Grade 12 Chemistry Notes – History and Development

3. 1 & 3. 2 Chemistry Notes Dalton * In 1805, John Dalton reintroduced the idea to explain 3 fundamental principles proveal Work * Atoms of contrary parts mother diametrical properties * Law of explicit proportion and multiple compositions hints of 2 or more divisions dissolve combine in a fixed ratio to song new substances take c being on their combining capacities (eg. weewee vs H2O2) * Law of conservation of mass atoms cannot be created or destroyed during a chemical reaction Conclusions * All study is cool of atoms Atoms be the sm everyest pieces of matter and cannot be down in the mouth down further * All atoms of unitary element have identical properties imbibe * Development of a cathode ray tube (by William Crookes) Thompson (1897) Experimental Work * Used a cathode ray tube a vacancy tube with electrodes at both ends * set that thither were charged particles that were get offling from integrity end of the tube to the other (from forbid end to comma nding end) Conclusion * Proposed that an atom was a positively charged set down sphere containing banishly charged negatrons raisin sc unmatched semblance What Thompson left hand us with? Atoms consist of negative negatrons embedded wi decoct a positively charged sphere * Analogy of raisin bankroll often use Milikins storied Oil Drop Experiment * find size and charge on electron * Discove going charge on angiotensin converting enzyme electron was 1. 6 x 1019 C How it worked? * Knew mass of angiotensin converting enzyme drop of oil, calculated gravity on star drop * Charge was employ to f tout ensembleing drops by illuminating fundament chamber with x-rays, exciting electrons, causing them to tie to oil. * Using a battery, electric emf was applied to the plates.When just right, the electromagnetic drag would balance out the force of gravity, suspending particles in midair. * Noticed charge was alship canal multiples of 1. 6 x 1019 * Q= mg/E Gold Foil Experiment * Radi oactive particles (alpha ir radioactivity sickness) were fired at thin gold sheets * Screens coated with zinc sulphide detected the presence of the alpha radiation * Vast majority of alpha particles passed slap-up d wholeness gold sheet, however, joltyly 1 in 8000 particles were deflected Chadwick and the Neutron When calculating the mass of detail nuclei, the calculated mass did not match with the associated charge of the nucleus * Chadwick proposed that neutral particles must(prenominal) be present to make up for the missing mass * Chadwick proposed a positive nucleus containing neutral particles Isotopes * Mass spectrometers were used to discover that all atoms of the comparable element were not the same * Elements contained several antithetical forms of isotopes (atoms with the same number of protons, but different song of neutrons) Problem with the Rutherford Model natural philosophy bodies be accelerating when they change speed and/or direction * And electron trav elling in a orotund orbit is invariably changing its direction and therefore accelerating * This acceleration would result in the electrons emitting electromagnetic radiation, fall behind electrons, and collapsing the atom as it doggingly spirals private because it is losing electrons Enter Max Plank * Her was canvas the emission of roost from stifling designs * What is visible gleamingen? When objects be het up, they emit un standardised food colouring in of light source depending on how hot the object is * Ex. white hot objects atomic number 18 emitting the whole range of the visible spectrum * red hot objects emit light with gesticulatelength of the unsee adapted longest wavelength * blue hot objects atomic number 18 the hottest as they emit light of shortest wavelength * juicy objects emit radiation. The hotter they ar, the more energetic the radiation emitted is. The electromagnetic radiation changes as the object gets hotter. * The color of light emitt ed reveals temperature Explaining Intensity vs. muscularity The stair expression which changed physics * Planck suggested that energies of the vibrating atoms in the fire uped substantialness were multiples of small quantities of brawn ( ability was not continuous) * Introduced the border quantum * The slope is actually more identical a staircase * for distributively one beat represents a quanta of susceptibility * A quanta is derived from mensuration and refers to the smallest affirmable unit of might that can be associated with a precise sub-microscopic sluice * An atom has to absorb or rick an entire package (quanta) of aptitude or none at all. there is no in between Heinrich Hertz the photoelectric take * Photoelectric effect when light is shone on a metal rise up, electrons are released from the surface of the metal. The number of electrons released per second can be measured by a committed ammeter * Frequency is different from intensity. electrons pull up stakes exclusively burst forth off if the relative frequency is right, however, how legion(predicate) electrons jump off will depend on the intensity of the light. How fast they jump off will also gain with high frequency * The amount of button in a light wave is proportionally related to its frequency.High frequency light has high energy, low frequency light has low energy (violet has the virtually energy and red has the least) maven puts 2 and 2 together * In 1905, Einstein au accordinglytic the Nobel Prize for applying Plancks idea to the photoelectric effect * When light strikes metal, some of the energy is used to allow the electron to come apart free from the metal, the rest of the energy is left over as the kinetic energy of the ejected electron * If one electron absorbs one photon (quanta of energy), it must be great profuse or the electron to be able to escape * No electrons escape at low photon energies because the energy of the single photon was meagre fo r the electron to escape the metal Energy of Quanta of Energy Photons * E = h x f, where E is the amount of energy in joules (J), h is Plancks constant 6. 6 x 10-34, and f is the frequency in hertz * A photon is a portion of energy, with energy prizes match to the frequency of the electromagnetic wave Einsteins Proposals Light is judge like a particle (photon) * Light know as bundles of photons, with severally photon independent of each other * This means that light has received particle properties as well * The energy of a photon is proportional to its frequency and zero point else. * Therefore, a phonon is a small packet of energy corresponding to a specific frequency of light (E=hf) Spectroscopy The spectroscope was invented by Robert Bunsen and Gustav Kirchhoff in the 1850s to meditate light * When white light passes by dint of spectroscope (containing a prism or diffraction grating), the light is divided into a continuous rainbow of colors (continuous spectrum) Bunse n and Kirchhoff (1859) invented the spectroscope * When elements were heated in a Bunsen burner flame, each element produced a flam color and a glossy debate spectrum that was characteristic of the element * Continuous Spectrum a display of all colors.It comes from the dispersion (refraction) of white light fugitive through a prism * tenacious Line spectrum ( immersion spectrum) certain colors are missing from a display of colors produced by white light discharge through a accelerator and then through a prism. These missing cable systems modify scientists to identify the gas that the light passed through * Bright line spectrum (emission spectrum) when a gas is energized by electricity or heat or light, the gas emits light of a specific color (not white light). When this light is passed through a prism it is refracted into a pattern of a few lustrous lines of color.Each substance has a unique, bright line signature. This pattern of colored lines represents the same patter n of dark lines of missing color in the dark line spectrum Bohrs theory was needed to explain the bright/dark spectrum and Einsteins photons 1. Electrons travel in an atom in circular orbits. Each orbit represents a specific energy take. All electrons in one orbit/energy level will have the same amount of energy, which is quantized (discrete packet) 2. There is maximum number of electrons allowed in each orbit 3. When electrons absorb a photon of light, they jump from a disgrace energy level to a higer energy level.This absorption of a photon of light energy results in a dark line in the absorption spectrum 4. When electrons jump from a higher energy level to a lower energy level, energy is released as a photon of light. This release of photon from the atom results in the bright line in the emission spectrum 5. When electrons are at the lowest energy level, they are in ground state How does Bohrs Energy levels of electrons relate to the periodic put off? * Each period represents one energy level Period 1 1 Energy level, Period 2 2 energy levels, etc. There is a maximum number of electrons in each lever (level 1 2 electrons, level 2 8 electrons, level 3 8 electrons) Power Point 2 Problems with Planetary Model * If electrons were accelerating, photons of electromagnetic radiation should be emitted * Obviously this is not the case * The Rutherford planetary model is insufficient as a model to explain matter Quantum Theory * All electrons in all atoms can be described by 4 unique quantum numbers * Quantum numbers are used to describe the approximate location and characteristics of electrons surrounding an atom ground on the energy levels of an atom * There are 4 quantum numbers article of belief quantum number (n) * Designates main E level of electron * Secondary quantum number (l) * Describes E sublevels of electrons * Magnetic Quantum Number (ml) * Relates to direction of electron orbit * Spin Quantum number (ms) * Relates to the straining of an electron Principle Quantum Number (n) * n=1, 2, 3, 4 etc. * n=1 means Energy level 1 and so on Secondary Quantum number, l * (l) describes shapes of sublevels (subshells) of the main energy level * Sommerfeld looked more closely at the H line spectrum. Found that main lines of bright line spectrum split into more lines. The number of sublevels equals the appreciate of the principle quantum number * Has integral value from 0 to (n-1) for each value of n * If n=3, then there are three sublevels. L = 0, 1, 2 * Each l number represents a possible shape of the orbital. (hence if l=0, 1, 2, then there are 3 possible shapes) 3rd Quantum Number Magnetic Quantum number, ml * describes the preference of electron orbital in topographic point (therefore orbitals could exist at different angles to each other in 3-d) * For each value of l, ml, can vary from -1 to 1 Shapes of Orbitals s (l=0) orbital is spherical, ml = 0 * p (l=1) , ml = -1, 0, 1 * d (l=2) , ml = -2, -1, 0, 1, 2 * f (l=3) orbitals are some(prenominal) more complex, ml = -3, -2, -1, 0, 1, 2, 3 miscellanea of Energy Subshells * Each distinct sublevel has specific number of orbitals. * Each orbital has a different orientation The fling quantum number, ms * Pauli each electron spins on its axis in one of 2 ways clockwise or counterclockwise * The spin quantum possesses only dickens values each +1/2 (clockwise) or -1/2 (counter-clockwise) New Orbital Way Orbitals are 3 dimensional probability dissemination graphs which help chemists visualize where electrons are most likely to be lay out Electron Orbitals * An electron orbital is described as the region of space where an electron may be found * Orbits are ring surrounding the nucleus, whereas orbitals are probability clouds or clouds of electron density * More than one orbital can be found within an energy level Paulis Exclusion Principle * No two electrons in an atom can have the same 4 quantum numbers