Test: Structure Of The Atom- 2 - Class 9 MCQ

To determine the electronic distribution in the Mg (Magnesium) atom, we need to consider its atomic number and the arrangement of electrons in its energy levels.
The atomic number of Mg is 12, which means it has 12 electrons. The electronic distribution can be represented as follows:
- The first energy level (closest to the nucleus) can hold a maximum of 2 electrons.
- The second energy level can hold a maximum of 8 electrons.
- The third energy level can hold a maximum of 8 electrons.
Based on this information, we can determine the correct electronic distribution in the Mg atom:
- The first energy level (1s) will contain 2 electrons.
- The second energy level (2s and 2p) will contain 8 electrons.
- The third energy level (3s) will contain 2 electrons.
Therefore, the correct representation of the electronic distribution in the Mg atom is:
2,8,2
This means that the Mg atom has 2 electrons in the first energy level, 8 electrons in the second energy level, and 2 electrons in the third energy level.

Incorrect Statement for Anode Rays:
Statement C: The charge/mass ratio of particles in anode rays is constant.
Explanation:
Anode rays are a stream of positively charged particles that are produced in a discharge tube when a high voltage is applied. These particles are usually positively charged ions or positive atomic or molecular fragments.
The incorrect statement is that the charge/mass ratio of particles in anode rays is constant. This statement is incorrect because the charge/mass ratio of particles in anode rays actually depends on the gas in the discharge tube used to produce them.
Here are the correct statements regarding anode rays:
Statement A: They are deflected by electric and magnetic fields.
- Anode rays are charged particles, so they can be deflected by both electric and magnetic fields.
Statement B: Their charge/mass ratio depends upon the gas in the discharge tube used to produce anode rays.
- The charge/mass ratio of anode rays depends on the nature of the gas in the discharge tube. Different gases produce different charge/mass ratios.
Statement D: They are produced by ionization of gas in the discharge tube.
- Anode rays are produced when gas in the discharge tube is ionized by the high voltage applied to it. The positively charged ions or fragments are then accelerated towards the anode, forming the anode rays.
In conclusion, the incorrect statement is that the charge/mass ratio of particles in anode rays is constant. The charge/mass ratio actually depends on the gas in the discharge tube used to produce anode rays.

Statement (i): The mass of the atom is assumed to be uniformly distributed over the atom.

• Correct. According to Thomson, the atom is a uniformly distributed mass.

Statement (iii): The electrons are uniformly distributed in the positively charged sphere.

• Correct. Electrons are embedded in the positively charged sphere like "plums in a pudding."

Rubidium atoms have 37 electrons and the shell structure is 2,8,18,8,1.
The ground state electronic  configuration  of ground state gaseous neutral rubidium is 
[ Kr].5 s¹.
 

Rutherford's model of atoms was a significant contribution to our understanding of atomic structure. Let's analyze each statement to determine which ones are correct:
(i) Considered the nucleus as positively charged: This statement is correct. Rutherford's model proposed that atoms have a small, dense, positively charged nucleus at the center, surrounded by negatively charged electrons.
(ii) Established that the α-particles are four times as heavy as a hydrogen atom: This statement is incorrect. Rutherford's experiments with α-particles led to the discovery that the nucleus is much more massive than the electrons, but it did not directly establish the specific mass ratio mentioned in this statement.
(iii) Can be compared to the solar system: This statement is correct. Rutherford's model likened the structure of the atom to a miniature solar system, with electrons orbiting around the central nucleus similar to planets orbiting the sun.
(iv) Was in agreement with Thomson's model: This statement is incorrect. Rutherford's model directly contradicted Thomson's model, which proposed a "plum pudding" structure of the atom with evenly distributed positive and negative charges.
Based on the analysis above, the correct statements are (i) and (iii). Therefore, the correct answer is A: (i) and (iii).

Explanation:
To determine the valency of an atom, we need to know the number of valence electrons it has. The valence electrons are the electrons in the outermost energy level of an atom.
In this case, the atom has 3 protons and 4 neutrons. Since the number of protons determines the atomic number of an atom, we can determine that the element with 3 protons is lithium (Li).
Lithium is located in group 1 of the periodic table, which means it has 1 valence electron. Therefore, the valency of an atom with 3 protons and 4 neutrons is 1.
Answer: C

Given Information:
- Number of electrons in element X = 15
- Number of neutrons in element X = 16
To determine the correct representation of the element:
We need to find the correct atomic number (number of protons) and mass number (sum of protons and neutrons) for the element.

Let's analyze each option provided and compare it with the given information.
Option A:
- Atomic number (protons) = 15 (as given)
- Mass number (protons + neutrons) = 15 + 16 = 31
- The symbol in the image is "P" (Phosphorus)
- The atomic number and mass number match with the given information.
- Option A is the correct representation of the element.
Option B:
- Atomic number (protons) = 16 (not 15 as given)
- Mass number (protons + neutrons) = 16 + 16 = 32
- The symbol in the image is "S" (Sulfur)
- The atomic number does not match with the given information.
Option C:
- Atomic number (protons) = 8 (not 15 as given)
- Mass number (protons + neutrons) = 8 + 8 = 16
- The symbol in the image is "O" (Oxygen)
- The atomic number does not match with the given information.
Option D:
- Atomic number (protons) = 9 (not 15 as given)
- Mass number (protons + neutrons) = 9 + 10 = 19
- The symbol in the image is "F" (Fluorine)
- The atomic number does not match with the given information.
Conclusion:
The correct representation of the element with 15 electrons and 16 neutrons is given in Option A with the symbol "P" (Phosphorus).

Statement: Which of the following statement is always correct?


Options:


A: An atom has equal number of electrons and protons.


B: An atom has equal number of electrons and neutrons.


C: An atom has equal number of protons and neutrons.


D: An atom has equal number of electrons, protons and neutrons.
Answer: A. An atom has equal number of electrons and protons.
Detailed


An atom is the basic unit of matter and consists of subatomic particles - protons, neutrons, and electrons. Let's analyze the given statements to determine the correct one.
1. Statement A: An atom has an equal number of electrons and protons.
- This statement is always correct because in a neutral atom, the number of electrons is equal to the number of protons. Electrons carry a negative charge (-1), while protons carry a positive charge (+1). The charges balance each other out, resulting in a neutral overall charge for the atom.
2. Statement B: An atom has an equal number of electrons and neutrons.
- This statement is incorrect. Neutrons are neutral particles and do not carry any charge. Therefore, the number of electrons and neutrons in an atom can be different.
3. Statement C: An atom has an equal number of protons and neutrons.
- This statement is incorrect. Protons and neutrons are different types of particles with different properties. While the number of protons determines the element and its atomic number, the number of neutrons can vary within isotopes of the same element.
4. Statement D: An atom has an equal number of electrons, protons, and neutrons.
- This statement is incorrect. The number of electrons, protons, and neutrons in an atom can be different. Only in a neutral atom, the number of electrons is equal to the number of protons.
Conclusion:


Among the given statements, statement A is always correct. In a neutral atom, the number of electrons is equal to the number of protons.

Rutherford's a-scattering experiment and its conclusion:

Background:

- Rutherford's a-scattering experiment was conducted by physicist Ernest Rutherford in 1911.
- The experiment involved bombarding a thin gold foil with alpha particles (helium nuclei) and observing their scattering pattern.

Experiment:

- Rutherford expected that the alpha particles would pass through the gold foil without significant deflection because the prevailing atomic model at the time suggested that atoms were composed of a uniform positive charge with electrons embedded in it.
- However, the experimental results surprised Rutherford.

Observations:

- Most of the alpha particles passed straight through the gold foil, indicating that the atoms were mostly empty space.
- Some alpha particles were deflected at small angles, suggesting the presence of a concentrated positive charge within the atom.
- A few alpha particles were deflected at very large angles, and some even bounced back, indicating the presence of an extremely dense and positively charged center within the atom.

Conclusion:

Based on the observations from the a-scattering experiment, Rutherford concluded that:
- The mass and the positive charge of an atom are concentrated in a tiny, dense, and positively charged region called the nucleus.
- The nucleus is surrounded by mostly empty space where electrons are located.
- The nucleus is very small compared to the overall size of the atom.
- The existing atomic model, known as the "Plum Pudding" model, was incorrect.

Answer:

The conclusion reached from Rutherford's a-scattering experiment is that the mass and the positive charge of an atom are concentrated in the nucleus (Option B).

Deuterium and an alpha particle have identical value of e/m.

 

Figures (ii) and (iv) not correctly represent the Bohr's model of an atom.
It is because maximum number of electrons in K (I) shell is 2, not 4, so (ii) is wrong and maximum capacity of L (II) shell is 8 electrons, not 9. So, (iv) is also wrong.

As we know, K shell contains 2 electrons  ; L she contains 8 electrons, M shell contains 18 electrons and N shell contains  32 electrons;  so total becomes 
⇒ 60 electrons. 

To determine the chronological order of the given atomic models, we need to understand when each model was proposed.
Thomson's Atomic Model (ii):
- Proposed by J.J. Thomson in 1897.
- Known as the "plum pudding" or "raisin pudding" model.
- According to this model, an atom is a positively charged sphere with negatively charged electrons embedded within it.
Rutherford's Atomic Model (i):
- Proposed by Ernest Rutherford in 1911.
- Also known as the "planetary" or "nuclear" model.
- This model suggested that an atom consists of a tiny, dense, positively charged nucleus at the center, around which negatively charged electrons revolve in specific orbits.
Bohr's Atomic Model (iii):
- Proposed by Niels Bohr in 1913.
- Based on Rutherford's model, Bohr suggested that electrons move in fixed energy levels or orbits around the nucleus.
- This model introduced the concept of quantized energy levels and explained the stability of atoms.
Now, let's arrange the atomic models in chronological order:
1. Thomson's Atomic Model (ii) - proposed in 1897.
2. Rutherford's Atomic Model (i) - proposed in 1911.
3. Bohr's Atomic Model (iii) - proposed in 1913.
Therefore, the correct chronological order of the atomic models is (ii), (i), and (iii).
Answer: C

The correct option is Option B.

Atomic number of calcium is 20. Number of protons = number of electrons = 20

First shell can accommodate 2 electrons so K=2.

Second shell can accommodate a maximum of 8 electrons so L=8.

Third shell can accommodate a maximum of 18 electrons but if we put the remaining 10 electrons it will violate the law that the outermost electron can accommodate 8 electrons so it will accommodate only 8 electrons.

So, the number of electrons in M is 8. Now the remaining two will be in N.

So the configuration is 2,8,8,2

The particles of which most passed straight through the gold foil were alpha particles, which are positively charged. The few alpha particles that were deflected back or to one side were being repelled by nuclei, which are also positively charged. Those that passes straight through did so because they didn't encounter any nuclei. The observation that most alpha particles passed straight through the gold foil led Rutherford to conclude that the the positive charge in an atom in concentrated in a very small area, the nucleus
 Atoms are mostly empty space. Electrons, which are negatively charged, are distributed throughout this space but take up a very small part of it

The chemical symbol Na⁺ represents a sodium ion. The atomic number of sodium (Na) is 11, which means it has 11 protons.
Given that Na⁺ has 12 neutrons, we can determine the mass number by adding the number of neutrons to the number of protons. So, for Na⁺:

Mass number = Number of neutrons + Number of protons Mass number = 12 neutrons + 11 protons Mass number = 23

The atomic number remains unchanged because it is determined by the number of protons, which is characteristic of each element. The loss or gain of electrons to form ions does not change the atomic number.

Therefore, the correct statement is: Na⁺ has an atomic number equal to 11 and a mass number of 23.