Atom - The smallest particle of an element that keeps up the property of that element., Elements - They are made up of only one type of atom, Periodic Table - It is the collection of all known elements. At present there are about 118 known elements in nature., Protons - They are positively charged sub-atomic particles found in the nucleus of an atom., Electrons - They are negatively charged sub-atomic particles that orbit the nucleus., Neutrons - They are neutrally charged sub-atomic particle i.e. they carry no charge., Atomic Number - The number of protons present in the nucleus of an atom., Atomic Mass Number - It tells us about number of protons and neutrons present in the nucleus of an atom of the element., How elements are arranged in periodic table? - Elements are listed according to their increasing number of protons., Diffusion - It is the spontaneous spreading out of particles to fill all the available space., Law of conservation of mass/matter - It says that the mass of a closed system will remain constant, regardless of the process acting inside the system, Matter - It is anything that has mass and occupies volume., History of Atoms - It is the history about the idea of atoms and its sub atomic particles and its discoveries., Democritus or Greeks - They were first to tell that matter is made up of small particles, they named it as ATOMOS (greek word; meaning indivisble), from there was deduced the word ATOM, John Dalton - He was an English Chemist. He performed number of experiments with gases to tell about atoms., Dalton's Atomic Theory - 1. Matter is made up of small particles called atoms. 2. Atoms are indivisble, William Crookes - He was an English Chemist, who carried out an experiment to investigate what was happening in a piece of apparatus called Cathode Ray Tube., Discovery of Electrons or Cathode rays Pt.1 - Crookes showed that rays were coming from the negative electrode (cathode) in the cathode tube after switching on the current, and that these rays cast a shadow of a Maltese cross at the far end of the tube. He had discovered cathode rays., Crookes Paddle Wheel aparatus - In order to investigate the properties the cathode rays Crookes carried out a second experiment known as Paddle Wheel Apparatus experiment. From his' this experiment he concluded that small particles which were coming from the cathode caused the paddle wheel to turn., J.J Thomson - He was an English chemist in Cambridge University. He is credited with discovery of ELECTRONS., Professor George Stoney - He suggested the name electron ., Cathode rays - Cathode Rays are streams of negatively charged particles called electrons., Cathode - The electrode connected to the negative end of the battery, Anode - The electrode connected to the positive end of the battery., Work of J.J Thomson - He carried out an experiment to investigate if cathode rays consisted of Charged particles, e:m - size of charge of electrons to its mass., Robert Milikan - An American physicist, who devised an experiment to measure the charge on the electron., Thomson Plum Pudding Model - He visualised the atom as a sphere of positive charge (pudding) with negatively charged electrons (plums) embedded in the sphere randomly.,

Key Definitions for Chemistry

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