Monday, February 24, 2025
Lecture 5- Properties of seawater
Water: Why water is habitable?
- Presence of water on earth makes life possible
- Organisms are mostly water
- Chemical structure of water gives it its unusual properties
What is an atom?
- Atoms-building blocks of all matter
- Subatomic particles
o protons
o neutrons
o electrons
- Number of protons distinguishes chemical elements
What is a molecule?
- Two or more atoms held together by shared electrons
- Smallest form of a substance
o Example: O2 in the atmosphere
What makes up a water molecule?
- Strong covalent bonds between two hydrogen (H) and one oxygen atoms
o Shared electrons
- Both H atoms on the same side of O atom
o Bent molecule shape gives water its unique properties
- Dipolar
o Positively and negatively changed sides
What is hydrogen bonding
- A function of dipolarity:
- Small negative charge at O end
- Small positive charge at H end
- Attraction between positive and negative ends of water molecules to each other or
other ions.
Why is hydrogen bonding important?
- Hydrogen bonds are weaker than covalent bonds but still strong enough to contribute
to:
o Cohesion-molecules sticking together
o High water surface tension
o High solubility of chemical compounds of water
o Unusual thermal properties of water
o Unusual density of water
, High solubility: Water as a solvent
- Electrostatic attraction produces ionic bond: donation of electrons
o Table salt
- Water molecules stick to other polar molecule
Clicker question: Many of the unique properties of water, such as cohesion and its
reputation as a universal solvent, come from its atomic structure. What causes these
properties?
a. Atoms in the water molecules are stuck together with atomic bonds
b. Atoms in water molecules are stuck together with covalent bonds
c. Water molecules are electrically polarized
d. Water molecules contain sodium (Na) ions that break down substances
e. Many other ions can substitute for the hydrogen (H) atoms in a water molecule
Explanation: Because the hydrogen atoms are situated on one side of the water molecule, this
side of the water molecule has slight positive charge, and the oxygen side has a slight negative
charge. This electrical polarization causes water molecules to stick together with hydrogen
bonds. This given them cohesion. The polarization also allows water to break down substances
whose molecules are glued by ionic bonds by attracting the constituent ions. A is nonsense; B is
correct but not the answer. D and E are nonsense.
Water’s thermal properties: High heat capacity
- Water is solid, liquid and gas at earth surface
- Water influences earth’s heat budget
Water’s thermal properties: describing heat and temperature
- Heat- transfer of both kinetic and potential energy from one object to another due to
temperature differences
- Temperature- average kinetic energy of molecules in a substance
- Calorie is the amount of heat needed to raise temperature of 1 gram of water by 1°c
Water’s thermal properties: Water freezing points and boiling points
- Freezing points= melting point: 0°C (32°F)
- Boiling point=condensation point: 100°C (212°F)
- Freezing and boiling points of water unusually high compared to other substances.
Water thermal properties: heat capacity and specific heat
- Heat capacity – amount of heat required to raise the temperature of 1 gram of any
substance by 1°C
- Water has a high capacity- can take in or lose much heat without changing temperature
- Specific heat- heat capacity per unit mass
Lecture 5- Properties of seawater
Water: Why water is habitable?
- Presence of water on earth makes life possible
- Organisms are mostly water
- Chemical structure of water gives it its unusual properties
What is an atom?
- Atoms-building blocks of all matter
- Subatomic particles
o protons
o neutrons
o electrons
- Number of protons distinguishes chemical elements
What is a molecule?
- Two or more atoms held together by shared electrons
- Smallest form of a substance
o Example: O2 in the atmosphere
What makes up a water molecule?
- Strong covalent bonds between two hydrogen (H) and one oxygen atoms
o Shared electrons
- Both H atoms on the same side of O atom
o Bent molecule shape gives water its unique properties
- Dipolar
o Positively and negatively changed sides
What is hydrogen bonding
- A function of dipolarity:
- Small negative charge at O end
- Small positive charge at H end
- Attraction between positive and negative ends of water molecules to each other or
other ions.
Why is hydrogen bonding important?
- Hydrogen bonds are weaker than covalent bonds but still strong enough to contribute
to:
o Cohesion-molecules sticking together
o High water surface tension
o High solubility of chemical compounds of water
o Unusual thermal properties of water
o Unusual density of water
, High solubility: Water as a solvent
- Electrostatic attraction produces ionic bond: donation of electrons
o Table salt
- Water molecules stick to other polar molecule
Clicker question: Many of the unique properties of water, such as cohesion and its
reputation as a universal solvent, come from its atomic structure. What causes these
properties?
a. Atoms in the water molecules are stuck together with atomic bonds
b. Atoms in water molecules are stuck together with covalent bonds
c. Water molecules are electrically polarized
d. Water molecules contain sodium (Na) ions that break down substances
e. Many other ions can substitute for the hydrogen (H) atoms in a water molecule
Explanation: Because the hydrogen atoms are situated on one side of the water molecule, this
side of the water molecule has slight positive charge, and the oxygen side has a slight negative
charge. This electrical polarization causes water molecules to stick together with hydrogen
bonds. This given them cohesion. The polarization also allows water to break down substances
whose molecules are glued by ionic bonds by attracting the constituent ions. A is nonsense; B is
correct but not the answer. D and E are nonsense.
Water’s thermal properties: High heat capacity
- Water is solid, liquid and gas at earth surface
- Water influences earth’s heat budget
Water’s thermal properties: describing heat and temperature
- Heat- transfer of both kinetic and potential energy from one object to another due to
temperature differences
- Temperature- average kinetic energy of molecules in a substance
- Calorie is the amount of heat needed to raise temperature of 1 gram of water by 1°c
Water’s thermal properties: Water freezing points and boiling points
- Freezing points= melting point: 0°C (32°F)
- Boiling point=condensation point: 100°C (212°F)
- Freezing and boiling points of water unusually high compared to other substances.
Water thermal properties: heat capacity and specific heat
- Heat capacity – amount of heat required to raise the temperature of 1 gram of any
substance by 1°C
- Water has a high capacity- can take in or lose much heat without changing temperature
- Specific heat- heat capacity per unit mass
