Atomic structure. Atomic Structure The structure of the atom ELECTRON PROTON NEUTRON.
1.2 atomic structure
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Transcript of 1.2 atomic structure
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1.2 Atomic Structure(Time needed: 6 class periods)
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Learning outcomes
• Matter is composed of particles, which may be atoms, molecules or ions.
• Atoms. Minute size of atoms.• Law of conservation of mass.
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DIFFUSION- evidence for the existence of small particles
• SPREADING OUT OF GASES• COLOUR OF INK SREADING OUT WHEN MIXED
WITH WATER• HYDROGEN CHLORIDE AND AMMONIA
SOLUTION
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AMMONIUM CHLORIDE
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law of conservation of mass/matter
• The law of conservation of mass/matter, also known as law of mass/matter conservation says that the mass of a closed system will remain constant, regardless of the processes acting inside the system. • Matter cannot be created/destroyed, although it may be
rearranged. • For any chemical process in a closed system, the mass of
the reactants must equal the mass of the products.
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Learning Outcomes• Very brief outline of the historical development of atomic theory
(outline principles only; mathematical treatment not required): Dalton: atomic theory;• Crookes: vacuum tubes, cathode rays; • Stoney: naming of the electron; • Thomson: negative charge of the electron; e/m for electrons
(experimental details not required); • Millikan: magnitude of charge of electrons as shown by oil drop
experiment (experimental details not required); • Rutherford: discovery of the nucleus as shown by the α−particle
scattering experiment;• discovery of protons in nuclei of various atoms; • Bohr: model of the atom;• Chadwick: discovery of the neutron.
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HISTORY OF THE ATOM
• GREEKS – MATTER MADE OF TINY INDIVISIBLE PARTICLES
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DALTON 1766-1844
• ALL MATTER MADE OF SMALL PARTICLES CALLED ATOMS
• ATOMS ARE INDIVISIBLE• ATOMS CANNOT BE CREATED OR DESTROYED
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DISCOVERY OF THE ELECTRON
• CROOKES CONDUCTED EXPERIMENTS WITH A GLASS TUBE
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CROOKES TUBE
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CROOKES TUBES
• CATHODE CONNECTED TO NEGATIVE ELECTRODE
• ANODE CONNECTED TO THE POSITIVE ELECTRODE
• CNAP
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VACUUM TUBES
• GAS AT LOW PRESSURE• ELECTRIC CURRENT PASSED THROUGH• RADIATION CAME FROM THE END OF THE
TUBE CONNECTED TO THE NEGATIVE(CATHODE) END OF THE BATTERY
• CATHODE RAYS
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TUBES
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CROOKES PADDLE TUBE
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CATHODE RAYS
• CAST SHADOWS• CAUSE GLASS TO GLOW• TURN A PADDLE WHEEL• RAYS ARE MADE OF PARTICLES
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JJ THOMPSON
• HOLE IN ANODE TO ALLOW BEAM OF RAYS TO PASS THROUGH.
• BEAM COULD BE DEFLECTED BY ELECTRIC PLATES.
• THEREFORE BEAM IS MADE OF NEGATIVE PARTICLES.
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JJ THOMPSONS APPARATUS
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JJ THOMPSON
• USED A MAGNETIC FIELD FROM AN ELECTROMAGNET TO DEFLECT THE ELECTRONS
• CALCULATED THE RATIO OF CHARGE TO MASS FOR ELECTRON
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GEORGE STONEY
• NAMED PARTICLES ELECTRONS
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ROBERT MILLIKAN
• FAMOUS OIL-DROP EXPERIMENT• IT MEASURED THE CHARGE ON THE ELECTRON• X-RAYS IONISED AIR MOLECULES BY STRIPING
ELECTRONS OFF THEIR ATOMS.• OIL DROPLETS PICKED UP ELECTRONS BECAME NEGATIVE• INCREASED THE + CHARGE UNTIL THE DROPLET
HOVERED.• TOOK MEASUREMENTS AND CALCULATED THE CHARGE
ON THE ELECTRON.
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ROBERT MILLIKAN
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ROBERT MILLIKAN
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THOMPSON’S ATOM
• ATOM A SPHERE OF POSITIVE CHARGES WITH NEGATIVE ELECTONS EMBEDDED
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ERNEST RUTHERFORD
• FIRED THIN ALPHA PARTICLES AT A TIN GOLD FOIL
• THOMPSONS PLUM PUDDING MODEL PREDICTED THAT THEY WOULD PASS THRU’ WITH LITTLE DEFLECTION
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RUTHERFORD’S EXPT
•
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RUTHERFORD’S EXPT
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EXPECTED RESULT
• ALPHA PARTICLES SHOULD PASS THROUGH WITH LITTLE DEFLECTION
+ +
+
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ACTUAL RESULT
• MOST PASS THROUGH UNDEFLECTED• SOME BOUNCED RIGHT BACK!
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EXPLANATION
• HARD DENSE CORE OF POSITIVE MATTER IN THE CENTER OF EACH ATOM-NUCLEUS
• ATOMS ARE MOSTLY EMPTY SPACE.
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THE PROTON
• RUTHERFORD CONTINUED TO BOMBARD DIFFERENT ELEMENTS SUCH AS NITROGEN AND OXYGEN
• SMALL POSITIVE PARTICLES WERE GIVEN OFF--- PROTONS
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THE NEUTRON
• JAMES CHADWICK BOMBARDED BERYLLIUM WITH ALPHA PARTICLES.
• SMALL PARTICLES WERE GIVEN OFF WHICH WERE NEUTRAL AND HAD THE SAME MASS AS THE PROTON—THE NEUTRON.
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Bohr’s atom
• Electrons travel in orbits around the nucleus
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Learning Outcomes
• Properties of electrons, protons and neutrons (relative mass, relative charge, location within atom).
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Proton
• Protons are positively charged particles found within atomic nucleus
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Atomic number (Z ), mass number (A), isotopes; hydrogen and carbon as examples of isotopes.Relative atomic mass (A r). The12C scale for relative atomicmasses.
Learning Outcomes
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Atomic number
• Also called proton number, this is the number of protons the atom has
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Atomic number
• Also called proton number, this is the number of protons the atom has
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The Number of Electrons
• Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.
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Mass number
•Mass Number = (Number of Protons) + (Number of Neutrons)
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Isotope
• Atoms that have the same number of protons but different numbers of neutrons are called isotopes
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Hydrogen isotopes
• The element hydrogen for example, has three commonly known isotopes: protium, deuterium and tritium
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Deuterium
•an atom of deuterium consists of one proton one neutron and one electron
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Tritium
•An atom of tritium consists of one proton two neutrons and one electrons
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Relative Atomic Mass
• The relative atomic mass of an element the mass of one of the element's atoms -- relative to the mass of an atom of Carbon 12,
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Learning Outcomes
• Calculation of approximate relative atomic masses from abundance of isotopes of given mass number (e.g. Calculation of approximate relative atomic mass of chlorine).
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Chlorine
•Chlorine-35 and Chlorine-37 are both isotopes of chlorine
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Relative mass of chlorine
• Chlorine consists of roughly 75% Chlorine-35 and roughly 25% Chlorine-37. We take an average of the two figures The relative atomic mass of chlorine is usually quoted as 35.5.
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Learning outcomes
• Use of the mass spectrometer in determining relative atomic mass.
• Fundamental processes that occur in a mass spectrometer:
• vaporisation of substance,• production of positive ions,• acceleration, separation,• detection (mathematical• treatment excluded).
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THE MASS SPECTROMETER
• Atoms can be deflected by magnetic fields - provided the atom is first turned into an ion.
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Stage 1: Ionisation
• The atom is ionised by knocking one or more electrons off to give a positive ion.
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Stage 2: Acceleration
• The ions are accelerated so that they all have the same kinetic energy.
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Stage 3: Deflection
• The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected.
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Stage 4: Detection
• The beam of ions passing through the machine is detected electrically.
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