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History of the Atom Chapter 11 Section 1 Development of the Atomic Theory Half Full or Half Empty? Completely Full of Matter! – Half full of water – Half full of air Reminder… • matter - anything that has mass and takes up space – matter is NOT… • Light, Heat, Emotions, Thoughts, & Ideas • Matter is made up of – atoms – the smallest particles into which an element can be divided and will remain the same substance • make up elements • often called the building blocks of matter Think… Suppose you cut wood into smaller and smaller pieces. Do the small pieces seem to be made of the same matter as the large chunk you started with? History of Matter • Democritus (460 B.C. – 370 B.C.) – Greek Philosopher – Thought the universe was made of empty space and tiny bits of stuff which could not be divided into smaller pieces – Named these tiny pieces atoms (Greek word atomos “indivisible: cannot be divided”) – Atoms were hard, small particles – Believed different types of atoms existed for every type of matter and came in different shapes/sizes – Ideas were not accepted for nearly 2000 years! To learn more about something in science that is too small to be seen, scientist create….. MODELS History of the Atom • John Dalton (Early 1800’s) – Schoolteacher and Chemist – Atomic Model (Atomic Theory of Matter) • Set of Ideas (idea model not physical model) –All substances are made of atoms –Atoms are small particles that cannot be created, divided, or destroyed –Atoms of the same element are exactly alike –Atoms join with other atoms to make new substances History of the Atom • J.J. Thomson (Late 1800’s to Early 1900’s) – English Scientist – Discovered Electrons • Cathode Ray Tube Experiment • Atoms were not too tiny to divide History of the Atom… • J.J. Thomson (Late 1800’s to Early 1900’s) – Atomic Model • Ball of positive charge with electrons embedded in it History of the Atom • Rutherford (Early 1900’s) – British Chemist and Physicist – Discovered the Nucleus & the Proton (Gold Foil) – Model of Atom • Electrons were scattered in the empty space around the positively charged nucleus. History of the Atom • James Chadwick (1930’s) – Student of Rutherford’s – Discovered Neutrons: Ran further experiments using the results of the Gold Foil Experiment • Found that the particles were heavier because of Neutrons – Atomic Model: Proton – Neutron Center History of the Atom • Niels Bohr (Early 1900’s) – Discovered Electron Energy Levels – Electrons can jump paths/levels Current Model • Electron movement is not completely certain • Electrons stay in the energy levels of the electron cloud