J. J. Thomson, in 1897, discovered negatively charged particles emitted by the cathode towards the anode in a cathode ray experiment. NCERT Solution for Class 9 science - structure of the atom 56, Question 19. The mass number of an element is the sum of the number of protons and neutrons present in the atom of that element. Therefore, if K and L-shells of an atom are full, then the total number of electrons in the atom would be (2 + 8) = 10 electrons. This tendency would make an atom highly unstable while the atom is highly stable. Fundamental Constituents of an Atom. Chapter 4 the structure of the atom answer key questions. Then, the remaining mass (4 − 2) u = 2 u is contributed by neutrons. Drawbacks of the Model: Although Rutherford presented an entirely new model regarding the structure of the atom, there were a lot of drawbacks which he failed to explain, are-.
The nucleus of an atom consists of Protons, and the atomic number is equal to the number of protons present in one atom of an element. For example, the atom of boron has 5 protons and 6 neutrons. Since helium atom has two protons, mass contributed by the two protons is (2 × 1) u = 2 u. There are three subatomic particles: protons, neutrons and electrons. Describe the limitations of J. J Thomson's model of the atom. Grasping these essential points of the chapter structure of an atom will be helpful for you-. Distribution of Electrons in Distinct Shells. Bohr's model gives an elaborative explanation on the structure of an atom and overcomes the objections faced by all the other models on the structure of an atom. Its electronic configuration is 2, 1. In 1897, J. Chapter 4 the structure of the atom answer key.com. J. Thomson discovered the existence of the electron, marking the beginning of modern atomic physics. View NCERT Solutions for all chapters of Class 9.
Mass Number = Atomic Number + Number of Neutrons in the Nucleus. Ii) The outermost orbit can be accommodated by a maximum number of 8 electrons. Chapter 4 the structure of the atom answer key google image. An atom of Na has a total of 11 electrons. But, an electron revolving in circular orbits will not be stable because during revolution, it will experience acceleration. State the limitations of Rutherford's model of the atom. A) the same physical properties. In such a case, the atom would be highly unstable and collapse.
An atom consists of a positively charged sphere with electrons embedded in it. The chapter, Structure of the Atom covers the following topics: - Charged Particles in Matter. An atom consists of a positively charged particles concentrated at the centre known as the nucleus. Magnesium (Mg) has a configuration (2, 8, and 2), so the valency is two.
A helium atom has two neutrons. The mass of an atom is the sum of the masses of protons and neutrons present in its nucleus. Recent flashcard sets. The discovery of atoms was a revolutionary beginning to a new and detailed world of Science. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the nucleus. Thus, the atomic number of nitrogen is 7. The mass of an electron is 9. Chapter 4-The Structure of the Atom Flashcards. For third orbit, it is 2 n 2 = 2 × 3 2 = 18.
The first orbit (i. e., for n = 1) is represented by letter K. Similarly, for n = 2, it is L − shell, for n = 3, it is M − shell and for n = 4, it is N − shell. Important Questions and Answers. Question 11: The average atomic mass of a sample of an element X is 16. Hence, the valency of the element is 1 (since the outermost shell has only one electron). The neutron carries no electrical charge and has the same mass as the proton. Question 4: What do you think would be the observation if the α -particle scattering experiment is carried out using a foil of a metal other than gold? As the atom is electrically neutral, the number of protons and electrons are the same.
Neutrons are neutral. Number of Electrons present in an atom= Atomic number (Z). Students also viewed. Therefore, the atomic number of the atom is 8. These rays consist of positively charged particles known as protons.
State comparison of all the proposed models of an atom given in this chapter. Similarly, for second orbit, it is 2 n 2 = 2×2 2 = 8. These subatomic particles cannot be freed and studied in isolation. Outside of the nucleus are energy levels (also called shells), which contain one or more electrons. The notation Z denotes an Atomic number. The revolving electron would lose its energy and finally fall into the nucleus, the atom would be highly unstable. The maximum number of electrons that can occupy K and L-shells of an atom are 2 and 8 respectively. Let the percentage of isotope be y%. Isotopes have the same electronic configuration].
These valence electrons are responsible for the valency of an atom. A convenient unit of length for measuring atomic sizes is the angstrom (Å), which is defined as 1 × 10-10 meters. The outermost orbit can hold a maximum of 8 electrons. This reactivity is responsible for the formation of molecules between two or more atoms. According to J. Thomson's model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. Atomic Number and Mass Number.