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Sesion#05PERIODIC TABLE Irma Jurusan Kimia FakultasMatematikadanIlmuPengetehuanAlam

Indikator Menjelaskan Konsep Penyusunan Unsur menurut Lavoiser, Dalton, Dobereiner, Newland, Chancourtuis, Meyer, Mendeleev, dan Moseley (Sistem Periodik Modern) Menjelaskan Sifat Logam, Jari-jari atom, Jari-jari ion, Afinitas Elektron,Keelektronegatifan serta sifat-sifat Magnetik unsur 06/01/2011 3 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Trends in Some Periodic Properties The physical and chemical behavior of the elements is based on the electron configurations of their atoms. e- configurations can be used to explain many of the repeating or “periodic” properties of the elements. Chemists developed the Periodic Table to help organize and classify the elements. 06/01/2011 4 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Lavoisier created a table for 33 elements

Classified as gases, nonmetals, metals, and earths,[object Object]

John Dalton, 1803 Dalton’s atomic theory : 1) All Atoms of any one element are exactly alike in all aspects; in particular, same weight. 2) Atoms of different elements have different properties; in particular, different weight. 3) A compound, as distinguished from an element is composed of a certain definite integral number of atoms of each of the elements present. 4) In the chemical reactions that may occur, none of the atoms are destroyed and no new ones are created. 06/01/2011 10 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

J.W. Dobereiner, 1800 Observed elements could be classified into sets of three, called Triads Ex. Li, Na, K Ex. Ca, Sr, Ba Cl, Br, I Elements within a triad have similar chemical properties. In each triad, the properties of the middle element are close to the averages of the properties of the 1st and 3rd element. 06/01/2011 14 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

J.A.R Newlands, 1865 By this time, 62 elements were known. He observed that when elements were arranged in order of increasing atomic mass, the properties of the 8th element were like he 1st, 9th Law of Octaves To Newlands, Li to Na is an octave of eight elements. 06/01/2011 16 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

We say Li to Ne is a period of eight elements, and that that Li and Na are in different periods. Indeed, the Li to Na series consists of nine elements. 06/01/2011 18 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Dmitri Mendeleev, 1871 ,[object Object]

H.G.J. Moseley, 1914 Henry Moseley (1887-1915) subjected known elements to x-rays and was able to derive a relationship between x-ray frequency and number of protons. 06/01/2011 27 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Electron Shells and Sizes of Atoms Atoms are not hard shells, Radii are often measured by assuming atoms touch each other when bonded and then considering bond distances. Because covalently bonded atoms overlap orbitals, and other bonding types do not. Measured radii are specified to be metallic, or covalent. Atomic radii of a particular element can vary somewhat from substance to substance. I2 has a bond length of 2.66Å so each I atom has a radius of 1.33Å Bond lengths can conversely be estimated by adding atomic radii. 06/01/2011 29 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Electron Shells and Sizes of Atoms Size in main group elements follow 2 general rules 1. Atomic Radii increases going down in a group 2. Atomic Radii decreases going left to right in a period Moving down in a group: Zeff is constant because Z and S increase equally Electrons in a higher n and therefore larger Moving across: Z increases and S does not (electrons in same shell don't shield each other well) so e- attracted more strongly and are closer/smaller In transition metals there is an initial decrease in size but then remains relatively constant 06/01/2011 30 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Because electrons are added farther from the nucleus, there is less attraction.

Ionization Energy energy required to remove an electron from 1 mole of the element (to make it positive or more positive) always positive value i.e. endothermic First ionization energy IE1– to remove 1st e- Elements with small IE1 tend to form cations, large IE1 anions 06/01/2011 38 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Mg (g) + 735 kJ -> Mg+ (g) + e- Mg+ (g) + 1451 kJ -> Mg2+ (g) + e- Ionization Energy Mg2+ (g) + 7733 kJ -> Mg3+ (g) + e- Energy cost is very high to dip into a shell of lower n. 06/01/2011 39 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Ionization Energy Trends: Generally as size decreases, IE1 increases. 1. IE1 generally increases from left to right, some exceptions 2. IE1 generally decreases going down in a group 3. transition and f-block elements have much smaller variances in IE1 But Why? Across - increasing Zeff and smaller size(e- closer to nucleus) exceptions - Be to B because s shields p and lowers Zeff N to O because repulsions in first paired electron Down - Zeff constant and larger so easier to ionize 06/01/2011 40 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Ionization Energy Second ionization energy IE2 – to remove 2nd e- Always larger than IE1 as e- are removed, Z remains constant and remaining e- are harder to remove A huge increases occurs in ionization energies when core electrons are reached because of the lower shielding/higher Zeff. Result - Rx only involve outer e- 06/01/2011 41 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Trends in Ionization Energy IE increases across a period because Z* increases. Metals lose electrons more easily than nonmetals. Metals are good reducing agents. Nonmetals lose electrons with difficulty. 06/01/2011 42 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Ionic Size Cations are smaller than the parent atom Anions are larger than the parent atom. Ionic size increase down in a group In an isoelectronic series, the most negative ion is largest, the most positive is smallest. Atoms making more than one ion, most positive is smallest. 06/01/2011 47 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

The electron/proton attraction has gone UP and so size DECREASES. + + Li , 78 pm 2e and 3 p Ionic Size Forming a cation. Li,152 pm 3e and 3p 06/01/2011 48 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

- - F, 71 pm F , 133 pm 9e and 9p 10 e and 9 p Ionic Size ,[object Object]

The electron/proton attraction has gone DOWN and so size INCREASES.

Electron Affinities energy required to put an e- on an atom (making it negative or more negative) EA1 usually negative EA2 always positive Irregular trend: increases going right and up Remember: Full shells best, full subshells good, and half full is kinda cool Cl and other halogens need only 1 e- so most exothermic reaction noble gases have endo because new electron in higher n Mg, Be endo because new e in higher l N endo because new e paired 06/01/2011 53 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Electron Affinity A few elements GAIN electrons to form anions. Electron affinity is the energy change when an electron is added: A(g) + e- -> A-(g) E.A. = ∆E 06/01/2011 54 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Electron Affinity of Oxygen ∆E is EXOthermic because O has an affinity for an e-.      -  [He] O ion + electron       [He] O atom EA = - 141 kJ 06/01/2011 55 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Electron Affinity of Nitrogen ∆E is zero for N- due to electron-electron repulsions.      [He] N atom + electron   N- ion    [He] EA = 0 kJ 06/01/2011 56 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Trends in Electron Affinity ,[object Object]

Metallic Behavior Metallic behavior increases left and down Metals tend to lose electrons in reactions because they have lower IE. Highly metallic elements, are likely to make positive ions Least metallic elements are likely to make negative ions In middle are more likely to make covalent bonds 06/01/2011 62 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

Metallic Behavior The highly metallic oxides make bases in water Least metallic oxides make acids in water Some in between are amphoteric in water Amphoteric – can act as acids and bases. 06/01/2011 63 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

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