95electrons in the same orbital have different rus values .docx
- 1. 95 electrons in the same orbital have different rus values (one is +Yz and another -%),they are said to be paired. Electron Configuration The energy of an electron in a hydrogen (H) atom is determined solely by its principal quantum number n. However for many-electron atoms the orbital energies depend on both the principal quantum number n andthe angular momenfum quantum number /. Thus the energy of the orbitals in a many-electron atom increases in the order: ls < 2s < 2p < 3s a 3p < 4s < 3d < 4p < 5s, and so on. This order is also the order of filling electrons into the orbitals in a many-electron atom. The guiding principle in assigning electrons to the orbitals in a many-electron atom contains a set of three ru1es called the Aufbau principle: 1. Lower-energy orbitals f,rll before higher-energy orbitals. 2. An atomic orbital can contain only two electrons, which must have opposite spins. (Pauli exclusion principle: no two electrons in an atom can have the same four quantum numbers.) 3 . When electrons are assigne d to p, d, or f orbitals, each successive electron enters a
- 2. different orbital of the subshell, each electron having the same spin as the previous one; this proceeds until the subshell is half-full, after which electrons pair in the orbitals one by one. (Hund's rule: the most stable arrangement of electrons in the subshell is that with the maximum number of unpaired electrons, all with the same spin.) Flame Test The resultant lowest-energy electron configuration is called the ground-state configrnation of the atom. The electrons in the atom's outermost shell are called valance electrons. When the atom absorbs enough energy, one or more of the valance electrons move to a higher energy orbital, and the atom is said to be in an excited state. The excited states are generally short-lived and rapidly decay back to the ground state by releasing radiant energy in the form of light. The energy and frequency of the light that is released during the decay transition depend on the difference in energy between the ground state and the excited state. The energy difference (AQ, the frequency (v), and the wavelength (2) of the light during emission are related by the equation, LE : hv: hclTwhere h ts Planck's constant and c is the speed of light. When the wavelengths of the light emitted fall in the visible region (400-800 nm), colors willbe observed. Atoms of certain elements emit light u'hen the elements or their compounds are heated in a gas flame.
- 3. The flame takes on a distinctive color detemined by the particular element (flame test). Each atom has its characteristic emission lines, therefore flame tests can be used to detect certain elements in unknown cornpounds. b!L q) Excited state LE: hv: hclT trl Ground state L I t I t t I D D t t D I t , t t
- 4. t t t I t t t t t t I I I 94 the energy of the electron increases, and the electron is farther away from the nucleus. A coliection of orbitals with the same n is called an electron shell. The value n alsolimits the values of the other two quanfum numbers. The Angular Momentum euantum Numb er, l: 0r lr2, ..., (n _ l) The angular momentum quantum number / defines the three- aimensional shape of the orbital' The electrons of a given shell can be grouped into subshells, which are designated by letters s, P, d, orf tathu than by number. For a given shell there are n different subshells or orbitals. For example, when fr:2, I cinbe 0 and 1. Therefore there are two subshells, s subshell (/:0) andp subshell (l: l).
- 5. The Magnetic Quantum Numb er, mt = J, (J* 1), ..., _1, 0, +1, ..., (t _ l), t The magnetic quantum number mr desqlbe. it. rputiul orientation of tle oiuitut in space. For an orbital whose angular quantum number is i, mr can have any integral value, including 0, between -l and 1 . Thus for a subshell of quantum number I, there are 2l + | different spatial orientations for those orbitals. For example, when l: l, mthas threevalues- -1, 0, and +l-implying that there are three typep orbitals: one with mt: _r, another with mr: 0, and a third with mr : i-L. In summary, the first quantum number (n) locates the electron in a particular shell and determines the energy, the distance from the nucleus, and the rarrge of possible shapes. The second quantum number (/) places the electron in a particular subshell or orbital within the shell and gives the shape of the orbital. The third quantum number (m) then specifies in which orbital within the subshell the electron is located. The relationship !tlyt:" the three quantum numbers and the orbital designation are summarized in the following table. Principal quantum Angular quantum Magnetic quantum Number Subshell n I number m 0 of orbitals 1 0
- 6. 1s 2 0 0 -1, 0, +1 I -) 2s 2p (p,, py, p,) J I a J 0 I 0 -1, 0, +1 -2, -1, 0, +7 , +2 5 3s 3p 3d (d*y, d),,, drr, drz-r-2, drz)
- 7. 2 Spin Quantum Numbat,, tns: +y2, -y2 To describe an electron in_ an atom completely, the spin quanfum number, ms, isneeded in conjunction with the other three quantum numberi. Thi spin quantum number can have either of two values: */z or -%. A spin of +Yzis usually represented by an up alrow(t), and a spin of -%is represented by u io*, alrow (it wh"" electrons have the same m' quantum number (both+% or both -Yz),they are said to have parallel spins. When 1 93 EPERIIIENT 9 prame Test, Atomic Structure and euantum Numtrers In this laboratory you will observe characteristic flame colors exhibited by certain :iT;'ffir}l#tJr:: leam the principles of atomic ,t*.tu.", electronic configuration, -{pparatus: Nichrome wire spiral, Bunsen burner chemicals: concentrated HCI(aq), 0.1 M Nacl, 0.1 M KCl, 0.1 M CaClz, 0.1 M SrClu, Safety Precautions: Handle concentrated hydrochloric acid carefully since it is verycomosive' causing damage upon any
- 8. contaci with the boJv, clothes or books. Avoid spills,splashes' and contact with .$1 a"v spills must u. r.rt uiiled with sodium carbonate. Ifany acid comes in contact with skin, immediately flood *lit *ut... Report any spill to1',our instructor immediately so it can be neutralized and cleaned up. wear safetyglasses/goggles to protect your eyes. An element is a form of matter,nrrlIffi?il"ort;1fl* ,r,,o simpler substances bychemical means' It is made of tiny particles called u,o-* gu.h atom is composed of threefundamental particres.posrtivery ct r.ged protons, ,"gatir.ry charged electrons, anduncharged neutrons' The dense tentrai rril.r* of an ortom contains protons and neukonswith electrons moving around the nucleus at arelatively large distance. The number ofprotons in the nucleus of an atom of an element is the uto*i. number (Z) of theelement.The sum of the number ofprotons and the number orr.ri.om in the nucleus is the massnumber (A) of the atom. Thus the number of neutrons ir, * uro- is equar to thedifference between the mass number and the atomic n*u"r, i.e., (A - Z).Forany neutralatom the number of electrons is equal to the number "ip.o,o"r. The identity of anelement is determined by the atomic number. Atoms wiih identical atomic numbers butdifferent mass numbers are called isotopes. An electron has both particle-like and wave-like properties. The energy of an electron inan atom is quantized' The behavior of each etect.oni, hya.og"., and other atoms can bedescribed by a wave equation. The solutions to the;;;;"rtion, called wave./unctionsor orbitals, predict the alowed energy states of an electr""';;;;;;; *iG *findingthat electron in a particular region oian atom. Each wave function has a set of threequanfum numbers: n, l, and mr.For the hydrogen atom, onry the first of these threenumbers is required to describe the energy of the electron, but all three are needed todefine the probability of finding the electron in a given region of space. The values of
- 9. allthree quanfum numbers are integers but cannot be selecteJrandomly. The Principal Quantum Numb er, n = 1,213,, ..., n The principal quantum number n determin. th" .r".gy of an electron and is also ameasure of the most probable distance of the electrorifrom the nu"l"us. es , i*..ur"., 96 PROCEDURE FOR FLAME TEST Nichrome Wire Clean-up Use the following procedure to clean the Nichrome wire before performing the flame test. Adjust the Bunsen flame to pure blue. Heat the wire to incandescence in the edge of the flame. At first you will observe a coloration of the flame; this is due to the presence of the metal ions on the surface of the wire. The coioration should disappear in a few seconds. If it does not, remove the wire from the flame, let it cool for about 5 seconds, and then dip the wire into a few milliliters of concentrated hydrochloric acid in a test tube Reheat the wire and repeat these steps until no color emanates from the wire. Flame Tests 1. Obtain seven (7) clean test tubes. 2. To each test tube add 1 mL of 0.1 M of solutions of NaCl, KCl, CaClz, SrClz, BaClz,
- 10. CuClz andZnClz. 3. Test each solution by dipping the cleaned Nichrome wire in the solution and then transferring it to the flame. 4. Record the flame color in your notebook. 5. Clean the wire thoroughly by following the wire clean-up procedures each time you change test solutions. WASTE DISPOSAL Solution s of NaCl, KCl, and CaClzz Flush down the sink with rururing water.