Chemical bonding electronegativity


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Chemical bonding electronegativity

  1. 1. Chemical Bonding <ul><li>So far we have dealt with isolated atoms and their electronic properties.   </li></ul><ul><li>Many chemists are interested in molecules and compounds.   </li></ul><ul><li>All the tremendous variety of materials found in our physical world may be interpreted and understood as a combination of about 100 elements. </li></ul>
  2. 2. Chemical Bonds <ul><li>A chemical bond is the glue which holds two or more atoms together to make molecules and ionic substances. </li></ul><ul><li>When atoms interact to form a chemical bond, only their outermost regions are in contact. </li></ul><ul><li>Usually, only the outermost (valence) electrons are involved in bonding. Some transition metals are exceptions to this rule. </li></ul>
  3. 3. Properties of Ionic and Covalent Compounds <ul><li>Property </li></ul><ul><li>state at room temperature </li></ul><ul><li>melting point </li></ul><ul><li>electrical conductivity as a liquid/solution </li></ul><ul><li>solubility in water </li></ul><ul><li>Ionic Compounds </li></ul><ul><li>solid </li></ul><ul><li>high </li></ul><ul><li>yes </li></ul><ul><li>most are very soluble </li></ul>Covalent Compounds solid, liquid or gas low no most are not very soluble
  4. 4. Types of Bonds <ul><li>Covalent bond - a chemical bond formed by the sharing of a pair of electrons between atoms.   </li></ul><ul><li>Polar bond – a chemical bond formed when electrons are shared between atoms, but the electrons spend more time around one atom than another.   </li></ul><ul><li>Ionic bond - formed by the attraction between positive and negative ions - it is electrostatic in nature. </li></ul><ul><li>Bonding type is a continuum from covalent to polar covalent to ionic . </li></ul>
  5. 5. Electronegativity <ul><li>Electronegativity is a measure of how strongly an atom attracts the bonding electrons in a chemical bond. The higher the electronegativity, the stronger an atom's attraction for bonding electrons. </li></ul>
  6. 6. Electronegativity and Bond Type <ul><li>The difference in electronegativity determines the type of bond between two atoms. It is a continuous scale. </li></ul><ul><li>Subtract the electronegativity of one atom from the electronegativity of the other (no negative numbers). </li></ul>0 0.5 1.7 3.3 covalent polar covalent ionic H 2 CH 4 H 2 O NaCl F 2
  7. 7. THE IONIC BOND <ul><li>Ionic compounds are held together, for the most part, by strong electrostatic forces between oppositely charged species. </li></ul><ul><li>Ions are formed through the transfer of electrons from one atom to another. </li></ul><ul><li>Electrons are given by metal atoms to nonmetal atoms. The metal atom forms a cation, the nonmetal an anion. </li></ul>
  8. 8. COVALENT BONDS <ul><li>Covalent bonds are formed when 2 atoms share one or more pairs of electrons </li></ul><ul><li>In general, covalent bonds are formed between nonmetal atoms. </li></ul><ul><li>Hydrogen gas H 2 is the simplest molecule. The two electrons are shared equally between the two atoms, because they are pulling on the electrons with the equal strength (electronegativity). </li></ul><ul><li>CH 4 is also considered covalent, and the carbon shares its electrons with all four hydrogens. </li></ul>
  9. 9. Polar Covalent Bonds <ul><li>A polar covalent bond is a covalent bond in which the electrons are shared, but spend more time in the vicinity of one of the atoms than another. </li></ul><ul><li>e.g. in HCl the two bonding electrons spend more time in the vicinity of the Cl atom than the H atom. </li></ul><ul><li>The arrow indicates the direction of the ‘dipole moment’ or ‘partial negative charge’ in the direction of the chlorine atom </li></ul><ul><li>Water is the most important polar molecule of all for life. </li></ul>