We know that matter is anything which has mass and occupies space. We want to study about the following 3 aspects related to matter:
(i) The composition of matter
(ii) The structure of matter
(iii) The properties of matter
• Chemistry is that branch of science which deals with the above aspects
• Those 3 aspects can be studied in a better way, if we know the basic constituents of matter
• Atoms and molecules are the basic constituents of matter
• Chemistry is in fact the science of atoms and molecules
• Can we weigh atoms and molecules?
• Can we perceive atoms and molecules?
• In other words, can we make ourselves aware that (and help others become aware that) such minute entities as atoms and molecules do exist?
• In this chapter, we will try to find the answers to these questions
• We know that, matter can exist in three physical states:
Solid, Liquid and Gas
• The constituent particles of matter has three properties:
(i) Space available between the particles
(ii) Attraction between the particles
(iii) Ability for movement
• The magnitudes of the above three properties are different in solid, liquid and gas. This can be written down in a tabular form:
• We see a regular pattern in the table. So it is easy to remember
• Because of the different conditions experienced by the ‘particles in the 3 different states’, the ‘3 different states’ themselves exhibit different characteristics
• This can also be written down in a tabular form:
• Here also we see a regular pattern in the table. So it is easy to remember
♦ On heating, solid usually changes to liquid
♦ The liquid, on further heating changes into gaseous state
• The reverse process is also applicable:
♦ When a gas is cooled, it changes into a liquid
♦ The liquid, on further cooling changes into solid state
1. At the macroscopic level, matter exists in two forms:
(i) Mixtures (ii) Pure substances
• This is shown in the diagram below:
2. Many substances present around us are mixtures. Some examples are:
• Sugar solution
♦ This is a mixture of sugar and water
• Ocean water
♦ This is a mixture of salt and water
• Air
♦ This is a mixture of various gases like oxygen, nitrogen, hydrogen etc.,
• Cement mortar
♦ This is a mixture of cement, sand and water
• concrete
♦ This is a mixture of cement, broken stone, sand and water
3. Mixtures can be further classified as:
(i) Homogeneous mixtures (ii) Heterogeneous mixtures
■ In a homogeneous mixture, the components are mixed thoroughly and uniformly
4. Suppose that, one part of substance A and two parts of substance B are taken to make a mixture
• We can take any number of samples we like from that mixture
• If that mixture is homogeneous, then:
• In all samples, substances A and B will be present in the ratio 1:2
5. An example is shown in the fig. below:
This fig. is obtained from wikipedia. The links are given below:
Link 1
Link 2
6. In a heterogeneous mixture, the components are not mixed thoroughly. Consider the fig above
• If we take samples from the left side of the heterogeneous mixture, those samples will contain more green particles
• If we take samples from the right side of the heterogeneous mixture, those samples will contain more violet particles
• Rice containing dirt particles like small stones, is an example of heterogeneous mixture
• Note that, no one deliberately mixes dirt with rice. The dirt comes into contact with the rice by accident. Since there is no deliberate mixing, a 'thorough mixing' does not take place. So the dirt is accumulated in some portions of the rice stock. It is a heterogeneous mixture. After processing and cleaning at a mechanized facility, we get pure rice.
7. Well mixed concrete is an example of homogeneous mixture
8. The components of a mixture (both homogeneous and heterogeneous) can be separated by methods like filtration, crystallization, distillation, using separating funnel, simple hand picking, etc.,
9. Next we consider pure substances. Consider a pure substance. We can take any number of samples we like from that substance
• All samples will contain only one substance
• The question of ‘how well the mixing is done’ does not arise
♦ Because there is only one substance. We cannot mix it with itself
• The question of ‘in what ratio the mixing is done’ does not arise
♦ Because there is only one substance
♦ A ratio will be present only if there are more than one substances
• The question of ‘what method to use to separate the components’ does not arise
♦ Because there is only one substance. There is nothing to separate
10. However, pure substances can be further classified as:
(i) Elements (ii) Compounds
11. In elements, there will be only one type of particles. Some examples:
• A sample of sodium consists of only one pure substance: sodium
• A sample of hydrogen consists of only one pure substance: hydrogen
12. But it is important to remember this:
• In a sample of a pure substance, that substance may exist as an atom, or as a molecule
• This depends on the nature of the substance. Some examples:
• A sample of helium will consists of only one pure substance: helium
♦ In that sample we will find only individual helium atoms
• A sample of oxygen will consists of only one pure substance: oxygen
♦ In that sample we will find only individual oxygen molecules
♦ We will not find any oxygen atoms
♦ We have seen the reason in earlier classes (Details here)
13. Next we consider compounds
• We know that, substances like carbon, oxygen, hydrogen etc., are elements
• The atoms of any element will be different from the atoms of other elements
• For example, atom of carbon will be different from the atom of oxygen
■ When atoms of different elements combine together, we get ‘molecules of compounds’
Some example:
• A sample of carbon dioxide will consist of molecules of carbon dioxide
♦ Each of those molecules will contain one carbon atom and two oxygen atoms
• A sample of water will consist of molecules water
♦ Each of those molecules will contain two hydrogen atoms and one oxygen atom
14. We must note an important difference between the following two:
(i) A sample taken from a mixture
(ii) A sample of a compound
• In the first case, we can separate the constituents using physical methods
• In the second case, we cannot separate the constituents using physical methods
♦ We will have to use chemical methods to separate them
(i) The composition of matter
(ii) The structure of matter
(iii) The properties of matter
• Chemistry is that branch of science which deals with the above aspects
• Those 3 aspects can be studied in a better way, if we know the basic constituents of matter
• Atoms and molecules are the basic constituents of matter
• Chemistry is in fact the science of atoms and molecules
• Can we see the atoms and molecules with our naked eyes?
• Can we perceive atoms and molecules?
• In other words, can we make ourselves aware that (and help others become aware that) such minute entities as atoms and molecules do exist?
• In this chapter, we will try to find the answers to these questions
Nature of matter
• We know that, matter can exist in three physical states:
Solid, Liquid and Gas
• The constituent particles of matter has three properties:
(i) Space available between the particles
(ii) Attraction between the particles
(iii) Ability for movement
• The magnitudes of the above three properties are different in solid, liquid and gas. This can be written down in a tabular form:
• Because of the different conditions experienced by the ‘particles in the 3 different states’, the ‘3 different states’ themselves exhibit different characteristics
• This can also be written down in a tabular form:
• We know that, the 3 states of matter are interconvertible. This is shown in the diagram below:
♦ The liquid, on further heating changes into gaseous state
• The reverse process is also applicable:
♦ When a gas is cooled, it changes into a liquid
♦ The liquid, on further cooling changes into solid state
Now we will see classification of matter. We will write it in steps:
(i) Mixtures (ii) Pure substances
• This is shown in the diagram below:
2. Many substances present around us are mixtures. Some examples are:
• Sugar solution
♦ This is a mixture of sugar and water
• Ocean water
♦ This is a mixture of salt and water
• Air
♦ This is a mixture of various gases like oxygen, nitrogen, hydrogen etc.,
• Cement mortar
♦ This is a mixture of cement, sand and water
• concrete
♦ This is a mixture of cement, broken stone, sand and water
3. Mixtures can be further classified as:
(i) Homogeneous mixtures (ii) Heterogeneous mixtures
■ In a homogeneous mixture, the components are mixed thoroughly and uniformly
4. Suppose that, one part of substance A and two parts of substance B are taken to make a mixture
• We can take any number of samples we like from that mixture
• If that mixture is homogeneous, then:
• In all samples, substances A and B will be present in the ratio 1:2
5. An example is shown in the fig. below:
This fig. is obtained from wikipedia. The links are given below:
Link 1
Link 2
6. In a heterogeneous mixture, the components are not mixed thoroughly. Consider the fig above
• If we take samples from the left side of the heterogeneous mixture, those samples will contain more green particles
• If we take samples from the right side of the heterogeneous mixture, those samples will contain more violet particles
• Rice containing dirt particles like small stones, is an example of heterogeneous mixture
• Note that, no one deliberately mixes dirt with rice. The dirt comes into contact with the rice by accident. Since there is no deliberate mixing, a 'thorough mixing' does not take place. So the dirt is accumulated in some portions of the rice stock. It is a heterogeneous mixture. After processing and cleaning at a mechanized facility, we get pure rice.
7. Well mixed concrete is an example of homogeneous mixture
8. The components of a mixture (both homogeneous and heterogeneous) can be separated by methods like filtration, crystallization, distillation, using separating funnel, simple hand picking, etc.,
9. Next we consider pure substances. Consider a pure substance. We can take any number of samples we like from that substance
• All samples will contain only one substance
• The question of ‘how well the mixing is done’ does not arise
♦ Because there is only one substance. We cannot mix it with itself
• The question of ‘in what ratio the mixing is done’ does not arise
♦ Because there is only one substance
♦ A ratio will be present only if there are more than one substances
• The question of ‘what method to use to separate the components’ does not arise
♦ Because there is only one substance. There is nothing to separate
10. However, pure substances can be further classified as:
(i) Elements (ii) Compounds
11. In elements, there will be only one type of particles. Some examples:
• A sample of sodium consists of only one pure substance: sodium
• A sample of hydrogen consists of only one pure substance: hydrogen
12. But it is important to remember this:
• In a sample of a pure substance, that substance may exist as an atom, or as a molecule
• This depends on the nature of the substance. Some examples:
• A sample of helium will consists of only one pure substance: helium
♦ In that sample we will find only individual helium atoms
• A sample of oxygen will consists of only one pure substance: oxygen
♦ In that sample we will find only individual oxygen molecules
♦ We will not find any oxygen atoms
♦ We have seen the reason in earlier classes (Details here)
13. Next we consider compounds
• We know that, substances like carbon, oxygen, hydrogen etc., are elements
• The atoms of any element will be different from the atoms of other elements
• For example, atom of carbon will be different from the atom of oxygen
■ When atoms of different elements combine together, we get ‘molecules of compounds’
Some example:
• A sample of carbon dioxide will consist of molecules of carbon dioxide
♦ Each of those molecules will contain one carbon atom and two oxygen atoms
• A sample of water will consist of molecules water
♦ Each of those molecules will contain two hydrogen atoms and one oxygen atom
14. We must note an important difference between the following two:
(i) A sample taken from a mixture
(ii) A sample of a compound
• In the first case, we can separate the constituents using physical methods
• In the second case, we cannot separate the constituents using physical methods
♦ We will have to use chemical methods to separate them
In the next section, we will see properties of matter and their measurements. We will also see atomic and molecular masses
No comments:
Post a Comment