Development of the Atomic Model Essay

460 370? BC Democritus first theory of ingredient All matter is composed of constituents c eithered atoms which brush asidet be subdivided distinct materials had different properties because their atoms were different atoms sustain different sizes, regular shape, are in constant motion, and have empty space450 BC Empedocles matter is composed of four elements earth, air, fire, water384 322 Aristotle no voids Opposed Democritus theory 4 elements earth, fire, air water with dry, hot, moist and cold500 1600 A.D. age of interpersonal chemistryLate 1700s law of conservation of bay window mass doesnt change during a chemic reaction1799 Proust law of constant composition compounds always have same proportion by mass of their elements1766-1844 John Dalton (English) postulates atoms as a billiard ball mold all matter is made of particles called atoms all atoms of an element are identical atoms of different elements have different properties atoms combine to form comp ounds atoms are incomplete created nor destroyed during a chemical reactionLate 1800s Sir William Crookes and others used sealed nut tubes to generate a glow Cathode rays were attracted to positive plates accordingly negatively charged Rays could be blocked therefore a particle Negatively charged particles were called negatrons1897 JJ Thomson used cathode ray tube and developed raisin bun model Electrons randomly distributed through positive mass told not to touch broke everything but could see what was disparage with equipment1904 Hantaro Nagaoka developed Saturn model1911 Earnest Rutherford Thomsons research assistant testing Thomsons theory luxurious foil experiment surprised give care shooting a cannon ball at a piece of tissue paper and having the cannon ball bounce back at you Most of atom is empty space, positively charged nucleus Electrons in a cloud around the nucleus had r each(prenominal) of gold and k overbold how to use them to get answers didnt me ntion electrons because he didnt live on what they did he did know they werent in orbits because the nothing degenerates and in the atom, it doesnt1886 Goldstein discovery of the proton (shown to be a fundamental particle 20 years later) 1837 times heavier than an electron1932 James Chadwick discovered neutrons by bombarding Be with alpha particles Gave discharge rays which werent deflected by outside guinea pigs Neutron had mass approximately equal to a proton1900 Max Planck nil is absorbed and released in chunks called quantum (compare playing a piano vs a violin)Einstein radiant competency energy packets called photons described photoelectric effect from observing that radiant energy on metal releases electrons1913 Niels Bohr (worked first with JJ Thomson and so with Rutherford) developed model for hydrogen where the electron orbits the nucleus. He developedthe H emission spectra and the explanation was the foundation for n, the regulation quantum number the con cept of energy levels Mathematical predictions of lines only worked for hydrogen won a Nobel prize for spirit at the solar system and comparing it to the atom1924 Louis de Broglie showed that if radiant energy could act like a stream of particles, then matter could act like a wave the wave prop of electrons1927 Werner Heisenberg developed uncertainty principle impossible to know both exact momentum and location of an electron due to dual nature of matter1926 Erwin Schodinger Schodingers wave equation quantum mechanics (advanced calculus needed) takes into mark the wave and particle nature of electrons. equation (2 gives info on location of electron in cost of probability density wave functions are called orbitals pic, where E is energy, e2 is electric potential, r is orbital radius and h is Plancks constant1925 Wolfgang Pauli each orbital has only 2 electrons is now explained due to direction of twirl of electrons. Spinning electrons create magnetic field. Only 2 ele ctrons of opposite spin in an orbital referred to as Pauli exclusion principleHunds rule half fill each orbital before adding secondly electronAufbau principle energy sublevel must be filled before moving onto next higher(prenominal) sublevelPrinciple Quantum Number, n integer that Bohr used to label the orbits and energy levels a main shell of electrons seen in low resolution spectra still used today although we now use orbitals instead of orbitsSecondary Quantum Number, l Arnold Sommerfeld (1915) extended Bohrs theory. H has 3 elliptical orbitals for n = 2 Explained the observed line dissever seen for H in high resolution line spectra Introduced l to describe sublevels l has values 0 to n-1 relates energy levels to shape of electron orbital and explains regions of the periodic table l=0, s orbital disconnected l=1, p orbital principle l=2, d orbital diffuse l=3, f orbital fundamentalMagnetic Quantum Number, ml from experimentation with emission line spectra place a at tack discharge tube near a strong external magnet, and some single lines split into new lines not initially seen done by Pieter Zeeman in 1897 called normal Zeeman Effect Zeeman Effect explained by Sommerfeld and pecker Debye (1916) They proposed that the orbits could exist at various angles If orbits in space are in different planes, the energies of the orbits are different when the atom is near a strong magnet For each value of l, ml can veer from l to +l If l = 1, ml can be -1, 0, 1 suggesting 3 orbits with the same energy and shape but with a different orientation in space (degenerate orbitals)Spin Quantum Number, ms to explain more and new evidence, ie the additional line splitting seen in a magnetic field student of Bohr and Sommerfeld Pauli suggested each electron spins on its axis and is like a tiny magnet. Could only have one of two spins equal in magnitude, opposite in direction (vector) Values + or glacial pair is a stable arrangement like bar magnets sto red in pairs arranged opposite to each other (produce no magnetism) If single unpaired electrons present, magnetism is present and atom is affected by magnetic fieldsOverall each electron in an atom is described by a tick off of 4 quantum numbers fits perfectly arrangement of electrons and the structure of the periodic table