Notes

Class 9 chemistry chapter 4 - structure of the Atom          NOTESWALA 2020 Structure of the Atom Atoms •the building blocks of matter. •the smallest unit of matter.  Cathode ray experiment •J. J. Thomson discovered the existence of electrons. •He did this using a cathode ray tube, which is a vacuum-sealed tube with a cathode and anode on one end that created a beam of electrons travelling towards the other end of the tube. •The air inside the chamber is subjected to high voltage and electricity flows through the air from the negative electrode to the positive electrode. •The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube. •The experiment showed that the atom was not a simple, indivisible particle and contained at least one subatomic particle – the electron. Electrons •Electrons are the negatively charged sub-atomic particles of an atom. •The mass of an electron is considered to

               NOTESWALA    The Fundamental Unit of Life The body of all organisms is made up of very small units called cell. A cell is capable of independent existence and can carry out all the functions which are necessary for a living being. Unicellular organisms are capable of independent existence which shows a cell’s capability to exist independently like in amoeba. Due to this, a cell is called the fundamental, structural and functional unit of living organisms and basic unit of life. * Discovery of Cell and Cell Theory Cell was first discovered by Robert Hooke in 1665. He observed that just like honeycomb, organisms are also composed of small compartments. He named these compartments as Cells. Cell theory state that : All living organisms are composed of cells. Cell is the fundamental unit of life. All new cells come from pre-existing cells. * Shape and Size of Cells Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped, or totally ir