Atomic and Molecular Masses MCQ Quiz - Objective Question with Answer for Atomic and Molecular Masses - Download Free PDF

The correct answer is option 1: Statement 1 and 3 are correct, Statement 2 is incorrect.

Key Points

• Statement 1: The atomic number of an element is equal to the number of protons in the nucleus. This statement is correct as the atomic number is defined by the number of protons in an atom's nucleus.
• Statement 2: The mass number is the sum of the protons and electrons in an atom. This statement is incorrect as the mass number is the sum of protons and neutrons in the atom.
• Statement 3: Isotopes of an element have the same atomic number but different mass numbers. This statement is correct as isotopes have the same number of protons but different numbers of neutrons.
• Therefore, the correct option is that Statement 1 and 3 are correct, and Statement 2 is incorrect.

Additional Information

• Atomic Number: The number of protons in the nucleus of an atom, which defines the element.
• Mass Number: The total number of protons and neutrons in the nucleus of an atom.
• Isotopes: Variants of a particular chemical element that have the same number of protons but different numbers of neutrons.
• Protons, Neutrons, and Electrons: Protons are positively charged particles, neutrons are neutral particles, and electrons are negatively charged particles that orbit the nucleus.
• Periodic Table: A tabular arrangement of elements ordered by their atomic number, electron configuration, and recurring chemical properties.

The Correct answer is both particle and wave nature.

Key Points

• Subatomic particles like electrons, protons, and neutrons exhibit dual nature, meaning they behave both as particles and waves.
• The concept was established by the Wave-Particle Duality Theory, which states that particles can exhibit properties of waves, and vice versa.
• Louis de Broglie, a French physicist, proposed the concept of wave-particle duality for subatomic particles in 1924.
• According to de Broglie, every moving particle or object has a wavelength, which is inversely proportional to its momentum. This is expressed mathematically by the equation: λ = h/p, where λ is the wavelength, h is Planck's constant, and p is momentum.
• Experimental evidence supporting this concept includes phenomena such as electron diffraction, where electrons show interference patterns similar to waves.
• The wave nature of particles is crucial in quantum mechanics and helps explain behaviors at the atomic and subatomic levels that classical physics cannot.
• This dual nature has practical applications in technologies like electron microscopes, where wave-like properties of electrons are utilized to achieve high-resolution imaging.
• The phenomenon is significant in understanding concepts like quantum superposition and the functioning of particles in quantum systems.

 Additional Information

• Macroparticle Nature
  • Macroparticles are typically larger particles that do not exhibit quantum behaviors like wave-particle duality.
  • Examples include grains of sand or other visible particles governed by classical physics laws.
  • The term does not apply to subatomic particles like electrons, protons, and neutrons.
• Only Particle Nature
  • While classical physics often treated electrons and other subatomic particles as particles, experiments like electron diffraction showed that this view is incomplete.
  • The discovery of their wave nature challenged the classical understanding and helped establish quantum mechanics.
• Only Wave Nature
  • While subatomic particles exhibit wave-like behaviors, they also display particle-like properties such as having mass and momentum.
  • The dual nature concept encompasses both particle and wave aspects, making the "only wave nature" explanation insufficient.

The correct answer is Isotones.

Key Points

• Isotopes are variants of a particular element with different numbers of neutrons. For example, the two isotopes of Uranium are ²³⁵U₉₂  and ²³⁹U₉₂ . 
• Isobars are elements that have the same number of nucleons (sum of protons and neutrons). The series of elements with 40 Mass numbers serve as a good example; ⁴⁰S₁₆, ⁴⁰Cl₁₇, ⁴⁰Ar₁₈, ⁴⁰K₁₉, and ⁴⁰Ca₂₀. 
• Isotones are atoms that have the same neutron number but different proton numbers. For example, ³⁶S₁₆, ³⁷Cl₁₇, ³⁸Ar₁₈, ³⁹K₁₉, and ⁴⁰Ca₂₀ are all isotones of 20 since they all contain 20 neutrons. Hence option 3 is correct.
• An isomer is one of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties

The correct answer is Option 3.

Key Points

• A proton is approximately 1836 times heavier than an electron.
• The mass of a proton is about 1.6726 x 10^-27 kilograms.
• In contrast, the mass of an electron is about 9.1094 x 10^-31 kilograms.
• This significant difference in mass is due to the fact that protons are made up of three quarks held together by the strong nuclear force, while electrons are elementary particles.

Additional Information

• Proton:
  • Protons are positively charged subatomic particles found in the nucleus of an atom.
  • They were discovered by Ernest Rutherford in 1917.
  • Protons determine the atomic number of an element, which defines its position in the periodic table.
• Electron:
  • Electrons are negatively charged subatomic particles that orbit the nucleus of an atom.
  • They were discovered by J.J. Thomson in 1897.
  • Electrons play a crucial role in chemical bonding and electricity.
• Quark:
  • Quarks are elementary particles and fundamental constituents of matter.
  • Protons and neutrons are made up of three quarks each.
  • There are six types of quarks: up, down, charm, strange, top, and bottom.
• Strong Nuclear Force:
  • The strong nuclear force is one of the four fundamental forces of nature.
  • It is the force that holds protons and neutrons together in the nucleus.
  • This force is incredibly strong but acts over very short distances.

The correct answer is 14 ∶ 3

Key Points

Ammonia (NH3)

• The law of constant composition states that a given chemical compound always contains its component elements in a fixed ratio (by mass) and does not depend on its source and method of preparation.
• Nitrogen makes up about 14/17 of the mass of any sample of pure Ammonia, while Hydrogen makes up the remaining 3/17 of the mass. (Atomic weight of nitrogen is 14 and that of hydrogen is 1)
• That is Ammonia, Nitrogen, and Hydrogen are always present in the ratio 14:3 by mass.
• 1 atom of Nitrogen is always combined with 3 atoms of Hydrogen.

Additional Information

• Atomic mass is the quantity of matter contained in an atom of an element. 
• It is expressed as a multiple of one-twelfth the mass of the carbon-12 atom.
• Mass ratio, often called "per cent composition by mass," is the proportion of a particular molecule that consists of each of that molecule's constituent elements.

The correct answer is Potassium.

Key Points

• Potassium belongs to a group - (1) and period - (IV) of the periodic table. Hence among the given options, Potassium has a maximum atomic radius.
• Carbon and Nitrogen belong to the period - (II) of the periodic table and on the right side hence it is obvious that atomic radii of Carbon and Nitrogen are very much small than Sodium and Potassium.
• Sodium and Potassium belong to a group - (1) and  Potassium is placed below Sodium hence the atomic radius of Potassium more than Sodium.

Important Points 

• The atomic size generally decreases across a period as we move from left to right in a particular period. due to an increase in nuclear charge.
• The atomic size generally increases across groups as we move from top to bottom in a particular group due to the addition of new shells to atoms.

Additional Information

The correct answer is 20.

CONCEPT:

• Heavy water: It is a form of water that contains only deuterium rather than the common hydrogen-1 isotope that makes up most of the hydrogen in normal water.
  • Formula: D₂O
  • Boiling point:101.4 °C
  • Molar mass: 20 gm/mole
  • Melting point: 3.8 °C
  • Density: 1.11 gm/cm³
  • Refractive index:1.328

EXPLANATION:

• Heavy water has deuterium(D) which is an isotope of hydrogen.
• While hydrogen has 1 proton and 0 neutrons in its nucleus giving it an atomic weight of 1, deuterium has 1 proton and 1 neutron in its nucleus.
• So deuterium has atomic weight 2.
• So heavy water, which has molecular formula D₂O, has molecular mass = 16(for oxygen)+(2× 2)(for two deuteriums)= 20

The correct answer is Na.

• The decreasing order of atomic radius is Na (227pm) > P (195pm) > S (180pm) > Cl (175pm).

Explanation:

• When two atoms have the same value of n for the valence electrons, the atom with the greater number of protons will generally have a greater effective nuclear charge to draw the valence electrons closer to the nucleus and, thus, decrease the atomic radius. 
• Since chlorine's 17 protons are greater than sodium's 11 protons, chlorine will have a greater effective nuclear charge to draw chlorine's valence electrons closer to the nucleus and, thus, chlorine is expected to have a smaller atomic radius.
• While sodium with the lower effective nuclear charge is expected to have a larger atomic radius.

Important Points

• In the periodic table, the atomic radius of elements tends to decrease as you move across a row from left to right.
• Ionic radii increase down a group as more shells are added.

Key Points

• Sodium is highly reactive so that it is stored in oil or kerosene because it spontaneously ignites in water.
• At room temperature, sodium metal is soft enough that you can cut it with a butter knife.
• White phosphorus is used in flares and incendiary devices.
• Red phosphorus is in the material stuck on the side of matchboxes, used to strike against safety matches to light them.

The correct answer is C-12.

• The International Union of Chemists selected the most stable carbon isotope (C-12) or ¹²C as the standard for comparison of the atomic masses of various elements.
  • The mass of C-12 is taken as a 12 atomic mass unit (standard).
  • A Carbon-12 contains six protons, six neutrons, and six electrons.

Additional Information

• The amount of carbon-14 found in fossils allows paleontologists to determine their age.
  • A carbon-14 contains six protons, eight neutrons, and six electrons.
• C-16 is a new Isotope of Carbon.
• Oxygen-16 (¹⁶O) is a stable isotope of oxygen contains 8 neutrons and 8 protons.
  • Oxygen is composed of three stable isotopes, ¹⁶O, ¹⁷O, and ¹⁸O.
• N-14 is a stable isotope of nitrogen, contain 7 protons and 7 neutrons.

 Key Points

• A British physicist J.J.Thomson Heightened the theory of Dalton.
• Thomson found the existence of extremely minute particles inside the atom.
• He compared the atom with a 'watermelon' in which the Red part resembles the positively charged portions while the black seed resembles the negatively charged electrons.
• The atom itself is neutral in nature, as it has equal positive and negatively charged electrons.
• Thomson discovered 'Electrons' for which he got Nobel prize in 1906 A.D.
• Thomson proposed a better atomic theory than Dalton's atomic model.
• According to him, a positive charge is dispersed everywhere and the idea that atoms are made up of negative electrons embedded in a gel of positive charge was wrong.
• Electrons were accidentally discovered by J. J. Thomson while studying the cathode rays.
• The name electron was given by 'stony'.
• Cathode rays are emitted from the cathode in a straight line if these rays strike on metal objects there is the formation of 'X-rays'.

Additional Information

James Chadwick-

• Sir James Chadwick was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932.
• By 1920, physicists knew that most of the mass of the atom was located in a nucleus at its center and that this central core contained protons.
• In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.

• Rutherford overturned Thomson's atom model in 1911 with his well-known Gold Foil experiment.
• Rutherford made an experiment, he beamed alpha particles through a thin gold foil. From this, he came to know that:
  • Most alpha particles passed through the gold foil, very few particles bounced back exactly towards the source.
  • Some of the particles deviate at various angles.
  • He concluded that an atom has a tiny, dense, 'positively charged' core, where all mass is concentrated; known as Nucleus.
  • The thickness of gold foil - 0.00004 cm.
  • Alpha particle - A helium nucleus.

• In 1803 A.D. he put forth his famous atomic theory.
  • The matter is made up of small particles called atoms.
  • Atoms can not be created, divided into smaller particles, nor destroyed in the chemical process.
  • Atom is a rigid and massive ball-like structure.

Concept:

• Isotones are atoms or nuclei which have an equal number of neutrons.
• ₁₇Cl³⁷ and ₁₉K³⁹ both have the same number of neutrons.
• Isobars are Atoms of a chemical element that have the same atomic mass but a different atomic number.
• Isotopes are Atoms of a chemical element that have the same atomic number but a different atomic mass.

In 6C13, 7N14

For 6C13

No of proton = 6

No of proton + No of neutron = 13

The correct answer is Option(2).i.e.40 µ. 

Key Points

• The Atomic Mass of Calcium is 40.078 µ ≈ 40 µ.
• Atom: 
  • An atom is the smallest invisible unit of matter that constitutes a chemical element.
  • Every plasma, solid, gas & liquid, composed of ionized or neutral atoms.
  • Around 100 picometers across, atoms are extremely small. 
• Atomic Mass: 
  • The Atomic Theory of Dalton suggested that each element has a unique atomic mass.
  • The law of constant proportions could be explained easily by the implementation of Dalton's theory.
  • As the size of an atom is relatively small, it is quite difficult to determine the mass of an atom.
  • That's why the scientists started evaluating the mass of an atom by differentiating it with the mass of a standard atom.
  • The atomic mass is 12u (12 atomic mass units).
  • Thus it states that 1 atomic mass = Mass of 1/12 the mass of a carbon-12 atom.
• The following table shows the list of elements with the respective atomic masses. 

  Elements	Atomic Mass
  Hydrogen	1 µ
  Carbon	12 µ
  Nitrogen	14 µ
  Oxygen	16 µ
  Magnesium	24 µ
  Sodium	23 µ
  Calcium	40 µ

The correct answer is 14C6

Concept:

Isotopes are defined as the atoms of the same element, having the same atomic number but different mass numbers.

For example, Hydrogen (1H) has three naturally occurring isotopes 1H, 2H, and 3H.

Explanation:

From the above explanation, we can see that isotope of any material have different atomic mass i.e., number of nucleons are different but the number of protons is the same 

• From the above periodic table, we can see that carbon has 12 nucleons i.e., 6 protons and 6 neutrons.
• Whereas Carbon-14 is one of the isotopes of carbon in which is used for carbon dating 

The correct answer is Raoult’s law.

Raoult’s law states that a solvent’s partial vapour pressure in a solution (or mixture) is equal or identical to the vapour pressure of the pure solvent multiplied by its mole fraction in the solution.

Mathematically, Raoult’s law equation is written as;

P_solution = Χ_solventP⁰_solvent

Where,

Psolution = vapour pressure of the solution
Χ_solvent  = mole fraction of the solvent
P⁰_solvent = vapour pressure of the pure solvent

Important Points

• Number of grams of Helium (He) = 60 gm
• Molecular mass is the sum of total protons and neutrons.
• The molecular mass of Helium = 2 × 2 = 4
• Now multiply the mass with a number of elements we get = 4 × 1 = 4
• One mole is equal to the total mass of the molecule.
• We know one mole is equal to 4 gm of Helium molecule.
• Now a number of moles in 60 gm of Helium is (n) = 60/4

n = 15 moles

• The number of moles in 60 gm is 15 moles.