Lecture 3

Lecture 3 - 2.5 Electron Arrangement and the ...

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Unformatted text preview: 2.5 Electron Arrangement and the Periodic Table The Quantum Mechanical Atom Principal Energy Levels, Sublevels, and Orbitals Electron ConfiguraAons Guidelines for WriAng Electron ConfiguraAons Electron ConfiguraAons and the Periodic Table 2.6 Valence Electrons and the Octet Rule Valence Electrons The Octet Rule Shorthand Electron ConfiguraAons Ions Ion FormaAon and the Octet Rule 2.7 Trends in the Periodic Table Atomic Size Ion Size IonizaAon Energy Electron Affinity Element: electronic structure and its position in the periodic table •  Electron configuration - the arrangement of electrons in atoms •  Valence electrons - outermost electrons, involved in chemical bonding Electron configuration determines position in periodic table Electron configuration determines chemical properties The Quantum Mechanical Atom •  Bohr’s model: only good for Hydrogen atom, position of electron too specific (principle energy level), only considered particle nature •  Schröedinger theory (quantum mechanics): consider wavelike nature of the electrons; probability rather than a fixed position Bohr’s Model for H atom Quantum mechanics model and Schröedinger equaAons Quantum mechanics: develop equations to determine the probability of finding an electron in a specific region in space, expressed by (i) Principal energy levels (n = 1,2,3…) (as Bohr did), (ii) Each level has one or more sublevels or subshells (s, p, d, f), (iii) each sublevel contains one or more atomic orbitals Schrodinger equation ⎡ྎ ⎤ྏ h 2 ⎛ྎ d 2 d 2 d 2 ⎞ྏ − 2 ⎜ྎ 2 + 2 + 2 ⎟ྏ + V (x, y, z )⎥ྏ ψ (x, y, z ) = Eψ (x, y, z ) ⎢ྎ ⎜ྎ dz ⎟ྏ ⎠ྏ ⎣ྏ 8π me ⎝ྎ dx dy ⎦ྏ Hψ = Eψ E: energy of the atom me: mass of electron ψ: wave function ψ2: probability density H: Hamiltonian operator Erwin Schrodinger, 1887-1961, 1933n "for the discovery of new productive forms of atomic theory" Principal Energy Levels, Sublevels, and Orbitals Principal Energy Levels: related to the average distance from the nucleus, ①  ②  ③  ④  denoted by n value, n = 1 level is closest to the nucleus; n = 1, 2, 3, … at each principal energy level can hold maximally 2(n)2 electrons n value is proporAonal to the energy and distance from the nucleus, the number of sublevels in a principal energy level equals to n n = 1 2(1)2 maximally 2e− n = 2 2(2)2 maximally 8e− n = 3 2(3)2 maximally 18e− Sublevel (Subshells): a set of energy- equal orbitals within a principal energy level Increase in energy: s < p < d < f Use principal level and sublevel to denote the locaAon of an electron, 1s, 2s, 2p,… Electrons in 3d have more energy than electrons in the 3p Sublevels in Each principal Energy Level Principle energy level (n) Possible subshells 1 1s 2 2s, 2p 3 3s, 3p, 3d 4 4s, 4p, 4d, 4f Orbitals Atomic Orbital – a specific region of a sublevel, maximally two electrons Orbitals are named by principal energy level + sublevel: 1s, 2s, 3s, 2p, etc. Each type of orbital has a characterisAc shape s : spherically symmetrical p : a shape much like a dumbbell S orbitals three p orbitals p d Principal energy level, subshells, orbitals principal energy level subshells orbitals 1 s 1s 2 s, p 2s, 2px, 2py, 2pz 3 s, p, d 3s, 3px, 3py, 3pz, 3dxy, 3dyz, 3dzx, 3dx2- y2, 3dz2, 4 s, p, d, f subshell # orbitals Max # electrons s 1 2 p 3 6 d 5 10 f 7 14 Electron spin Electron ConfiguraAon Electron ConfiguraDon - the arrangement of electrons in atomic orbitals. AuEau Principle - or building up principle of electron configuraAon electrons fill the lowest- energy orbital available (s < p < d <f ) Pauli Exclusion Principle – each orbital can hold up to two electrons with their spins in opposite direcAons. Hund’s Rule – each orbital in a subshell is half- filled (with one electron) and prior to filling the orbitals (with two electrons.) Fill the oritals according to the order given in the figure. IllustraDng Orbital Occupancies The electron configuraAon # n of electrons in the sublevel l as s,p,d,f 1s2 2 p4 The orbital diagram (box or circle) Orbital diagrams show orbitals as boxes and electrons as arrows. Rules for WriAng Electron ConfiguraAons ①  ②  ③  ④  ⑤  ⑥  ⑦  total number of electrons in the atom from the atomic number. Electrons occupy the lowest energy orbitals available, beginning with 1s. Each principal energy level, n contains only n sublevels. Each sublevel is composed of one or more orbitals (one s, three p, five d). No more than 2 electrons in any orbital, the two are paired. Maximum number of electrons in any principal energy level is 2(n)2. Fill orbitals from lowest to highest energy. H 1s1 1s 1s2 1s Li 1s2 2s1 1s 2s Practce Give te complet electon configuraton of each element –  Be –  N –  Na –  Cl –  Ag Which element has te folowing electonic configuraton? Electron ConfiguraAon and the Periodic Table. Valence Electrons – outer most electrons in an atom. The electrons involved in bonding. The noble gases are extremely stable (octet electrons) Called inert as they don’t readily bond to other elements Stable electron configuraAon is called the “noble gas” configuraAon Octet Rule – elements react to arain the the noble gas configuraAon Atoms will gain, lose or share electrons in chemical reacAons to arain octet Elements in families other than the noble gases are more reacAve Strive to achieve a more stable electron configuraAon Change the number of electrons in the atom to result in full s and p sublevels Shorthand Electron ConfiguraAons Uses noble gas symbols to represent the inner shell and the outer shell or valance shell is wriren aver Aluminum- full electron configuraAon is: 1s22s22p63s23p1 What noble gas configuraAon is this? Neon ConfiguraAon is wriren: [Ne]3s23p1 Practce Writ te shortand electon configuratons •  N •  S •  Ti •  Sn Ions Ions – atom gain or loss of one or more electrons CaDon - posiAvely charged, result from the loss of electrons 23Na à༎ 23Na+ + 1e- Anion - negaAvely charged, results from the gain of electrons 19F + 1 e- à༎ 19F- Ion FormaAon and the Octet Rule Metallic elements tend to form posiAvely charged ions (caDons) by losing all their valence electrons to obtain a configuraAon of the noble gas Na Sodium atom Na 11e- , 1 valence e- [Ne]3s1 Na+ + e- Sodium ion Na+ 10e- [Ne] Ion FormaAon and the Octet Rule All atoms of the same group lose the same number of electrons ResulAng ion has the same number of electrons as the noble gas atom Al3+ + 3e- Al Aluminum ion Aluminum atom 10e- 13e- , 3 valence e- [Ne] [Ne]3s23p1 TransiAon metals oven form more than one stable ion Fe2+ and Fe3+ is a common example Fe [Ar]4s23d6 Fe2+ [Ar]4s13d5 Fe3+ [Ar]4s03d5 Isoelectronic – ionic or atomic species have the same number of electrons. F 1s22s22p5 F-1 1s22s22p6 F-1 is isoelectronic with Ne Practce Give te charge of te most probable ion resultng fom tese elements Ca Sr S P Which of te folowing pairs of atms and ions are isoelectonic? Cl- , Ar Na+, Ne Mg2+, Na+ O2- , F- How many protns, neutons and electons are in te folowing ions? 32 239 + 19 K 16 S 24 12 Mg 2+ Many atomic properAes correlate with electronic structure and so also with their posiAon in the periodic table: atomic size, ion size, ionizaAon energy, electron affinity Atomic Size The size of an element increases moving down from top to borom of a group The size of an element decreases from lev to right across a period CaAon Size ①  ②  ③  ④  CaAons are smaller than their parent atom More protons than electrons creates an increased nuclear charge Extra protons pulls the remaining electrons closer to the nucleus Ions with mulAple posiAve charges are even smaller than the corresponding monoposiAve ions Which would be smaler, Fe2+ or Fe3+? ⑤  When a caAon is formed isoelectronic with a noble gas the valence shell is lost decreasing the diameter of the ion relaAve to the parent atom Anion Size ①  Anions are larger than their parent atom. ②  Anions have more electrons than protons ③  Excess negaAve charge reduces the pull of the nucleus on each individual electron ④  Ions with mulAple negaAve charges are even larger than the corresponding monoposiAve ions RelaAve Size of Select Ions and Their Parent Atoms IonizaAon Energy IonizaDon energy - The energy required to remove an electron from an isolated atom The magnitude of ionizaAon energy correlates with the strength of the arracAve force between the nucleus and the outermost electron The lower the ionizaAon energy, the easier it is to form a caAon ionizaAon energy + Na à༎ Na+ + e- Electron Affinity Electron Affinity - The energy released when a single electron is added to an isolated atom Electron affinity gives informaAon about the ease of anion formaAon Large electron affinity indicates an atom becomes more stable as it forms an anion Br + e- à༎ Br- + energy IonizaAon energy decreases down a group as the outermost electrons are farther from the nucleus IonizaAon energy increases across a period because the outermost electrons are more Aghtly held Electron affinity generally decreases down a group Electron affinity generally increases across a period Practce Rank Be, N, and F in order of increasing atmic size ionizaton energy electon affinit Rank Cl, Br, I, and F in order of increasing atmic size ionizaton energy electon affinit ...
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