐ž + ๐‡๐ฒ๐๐ซ๐จ๐ ๐ž๐ง")`

`color{red}("๐Œ๐ž๐ญ๐š๐ฅ๐ฌ ๐จ๐ฑ๐ข๐๐ž๐ฌ + ๐–๐š๐ญ๐ž๐ซ โ†’ ๐Œ๐ž๐ญ๐š๐ฅ ๐ก๐ฒ๐๐ซ๐จ๐ฑ๐ข๐๐ž ")`

`color{green}(โ˜…)` Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.

`color{red}(2K(s) + 2H_2O (l) โ†’ 2KOH (aq) + H_2 (g) + " heat energy")`

`color{red}(2Na(s) + 2H_2O(l) โ†’ 2NaOH (aq) + H_2(g) + " heat energy ")`

`color{green}(โ˜…)` The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire.

`color{red}(Ca(s) + 2H_2O(l) โ†’ Ca(OH)_2 (aq) + H_2(g))`

Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.

Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.

`color{green}(โ˜…)` Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.

`color{red}(2Al(s) + 3 H_2O(g) โ†’ Al_2O_3 (s) + 3H_2 (g))`

`color{red}(3Fe(s) + 4 H_2O(g) โ†’ Fe_3O_4 (s) + 4 H_2(g))`

Metals such as lead, copper, silver and gold do not react with water at all.

`color{green}("๐Ÿ‘ ๐‘๐„๐€๐‚๐“๐ˆ๐Ž๐ ๐–๐ˆ๐“๐‡ ๐€๐‚๐ˆ๐ƒ๐’:")`

`color{green}(โ˜…)` Metals react with acids to give a salt and hydrogen gas.

`color{red}("๐Œ๐ž๐ญ๐š๐ฅ + ๐ƒ๐ข๐ฅ๐ฎ๐ญ๐ž ๐š๐œ๐ข๐ โ†’ ๐’๐š๐ฅ๐ญ + ๐‡๐ฒ๐๐ซ๐จ๐ ๐ž๐ง ")`

`color{green}(โ˜…)` Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because `color{red}(HNO_3)` is a strong oxidising agent. It oxidises the `color{red}(H_2)` produced to water and itself gets reduced to any of the nitrogen oxides `color{red}((N_2O, NO, NO_2 ))`.

`color{green}(โ˜…)` But magnesium `color{red}((Mg))` and manganese `color{red}((Mn))` react with very dilute `color{red}(HNO_3)` to evolve `color{red}(H_2)` gas.

`color{green}(โ˜…)` The reactivity decreases in the order `color{red}(Mg > Al > Zn > Fe)`. In the case of copper, no bubbles were seen and the temperature also remained unchanged. This shows that copper does not react with dilute `color{red}(HCl)`.

`color{red}(" ๐‰๐”๐’๐“ ๐…๐Ž๐‘ ๐‚๐”๐‘๐ˆ๐Ž๐”๐’ ")`

`color{green}(โ˜…)` Aqua regia, (Latin for โ€˜royal waterโ€™) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.

`color{green}("๐Ÿ’ ๐‘๐„๐€๐‚๐“๐ˆ๐Ž๐ ๐–๐ˆ๐“๐‡ ๐’๐Ž๐‹๐”๐“๐ˆ๐Ž๐๐’ ๐Ž๐… ๐Ž๐“๐‡๐„๐‘ ๐Œ๐„๐“๐€๐‹ ๐’๐€๐‹๐“๐’:")`

`color{green}(โ˜…)` Reactive metals can displace less reactive metals from their compounds in solution or molten form.

`color{green}(โ˜…)` Displacement reactions give better evidence about the reactivity of metals. It is simple and easy if metal A displaces metal B from its solution, it is more reactive than B.

`color{red}("๐Œ๐ž๐ญ๐š๐ฅ ๐€ + ๐’๐š๐ฅ๐ญ ๐ฌ๐จ๐ฅ๐ฎ๐ญ๐ข๐จ๐ง ๐จ๐Ÿ ๐ โ†’ ๐’๐š๐ฅ๐ญ ๐ฌ๐จ๐ฅ๐ฎ๐ญ๐ข๐จ๐ง ๐จ๐Ÿ ๐€ + ๐Œ๐ž๐ญ๐š๐ฅ ๐ ")`

๐“๐ก๐ž ๐‘๐ž๐š๐œ๐ญ๐ข๐ฏ๐ข๐ญ๐ฒ ๐’๐ž๐ซ๐ข๐ž๐ฌ

`color{green}(โ˜…)` A list of metals arranged in the order of their decreasing activities is called reactivity series.

๐‡๐Ž๐– ๐ƒ๐Ž ๐Œ๐„๐“๐€๐‹๐’ ๐€๐๐ƒ ๐๐Ž๐-๐Œ๐„๐“๐€๐‹๐’ ๐‘๐„๐€๐‚๐“

`color{green}(โ˜…)` The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.

`color{green}(โ˜…)` Sodium and chloride ions, being oppositely charged, attract each other and are held by strong electrostatic forces of attraction to exist as sodium chloride (NaCl). It should be noted that sodium chloride does not exist as molecules but aggregates of oppositely charged ions.


`color{green}("(๐ข) ๐๐ก๐ฒ๐ฌ๐ข๐œ๐š๐ฅ ๐ง๐š๐ญ๐ฎ๐ซ๐ž:")` Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.

`color{green}("(๐ข๐ข) ๐Œ๐ž๐ฅ๐ญ๐ข๐ง๐  ๐š๐ง๐ ๐๐จ๐ข๐ฅ๐ข๐ง๐  ๐ฉ๐จ๐ข๐ง๐ญ๐ฌ:")` Ionic compounds have high melting and boiling points . This is because a considerable amount of energy is required to break the strong inter-ionic. attraction.

`color{green}("(๐ข๐ข๐ข) ๐’๐จ๐ฅ๐ฎ๐›๐ข๐ฅ๐ข๐ญ๐ฒ :")` Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.

`color{green}("(๐ข๐ฏ) ๐‚๐จ๐ง๐๐ฎ๐œ๐ญ๐ข๐จ๐ง ๐จ๐Ÿ ๐„๐ฅ๐ž๐œ๐ญ๐ซ๐ข๐œ๐ข๐ญ๐ฒ :")` A solution conducts electricity when there occurs the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. ๐ˆ๐จ๐ง๐ข๐œ ๐œ๐จ๐ฆ๐ฉ๐จ๐ฎ๐ง๐๐ฌ ๐ข๐ง ๐ญ๐ก๐ž ๐ฌ๐จ๐ฅ๐ข๐ ๐ฌ๐ญ๐š๐ญ๐ž ๐๐จ ๐ง๐จ๐ญ ๐œ๐จ๐ง๐๐ฎ๐œ๐ญ ๐ž๐ฅ๐ž๐œ๐ญ๐ซ๐ข๐œ๐ข๐ญ๐ฒ because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the elecrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.