Lecture on Electronegativity and Bonding

Covalent Bonds and Electronegativity

• Atoms in a covalent bond do not always equally share electrons.
• Differences in electronegativity, the ability to attract electrons, affect electron sharing.

Example: Chlorine and Sodium

• Chlorine
  • Higher electronegativity.
  • Strips an electron from sodium's outer shell.
• Sodium
  • Lower electronegativity.
  • Readily surrenders an electron to chlorine.

Electronegativity in Water Molecules

• Water is composed of two hydrogen atoms and one oxygen atom.
• Oxygen
  • Higher electronegativity than hydrogen.
  • Electrons in the covalent bond spend more time near oxygen.
  • Oxygen atom takes on a slightly negative charge.
• Hydrogen
  • Becomes slightly positive.

Polar Covalent Bonds

• Bonds between oxygen and hydrogen become polar due to unequal electron sharing.
• Polar Definition: Atoms on either side of the bond have partial and opposite charges.

Water Molecule Interactions

• In an environment with other water molecules:
  • Molecules orient so the negative end of one molecule is opposite the positive end of another.
  • This orientation forms a weak attractive force known as a hydrogen bond.

Hydrogen Bonds in Water

• Abundant in water, with each molecule able to engage in up to four hydrogen bonds.
• Weaker than covalent bonds.
• Tend to be temporary, constantly breaking and reforming.

Importance of Hydrogen Bonds

• The large number of hydrogen bonds and their temporary nature give water its unique properties.
• Essential for water's role as the basis for life on Earth.