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Ayesha
was waiting for dinner. Today Ammi was making her favourite food – puri and
spicy potatoes. Ayesha watched as her mother rolled out the puri and put it in
the hot oil. She saw that at first the puri sank to the
bottom
of the pan.
As
it puffed up, the puri came up and started floating on the oil. One puri did
not puff up and did not float like the others. On seeing this, Ayesha took some
dough and rolled it into a ball. She flattened it and put it in
a
bowl of water. Alas! it sank to the
bottom and stayed there.
In
the evening Ayesha went for a bath. She had just come out when her mother
called, “Ayesha, you have dropped the soap in the water again.
Take
it out and put it in the soap case.” Ayesha was in a hurry and the soap case
fell out of her hands. It started floating on water. Ayesha
gently
put the soap in the soap case. She saw that the case continued to float, even
with the soap in it.
A
wooden boat in water will float. But a needle will sink! Why does this happen?
Let
me think... An iron ship will also float, though its’ much heavier
than
my boat!
Archimedes'
Principle of Buoyancy:
Archimedes'
principle indicates that the upward buoyant force that is
exerted on a body immersed in a fluid, whether fully or partially
submerged, is equal to the weight of the fluid that the body displaces.
Because
The reason that a ship floats is that it displaces a lot
of water. The displaced water wants to return to it's original
location, where the ship is now, and this pushes
the ship upwards. The force which pushes the ship up is called
the buoyancy force.
Archimedes
continued to do more experiments and came up with a buoyancy principle, that a
ship will float when the weight of the water it displaces equals the weight of
the ship and anything will float if it is shaped to displace its own weight of
water before it reaches the point where it will submerge.
This
is kind of a technical way of looking at it. A ship that is launched sinks into
the sea until the weight of the water it displaces is equal to its own weight.
As the ship is loaded, it sinks deeper, displacing more water, and so the
magnitude of the buoyant force continuously matches the weight of the ship and
its cargo.
But
a needle, light as a leaf, thin as a pin, will sink right in! Why does this
happen?
The
density of nail (as of iron) is much larger than the water.
So it sinks easily. The weight of the water displaced by
the ship is equal to its weight, so it floats. Whereas the
weight of the water displaced by the iron nail is less than
its weight so the iron nail sinks.
Have
you seen that some thing float on water while others sink? Think how this happens!
The poem here raises such questions.
Dead
Sea:
All
oceans and seas have salty water. The saltiest of all is the Dead Sea. How
salty? Imagine 300 grams of salt in one litre of water! Would you be able to
even taste such salty water? It would be very bitter.
Interestingly,
even if a person does not know how to swim, she would not drown in this sea.
She will float in water, as if lying down on it!
Remember
the lemon you floated in salty water?
What
dissolved, what did not?
On
Sunday Ayesha’s cousin brother Hamid came to her house
to
play. As soon as he came he asked his aunt to make his favourite shakkarpara (a
sweet dish).
Ammi
said, “Let me come back from the market, then I will make some for you. Why don’t
you help me? Take two glasses of water and put a bowl of sugar in it. Mix it
till it dissolves.” Hamid thought, “Let me
finish
this work fast. Then I will watch TV”.
Dandi
March:
This
incident took place in 1930, before India became independent. For many years
the British had made a law that did not allow people to make salt themselves.
They
had also put a heavy tax on salt. By this law people could not
make
salt even for use at home. “How can anybody live without salt?” Gandhiji said,
“How can a law not allow us to use freely what nature has given!” Gandhiji, with
several other people, went on a yatra (long walk) from Ahmedabad to the Dandi seashore
in Gujarat, to protest against
this
law.
Do
you know how salt is made? The sea water is collected in shallow beds dug in the
sand. Water is allowed to dry in the sun. After
Introduction: You are familiar with a number of materials like iron, aluminium, copper, etc. Some materials have been given in Table 4.1.Metals and non-metals combine with each other to form different types of bonds. While metal combines with non-metal to form an ionic bond, non-metal combines with another non-metal to form covalent bond. Metals are said to have low ionisation energy and low electron affinities. Metals tend to lose electrons easily due to low electron affinity. On the other hand, non-metals have high ionisation energy and high electron affinities and hence tend to gain electrons easily.
Man’s friendship with metals dates from prehistoric times. Initially, man became familiar with those metals which were occurring free in nature, like gold and copper. Gold was found at the burial sites. Then man came across copper and this was the first metal man started using extensively. This is the reason why this period was called the Copper Age. This was followed by the Bronze Age and the Iron Age.
There are more than 100 elements known today. On the basis of their general characteristics, they are broadly divided into two major groups: (i) Metals and (ii) Non-metals. There is yet another group of elements which shows characteristics of both metals and non-metals. Such elements are called metalloids. Among the total elements discovered, approximately 80% of them are metals and the remaining are either non-metals or metalloids.
Position in the periodic table: In the periodic table, metals are placed on the left hand side and in the centre, whereas non-metals are placed on the right hand side with the exception of hydrogen, which is placed with metals on the extreme left. The metalloids form a border diagonal line, separating metals from non-metals, as shown in the diagram below:
All the elements around us are categorised into three categories metals, non-metals and metalloids. Thus we can say that all the elements in the periodic table are divided into these three categories. Metals and Non-metals are two types of substances that may be distinguished by their physical and chemical characteristics. Metals are elements that are typically hard due to the presence of a strong metallic connection between the atoms. Non-metals, on the other hand, are generally soft in nature.
Metals are substances that are formed naturally below the surface of the Earth. Most of the metals are lustrous, i.e. they are shiny. Metals are made of substances that were never alive. This means that they are inorganic. They are natural compounds of the earth’s crust, which are generally found in the form of metal ores. They are associated with each other and also with other elements. Metals are present in the rocks that are washed up by surface water and groundwater. They also appear in atmospheric dust. They are strong, ductile, malleable and good conductors of heat and electricity. Metals are used in the manufacturing of automobiles, satellites, and cooking utensils, among other things. The majority of metals are typically hard. Sodium and potassium are notable exceptions. Knives can be used to cut them. Most metals are solid except mercury which is a liquid metal at room temperature. Some common metals, such as Gold, Silver and Copper are shown in the image below.
List of Common Metals
Physical Properties of Metals
The various physical properties of the metal are: 1. Appearance: Metals usually have a silver or grey colour (except copper and gold). Copper has a reddish-brown colour whereas gold has a yellow colour. Metals are widely used in our daily life for a large number of purposes. The cooking utensils, electric fans, sewing machines, cars, buses, trucks, trains, ships and aeroplanes, are all made of metals or mixtures of metals called alloys. In fact, the list of articles made of metals which we use in our daily life is unending.
Metals are solids at the room temperature. Generally, metals are very hard solids. All the metals like iron, copper, aluminium, silver and gold, etc., are solids at the room temperature. Exceptions: Only one metal, mercury, is in liquid state at the room temperature. Whereas gallium is a liquid at 30°C.
Metals generally have high melting points and boiling points. This means that most of the metals melt and vapourise at high temperatures. Iron is a very important metal. We use about nine times more iron than all the other metals put together. Iron is made into steel and used for making large things like bridges , as well as small things like needles. For example, iron is a metal having a high melting point of 1535°C. This means that solid iron melts and turns into liquid iron (or molten iron) on heating to a high temperature of 1535°C. Copper metal has also a high melting point of 1083°C.Exceptions: Metals like sodium and potassium have low melting points (of less than 100°C). Another metal gallium has such a low melting point that it starts melting in hand (by the heat of our body).
Metals are generally hard. Most of the metals are hard. But all the metals are not equally hard. The hardness varies from metal to metal. Most of the metals like iron, copper, aluminium, etc., are very hard. They cannot be cut with a knife.
The ability to hold large weights without breaking is called tensile strength. Metals are hard and have high tensile strength. For example, iron metal (in the form of steel) is very strong having a high tensile strength. Due to this, iron metal is used in the construction of bridges, buildings, railway lines, gliders, machines, vehicles and chains, etc. Though most of the metals are strong but some of the metals are not strong. For example, sodium and potassium metals are not strong. They have low tensile strength.
Metals have high densities. This means that metals are heavy substances. For example, the density of iron metal is 7.8 g/cm3 which is quite high. There are, however, some exceptions. Sodium and potassium metals have low densities. They are very light metals.
Metals can be beaten into thin sheets with a hammer (without breaking). This property of metals is called Malleability. Gold and silver metals are some of the best malleable metals. Aluminium and copper metals are also highly malleable metals. All these metals can be beaten with a hammer to form very thin sheets called foils. For example, silver metal can be hammered into thin silver foils because of its high malleability. The silver foils are used for decorating sweets. Similarly, aluminium metal is quite malleable and can be converted into thin sheets called aluminium foils.
Aluminium foils are used for packing food items like biscuits, chocolates, medicines, cigarettes, etc. Milk bottle caps are also made of aluminium foil. Aluminium sheets are used for making cooking utensils. Copper metal is also highly malleable. So, copper sheets are used to make utensils and other containers. Thus, malleability is an important characteristic property of metals.
Ductility: The capacity of a substance to be drawn into a wire is known as ductility, and it is this property that permits metals to be used as cable wires and for soldering. All the metals are not equally ductile. Some are more ductile than the others. Gold and silver are among the best ductile metals. For example, just 100 milligrams of a highly ductile metal like silver can be drawn into a thin wire about 200 metres long. Copper and aluminium metals are also very ductile and can be drawn into thin wires which are used in electrical wiring. So, we can say that metals are malleable and ductile. It is due to the properties of malleability and ductility that metals can be given different shapes to make various articles.
Sonorous: Metals are sonorous in nature they produce a deep or ringing sound when struck with another hard object. Metals are sonorous. This means that metals make a ringing sound when we strike them. It is due to the property of sonorousness of metals that they are used for making bells, plate type musical instruments like cymbals (manjira), and wires (or strings) for stringed musical instruments such as violin, guitar, sitar and tanpoora, etc. Metals differ significantly from non-metals in many of the physical and chemical properties. Let us study them in detail.
Lustrous: Most metals are lustrous in nature, i.e. they have a shiny appearance. Metals are lustrous (or shiny), and can be polished. Gold, silver and copper are shiny metals and they can be polished. The property of a metal having a shining surface is called metallic lustre (chamak). The shiny appearance of metals makes them useful in making jewellery and decoration pieces. For example, gold and silver are used for making jewellery because they are bright and shiny. The shiny surface of metals makes them good reflectors of light. Silver metal is an excellent reflector of light.
Conductivity is the ability of a substance allows heat and electricity to pass through them easily. Metals are generally good conductors of heat (The conduction of heat is also called thermal conductivity). Silver metal is the best conductor of heat. It has the highest thermal conductivity. Copper and aluminium metals are also very good conductors of heat. The cooking utensils and water boilers, etc., are usually made of copper or aluminium metals because they are very good conductors of heat. The poorest conductor of heat among the metals is lead. Mercury metal is also a poor conductor of heat. Metals are good conductors of electricity. The metals offer very little resistance to the flow of electric current and hence show high electrical conductivity.
The electric wires are made of copper and aluminium metals because they are very good conductors of electricity. The metals like iron and mercury offer comparatively greater resistance to the flow of current, so they have lower electrical conductivity.
Solid: Metals are generally solid in nature except for Mercury which is a liquid metal.
Metals have various chemical properties some of the properties of metals are listed below. Metals produce metal oxide when reacting with the oxygen in the air. Some metals like sodium and potassium are highly reactive and they can react vigorously with moisture in the air and are thus, stored in an oil bottle. Metals are highly corrosive and they react with oxygen and water in the air to form rust. Meals react with bases to form salt and liberate hydrogen. Metals are good reducing agents
Metals are usually very strong, durable and highly immune to everyday wear and tear. As such, they need been used in past for tons of things. Even now, with developments in technology and a slew of other factors, metals’ applications have expanded significantly. Metals are even important in the economy.
Construction Industry: Metals are the most component within the housing industry. Iron and steel are amongst the most utilized metals in the construction of buildings and even homes.
Electronics: Metals are utilised to make cables and parts for electrically powered devices and gadgets because they are good conductors of electricity. TVs, cell phones, refrigerators, irons, and computers are just a few examples.
Medicine: Metal elements are required for a variety of functions, including nerve impulse transmission, oxygen flow, enzyme reaction, and so on. To treat particular deficiencies or illnesses, several medicines are combined with metal compounds. Antacids contain metals such as iron, calcium, magnesium, potassium, titanium, and aluminium, which are commonly used in medicine.
Automobiles and Machinery: They are widely employed in the production of machines for industry, agriculture, and farming, as well as autos such as road vehicles, railways, aeroplanes, and rockets. Iron, aluminium, and steel are the most often used metals in this area. The majority of cooking utensils are constructed of metals such as steel, aluminium, and copper. Metals are preferred because of their excellent thermal resistance.
Other Uses: These days, most furniture is made of metal. Metals are also employed in the military, where they are used in the production of weapons and ammunition. Galvanizing protects metals from rusting by using certain metals.
Elements that lack the attributes of metals are called non-metals. Non-metals are good insulators of heat and electricity. They are mostly gases and liquids. Some non-metals are solid at room temperature. E.g. Carbon, sulphur and phosphorus.
Some common non-metals are shown in the image below.
The various physical properties of the non-metal are, Non-metals are poor conductors of heat and electricity. A notable exception is “Graphite” which is a good conductor of heat and electricity. Non-metal are not ductile in nature except for the carbon nanotube which is ductile in nature. Non-metal are not malleable and they are brittle i.e. they break when hit by a hammer or when force is applied. Non-metal are not lustrous as they do not have any shiny appearance. Non-metals don’t produce a deep ringing sound when they are hit with another material. Thus, they are not sonorous.
Non-metals are dull in appearance and are present in different colours. For example, sulphur is yellow, phosphorus is white or red, graphite is black, chlorine is yellowish-green, bromine is red- brown whereas hydrogen and oxygen are colourless.
Physical State
Non-metals can exist in all the three physical states: solid, liquid and gaseous. For example, carbon, sulphur and phosphorus are solid non-metals; bromine is a liquid non- metal; whereas hydrogen, oxygen, nitrogen and chlorine are gaseous non-metals. Diamond ( a non-metal) is the hardest substance known.
Non-metals have comparatively low melting points and boiling points This means that non- metals melt and vapourise at comparatively low temperatures. For example, sulphur is a non-metal having a low melting point of 119°C. The majority of non- metals have very low boiling points due to which they exist as gases at room temperature. Only one non-metal graphite has a very high melting point of 3700°C.
Non-metals are generally soft . Most of the solid non-metals are quite soft. They can be easily cut with a knife. For example, sulphur and phosphorus are solid non-metals which are quite soft and can be easily cut with a knife. Only one non-metal carbon (in the form of diamond) is very hard. In fact, diamond (which is an allotropic form of carbon) is the hardest natural substance known.
Non-metals are not strong. They have low tensile strength. This means that non-metals cannot hold large weights (without breaking). For example, graphite is a non-metal which is not strong. It has a low tensile strength. When a large weight is placed on a graphite sheet, it breaks.
Non-metals have low densities. This means that non-metals are light substances. For example, sulphur is a solid non-metal having a low density of 2 g/cm3, which is quite low. The density of gaseous non-metals is very low. One non-metal iodine has higher density compared to other non-metals.
Non-metals are not malleable and are brittle. This means that non- metals cannot be beaten into thin sheets with a hammer. Non-metals break into small pieces when hammered. For example, sulphur and phosphorus are solid non-metals which are not malleable, they cannot be beaten into thin sheets with a hammer. Thus, we cannot get thin sheets from non-metals. Sulphur and phosphorus non-metals are brittle. When beaten with a hammer, they break into small pieces. Brittleness is a characteristic property of solid non-metals.
Non-metals are not ductile. This means that non-metals cannot be drawn into wires. They are easily snapped on stretching. For example, sulphur and phosphorus are non-metals and they are not ductile. When stretched, sulphur and phosphorus break into pieces and do not form wires. Thus, we cannot get wires from non-metals. Non-metals are neither malleable nor ductile. Non- metals are brittle.
Non-metals are not lustrous (not shiny). They are dull in appearance. Non-metals do not have lustre which means that non-metals do not have a shining surface. The solid non-metals have a dull appearance. For example, sulphur and phosphorus are non-metals which have no lustre, that is, they do not have a shining surface. They appear to be dull. Iodine is a non-metal having lustrous appearance. It has a shining surface (like that of metals).
Non-metals are bad conductors of heat and electricity. This means that non-metals do not allow heat and electricity to pass through them. For example, sulphur and phosphorus which do not conduct heat or electricity. Many of the non-metals are, in fact, insulators. A form of the carbon element, diamond is a non-metal which is a good conductor of heat. And another form of carbon element, graphite is a non-metal which is a good conductor of electricity. Being a good conductor of electricity, graphite is used for making electrodes (as that in dry cells).
Non-metals have various chemical properties some of the properties of non-metals are listed below. Non-Metals are more reactive than metals. Non-Metals react with oxygen to form acidic oxide. Non-metals react with other non-metals at high temperatures
You should be able to guess why metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils, water boilers, etc. You are also familiar with the uses of some nonmetals. Here are some interesting ones. We are sure that you will guess them right: Non-metal is essential for our life which all living beings inhale during breathing, Non-metals used in fertilisers to enhance the growth of plants, Non-metal used in water purification process, Non-metal used in the purple coloured solution which is applied on wounds as an antiseptic, Non-metals used in crackers.
Various uses and applications of non-metals are, The respiration process is aided by oxygen, which is 21 % by volume. It’s also utilised to make steel and maintain a high temperature during the metal fabrication process. In the hospital, oxygen cylinders are used. As a bleaching chemical, chlorine is effective in eliminating stains and colour patches. Chlorine is used to make a variety of polymers and pesticides. It aids with water filtration. How? Bacteria are killed when chlorine is added to drinking water. For scientific experiments, helium is employed as an inert gas. Weather balloons use it as well. Iodine is used as an antiseptic in the treatment of wounds and cuts, as well as in the treatment of throat infections. Fertilizers: Nitrogen is found in fertilizers. It aids in the growth of plants. It boosts the plant’s growth rate. Plants can also benefit from non-metallic phosphorus. These two nonmetals are essential for plant growth. Crackers: Sulphur and phosphorus are used in fireworks.
Differences Between Metals And Non-Metals
The study of metals and non-metals is very important in the study of chemistry. The basic difference between metals and non-metals is discussed in the image below,
Metals and non-metals can be differentiated easily by knowing their physical properties like boiling point, melting point, ductility, malleability, thermal conductivity and chemical properties like electronegativities. Oxidising and reducing properties, corrosion properties, etc. The distinct feature that helps in differentiating metals and non-metals is metals like aluminium and copper is a high thermal and electrical conductivity, whereas non-metals like sulphur and phosphorus metal are the insulators. Some examples of metals include copper, silver, gold, caesium, platinum, aluminium, iron, nickel etc. Examples of non-metals are oxygen, nitrogen, potassium, sulphur, arsenic, etc.
Taste
buds are sensory organs that are found on yourTONGUE and allow you to
experience tastes that are sweet, salty, sour, and bitter. How exactly do your
taste buds work? Well, stick out your tongue and look in the mirror.
Taste
buds contain the receptors for taste. They are located around the
small structures on the upper surface of the tongue, soft palate, upper
esophagus, the cheek, epiglottis, which are called papillae. The myth of the
tongue map; that 1 tastes bitter, 2 tastes sour, 3 tastes salt, and 4 tastes
sweet.
Jhumpa
ran into the kitchen and caught hold of her mother saying, “Ma, I am not going
to eat this bitter karela (bittergourd). Give me gur (jaggery) and roti.”
Ma smiled and said, “You ate roti and sugar in
the morning.” Jhoolan teased Jhumpa, “Don’t you get bored of only one kind of
taste?” Jhumpa replied quickly, “Do you get bored with licking imli
(tarmarind)? I bet your mouth is watering just by hearing the word imli.”
“Sure I love the sour imli. But I eat sweet
and salty things too. I even eat karela,” said Jhoolan and looked at her
mother.
They
both laughed heartily. Jhoolan said to Jhumpa, “Let’s play a game. You close
your eyes and open your mouth. I will put something to eat in your mouth. You
have to tell what it is.”
Jhoolan
took a few drops of lemon juice in a spoon and put them in Jhumpa’s mouth.
“Sour lemon,” Jhumpa replied quickly.
Jhoolan
then picked up a small piece of jaggery. Her mother suggested, “Crush it,
otherwise she will know what it is?” Jhoolan crushed the jaggery but Jhumpa
easily guessed it.
They
played the game with different food items. Jhumpa could tell the fried fish
even before tasting it. Jhoolan said, “Now close your nose, and tell me what
this is?” Jhumpa was confused, “It is a bit bitter, a little salty and somewhat
sour.
Give
me one more spoonful.” Jhoolan took another spoonful of the cooked karela,
uncovered Jhumpa’s eyes, and said, “Here it is, eat!” Jhumpa laughed, “Yes,
give me more.”
Nitu
was given a glucose drip:
Nitu
was very sick. All day she was vomiting and she also had loose motions.
Whatever she ate, she vomited. Her father gave her sugar and salt solution. By
evening Nitu was feeling weak and dizzy. When she got up to go to the doctor
she fainted.
Her
father had to carry her to the doctor. The doctor said that Nitu should get
admitted in the hospital. She needs to be given a glucose drip. Hearing this,
Nitu got confused. She knew that during the games period in school, the teacher
sometimes gave them glucose to drink.
But
what was a glucose drip? Doctor aunty explained, “Your stomach is
upset.
Your body is not keeping any food and water and it has become very weak. The
glucose drip will give you some strength quickly, even without eating.”
Story
– A Stomach with a Window:
In
the poem, you read about a soldier called Martin. In 1822, he was eighteen
years old and was very healthy. When he was shot, he got seriously hurt. At
that time Dr. Beaumont was called to treat him.
Dr.
Beaumont cleaned the wound and put the dressing. After one and a half years,
the doctor found that Martin’s wound had healed except for one thing.
He
had a big hole in his stomach. The hole was covered with a loose flap of skin,
like the washer in a football. Press the skin and you could peep into Martin’s
stomach! Not only that, the doctor could also take out food from the stomach by
putting a tube in the hole.
Dr.
Beaumont felt he had found a treasure. Can you guess how much time he spent on
doing different experiments on this stomach?
Nine
years! During this time Martin grew up and got married. At that time scientists
did not know how food was digested? How does the liquid (digestive juices) in
the stomach help? Does it only help in making the food wet and soft? Or does it
also help in digestion?
Dr.
Beaumont took some liquid (juices) out of the stomach. He wanted to see what
would happen to a food item kept in a glass filled with it. Would it get
digested on its own? For this he did an experiment. With the help of a tube, he
took out some digestive juice from the stomach.
At
8.30am he put twenty tiny pieces of boiled fish in 10 millilitres of the juice.
He kept the glass at the same temperature as that of our stomach – about 30°C.
When he checked at 2 pm he found that the pieces of fish had dissolved.
Dr.
Beaumont tried this experiment with different food items. He gave Martin the
same food at the same time and then compared how long it took for food to be
digested in the glass and in Martin’s stomach. He recorded his observations in
a table.
TABLE:
So,
what does our stomach do? Dr. Beaumont did many experiments and found out many
secrets about digestion. He found that food digests faster in the stomach than outside.
Did you notice this in the table?
Our
stomach churns the food to digest it. The doctor also saw that the food did not
digest properly when Martin was sad. He also found that the juice in our
stomach is acidic. Have you heard of anyone talking about acidity -especially
when that person has not eaten well or the food is not digested properly.
Dr.
Beaumont’s experiments became famous across the world. After this many
scientists did many such experiments. What did you say? No, they did not shoot
people in the stomach. Nor did they wait for a patient with a hole in the
stomach. They used other scientific ways to look inside our bodies.
Children Did you like the story of Martin or,
should we say, the story of our own stomach?
