AP BIOLOGY UNIT 1 : CHEMISTRY OF LIFE NOTES
1.1 - Structure of water and hydrogen bonding
Types of bonds
- Ionic bonds : bond formed by the loss or gain of electrons between
metals and nonmetals ex NaCl
- Covalent bonds : bond formed by the sharing of electrons between
nonmetals ex O2
- Polar covalent bonds : covalent bonds that involve unequal sharing of
electrons due to an atom bonding to a more electronegative atom.
They form partial charges ex H2O
- Non-Polar covalent bonds : covalent bonds that involve equal sharing
of electrons ex O2
- Types of electron sharing : Single (pair of e), Double (2 pairs of e),
Triple (3 pairs of e)
- Hydrogen bonds : when a hydrogen atom bonds covalently with an
atom carrying partial negative charge (N,O,F)
- Electronegativity : Tendency of an atom to pull on its shared electron
in a covalent bond
- Weakest bond is the hydrogen bond and the strongest bond is the
ionic bond
Water molecules are composed of 1 oxygen atom and two hydrogen atoms
covalently bonded to each other WITHIN the molecule
When a water molecule bonds to ANOTHER WATER MOLECULE its a
hydrogen bond (hydrogen bonds with the oxygen of another molecule)
, Oxygen is more electronegative than hydrogen so it has a negative partial
charge and hydrogen is less electronegative than oxygen so it leaves a
partial positive charge
Oxygen has 2 lone pairs of electrons and the electrons are repelling
strongly from each other which creates the water’s bent structure
Properties of water molecules
- Cohesion
- Adhesion
- Universal solvent
- Surface tension
- Less dense when solid
- Evaporative cooling
- Temperature control
Water forms hydrogen bonds between water molecules, so water
requires more energy to evaporate than molecules that do not form
hydrogen bonds.
1 - Cohesion : when two water molecules are attracted to each other and
stick together due to hydrogen bonding
2 - Adhesion : when a water molecule is attracted to another molecule due
to hydrogen bonding, it determines its ability to stick to other surfaces.
- Together, it leads to capillary action, when the water molecules go
against gravity forces due to adhesion and cohesion properties.
Cohesion helps water molecules to move up in one form
- to move upward without going down is related to adhesion sticking to
the cell walls of the xylem
- Vascular Bundles consist of xylem (transports water and dissolved
mineral salts) and phloem (transports sugars and other stuff
produced by photosynthesis), water moves in the plant due to
adhesion, cohesion and capillary action
3 - Universal solvent : hydrogen bonds constantly break and reform in its
liquid state so this allows water to create new bonds with the substances
dissolved in it (polar/ionic bonds)
1.1 - Structure of water and hydrogen bonding
Types of bonds
- Ionic bonds : bond formed by the loss or gain of electrons between
metals and nonmetals ex NaCl
- Covalent bonds : bond formed by the sharing of electrons between
nonmetals ex O2
- Polar covalent bonds : covalent bonds that involve unequal sharing of
electrons due to an atom bonding to a more electronegative atom.
They form partial charges ex H2O
- Non-Polar covalent bonds : covalent bonds that involve equal sharing
of electrons ex O2
- Types of electron sharing : Single (pair of e), Double (2 pairs of e),
Triple (3 pairs of e)
- Hydrogen bonds : when a hydrogen atom bonds covalently with an
atom carrying partial negative charge (N,O,F)
- Electronegativity : Tendency of an atom to pull on its shared electron
in a covalent bond
- Weakest bond is the hydrogen bond and the strongest bond is the
ionic bond
Water molecules are composed of 1 oxygen atom and two hydrogen atoms
covalently bonded to each other WITHIN the molecule
When a water molecule bonds to ANOTHER WATER MOLECULE its a
hydrogen bond (hydrogen bonds with the oxygen of another molecule)
, Oxygen is more electronegative than hydrogen so it has a negative partial
charge and hydrogen is less electronegative than oxygen so it leaves a
partial positive charge
Oxygen has 2 lone pairs of electrons and the electrons are repelling
strongly from each other which creates the water’s bent structure
Properties of water molecules
- Cohesion
- Adhesion
- Universal solvent
- Surface tension
- Less dense when solid
- Evaporative cooling
- Temperature control
Water forms hydrogen bonds between water molecules, so water
requires more energy to evaporate than molecules that do not form
hydrogen bonds.
1 - Cohesion : when two water molecules are attracted to each other and
stick together due to hydrogen bonding
2 - Adhesion : when a water molecule is attracted to another molecule due
to hydrogen bonding, it determines its ability to stick to other surfaces.
- Together, it leads to capillary action, when the water molecules go
against gravity forces due to adhesion and cohesion properties.
Cohesion helps water molecules to move up in one form
- to move upward without going down is related to adhesion sticking to
the cell walls of the xylem
- Vascular Bundles consist of xylem (transports water and dissolved
mineral salts) and phloem (transports sugars and other stuff
produced by photosynthesis), water moves in the plant due to
adhesion, cohesion and capillary action
3 - Universal solvent : hydrogen bonds constantly break and reform in its
liquid state so this allows water to create new bonds with the substances
dissolved in it (polar/ionic bonds)
