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Chemistry Lecture Notes

Chemistry Lecture Notes - Law of constant composition Ex...

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09/27/07 Law of constant composition Ex) water: H20 =2H +O Law of conservation of mass(matter)  : allows us to explain many chemical  reactions. (Atoms can neither be created nor be destroyed) Ex) 2HgO +  Heat   2 Hg(l) +  O2 (g); 100g   100g Law of conservation of energy: Matter/energy can neither be created nor be  destryoed, but rather, they are transformed into other forms of structures. 10/02/07 - Bonding occurs because sum is lower in E than isolated atom. - Atoms tend to be stable and to spend minimum energy level - Gain/lose of energy is the reason that bond forms and reactions occur. - Energy is the reason bonding and reactions occur; usually products are  lower in energy than reactants Bonding (Stoichiometric relationship) Classical description of bonding - Bonding is the glue that holds different atoms together; it involves one  of two types of things - Electrostatics ( +/-) charge differentials - Sharing of electrons - Bonding helps us to explain chemical reactivity & chemical formulas Classical bonding motifs - Pure Ionic ( +/-) =  electrostatics - Covalent (Sharing e-) electrons do not have to be shared equally. (Dots  for unattached electrons, lines for attaches ones) - Metallic  (ex) Au: Metal cations are surrounded by flowing e-s  (Molecular orbital theory)  Picture:
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- Coordinate covalent (ex) NH4+BF3 in this reaction process, electrons are conditionally shared. It has characteristics of both ionic and - Polar covalent consists of covalent and ionic characteristics. o More covalent a bond is, more dipole moment, and less polarization of molecules. - Most of the bonds are neither pure covalent, nor pure ionic, but rather, they are having both characteristics. - When the system breaks apart, it breaks a part only in one way. Electrons - Core electrons (2): that are preserved for balance of atoms - Valence electrons (8): that are responsible for bondings. Ionization energy (IE): Amount of energy to required to remove an electron from a gaseous neutral atom states; ∆E is positive if E must be added. - If E is given all IE’s are always positive because it takes E to remove an electron. IE is always less then IE 2 . - We are removing e -  from an atom so IE 2  is much more positive then IE.  o Ex) A child’s handful candies IE<IE 2 < < <IE 3 - In order to remove an electron from an atom whose valence electron has 2, 10, 18, 32, the core configuration requires very very high - It’s difficult to remove electrons ↗ (IE increases ↗) - IE is always  positive because we have to add energy to remove e - s - ∆E is positive if energy is added, and ∆E is negative when energy is given off - In parallel metallic character, metals have low IE, but non-metals have very high IE.
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