8th Science Notes, 7. Metals and Nonmetals

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माहिती विज्ञानाची 🎷

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🚦 Difference between metal and nonmetal.

• Under ordinary temperature metals stay in solid state. 
• At ordinary temperature nonmetals occur as solids, liquids and gases.

🎢Metals have lustre.

Nonmetals do not have lustre,

• Generally metals are hard.
• nonmetals are brittle.

🎳When a metal is pulled through a hole its wire is formed. This property of metal is

called ductility.

Non metals do not show ductility property.

• After hammering metals a thin sheet forming. This property is called malleability of metals.
• Non metals are not malleable.

🏇Metals are good conductors of heat.

Non metals are bad conductors of heat. 

• Metals are good conductors of electricity.
• Non metals are bad conductors of electricity,

🏈Metals have high density.

Nonmetals have low densities.

• Generally metals have high melting points and boiling points.
• Nonmetals have low melting and boiling points.

🎻Metals are sonorous. They produce sound on striking.

Non metals are non sonorous.

•  Majority of metals have up to three electrons in their outermost shell.
• Most of the nonmetals have 4 to 7 electrons in their valence shells.

🏀Metals have a tendency to lose their valence electrons to form positively charged ions, i.e, cations.

Non metals have a tendency to accept electrons in their valence shell to form negatively charged ions called anions.

• The metal oxides are basic in nature.
• The oxides of nonmetals are acidic in nature.

🏊Most of the metals react with dilute acids to form metal salts while hydrogen gas is released.

Nonmetals do not react with dilute acids.

• Some metals like sodium and potassium react with cold water, magnesium, iron metal react with steam.
• Nonmetals do not react with water.

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      🥭.  Metalloids 

Metalloids are elements that exhibit intermediate properties between metals and non-metals.

Ex. Arsenic (As), Silicon (Si), Germanium (Ge), Antimony (Sb)

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🌼  Some Exception: 

1. Mercury is in liquid state even at room temperature.
2. Gallium is in a liquid state at temperatures above its melting point of approximately 29.76 ^°C
3. Sodium and potassium are soft and can be easily cut by a knife.
4. Sodium, potassium and lithium are  having lower density then water. 
5. The density of lithium is only 0.53 g/cc.
6. Metals have low melting points and boiling points. Exceptions : Hg, Ga, Na, K.
7. Diamond and iodine crystals are lustrous.
8. Diamond an allotrope of carbon is the hardest natural substance.
9. Graphite an allotrope of carbon is a very good conductor of electricity.
10. The solid nonmetals carbon and boron melt at high temperature.

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 👉  Noble Metal :

 Some metals like gold (Au), silver (Ag), platinum (Pt), palladium (Pd) and rhodium (Rh) are noble metals.

 Noble Metal  occur in nature in the elemental state.  .

Uses of Noble metals :

1. Gold, silver and platinum are used to prepare ornaments.

2. Silver used in medicines. (It has antibacterial property).

3. Gold and silver also use to make medals.

4. Gold and silver also used to make few electronic devices.

5. Platinum, palladium metals are used as catalyst.

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🎺  100% pure gold is 24 carat.

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 🛞   Corrosion : 

Gases in the air react with metals in presence of moisture to form metal compounds. The metals get affected by this process and undergo what is called corrosion.

Ex. 

1. Green coloured copper carbonate has been formed by a reaction of copper with the carbon dioxide and moisture in the air.
2. A reddish coloured deposit is formed on iron by reaction with oxygen gas.
3. A blackish coloured deposit is formed on silver by reaction with hydrogen sulphide gas.

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✴️. prevention of corrosion

To prevent corrosion of metals, layers of oil, grease, varnish and paint are applied on them. 

Plating with another noncorroding metal is done such as Iron is arrested by zinc plating is called as GALVANIZATION.

By preparing alloy.

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Alloy : 

Defination: A homogeneous mixture of two or more metals or a homogeneous mixture metal with nonmetals is called alloy.

Alloys are made by mixing the constituent elements in as per the requirement.

Example. The stainless steel utensils used at home are made of an alloy of iron (Fe) with carbon (C), chromium (Cr) and nickel (Ni). 

The alloy bronze is formed from copper (Cu) and tin (Sn).

Kutubminar in Delhi

There is an iron pillar in the premices of Kutubminar in Delhi, made about 1500 year ago. The pillar is lustrous even after so many years. This is becasuse our ansestors had made it from an alloy. It contains small proportion of carbon (C), silicon (Si) and phosphorus (P) mixed in iron (Fe).

We might have seen the vertical cracks in stainless steel vessels. The reason behind this is a cheap variety of stainless steel is made sometimes by using copper instead of costly nickel. 

Nonmetal bromine is in liquid state at normal temperature.

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How aluminium ion form.

    Al  -------> Al^{+++ +    +} 3 e^-

(2,8,3)           (2,8)

Aluminium    Aluminium ion

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Chemical reactions.

1. Carbon burn in air.

C + O₂  ------> CO₂

  Carbon burn in air to form carbon dioxide.

2. Carbon dioxide gas passed through sodium hydroxide.

2NaOH +  CO₂ ------> Na₂CO₃ + H₂O

Carbon dioxide gas passed through sodium hydroxide to form sodium carbonate. 

3. Carbon dioxide gas passed through water. 

 H₂O + CO₂ ------> H₂CO₃

Carbon dioxide gas passed through water to form carbonic acid.

4. Sulphur dioxide gas passed through water. 

 H₂O + SO₂ ------> H₂SO₃

Sulphur dioxide gas passed through water to form sulphurous acid.

5. Sulphur trioxide gas passed through water

 H₂O + SO₃ ------> H₂SO₄

Sulphur trioxide gas passed through water to form sulfuric acid.

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