Che.m

• All matter is composed of atoms that are extremely small and indivisible particles.
• The atom is the basic unit of an element that can enter into chemical combination.
• All atoms of a given element are identical with same size, mass and chemical properties.
• Atoms of different elements combine with each other in a definite ratio of small whole numbers to form the same compound.
• During chemical reaction, atoms are either combined, united or rearranged, none are created or destroyed.
• Michael Faraday - an English chemist; showed that there is a relationship between electricity and matter.
• Sir William Crookes - showed that if high voltage was passed through a gas discharging tube, some sort of invisible rays moved from the negative to the positive electrode.
• cathode - negative electrode; cathode rays - rays from the cathode
• cathode-ray tube- gas discharging tube and known as Crookes tube
• Eugene Goldstein - found that when cathode rays are formed in the gas discharge tube, positive particles remain; he discovered the protons
• Wilhelm Roentgen - discovered materials that emit radiation; discovered X-rays in 1895 which showed that atoms is not invisible but composed of smaller particles
• Antoine Henri Becquerel - discovered radioactivity in uranium in 1896 which also showed that atoms is not invisible but composed of smaller particles
• Joseph John Thompson -discovered electrons; he was known for his "raisin pudding theory" which proposes that the atom is a mass of positive charge with electrons scattered throughout it as far apart as possible wherein the pudding represents the mass of positive charges and raisins are the electrons.
• Robert Andrews Millikan - he was able to measure the charge of electron through his oil - drop experiment and found that this was always some whole number multiple of 1.06 x 10-19 coul.
• Ernest Rutherford - carried out experiments in which he bombarded a thin sheet of gold foil with tiny positively charged particles called alpha particles
• He found that most of the alpha particles passed right through the gold foil and he concluded that the positive part of the atom must be concentrated in a small part of the atom.
• He also proposed the planetary or nuclear model of the atom wherein the positive part (protons) is in the center of the atom called nucleus and the electrons are considered to be spinning around the nucleus as the planets do around the sun.