December 1 The wavemechanical model of the atom

December 1 The wave-mechanical model of the atom Homework Finish worksheet

The Wave Model • Today’s atomic model is based on the principles of wave mechanics. • According to theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.

Quantum Model

• The modern model of the atom is called the quantum model or the wavemechanical model.

• By 1900 scientist were studying energy and waves. • It was proposed that energy was made of tiny packets called quanta, these packets acted like particles.

• Quantum – singular – package or bundle or energy. If the energy is light is a photon. • Quanta is the plural of quantum.

Duality wave -particle • Louis De Broglie discovered that the electron also behaves sometimes as a particle and sometimes as a wave

Orbitals • In the wave-mechanical model the electrons are found not in fixed orbits around the nucleus but in ORBITALS. • ORBITALS are regions in which an electron of a particular amount of energy is most likely to be found.

Probability • The wave mechanical model describes the atom using PROBABILITY of finding electrons at different distances from the nucleus.

Quantum theory • In 1926 Erwin Schrodinger used the quantum theory to write an equation describing the location and energy of the electron in the atom of hydrogen.

The quantum model principles • • • Electrons are found in orbitals. There are different energy levels. Electrons can gain or lose fixed amounts of energy (quanta) to move to different energy levels. When the electrons occupy the lowest available orbitals the atom is in the ground state. If the atom absorbs a quantum of energy the electrons jump to a higher energy level. This UNSTABLE CONDITION is called EXCITED STATE. When the electrons return to the ground state they emit the same amount of energy they absorbed as LIGHT of different colors. The emitted light can be analyzed with a spectroscope and the resulting spectrum can be used to identify the atoms.

Energy levels • A space in which electrons are likely to be found. • Electrons whirl about the nucleus billions of times in one second • They are not moving around in random patterns. • Location of electrons depends upon how much energy the electron has.

Energy levels or shells • Electrons with the lowest energy are found in the energy level closest to the nucleus • Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

DECEMBER 5 • • Electromagnetic spectrum and color Quantum leap The modern atomic theory Vocabulary Quanta – quantum - orbitals Ground state – excited state wavelength – spectrum – spectra $ $$$$$ MONEY FOR REVIEW BOOK

Waves • Waves carry energy and have cycles. Each cycle of a wave begins at the origin and ends in the origin. • The wavelength (l lambda) of a wave is a measurement of how long it is. It is measured in length units. • The longer the wavelength, the smaller amount of energy that is associated with. • * Short wavelength high energy. • * Long wavelength low energy.

Waves Light consists of electromagnetic waves

How is Light Energy related to Color? • White light is made up of all colors of the spectrum (ROYGBIB) • When passed through a prism a continuous spectrum (rainbow effect) is obtained

Nature of light • Light is a form of electromagnetic wave. Each color of the visible light is associated with a different wavelength. • R (700 nm) • O • Y • G • B • I • V (400 nm)

Line Spectra If high voltage is applied to atoms in gas phase at low pressure light is emitted from the gas. If the light is analyzed with an SPECTROSCOPE the spectrum obtained is not continuous.

Line Spectra • This type of spectra is used to identify atoms of different elements and were used to explain the new model of the atom.

Bright line spectrum • When an atom ABSORBS energy, the electrons JUMP (LEAP) to a higher energy level. They are in the EXCITED STATE. • When the electrons return to the normal level (GROUND STATE) , they emit energy as LIGHT. The light emitted light produce the bright line spectrum that is characteristic of each element.

Electrons Surround the Nucleus • Electrons surround the nucleus and travel at the speed of light • They are found in only certain allowed energy levels or orbitals • Electrons are at the lowest energy level – the ground state.

Different Energy States are Possible • When the electrons in an atom become excited by absorbing energy from the surroundings, they jump to new higher energy levels. • The excited state is less stable than the lower energy state therefore the electron falls back or returns to the lower energy ground state.

Return to Ground State • When electrons fall back a wave with a specific amount of energy is emitted – called a photon. If we see color then the emission is in the visible range • We perceive this as unique colors associated with particular elements

Ground state configuration vs excited state configuration • 11 Na 2 -8 -1 This is the ground state. • If atom is excited some possible electron configuration would be • 2 -7 -2 or 1 -8 -2 or 1 -6 -3 • The number of electrons must add to the atomic number but the order is not the one that appears in the periodic table.

Indivisible Electron Greek X Dalton X Nucleus Thomson X Rutherford X X Bohr X X Wave X X Orbit Electron Cloud X X