Bonding Theory
Bonding is based on the difference in electronegativities of two atoms in a bond. Electronegativity is the tendency to gain electrons in a bond. This is dependent on the ability of the nucleus to pull on electrons.
General Patterns Element Electronegativity Result Metal Low Give Away Electrons Non-metals High Gain Electrons
Bonding is determined by comparing electronegativities and comparing the percent bond character.
Percent Bond Character: How the bond behaves – ionic or covalent a bond with 50/50 Bond character means that it behaves ionically 50% of the time and covalently 50% of the time.
1.67
The “half way” point is 1.67. This means the bond behaves like an ionic bond 50% of the time and a covalent bond 50% of the time. The greater the difference, the more ionic character The smaller the difference, the more covalent character
If the difference is greater than 1 If the difference is greater than 1.67 Ionic If the difference is less than 1.67 Covalent or Metallic
Above 1.67 means there is a greater difference and the atoms will bond ionically. The lower electronegativity atom will give its electrons to the higher electronegativity. Below 1.67 means the electrons will be shared because neither wants to give up electrons, unless the elements are metals.
EX: Bond of Oxygen and Magnesium Electronegativity Values O = 3 EX: Bond of Oxygen and Magnesium Electronegativity Values O = 3.44 Mg = 1.31 Difference = 2.13 Ionic
Bond of Oxygen and Nitrogen Electronegativity Values O = 3. 44 N = 3 Bond of Oxygen and Nitrogen Electronegativity Values O = 3.44 N = 3.04 Difference = 0.4 Covalent
Practice: Determine if the following are ionic or covalent K-Cl Ca-N Si-P Al-S Cu-Zn
Bond Strength and Characteristics Ionic Bond Strength: 1. Greater difference between the electronegativity values makes the bond stronger. Ex: Na–Cl = 2.23 K-Cl = 2.34 MORE IONIC CHARACTER Therefore K-Cl bond is stronger because the Chlorine pulls the electron toward it more than when it is bonded to Na. Resulting electrostatic force is stronger.
Bond Strength and Characteristics 2. Difference in charges Na-Cl: Na is +1 and Cl is -1 Mg-O: Mg is +2 and O is -2 Stronger attraction, stronger bond
Bond Strength and Characteristics Ionic Bond Characterisitics: Solid at room temperature Brittle as solids High melting point and boiling point Non-conductors as solids Conductors as liquids or dissolved in water
Bond Strength and Characteristics Covalent Bond Strength: Based on the number of shared electrons, NOT the difference in e-neg Single bond < Double bond < Triple Bond
Bond Strength and Characteristics Ex: Cl2, O2 and N2
Bond Strength and Characteristics Ex: Cl2, O2 and N2
Bond Strength and Characteristics Ex: Cl2, O2 and N2
Bond Strength and Characteristics Ex: Cl2, O2 and N2
Bond Strength and Characteristics Covalent Bond Characteristics: Can be solid, liquid or gas at room temperature. (Ex: sugar, water, CO2) Non-conductors in all states Typically low melting points and boiling points (some exceptions – diamonds) Solids usually brittle