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chapter_07au_1 - Chapter 7 Periodic Properties of the...

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Periodic Properties of the Elements Chapter 7 Periodic Properties of the Elements
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Periodic Properties of the Elements Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical, however.
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Periodic Properties of the Elements Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped. eRn Rt ePb e=eka
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Periodic Properties of the Elements Development of Periodic Table Mendeleev, for instance, predicted the discovery of germanium (which he called eka- silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.
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Periodic Properties of the Elements Periodic Trends In this chapter, we will rationalize observed trends in Effective nuclear charge felt by valence e. Sizes of atoms and ions. Ionization energy. Electron affinity.
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Periodic Properties of the Elements Effective nuclear charge The amount of positive charge “felt” by outer electrons in atoms other than hydrogen is called the effective nuclear charge It is lower than the atomic number because of shielding Movie If the 2- charge of the 1 s 2 core of lithium were 100% effective at shielding the 2 s electron from the nucleus, the valence electron would “see” a charge of +1. Actually little larger
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Periodic Properties of the Elements Example of Na The effective nuclear charge, Z eff = Z S Z is the atomic number. S is a screening constant, usually close to the number of inner (core) electrons (closer in than those considered) . Screening never complete 1s 2s 2p 11 9 >7 >1 Note: Orbital rad. Inc. with n
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Periodic Properties of the Elements Trends in effective nuclear charge Periodic Table Inc. (Z inc. faster than s) O r b i t a l s h e 1s 2s 3s 4s 5s Z eff = Z S
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Periodic Properties of the Elements Sizes of Atoms The bonding atomic radius is defined as one- half of the distance between covalently bonded nuclei.
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Periodic Properties of the Elements Effective nuclear charge controls sizes of Atoms Bonding atomic radius tends to… …decrease from left to right across a row due to increasing Z eff . …increase from top to bottom of a column due to increasing value of n Movie
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Periodic Properties of the Elements Effective of adding and removing e: Positive ions are always smaller than the atoms from which they are formed Negative ions always larger than the atoms from which they are formed Movie Adding electrons leads to an increase in size of a particle, as illustrated for fluorine. Removing electrons decreases the size of the particle, as shown for lithium and iron.
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Properties of the Elements Sizes of Ions (down a column) Ions increase in size as you go down a column. Due to increasing
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chapter_07au_1 - Chapter 7 Periodic Properties of the...

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