AP College Biology 1.0

The percentage of water in human body

60%-70%

Most of an organism’s cellular chemistry and metabolism occur in the water-based “goo” inside its cells

Cytosol

A water molecule consists of:

2 hydrogen atoms bonded to an oxygen atom

Bent structure

The most stable arrangement is the one that puts them farthest apart from each other

Tetrahedron, with the O-H bonds forming two out of the four “legs”.

The lone pairs are slightly more ________ than the bond electrons

Repulsive

What does oyxgen do to keep electrons away from the hydrogen?

Hogging due to extreme electronegativity

What charge does the oxygen end of the water have?

Partial negative charge

What charge does the hydrogen end of the water have?

Partial positive charge

Water is classified as this because of its polar covalent bonds and its bent shape

Polar molecule

Thanks to this property, water molecules happily attract each other. The plus end of one—a hydrogen atom—associates with the minus end of another—an oxygen atom.

Polarity

These are weak interactions that form between a hydrogen with a partial positive charge and a more electronegative atom, such as oxygen.

Hydrogen bonds

The hydrogen atoms involved in hydrogen bonding must be attached to electronegative atoms, with examples such as:

1. Oxygen

2. Nitrogen

3. Fluorine

Water molecules are also attracted to:

1. Polar molecules

2. Ions

A charged or polar substance that interacts with and dissolves in water is said to be?

Hydrophilic

Hydro means?

Water

Philic means?

Loving

These do not interact well with water

Nonpolar molecules

1. Oils

2. Fats

They separate from it rather than dissolve in it and are called?

Hydrophobic

Phobic means?

Fearing

This refers to the attraction of molecules for other molecules of the same kind, and water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another.

Cohesion

What are responsible for surface tension?

Cohesive forces

A phenomenon that results in the tendency of a liquid’s surface to resist rupture when placed under tension or stress.

Surface tension

It causes water to form spherical droplets and allows it to support small objects, like a scrap of paper or a needle, if they are placed carefully on its surface.

Surface tension

This is the attraction of molecules of one kind for molecules of a different kind, and it can be quite strong for water, especially with other molecules bearing positive or negative charges.

Adhesion

For instance, adhesion enables water to _____ upwards through thin glass tubes (called capillary tubes) placed in a beaker of water.

Climb

This is upward motion against gravity

Capillary Action

It depends on the attraction between water molecules and the glass walls of the tube (adhesion), as well as on interactions between water molecules (cohesion).

Capillary Action

The curved surface formed by a liquid in a cylinder or tube is called a?

Meniscus

They are weak associations between the partially positive and partially negative ends of the molecules

Hydrogen bonds

It explains both the effectiveness of evaporative cooling (why sweating cools you off) and the low density of ice (why ice floats).

Hydrogen bonding

In liquid water, hydrogen bonds are constantly being formed and broken as the water molecules slide past each other. The breaking of these bonds is caused by the _________ of the water molecules due to the heat contained in the system.

Kinetic energy

When the heat is raised (for instance, as water is boiled), the higher kinetic energy of the water molecules causes the hydrogen bonds to break completely and allows water molecules to escape into the air as gas.

Water vapor or steam

On the other hand, when the temperature drops and water freezes, water molecules form a crystal structure maintained by hydrogen bonding (as there is too little heat energy left to break the hydrogen bonds). This structure makes…?

Ice less dense than liquid water.

This occurs when the temperature drops and kinetic (motion) energy of molecules is reduced—allows molecules to pack more tightly than in liquid form, giving the solid a greater density than the liquid. Water is an anomaly (that is, a weird standout) in its lower density as a solid.

Solidification

It is defined as the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius.

Specific heat capacity

The amount of heat needed to raise the temperature of 1 g water by 1 °C is has its own name, and this is?

Calorie

This is the amount of energy needed to change one gram of a liquid substance to a gas at constant temperature.

Heat of Vaporization

Water’s heat of vaporization is around?

540 cal/g at 100 °C

As water molecules evaporate, the surface they evaporate from gets cooler, a process called?

Evaporative cooling