History of the atom Dalton J.J. Thompson Rutherford Bohr.
Post on 03-Jan-2016
History of the atomDaltonJ.J. ThompsonRutherfordBohr
Daltons Atomic TheoryAll elements are composed of atoms which are indivisibleAtoms of the same element are identicalAtoms of different elements can mix together in simple whole number ratios to form compoundsChemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element cant be changed into atoms of another element
Law of Definite Proportions and Law of Multiple ProportionsLaw of Conservation of Matter
Early Atomic ModelsJ.J. Thompsons plum-pudding modelRutherfords Model of the atom
Problems with Rutherford Model
Couldnt account for the chemical properties of the elements (why do elements react in the way that they do?)
The Wave Nature of LightElectromagnetic RadiationForms of energy that exhibit wave like characteristicsWavelength How far apart the waves areFrequencyThe # of waves to pass a point in a certain timeframeWavelength and Frequency are Inversely Proportional
Wavelength and FrequencyNot Working very hard
Long WavelengthLow Frequency
Wavelength and FrequencyWorking VERY hard
Short WavelengthHigh Frequency
What does this tell you about the relationship between wavelength, frequency and energy?
The Photo Electric EffectIn the early 1900s an experiment was done that COULD NOT be explained by light being a wave.Different colors were shined on to a metal plateElectrons would come off the metal plate for ONLY CERTAIN FREQUENCIES (colors) OF LIGHTIf light only behaved like a wave ANY frequency of light would cause the electrons to be released.
Brick Wall AnalogyDifferent balls thrown at wallEach one with different massAll at same speed of 90 mile/hourEach ball is like a color or light - each has its own energyPing Pong BallNo effectSoftballNo effectSuper Dense Steel BallDislodges Brick and send it flyingJB
Einstein and the Photo Electric EffectThis observation led Einstein to believe that light acted like a particle and a waveThis is called the dual nature of lightLight carried packets of energy called quanta, or photons
Neils Bohr and the New Model of the AtomBohr hypothesized that electrons could only be at certain energy levels around the nucleusElectrons could jump from lower to higher energy states by absorbing a quantum of energyWhen an electron releases the energy it gained, specific colors or wavelengths of light are emittedMercury Line Spectra
Electrons and the AtomNucleusElectrons disappear from one orbit and reappear at another without visiting the space in between!JB
Energy and the ElectronGround State lowest energy state for an electronExcited state high energy state for e-Quantum exact amount of energy to move an electron from one energy level to another
Heisenberg Uncertainty PrincipleIt is impossible to pinpoint the exact location and velocity of an electron at any point in timeYou can estimate where an electron will be 90% of the timeAn electron cloud shows where an electron spends most of its time
Quantum Mechanical Atomic ModelSimilar to Bohr model except that e- cannot be found in distinct orbits around the nucleusDetermines how likely it is for an electron to be found in various regions around the nucleus.
Atomic OrbitalsRegion around the nucleus where an electron of a given energy is likely to be foundEach orbital has a characteristic size, shape, and energyThere are four different orbitals: s, p, d, f Different types of atomic orbitals
Principle Energy LevelsSymbolized by n = 1,2,3,4 etc.Each energy level contains sublevels denoted by a number and a letter (ex. 1s)Each sublevel contains a certain # of orbitals Every orbital can hold 2 e-
Energy Level# of SublevelsType of sublevel and orbitalsn=111s (1orbital)n=222s (1 orbital)2p (3 orbitals)n=333s (1 orbital)3p (3 orbitals)3d (5 orbitals)n=444s (1 orbital)4p (3 orbitals)4d (5 orbitals)4f (7 orbitals)
See table 5.1 on page 131
Electron ConfigurationsAufbau principle: e- occupy the lowest energy sublevels 1st (see pg. 133 figure 5.7)Pauli Exclusion Principle: every orbital can hold a maximum of 2 e- (paired e- spin in the opposite direction)Hunds Rule: e- fill all empty orbitals in a sublevel BEFORE they pair upAufbau Diagram
Valence ElectronsValence electrons electrons found in the highest energy level of an atomValence e- determine the chemical properties of the elementA filled outer energy level (stable octet) of 8 e- makes an atom stable (or for He 2e- fills its outer energy level)
Group Valence e- (and the orbitals they occupy)1A1 (s1)2A2 (s2)3A3 (s2p1)4A4 (s2p2)5A5 (s2p3)6A6 (s2p4)7A7 (s2p5)8A8 (s2p6)
Electron Dot DiagramsShows only number of valence e-Electrons shown as dots
Carbon has 4 valence e-