1ACh8 - Chapter 8 - Basic Concepts of Chemical Bonding...

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Chapter 8 - Basic Concepts of Chemical Bonding Types of Chemical Bonds Chemical bonds can be described with a variety of properties; this includes bond energy, bond length, Bond Energy The energy required to break a bond. Bond Length The distance between the nuclei of the bonding atoms. This distance where energy is a minimum between nucleus-nucleus repulsion, electron-electron repulsion, and electron- nucleus attraction. Octet Rule Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons. This consists of a full s and p sublevels. Atoms near Helium will attain only 2 valence electrons, a full s sublevel. Lewis Symbols A Lewis symbol shows the symbol of an atom or atoms in a compound with dots representing each valence electron. For a single atom, there is a maximum of eight dots around the atom, and we limit the representation to a maximum of two dots per side (top, bottom, left, right) Ionic Bonding The electrostatic attraction of closely packed, oppositely charged ions (typical between metals and nonmetals) Covalent Bond Exist where electrons are shared between nuclei (typical between nonmetal atoms) The electron density is located primarily between the two nuclei Metallic Bonds Metallic bonds consist of atoms bonded to several neighboring atoms with the electrons free to move among the 3-dimensional structure of the atoms.
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Ionic Bonds Ionic Compound A compound formed from a positive cation and a negative anion. A metal reacts with nonmetal forms an ionic compound. Ionic compounds are often brittle, crystalline (highly structured forming flat surfaces and clear edges), high melting points and high boiling points. Lattice Energy The strength of the ionic bonding of a solid ionic compound is given by the lattice energy, which is the energy required to completely separate a mole of an ionic solid into its gaseous ions. MX(s) M + (g) + X - (g) This energy value will be positive since the process is an endothermic process. All binary ionic compounds formed by an alkali metal and a halogen (except for cesium salts) have the same structure as sodium chloride where each atom is surrounded by six ions of the opposite charge. Lattice Energy Calculations Lattice energy can be represented by a modified form of Coulomb's law: Lattice energy = k(Q 1 Q 2 /r) where k depends on the structure of the solid and the electron configurations of the ions, r is the distance between ion centers; and Q 1 and Q 2 are the numerical ion charges The lattice energy increases as the charges on the ions increase and as the radii decrease. Since energy is a state function, this energy value can be calculated from a series of other reaction steps. Lattice energy is equal to the sum of the energy of formation of the ionic compound
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This note was uploaded on 04/17/2008 for the course CHEM 1 taught by Professor Evans during the Fall '06 term at UC Irvine.

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1ACh8 - Chapter 8 - Basic Concepts of Chemical Bonding...

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