2 The basic building blocks of matter that make-up everyday objects. Defining the AtomAn atom is the smallest particle of an element that retains its identity in a reaction.The basic building blocks of matter that make-up everyday objects.
7 DemoCritusEarly Greek Scholar-was the first to suggest the existence of atomsHe believed that atoms were indivisible and indestructible.Never developed a theory lacked experimental support
8 John Dalton’s Atomic Theories -All matter is composed of tiny indestructible particles called atoms.-Atoms cannot be made or destroyed.-All atoms of the same element are identical.-Different elements have different types of atoms.-Chemical reactions occur when atoms are rearranged.-Atoms of different elements can mix together to form compounds.
9 Dalton’s Theory Revised Most of Dalton’s theory is still accepted today EXCEPT that atoms are known to be divisible.Atoms can be broken down into 3 subatomic particles: electrons, protons and neutrons.
10 J.J. ThomsonUsed a cathode ray tube to prove the smallest particles present must have a negative charge.
19 J.J. ThomsonAtoms were electrically neutral, so there must be a + particle to cancel out the – charge from the electron.Developed the Plum Pudding Model (positive ball containing scattered electrons)
20 Ernest RutherfordFormer student of Thomson, DISPROVED the Plum Pudding Model of the atom.The Gold Foil Experiment: Sent a beam of + charges (alpha particles) through a piece of very thin gold foil.Angles of deflection were measured.
28 RutherfordResults: Most of the alpha particles passed straight through, most of the foil must be regions of “empty” space – not a + sphere like Thomson believed.+ charges and the atoms mass must be found in the center discovered the nucleus
29 The Nuclear AtomIn Rutherford’s atomic model, the protons and neutrons are located in the nucleus.The electrons are distributed around the nucleus and occupy almost all the volume of the atoms.
47 ATOMIC STRUCTUREParticleChargeMassproton+ ve charge1neutronNo charge1electron-ve chargenil
48 number of electrons = number of protons ATOMIC STRUCTUREHe2Atomic numberthe number of protons in an atom4Atomic massthe number of protons andneutrons in an atomnumber of electrons = number of protons
49 Why are atoms electrically neutral? HELIUM ATOMshellprotonN+-+N-neutronelectronWhy are atoms electrically neutral?