Unit 1: Chemistry of Life
Properties of water (1.1)
Water is a polar molecule that forms hydrogen bonds. Hydrogen bonds are weak;
weaker than covalent bonds. These bonds are formed by electrostatic attraction
between protons and electronegative atoms. The strength of a hydrogen bond can
be determined by electronegativity. The ability for water to form hydrogen bonds
allows for its unique properties.
↓Key terms mentioned:
Polar molecule: Asymmetric, unevenly distributed molecule with different
electronegativities. One side is partially positive, the other partially negative. They
contain polar covalent bonds and have a net dipole movement.
- Dipole movement: non-zero net separation of electrical charge
Exam tip: Don’t confuse polarity with charge; polarity refers to electronegativities
Electrostatic attraction: force of attraction between charges
Electronegativity: ability for an atom to attract electrons
Exam tip: charges are represented by delta (δ) with the charge indicated after it
(+) or (-)
Diagram of H₂O and its bonds
, Key:
O= oxygen
H= hydrogen
Unique properties of water:
- Adhesion
- Cohesion
- Surface tension
- High specific heat
- High solvency
- Less dense as a solid (ice)
Adhesion: tendency or attraction of molecules (like H₂O) to other molecules,
materials, or surfaces. This allows them to stick or cling to unlike molecules.
Adhesion takes place when there is a hydrogen bond between these unlike
molecules. This can happen due to polarity*, causing the oxygen in water(with a
negative charge) to be attracted to positive charges. Therefore the charges of
water and the molecule it “adheres” to play a significant role in the “adhesive”
properties of water.
* Remember: polarity refers to the unequal charges of a molecule, often
causing asymmetry
Cohesion: tendency or attraction of molecules (like H₂O) to stick to the same
molecules, where H₂O will stick to H₂O. Similar molecules will stick together via
hydrogen bonds between them.
Remembering the difference of adhesion vs cohesion
Adhesion Cohesion
“Adhesion” is like “adhere” “Cohesion” has the prefix “co”
- Think of tape sticking to paper. - This means ‘together’ or ‘jointly’.
They’re both different materials, Think of it as two alike molecules
but still stick together. working together in a team.
Properties of water (1.1)
Water is a polar molecule that forms hydrogen bonds. Hydrogen bonds are weak;
weaker than covalent bonds. These bonds are formed by electrostatic attraction
between protons and electronegative atoms. The strength of a hydrogen bond can
be determined by electronegativity. The ability for water to form hydrogen bonds
allows for its unique properties.
↓Key terms mentioned:
Polar molecule: Asymmetric, unevenly distributed molecule with different
electronegativities. One side is partially positive, the other partially negative. They
contain polar covalent bonds and have a net dipole movement.
- Dipole movement: non-zero net separation of electrical charge
Exam tip: Don’t confuse polarity with charge; polarity refers to electronegativities
Electrostatic attraction: force of attraction between charges
Electronegativity: ability for an atom to attract electrons
Exam tip: charges are represented by delta (δ) with the charge indicated after it
(+) or (-)
Diagram of H₂O and its bonds
, Key:
O= oxygen
H= hydrogen
Unique properties of water:
- Adhesion
- Cohesion
- Surface tension
- High specific heat
- High solvency
- Less dense as a solid (ice)
Adhesion: tendency or attraction of molecules (like H₂O) to other molecules,
materials, or surfaces. This allows them to stick or cling to unlike molecules.
Adhesion takes place when there is a hydrogen bond between these unlike
molecules. This can happen due to polarity*, causing the oxygen in water(with a
negative charge) to be attracted to positive charges. Therefore the charges of
water and the molecule it “adheres” to play a significant role in the “adhesive”
properties of water.
* Remember: polarity refers to the unequal charges of a molecule, often
causing asymmetry
Cohesion: tendency or attraction of molecules (like H₂O) to stick to the same
molecules, where H₂O will stick to H₂O. Similar molecules will stick together via
hydrogen bonds between them.
Remembering the difference of adhesion vs cohesion
Adhesion Cohesion
“Adhesion” is like “adhere” “Cohesion” has the prefix “co”
- Think of tape sticking to paper. - This means ‘together’ or ‘jointly’.
They’re both different materials, Think of it as two alike molecules
but still stick together. working together in a team.
