1.2 Atomic Structure (Time needed: 6 class periods)
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Transcript of 1.2 Atomic Structure (Time needed: 6 class periods)
Learning outcomes
• Matter is composed of particles, which may be atoms, molecules or ions.
• Atoms. Minute size of atoms.• Law of conservation of mass.
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
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.
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.
DALTON 1766-1844
• ALL MATTER MADE OF SMALL PARTICLES CALLED ATOMS
• ATOMS ARE INDIVISIBLE• ATOMS CANNOT BE CREATED OR DESTROYED
CROOKES TUBES
• CATHODE CONNECTED TO NEGATIVE ELECTRODE
• ANODE CONNECTED TO THE POSITIVE ELECTRODE
• CNAP
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
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.
JJ THOMPSON
• USED A MAGNETIC FIELD FROM AN ELECTROMAGNET TO DEFLECT THE ELECTRONS
• CALCULATED THE RATIO OF CHARGE TO MASS FOR ELECTRON
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.
ERNEST RUTHERFORD
• FIRED THIN ALPHA PARTICLES AT A TIN GOLD FOIL
• THOMPSONS PLUM PUDDING MODEL PREDICTED THAT THEY WOULD PASS THRU’ WITH LITTLE DEFLECTION
EXPLANATION
• HARD DENSE CORE OF POSITIVE MATTER IN THE CENTER OF EACH ATOM-NUCLEUS
• ATOMS ARE MOSTLY EMPTY SPACE.
THE PROTON
• RUTHERFORD CONTINUED TO BOMBARD DIFFERENT ELEMENTS SUCH AS NITROGEN AND OXYGEN
• SMALL POSITIVE PARTICLES WERE GIVEN OFF--- PROTONS
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.
Learning Outcomes
• Properties of electrons, protons and neutrons (relative mass, relative charge, location within atom).
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
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.
Isotope
• Atoms that have the same number of protons but different numbers of neutrons are called isotopes
Hydrogen isotopes
• The element hydrogen for example, has three commonly known isotopes: protium, deuterium and tritium
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,
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).
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.
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).
THE MASS SPECTROMETER
• Atoms can be deflected by magnetic fields - provided the atom is first turned into an ion.
Stage 1: Ionisation
• The atom is ionised by knocking one or more electrons off to give a positive ion.
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.