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Activity 4: Are Atoms Divisible? Ancient Greece 1. Greek philosopher Democritus 2. He thought atoms were uncuttable 3. Therefore: Atoms are indivisible particles Atomos—Greek meaning ‘indivisible 470-380 B.C. John Dalton—late 18th century 1. What are atoms? Dalton’s Atomic Model: Hard, indivisible sphere 1766-1834 2. Do Carbon atoms differ from Oxygen atoms? Yes HAS THIS EVER HAPPENED TO YOU? Are there things inside the atom? YES! Subatomic particles e- p+ n0 Discovery of electron (e-) Credited with the discovery of the electron in 1897. J.J. Thomson 1856-1940 •Thomson identified a glowing beam of particles that traveled through a chamber of gas when exposed to an electrical current. Cathode ray tube -This beam (cathode ray) was attracted to positive charges and repelled by negative charges. -Thomson concluded the beam must be composed of negatively charged particles. These came to be known as electrons. Thomson’s Atomic Model “Plum Pudding” Model POSITIVE CHARGE Negative electron plums are floating around in a sphere of positive pudding. ELECTRONS EMBEDDED WITHIN Discovery of the Nucleus 1871-1937 Ernest Rutherford Rutherford’s Au foil Experiment “+” charge Rutherford’s experiment Rutherford’s Nuclear Atom Negative electrons surround nucleus amidst lots of empty space. Positive Nucleus Discovery of the proton Eugen Goldstein In 1886, Goldstein observed rays in a cathode ray tube that traveled oppositely than the electrons previously discovered. Protons Located in nucleus Determine which element # of protons = atomic number equal to # of electrons in a neutral atom Chadwick 1. 1932 discovered the neutron 2. This subatomic particle is heavy enough to split a nucleus 3. Led the way to the creation of the atomic bomb LETS HAVE SOME PRACTICE Element Symbol Element Name Mass Number (Protons+Neutrons) Atomic Number (Protons) Atomic Number (Protons) 6 C Carbon 12 12 6 Mass Number (Proton+Neutrons) C Mass Number Almost all the mass of an atom comes from protons & neutrons # Protons + # Neutrons = mass number LETS HAVE SOME PRACTICE Atomic # = # of protons # protons = # electrons in an atom Mass # = number of protons and neutrons So,to get the # of neutrons we must Subtract Atomic # from the Mass # = # Neutrons 12 6 C 6 neutrons Practice Determine the # of protons,neutrons, & electrons Protons Neutrons Electrons He 2 2 2 B 5 6 5 Mg 12 12 12 Zn 30 35 30 Subatomic Particles Electron: enegative charge -31 kg 9.11 x 10 Proton: p+ positive charge -27 kg 1.67 x 10 Neutron: n or n0 no charge -27 kg 1.67 x 10 What did Battleship teach us? Battleship simulated Rutherford’s Gold Foil Experiment. Rutherford Alpha Particles Battleship Your missiles Nucleus Pattern Drawn Atom is mostly empty space All of the empty boxes Atoms vs Ions ATOMS IONS Protons = Electrons Protons ≠ Electrons Cations= More Protons Positive Charge Anions= More Electrons Negative Charge IONS cation (+) anion (-) Li+1 Cl-1 3 Protons 2 Electrons 17 Protons 18 Electrons Ions An ion is a particle with a positive (+) or negative (-) charge Atoms that gain electrons have charges Atoms that lose electrons have + charges Isotopes Atoms of an element can have different numbers of neutrons – these are isotopes The number of protons and electrons is always the same, but since more neutrons add more mass, the mass number can be different Isotopes Isotope Protons = Protons BUT……Neutrons are Different So Mass # is Different Atom Protons Neutrons Electrons Mass # Carbon12 Carbon13 Carbon14 6 6 6 12 6 7 6 13 6 8 6 14 How Big Is An Atom? Practice • The atomic number of an atom is always equal to the total number of: a. Neutrons in the nucleus b. Protons in the nucleus c. Neutrons plus protons in the nucleus d. Protons plus electrons in the atom Practice • An atom of 42Ca contains: a. 20 protons and 22 neutrons b. 20 protons and 42 neutrons c. 20 electrons and 42 neutrons d. 20 electrons and 22 protons Practice • The nucleus of an Fe-56 atom contains: a. 26 protons, 30 neutrons and 26 electrons b. 26 protons, 26 neutrons and 30 electrons c. 26 protons and 56 neutrons d. 26 protons and 30 neutrons Practice • A 52Cr3+ ion contains: a. 24 protons, 52 neutrons, 21 electrons b. 24 protons, 28 neutrons, 24 electrons c. 24 protons, 28 neutrons, 27 electrons d. 24 protons, 28 neutrons, 21 electrons Practice • What is the total number of electrons in an atom with an atomic number of 30 and a mass number of 65? a. 30 b. 65 c. 35 d. 95