Olympiad Science - Structure of the Atom
Exam Duration: 45 Mins Total Questions : 30
Which valence shell electron arrangement is that of a metallic element?
- (a)
2,1
- (b)
2,4
- (c)
2,5
- (d)
2,7
Metallic atoms usually have 1, 2 or 3 electrons in their valence shell.
An element X has two isotopes, which may be represented as \(\\ ^{ 238 }X\) and \(\\ ^{ 235 }X\). How does \(\\ ^{ 238 }X\)differ from \(\\ ^{ 235 }X\)?
- (a)
\(\\ ^{ 238 }X\)has 3 more protons and 3 more electrons than 235.
- (b)
\(\\ ^{ 238 }X\)has 3 more protons, but same number of electrons as 235
- (c)
\(\\ ^{ 238 }X\)has 3 more neutrons, but the electrons or protons are same as 235
- (d)
\(\\ ^{ 238 }X\)has 3 more protons, but same number of electrons as 235.
Since, the number of protons and electrons are the sarne in both isotopes, the difference in their number of neutrons is 238-235 = 3.
An atom of an element contains 17 protons, 18 neutrons and 17 electrons. Which of the following will be the atomic structure of another isotope of this element?
Protons | Neutrons | Electrons | |
(a) | 17 | 20 | 17 |
(b) | 17 | 18 | 16 |
(c) | 18 | 18 | 17 |
(d) | 20 | 18 | 17 |
- (a)
17-20-17
- (b)
17-18-16
- (c)
18-18-17
- (d)
20-18-17
The isotopes of the same element have the same number of protons and electrons, but different number of neutrons. So,element with 17 protons and electrons and 20 neutrons is an isotope of this element.
What does an atom and an ion of the isotope of sodium \(_{ 11 }^{ 22 }\) Na both contain?
- (a)
11 electrons
- (b)
12 neutrons
- (c)
23 protons
- (d)
23 neutrons
An atom of sodium has 11p, 12n and 11e. The sodium ion,\({ Na }^{ + }\) has 11p, 12n and 10e. So,both contain 12 neutrons each.
What can be deduced from the symbol \(_{ 2 }^{ 4 }\)He?
- (a)
An atom of helium contains two electrons.
- (b)
An atom of helium has two protons and four neutrons in its nucleus.
- (c)
The proton (atomic) number of helium is four.
- (d)
Helium acts as a diatomic molecule.
In the nuclide \(_{ 2 }^{ 4 }\)He, the atom has2 protons and 4 - 2 = 2 neutrons. Since, the atom is neutral, the number of electrons = number of protons = 2.
Which of the following ions has the same number of electrons as a krypton atom with atomic number 36 ?
- (a)
Chlorine
- (b)
Sodium
- (c)
Rubidium
- (d)
Xenon
Kr has 36 electrons. Rb has 37 electrons but when it forms \(\\ { Rb }^{ + }\)(it is a Group I element), there are only 36 electrons.
In elements \(_{ 15 }^{ 31 }{ P }\) and \(_{ 16 }^{ 32 }{ S }\) which of the following are the same?
- (a)
Number of nucleons
- (b)
Number of electrons
- (c)
Number of neutrons
- (d)
Number of protons
Element | Nucleon number | No.of.protons | No.of.neutrons |
\({ 31 }_{ P }\) | 31 | 15 | 16 |
\({ 32 }_{ S }\) | 32 | 16 | 16 |
n element X forms a unipositive ion with the electronic structure 2,8,8. What is the atomic number of X?
- (a)
16
- (b)
17
- (c)
18
- (d)
19
A unipositive ion (cation) is formed when a metal loses its outer electrons to form a stable electronic configuration 2,8,8,1 i.e., Z = 19.1tcan lose its valence electron during a chemical reaction to form ion,\({ X }^{ + }\),which has an electronic configuration of 2,8,8.
The letters X,Y and Z represent different atoms.
\(\boxed { _{ 19 }^{ 40 }{ X\quad }_{ 19 }^{ 39 }{ Y\quad }_{ 20 }^{ 40 }{ Z } } \)
What can be deduced from the proton numbers and nucleon numbers of X, Y and Z?
- (a)
X and Yare the same elements.
- (b)
X and Z are the same elements
- (c)
X has more protons than Y
- (d)
Z has more neutrons than Y.
Elements X and Y have same proton number, hence,they are the same elements. The number of neutrons of X,Y and Z are 21,20, 20 respectively.
What is the maximum number of electrons that can be accommodated in the \({ 4 }^{ th }\) energy level?
- (a)
32
- (b)
18
- (c)
2
- (d)
8
n = 4 (4th energy level)
The number of electrons that can be
accommodated in an energy level = \({ 2n }^{ 2 }\)
= \({ 2(4) }^{ 2 }\)= 2 x 16 = 32
A neutral atom of an element has a nucleus with a nuclear charge 13 times and mass 27 times as that of hydrogen nucleus. What is the ratio of electrons to protons in its stable positively charged ion?
- (a)
27: 13
- (b)
10: 13
- (c)
20:24
- (d)
10: 14
Let the neutral atom of the element be X. Given, the nuclear charge of X is 13 times that of hydrogen nucleus.
\(\Rightarrow \)Atomic number = 13
Mass of X is 27 times that of hydrogen nucleus \(\Rightarrow \)Mass number = 27.
Since \(\\ _{ 13 }^{ 27 }{ X }\), EC = 2, 8,3
If X forms a stable, positively charged ion, i.e.\({ X }^{ +3 }\)(as it has 3 valence electrons in its valence shell)
\({ X }^{ +3 }\) \(\Rightarrow \) Atomic number = 13 - 3 = 10.This implies that the number of electrons = 10. Number of protons = 13.
Ratio = 10 : 13 or 20: 26.
Which of the following observations of \(\alpha \)- ray scattering experiment led to the discovery of a small positively charged nucleus in the centre?
- (a)
Most of the\(\alpha \) - particles passed straight.
- (b)
(B) Most of the \(\alpha \) -particles rebounded after hitting the atoms.
- (c)
(C) Only a few \(\alpha \) - particles deflected away from their path.
- (d)
(D) Most of the \(\alpha \) -particles rebounded.
Only a few \(\alpha \) - particles got deflected away from their path proved the presence of small positively charged nucleus in the centre of the atom.
An element has atomic number 17 and mass number 37. There are 17 electrons outside the nucleus. Find the number of neutrons in it.
- (a)
20
- (b)
21
- (c)
17
- (d)
37
Z=17; A=37 n=A-Z=37-17 =20
What does the mass number of an atom represent?
- (a)
Only the number of protons
- (b)
The number of protons and neutrons
- (c)
The number of protons and electrons
- (d)
Only the number of neutrons
Mass number = no. of protons + no. of neutrons.
The atom of an element has 10 electrons, 10 protons and 12 neutrons. Find the mass number of the element.
- (a)
10
- (b)
12
- (c)
22
- (d)
32
Atomic number= No. of protons/electrons=10
Mass number = no. of protons + no. of neutrons = 10 + 12 = 22
Which of the following ions is the smallest in size?
- (a)
Mg2+
- (b)
Na+
- (c)
O2-
- (d)
F-
All the ions are isoelectronic, so size depends on the number of protons (size is inversely related to number of protons). Mg+2 has more number of protons compared to all the other ions. Hence,Mg+2 is the smallest ion
In an element, the number of protons, electrons and neutrons are 1, 0, 1 respectively. Identify the element.
- (a)
D+
- (b)
H+
- (c)
He
- (d)
Li+
21D has 1 electron,l proton and 1 neutron.This on ionisation, lost its only one electron and got converted to D+. Therefore, D+ has only 1 proton and 1 neutron
How many protons, neutrons and electrons
are contained in one atom of \(_{ 19 }^{ 39 }K\) ?
- (a)
19protons +20 neutrons +19electrons
- (b)
19 protons + 20 neutrons + 20 electrons
- (c)
20 protons + 19 neutrons + 20 electrons
- (d)
20 protons + 20 neutrons + 19 electrons
\(_{ 19 }^{ 39 }K\) gives the mass number (A) = 39
Identify the number of electrons present in the outermost shell of atoms of each of the following elements.
(i) Helium (ii) Magnesium (iii) Sulphur |
- (a)
(i) - 2, (ii) - 3, (iii)- 4
- (b)
(i) - 1, (ii) - 4, (iii) - 6
- (c)
(i) - 2, (ii) - 2, (iii) - 6
- (d)
(i) - 3, (ii) - 4, (iii) - 5
He - 2, Mg - 2,8,2, S - 2, 8, 6
:. 2, 2, 6 are the number of valence electrons present in He, Mg and S respectively.
The atomic numbers of three elements P, Q and Rare 5,9 and 13 respectively. Which two elements show similar chemical properties?
- (a)
P and Q
- (b)
P and R
- (c)
Q and R
- (d)
P,Q and R
The electronic configuration of elements.
P \(\rightarrow \) 2, 3 Q \(\rightarrow \) 2, 7 R \(\rightarrow \) 2, 8, 3
Elements P and R have the same number of valence electrons. Hence, they show the same chemical properties.
Identify the element having two electrons in the K shell of its atom.
- (a)
Hydrogen
- (b)
He+
- (c)
Helium
- (d)
Deuterium
Helium(He)-Atomic number 2, Electronic configuration is 2 and it has 2 electrons in K shell.
The total number of electrons in a nitrogen atom and a chlorine atom are 7 and 17 respectively. Find the number of valence electrons in them.
- (a)
3,1
- (b)
5,8
- (c)
4, 1
- (d)
5,7
Nitrogen (7) 2,5, Chlorine (17) 2,8,7 The number of valence electrons in both are 5 and 7 respectively.
An element has an atomic number 20. How many electrons will be present in K, L, M and N shells of its atom?
- (a)
2,8,6,4
- (b)
2,8,7,3
- (c)
3,7,7,3
- (d)
2,8,8,2
Z= 20
Electronic configuration in
K shell = 2
L shell =8
M shell =8
N shell =2
An atom and its ion differ in the number of
- (a)
electrons
- (b)
protons
- (c)
neutrons
- (d)
nucleons.
An atom forms an ion either by losing or gaining electrons. So, they differ in the number of electrons.
According to JJ.Thomson's atomic model, where are the negative charges of an atom embedded in?
- (a)
A lump of positive charge
- (b)
A lump of small atoms
- (c)
A lump of neutrons
- (d)
The nucleus
According to J.J.Thomson's atomic model, the negative charges of an atom are distributed uniformly in a lump of positive charge.
Which of the following conclusions cannot be drawn on Rutherford's atomic model?
- (a)
The total mass of an atom is concentrated at the centre of the atom.
- (b)
Nucleus is located inside the atom containing positively charged particles.
- (c)
Most of the atom is empty in space.
- (d)
Electrons revolve around the nucleus in stationary, circular orbits.
Rutherford's atomic model did not explain the stability of atom. He could not explain why the electrons revolve in stationary, circular orbits.
Which ofthe following is a pair of isobars?
- (a)
\(_{ 7 }^{ 15 }{ N }\), \(_{ 8 }^{ 16 }O\)
- (b)
\(_{ 6 }^{ 13 }C\), \(_{ 7 }^{ 14 }N\)
- (c)
\(_{ 6 }^{ 13 }C\), \(_{ 7 }^{ 13 }N\)
- (d)
\(_{ 6 }^{ 13 }C\), \(_{ 8 }^{ 15 }O\)
The pair \(_{ 6 }^{ 13 }C\) and \(_{ 7 }^{ 13 }N\) are isobars as they have the same mass number.
An isotope of helium is represented by the symbol 32He. How many protons, neutrons and electrons are there in an atom of the isotope?
Protons | Neutrons | Electrons | |
A | 1 | 2 | 1 |
B | 1 | 3 | 2 |
C | 2 | 1 | 2 |
D | 2 | 3 | 2 |
- (a)
1-2-1
- (b)
1-3-2
- (c)
2-1-2
- (d)
2-3-2
Given, Z = 2 ;A = 3 Z = number of protons = number of electrons = 2 Number of neutrons = A - Z = 3 - 2 = 1
How are the two atoms \(_{ 92 }^{ 235 }P\) and \(_{ 92 }^{ 238 }P\) similar?
(i) They have the same number of protons. (ii) They have the same number of neutrons. (iii) They have the same number of electrons. |
- (a)
Only (i)
- (b)
Only (i) and (ii)
- (c)
Only (i) and (iii)
- (d)
(i), (ii) and (iii)
\(_{ 92 }^{ 235 }P\) and \(_{ 92 }^{ 238 }P\) are isotopes having the same atomic number. Hence, the number of protons and electrons are 92 each.
In two atoms, the number of neutrons are (238 - 92) and (235 - 92) respectively. i.e., 146, 143
An element X combines with oxygen to form compounds P and Q. If the ratio of the valency of element X in Pto element X in Q is 3 : 5 respectively, what could be
the probable compounds P and Q ?
P | Q | |
(A) | CO | CO2 |
(B) | N2O3 | N2O5 |
(C) | H2O | H2O2 |
(D) | CH4 | C3H5 |
- (a)
CO CO2 - (b)
N2O3 N2O5 - (c)
H2O H2O2 - (d)
CH4 C3H5
Let the ratio be multiplied by x.
Valency of X in P = 3x
Valency of X in Q = 5x
P\(\rightarrow \)X3X O2 \(\rightarrow \)X2 O3X
Q\(\rightarrow \) X5X O2 \(\rightarrow \) X2 O5X
In the above options,N2 O3, N2 O5 are the probable compounds