# Structure of Atom - Online Test

Q1. According to Dalton’s atomic theor
Explaination / Solution:

Dalton was developed the theory of the structure of matter and this theory is known as Dalton’s atomic theory. His research was based on experiments and also from law of chemical combination. Dalton’s atomic theory was quickly explained the many heretofore unexplained chemical phenomena. Dalton’s atomic theory quickly became the theoretical foundation in chemistry. Dalton’s atomic theory stated that: All the matter is made of atoms which are tiny particles and indivisible. All the given atom of the element is identical in mass, size, shape, and in other properties. All different elements have different types of atoms and also different in their mass, size, shape, and in other properties. All the atom of an element cannot be made or destroyed.

Q2. Cathode rays or cathode ray particles are
Explaination / Solution:

Cathode rays - In 1897, British physicist J. J. Thomson showed the rays were composed of a previously unknown negatively charged particle, which was later named the electron.

Q3. The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV. What is the kinetic energy of the electron in this state?
Explaination / Solution:

Total energy of the electron, E = −3.4 eV Kinetic energy of the electron is equal to the negative of the total energy. K = −E = − (− 3.4) = +3.4 eV Hence, the kinetic energy of the electron in the given state is +3.4 eV.

Q4. Charge on the electron was determined by
Explaination / Solution:

In 1909, Robert Millikan and Harvey Fletcher conducted the oil drop experiment to determine the charge of an electron. They suspended tiny charged droplets of oil between two metal electrodes by balancing downward gravitational force with upward drag and electric forces. The experiment helped earn Millikan a Nobel prize in 1923

Q5. in the Thomson Model of Atom
Explaination / Solution:

• J. J. Thomson, who discovered the electron in 1897, proposed the plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model.
• In Thomson's model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding".
• The 1904 Thomson model was disproved by Hans Geiger's and Ernest Marsden's 1909 gold foil experiment.

Q6. Rutherford’s α–particle scattering experiment supported the discovery of
Explaination / Solution:

Rutherford's model of an atom : Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this. In this experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil.

On the basis of his experiment, Rutherford put forward the model of an atom, which had the following features:

• There is a positively charged centre in an atom called the nucleus.
• Nearly all the mass of an atom resides in the nucleus. The electrons revolve around the nucleus in well-defined orbits.
• The size of the nucleus is very small as compared to the size of the atom.

Q7. Correct expression for mass number A is
Explaination / Solution:

Mass number. The mass number (symbol A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. mass No. = no. of protons + no. of neutrons.

Q8. Isobars are the atoms with
Explaination / Solution:

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number.

Q9. Isotopes are the atoms with
Explaination / Solution:

The atoms of a chemical element can exist in different types. These are called isotopes. They have the same number of protons (and electrons), but different numbers of neutrons. Different isotopes of the same element have different masses.

Q10. Photoelectric effect established that light
Explaination / Solution:

The emission of free electrons from a metal surface when light is shone on it is called the photoemission or the photoelectric effect. This effect led to the conclusion that light is made up of packets or quantum of energy. Einstein already associated the light quantum with momentum. This strongly supported the particle nature of light and these particles were named photons. Thus, the wave-particle duality of light came into picture. Einstein won the Nobel Prize for Physics not for his work on relativity, but for explaining the photoelectric effect.