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Unformatted text preview: 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:- 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 IEs 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 childs 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 - Its 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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