Development of the Atomic Model Essay

460 370? BC Democritus first theory of fragment exclusively matter is composed of particles call(a)ed touchs which whoremongert be subdivided antithetic materials had different properties beca use of goods and services their atoms were different atoms progress to different sizes, regular shape, are in eonian motion, and score empty space450 BC Empedocles matter is composed of quaternary elements earth, air, fire, pee384 322 Aristotle no voids Opposed Democritus theory 4 elements earth, fire, air water with dry, hot, moist and cold500 1600 A.D. age of alchemyLate 1700s law of conservation of mass mass doesnt change during a chemical chemical 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 model all matter is made of particles called atoms all atoms of an element are identical atoms of different elements have different propertie s atoms coalesce to form compounds atoms are neither created nor destroyed during a chemical reactionLate 1800s Sir William Crookes and others utilise sealed glass tubes to depict a glow Cathode rays were attracted to positive plates therefore 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 distri unlessed by positive mass told not to touch broke everything but could regulate what was wrong with equipment1904 Hantaro Nagaoka developed Saturn model1911 Earnest Rutherford Thomsons research helper testing Thomsons theory golden foil experiment strike like shooting a cannon ball at a piece of tissue paper and having the cannon ball bounce covering fire at you Most of atom is empty space, positively charged nub Electrons in a cloud around the nucleus had hands of gold and k young how to use them to get answers di dnt mention electrons because he didnt sleep with what they did he did know they werent in orbits because the muscle 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 off rays which werent deflected by outside fields Neutron had mass close to equal to a proton1900 Max Planck energy is absorbed and released in chunks called quantum (compare playing a piano vs a violin)Einstein radiant energy energy packets called photons described photoelectric effect from observing that radiant energy on metal releases electrons1913 Niels Bohr (worked first with JJ Thomson then with Rutherford) developed model for hydrogen where the electron orbits the nucleus. He explainedthe H venting spectra and the explanation was the foundation for n, the formula quantum proceeds the concept of energy levels Mathematical predictions of lines only worked for hydrogen won a Nobel prize for looking at the solar system and comparing it to the atom1924 Louis de Broglie showed that if radiant energy could act like a bourgeon of particles, then matter could act like a quiver the wave property of electrons1927 Werner Heisenberg developed uncertainty principle impossible to know some(prenominal) exact momentum and localisation principle of an electron collectable to dual constitution of matter1926 Erwin Schodinger Schodingers wave equation quantum mechanics (advanced calculus needed) takes into neb the wave and particle nature of electrons. equation (2 gives info on location of electron in terms 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 instruction of spin of electrons. Spinning elect rons create magnetic field. Only 2 electrons of opposite spin in an orbital referred to as Pauli exclusion principleHunds rule half fill each orbital onwards adding second electronAufbau principle energy sublevel must be alter before moving onto next higher 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 ripping 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 annual table l=0, s orbital sharp l=1, p orbital principle l=2, d orbital diffuse l=3, f orbital fundamentalMagnetic Quantum Number, ml from experimentation with emission line spec tra place a gas discharge tube uprise a strong external magnet, and some single lines split into new lines not initially seen done by Pieter Zeeman in 1897 called normal Zeeman kernel Zeeman Effect explained by Sommerfeld and Peter 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 vary 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 Opposite pair is a stable governance like bar magnets stored in pairs arranged opposite to each other (produce no magnetism) If single unpaired electrons present, magnetism is present and atom is bear on by magnetic fieldsOverall each electron in an atom is described by a set of 4 quantum be fits perfectly arrangement of electrons and the structure of the periodic table