Choose the correct answer
1. The
maximum number of electrons in 3rd energy level is _______.
(a) 10
(b) 18
(c) 32
(d) 64
2. The mass of an atom is mostly due to its
(a) nucleus
(b) neutron
(c) electrons
(d) protons
3. If Rutherford had used neutrons instead of alpha particles in his scattering experiment, the neutrons would
(a) not deflected because they have no charge
(b) have deflected more often
(c) have been attracted to the nucleus easily
(d) have given the same result
4. Electron in its ground state does not ________
(a) Spin
(b) Revolve
(c) Radiate energy
(d) Reside in orbit
5. Which statement about 12X6 and 14Y6 is false
(a) they are isotopes
(b) they are the same elements
(c) they have the same number of electrons
(d) they have the same number of neutrons
6. The neutron particle
(a) has a mass equal to that of an electron
(b) has a mass approximately equal to that of a proton.
(c) has charge equal to but opposite to that of an electron
(d) has a positive charge
7. Isotopes of same elements have
(a) the same number of protons
(b) the same number of neutrons
(c) different numbers of neutrons
(d) the same mass number
8. Which one is the lightest
(a) X- (Alpha)Particles
(b) Hydrogen atom
(c) Electron
(d) Proton
9. The nucleus of an atom has all of the following characteristics except that it
(a) is positively charged
(b) is very dense
(c) contains nearly all of the atom’s mass
(d) contains nearly all of the atom’s volume
10. L-shell has sub-shell(s)
(a) s
(b) s and p
(c) s, p and d
(d) s,
p d, and f.
Short Questions
Aluminum is represented as 27Al13. Draw the structure of Aluminum. Write its electronic configuration.
To draw the structure of an element, we have to write its electronic configuration first. So, the electronic configuration of Aluminum, having the atomic number 13, is given as
|
In
shells |
K=2, L=8, M=3 |
|
In
Sub-shells |
1s2, 2s2, 2p6,
3s2, 3p1 |
The energy of an electron in K and L shells is the same or different? Explain
According to Bohr's atomic theory, we know that the farther the electron from the nucleus higher will be the energy, and vice versa. In other words, we can say that the “energy of the electron in an orbit is directly proportional to its distance from the nucleus”.
Conclusion: Thus we conclude that the energy of an electron in the K shell is lower than that of the L shell (being farther from the nucleus). It means K and L shells have different energies.
How many electrons are present in each of the following
atoms? Assuming that each is a neutral atom, identify the element.
(a) 1s2, 2s2, 2p6, 3s2, 3p1 (b) 1s2, 2s2, 2p6, 3s2, 3p5
(c) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2
In order to identify an element, we have to know its atomic number. In the above examples, the sum of electrons in sub-shells will give us atomic numbers, and thus identification will be made easy i.e.
(a) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2
As the sum of electrons is ‘11’ (2+2+6+1=11) and 11 is the atomic number of Sodium (Na). so the element is Sodium.
(b) 1s2, 2s2, 2p6, 3s2, 3p5
As the sum of electrons is ‘17’ (2+2+6+2+5=17) and 17 is the atomic number of Chlorine (Cl). so the element is Chlorine.
(c) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2
As the sum of electrons is ‘20’ (2+2+6+2+6+2=20) and 20 is the atomic number of Calcium (Ca). so the element is Calcium.
Why an atom is considered a neutral particle? Give reason(s).
Due to the balance between protons and electrons, an atom is
neutral
An atom is a neutral particle because in an atom the number of
electrons (Negative charge particles) is always equal to the number of protons
(Positive charge particles). As opposite charges cancel each other if they are
equal in magnitude (مقدار), so, therefore, the equal
and oppositely charged electrons and protons in an atom cancel each other and the atom becomes neutral.
For example,
Atomic No of Cl = 17
No of electrons = -17
No of Protons = +17
Net charge on atom = 0
So the atom becomes neutral.
The mass of an atom is present in its nucleus. Can you explain it?
The nucleus has two sub-atomic particles
As there are three sub-atomic particles in an atom i.e. protons, electrons, and neutrons. The electron is outside the nucleus while neutrons and protons are inside the nucleus. So as a nucleus consists of two particles i.e. protons (1837 times heavier than an electron) and neutrons (1842 times heavier than an electron) so its mass will be greater than the outside of the nucleus. So, most of the mass of an atom is present in its nucleus.
What is the reason that the physical properties of isotopes are different but their chemical properties are same?
Physical
properties of isotopes depend on atomic masses
The physical properties of isotopes depend on the atomic masses of the atoms. If the atomic masses are different the physical properties will also be different.
The chemical properties of isotopes depend on the atomic numbers of the atoms. If the atomic numbers are the same the chemical properties will also be the same.
Conclusion: From the above discussion, we conclude that due to different atomic masses isotopes have different physical properties.
How many electrons could be contained in the K, L, M, and N energy levels?
To find out the number of electrons in an orbit we have the 2n2 rule. For K-shell n=1, for L-shell n=2, for M-shell n=3 and for N-shell n=4. Higher is the value of n, the more electrons will the orbit accommodate. So
K shell contains 2 electrons i.e. 〖2n2〗=〖2(1)2〗=2
x 1=2
L shell contains 8 electrons i.e. 〖2n2〗=〖2(2)2〗=2x
4=8
M shell contains 18 electrons i.e. 〖2n2〗=〖2(3)2〗=2
x 9=18
N shell contains 32 electrons i.e. 〖2n2〗=〖2(4)2〗=2 x 16=32
Write detailed electronic configurations for 7Li3, 12C6 and 24Mg12.
|
Electronic configuration of
Li |
1s2, 2s1 |
|
Electronic configuration of C |
1s2, 2s2, 2p2 |
|
Electronic configuration of
Mg |
1s2, 2s2, 2p6, 3s2 |
Write the symbols for an isotope
(a) containing one
proton and two neutrons
(b) for which atomic
number is one and there is one neutron
(c) for which the
atomic number is one and the mass number is also one.
(a) 3H1
or 3T1
(b) 2H1
or 2D1
(c) 1P1
Why Dalton’s atomic theory is considered a base for modern atomic concepts.
According to one of the postulates of Dalton’s atomic theory, we know that matter is composed of extremely small particles called atoms. These atoms then combine to form compounds. All this information was first given by John Dalton. Later on, scientific investigations also proved Dalton’s statement. In this way, we can say that Dalton laid down the foundation of modern atomic concepts. However, it is now believed that an atom is composed of more than a hundred sub-atomic particles.
Complete the following table for neutral atoms of specific isotopes.
|
|
Isotopic symbol |
Atomic No |
Mass No |
Number of Protons |
No of electrons |
No of neutrons |
|
A |
133Xe54 |
54 |
131 |
54 |
54 |
77 |
|
B |
59Co27 |
27 |
59 |
27 |
27 |
32 |
|
C |
144Nd60 |
60 |
144 |
60 |
60 |
84 |
|
D |
48Ti22 |
22 |
48 |
22 |
22 |
26 |
|
E |
178Hf72 |
72 |
178 |
72 |
72 |
106 |
|
F |
128Te52 |
52 |
128 |
52 |
52 |
76 |
|
G |
40Ar18 |
18 |
40 |
18 |
18 |
22 |
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