Metals and Nonmetals Class 8 Science Notes Maharashtra State Board
All the objects or materials in the world are made from elements, compounds, or their mixtures. Scientists classified all the elements into three general types which are metals, nonmetals, and metalloids.
Metals
Gold, silver, iron, copper, aluminium, magnesium, calcium, sodium, and platinum are a few metals. Metals have luster. The metals are hard. Wire or sheets can be from them made of metal. Metals are good conductors of heat and electricity. Metals lose their valence electrons to produce positively charged ions, that is cations.
Physical Properties of Metals
1. Physical State:
Under ordinary temperatures, metals stay in the solid state. However, metals like mercury and gallium are exceptions, which are in liquid state even at room temperature.
2. Lustre:
Take copper vessels at your home. Scrub them with lemon and rinse with water. Observe the luster before and after cleaning. Light gets reflected from the cleaned or freshly cut surface of metal and the metal looks lustrous.
3. Hardness:
Generally, metals are hard, not soft.
Exception: Sodium and potassium are soft and can be easily cut by a knife.
4. Ductility:
Have you ever gone to a goldsmith’s shop? Have you seen the goldsmith making a wire of gold or silver? When a metal is pulled through a hole its wire is formed. This property of metal is called ductility.
5. Malleability:
Take an iron nail. Place it on a platform and keep on hammering it. After some time you will see a thin sheet forming. This property is called the malleability of metals.
6. Conduction of Heat:
Take a copper plate. Fix some wax at one of its ends. Heat the other end and observe what happens. Metals are good conductors of heat. Silver, copper, and aluminium are the best conductors of heat.
7. Conduction of Electricity:
Which metals are used to make electrical wires? Metals are good conductors of electricity. Lead is an exception, which is neither a good conductor of heat nor a good conductor of electricity.
8. Density:
Metals have high density Sodium, potassium, and lithium are exceptions, having lower density than water. The density of lithium is only 0.53 g/cc.
9. Melting Point & Boiling Point:
Generally, metals have high melting points and boiling points.
Exceptions: Hg, Ga, Na, K.
10. Sonority:
What is the metal that your school bell is made of? How does a bell function? Metals are sonorous. They produce sound on striking.
Nonmetals
Carbon, Sulphur, and Phosphorus are a few nonmetals. Generally, nonmetals are brittle and non-lustrous.
Physical Properties of Nonmetals:
1. Physical State:
At ordinary temperatures, nonmetals occur as solids, liquids, and gases.
For example, Solids: C, S, P; Liquids: Br2; Gases: H2, N2, O2
2. Lustre:
Nonmetals do not have luster, except diamond and iodine crystals. Some nonmetals are colorless while others have different colours. What is the color of carbon in the form of coal? Sulfur is yellow and bromine is brown.
3. Brittleness:
Take coal and hammer it. See what happens to it. Solid nonmetals are brittle. Some nonmetals are soft. Diamond (an allotrope of carbon) is an exception, which is the hardest natural substance.
4. Ductility & Malleability:
Non-metals are neither ductile nor malleable.
5. Conduction of Heat & Electricity:
Nonmetals are bad conductors of heat and electricity, except graphite (an allotrope of carbon) which is a very good conductor of electricity.
6. Density:
Nonmetals have low densities.
7. Melting & Boiling Point:
Nonmetals have low melting and boiling points.
Exceptions: the solid nonmetals carbon and boron melt at high temperatures.
Gold, Silver, and Aluminium are highly malleable metals. A sheet with a thickness of 1/10,000 mm and a wire with a diameter of 1/5000 mm can be made from gold.
Metalloids:
Some elements such as arsenic (As), Silicon (Si), Germanium (Ge), and Antimony (Sb) have properties that are intermediate between metals and nonmetals. Such elements are called metalloids.
Chemical Properties of Metals
1. Electronic Configuration:
The electronic configuration is the basis of the chemical behavior of elements. The majority of metals have upto three electrons in their outermost shell.
| Metal | Atomic Number | Electronic Configuration |
| 11Na | 11 | 2, 8, 1 |
| 12Mg | 12 | 2, 8, 2 |
| 13Al | 13 | 2, 8, 3 |
2. Formation of Ions:
Metals tend to lose their valence electrons to form positively charged ions, that is cations.
3. Reaction with Oxygen:
Metals combine with oxygen to form their oxides.
Metal + Oxygen → Metal Oxide
The metal oxides are basic. Metal oxides react with an acid to form salt and water.
Metal oxide + Acid → Salt + Water
4. Reaction with Acid:
Take dilute hydrochloric acid in a test tube. Then add zinc dust to it. Take a glowing splinter near the mouth of the tube. Observe the glowing splinter. You will notice some sound coming out from it. Most of the metals react with dilute acids to form metal salts while hydrogen gas is released.
Metal + Dilute Acid → Salt + Hydrogen Gas
5. Reaction with Water:
Most metals do not show any observable and fast reaction with cold water. But some metals like sodium and potassium react with cold water to produce their hydroxides and hydrogen gas. magnesium metal requires steam to give similar reactions.
Chemical Properties of Nonmetals
1. Electronic Configuration:
Most of the nonmetals have 4 to 7 electrons in their valence shells.
| Nonmetal | Atomic Number | Electronic Configuration |
| 7N | 7 | 2, 5 |
| 8O | 8 | 2, 6 |
| 17Cl | 17 | 2, 8, 7 |
2. Formation of Ions:
Non-metals tend to accept electrons in their valence shell to form negatively charged ions called anions.
3. Reaction with Oxygen:
Nonmetals combine with oxygen to form their oxides.
Nonmetal + Oxygen → Nonmetal Oxide
The oxides of nonmetals are acidic. They react with bases to form soluble salt and water.
C + O2 → CO2
CO2 + 2NaOH → Na2CO3 + H2O
The oxides of nonmetals react with water to form an acid.
CO2 + H2O → H2CO3 (Carbonic Acid)
SO2 + H2O → H2SO3 (Sulphurous Acid)
SO3 + H2O → H2SO4 (Sulphuric Acid)
4. Nonmetals do not react with dilute acids.
Noble Metal:
Some metals like gold, silver, platinum, palladium, and rhodium are noble. They occur in nature in the elemental state. Gold that is 100 percent pure is called 24-carat gold. Pure gold is soft. As a result, the ornaments made from pure gold bend or break due to pressure. Therefore goldsmiths mix it with a certain proportion of copper or silver. Ornaments are made from 22-carat gold or gold with still smaller carat value.
Uses of Noble Metals:
- Gold, silver, and platinum are used to prepare ornaments.
- Silver is used in medicines. (It has antibacterial properties).
- Gold and silver also used to make medals.
- Gold and silver are also used to make a few electronic devices.
- Platinum and palladium metals are used as catalysts.
Purity of Gold:
When we ask rate of gold in a gold shop, it always differs. Why is it? Gold is a noble metal, in nature, it occurs in element form. 100% pure gold is 24 carats. Pure gold is soft. Therefore gold ornaments prepared by pure gold may break or bend due to pressure. Hence gold-smith add a specific amount of copper or silver in pure gold. To prepare ornaments 22 carat gold is used.
| Carat | Percentage |
| 24 | 100 |
| 22 | 91.66 |
| 18 | 75 |
| 14 | 58.33 |
| 12 | 50 |
| 10 | 41.66 |
Corrosion:
Gases in the air react with metals in the presence of moisture to form metal compounds. The metals get affected by this process and undergo what is called corrosion. There is a statue of Liberty in the sea near New York City in America. The original surface of their statues was made of copper. But now it looks green. This is because green-colored copper carbonate has been formed by a reaction of copper with the carbon dioxide and moisture in the air. This is an example of corrosion.
A reddish-colored deposit is formed on iron by reaction with oxygen gas. A greenish-colored deposit is formed on copper by a reaction with carbon dioxide gas. A blackish-colored deposit is formed on silver by reaction with hydrogen sulphide gas. To prevent corrosion of metals, layers of oil, grease, varnish, and paint are applied on them. Also plating with another noncorroding metal is done. Iron is arrested by zinc plating. Due to these processes, the contact of metal surface with air is lost and corrosion cannot occur as the chemical reaction cannot occur.
Alloy:
A homogeneous mixture of two or more metals or a homogeneous mixture of metal with nonmetals is called an alloy. Alloys are made by mixing the constituent elements in as per the requirement. For example, the stainless steel utensils used at home are made of an alloy of iron with carbon, chromium, and nickel. The alloy bronze is formed from copper and tin.
There is an iron pillar in the premises of Kutubminar in Delhi, made about 1500 years ago. The pillar is lustrous even after so many years. This is because our ancestors made it from an alloy. It contains a small proportion of carbon, silicon, and phosphorus mixed in iron. A cheap variety of stainless steel is made sometimes by using copper instead of costly nickel. You might have seen the vertical cracks in stainless steel vessels. The reason is as above.
Comprehensive Maharashtra State Board Class 8 Science Notes Metals and Nonmetals can help students make connections between concepts.