Answer very briefly.
1. Name an element which has the same
number of electrons in its first and second
shell.
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2. Write the electronic configuration of K and
Cl
Ans:
K = 2, 8, 8, 1
Cl = 2, 8, 7
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3. Write down the names of the particles
represented by the following symbols and
explain the meaning of superscript and
subscript numbers attached.
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4. For an atom ‘X’, K, L and M shells are
completely filled. How many electrons will
be present in it?
Ans: 18
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5. What is the same about the electron
structures of:
a. Lithium, Sodium and Potassium.
a. Lithium, Sodium and Potassium
The outermost orbital of the above elements consists of 1 electron. Their valency is 1.
b. Beryllium, Magnesium and Calcium.
b. Beryllium, Magnesium and Calcium.
The outermost orbital of the above elements consists of 2 electrons. Their valency is 2.
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Answer briefly.
1. How was it shown that atom has empty
space?
Deflection of alpha particle by a gold leaf experiment shows the atom contains large empty space.
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2. Why do Cl-35 and Cl-37 have the same chemical
properties? In what respect do these atoms
differ?
2. The electron arrangement is also the same owing to same chemical properties.
3. These elements have the same atomic number but different mass numbers.
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3. Draw the structure of oxygen and sulphur
atoms.
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4. Calculate the number of neutrons, protons
and electrons:
(i) atomic number 3 and
mass number 7
(ii)atomic number 92 and
mass number 238.
(i) atomic number 3 and mass number 7
Atomic number = No. of protons
No. of protons = 3
No. of electrons = 3 (.. No. of protons = number of electrons)
Mass number = No. of protons + No. of neutrons
No. of neutrons =mass number -No. of protons
=7-3
No. of neutrons =4
(ii)atomic number 92 and mass number 238.
Atomic number = 92
Mass number = 238
Atomic number = No. of protons
No. of protons = 92
No. of electrons = 92
tadrut No. of neutrons = 238-92
= 146
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5. What are nucleons? How many nucleons are
present in Phosphorous? Draw its structure.
1. The protons and neutrons collectively found in the nucleus of an atom are called nucleons.
2. Nucleons in phosphorous,
Protons +Neutrons =Nucleons
15 + 16= 31
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Answer in detail.
1. What conclusions were made from the
observations of Gold foil experiment?
Rutherford generalized the conclusions of the gold foil experiment and suggested a model of the atom known as Rutherford's Atomic model.
Rutherford's Atomic model
According to this model:
1. The atom contains large empty space.
2. There is a positively charged mass at the centre of the atom, known as nucleus.
3. The size of the nucleus of an atom is very small compared to the size of an atom.
4. The electrons revolve around the nucleus in close circular paths called orbits.
5. An atom as a whole is electrically neutral, i.e., the number of protons and electrons in an atom are equal.
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2. Explain the postulates of Bohr’s atomic
model.
The main postulates of Bohr's model of an atom are,
1. In atoms the electron revolve around the nucleus in stationary circular paths called orbits or shells or energy levels.
2. While revolving around the nucleus in an orbit, an electron neither loses nor gains energy.
3. An electron in a shell can move to a higher or lower energy shell by absorbing or releasing a fixed amount of energy.
4. The orbits or shells are represented by the letter K, L, M, N,... or the numbers n = 1 ,2,3,4,....
5. The orbit closest to the nucleus is the K shell. It has the least amount of energy and the electrons present in it are called K electrons.
6. These orbits are associated with fixed amount of energy, so Bohr called them as energy level or energy shells.
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3. State the Gay Lussac’s law of combining
volumes. Explain with an illustration.
Definition:
Whenever gases react together, the volumes of the reacting gases bear a simple ratio, and the ratio is extended to the product when the product is also in gaseous state, provided all the volumes are measured under similar conditions of temperature and pressure.
This law may be illustrated by the following example:
1 It has been experimentally observed that one volume of hydrogen react with one volume of chlorine to form two volume of hydrogen chloride.
2. The ratio of volume which gases bears is 1:1:2 which is a simple whole number ratio
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