Lecture 2: Chemical Bonds/Water

Covalent Bonds

(strongest bond)

• Polar: unequal sharing of electrons

• Non-polar: equal sharing of electrons

ex: H₂ (H-H) ; single, non-polar

O₂ (O=O) ; double, non-polar

H₂O ; single, polar

Ionic Bonds

(weaker bond) electrons are shared more unequally, towards one atom

• result from the attraction between oppositely charged ions.

• often called “salts”

Hydrogen Bonds

(weak bond) a type of attraction between a partially positive hydrogen atom and a partially negative atom

• F.O.N (fluorine, oxygen, nitrogen)

Van der Waals Forces

(very weak interactions) attractions between molecules due to temporary dipoles.

ex: tiny sticky forces —> how geckos stick to walls

Electronegativity

more electronegative atom = partially negative

less electronegative atom = partially positive

Cations

positively charged ions

Anions

negatively charged ions

Ionic compounds can be a combination of…

• 1 cation + 1 anion

• multiple cations and anions

• ionic bonds between molecules

Cohesive Behavior

hydrogen bonds in water give it adhesive + cohesive properties

• adhesive: attraction forces between DIFFERENT molecules

• cohesion: attraction forces between SAME molecules

Ability to stabilize temperatures

water has high specific heat (requires more energy to heat up)

Expansion upon freezing

density of liquid > density of ice

• this does NOT allow large bodies of water to freeze all the way to the bottom, preserving life.

Water is a versatile solvent

Polar bonds in water make it an active solvent, able to dissolve many substances

• hydrophobic: substances that dissolve in water

  • usually have ionic or polar bonds

• hydrophilic: substances that do NOT dissolve in water

  • usually have non-polar bonds (i.e oils, fats)