Presentation on theme: "Chapter 5 Electron Configurations. 3 questions not answered by Rutherfords theory of atom Why dont electrons fall toward nucleus because of attractions?"— Presentation transcript:
3 questions not answered by Rutherfords theory of atom Why dont electrons fall toward nucleus because of attractions? Why do elements act so differently? Cl,Ar,K Why do others act similarly? Na, K, Li
Early 1900s Scientists noticed Emitted light from elements in a flame. This light seemed to be related to their electrons. To understand, we must understand light itself better.
Wave Nature of Light Visible light (ROYGBIV) is small part of total EM spectrum. See p.120 All waves along EM have –Wavelength: trough to trough or peak to peak measured in nm. –Frequency: number of waves passing a pt./sec, #waves/sec or number s -1
–Amplitude: height of wave –Speed (c): wavelength x freq. –Speed of light anywhere on EM is 3.0 x 10 8 m/s –Wavelength or frequency may vary, but c doesnt. –GXUvIMR (gamma, xray, ultraviolet, visible, infrared, microwave, radio)
Particle Nature of Light Planck studied light emitted from hot objects. Concluded that light can only be emitted in small, specific amounts called QUANTA. A quantum is minimum amount of energy gained or lost by an atom. Partial quanta not possible. E=h x freq. (E energy, h= 6.626 x10 -34
Photoelectric effect was hard to explain. –When light of a certain freq. hit some metals, they caused e - to be ejected from metal surface. –This is particle behavior. –Einstein 1 st recognized this as such. –Said light can be thought of as stream of photons that carry quanta.
Atomic Emission Spectrum When elements are heated or given an elect. Source, their e - are pushed up to higher levels (excited states) temporarily. E - cannot stay there long, and fall back to original levels. As they fall, they give off wavelengths of light. Each element has a diff. set it can emit. See p126 Like a fingerprint for element-unique set.
Quantum Theory Niels Bohr, Danish, 1913 Suggested that e - move around nucleus in certain allowed orbitals only.(Diagram) Did his work on spectra using H. His explanations worked for H, but not for other elements. Vis. Spectrum occurred when e - fell from other excited levels to 2 nd level. Levels not equidistant from each other.(dia)
Quantum Mechanics deBroglie (1924) proposed different idea Perhaps particles (e - ) were acting like waves. (Einstein already said they act like particles.) He developed eqn. for wlength of particle using E=h x freq. This is only true for very small particles like e -
Heisenberg Developed the uncertainty principle impossible to know position and velocity of particle at same time. Schrodinger developed concept of atomic orbitals. An orbital is a 3D space where an e - can be found 90% of time.
Organization of Electrons Levels-sublevels-orbitals-electrons A level is similar to Bohrs orbits and correspond to principal quantum number. Level is the general distance from the nucleus. –1 st level: 1 st shell, closest to nucleus –2 nd level: 2 nd shell, 2 nd from nucleus, etc.
Levels have sublevels. Sublevels have orbitals. Orbitals have e -. 4 types of sublevels: –S sublevel (one in every level), contains 1 spherically shaped orbital. –P sublevel (one in every level starting w/ 2nd), contains 3 dumbbell shaped orbitals. –D sublevel (one in every level starting w/3 rd ), contains 5 complex shaped orbitals.
–F sublevels are in every level starting with 4 th level. Each contains 7 orbitals. –Each orbital can hold 2 electrons that spin in opposite directions. –Therefore, s sublevel holds up to 2 e -. –P sublevel holds up to 6 e - –D sublevel up to 10, and F up to 14e -.
See rest of notes on e - configurations. Arrow notation E configuration Noble gas config.
Valence electrons Those e - in outermost level. In Ca, 4s 2, 2e - In Si, 3s 2 3p 2 : 4 valence e - In Al, 3s 2 3p 1: 3 valence e - These are very important e - because they are involved in chem. Bonding.
Lewis dot structures A symbolic representation of an atom where the symbol represents the nucleus and all filled levels. The valence e - are represented with dots. Place one at a time on 4 sides of the symbol. Pair up until used up. Usually does not exceed 8.