Polarity and Water Properties(Niggemeyer Biology)

Solutions

A solution is a uniform mixture of two or more substances. •Solute + Solvent = Solution. •The solvent is the substance present in greater amount that dissolves (breaks up/separates) the other substance. •The solute is the substance present in lesser amount and is dissolved by the solvent. •An aqueous solution is one in which water is the solvent. •Most solutions in cells are aqueous.

Adhesion

Adhesion occurs when unlike (usually polar) molecules attract each other. That is, it is an attraction between molecules of different substances. Again, this typically happens between two different types of polar substances BUT it can happen between non-polar substances

Capillary Action

Another example of adhesion is that of capillary action or capillarity. This kind of action occurs in very thin tubes. These tubes can be human-made, like glass, or natural "vascular tubes" found in plants and trees, etc. This "action" is caused by the adhesion of water molecules with the polar molecules in the inside wall of the tube and also the cohesion between adjacent water molecules. This scenario enables water molecules to "climb up" the tube, working against gravity. Again, these tubes must be very thin in order for capillary action to occur. This explains how water is diffused throughout plants

Beading

Cohesion causes water molecules to attract each other and pull together This causes water to form "beads" on a smoother surface.

δ stands for...

Dipole

Surface Tension

H - Bonds are slightly stronger between water molecules across the surface of a given volume of water molecules. This effect is caused by the cohesion between water molecules at the surface of a liquid. This creates a sort of tension at the surface that holds the water molecules more tightly. This is called surface tension. This surface tension enables some objects/organisms that are actually more dense than water to float on it. Strongest H bonds are at the top because no H-Bonds are above it so some items that are more dense can float on the top

H bonds

H bonds are shown in dots because they are weaker

Water as a bent molecule

H2O is a bent (v-shaped) molecule, making it asymmetrical or unbalanced in shape. This results in an imbalance of + & - charges. The result is that water is a polar molecule. 104.5

Cohesion (Microscopic Properties)

Hydrogen bonding found between water molecules is the underlying cause of cohesion. Same attracting same Cohesion in water is stronger than in other liquids. This is because a water molecule can form up to 4 H-bonds at one time with other H2O molecules.

Hydrogen bond in general

Hydrogen bonds typically form between H atoms in one molecule and O or N atoms in another nearby molecule. H bonds are weak. They are weaker than ionic & covalent bonds.

Heat and Temperature

Molecules in motion have kinetic energy (KE). Temperature is a measure of the average kinetic energy (KE) of a molecular system. When substances are heated, the average KE of the system is increased. So... When substances are heated, their temperatures go up. However, the amount of temperature change (ΔT) (per unit of heat input) varies with the type of substance being heated.

Density of Ice

Most solids are more dense than their liquid. Solid water (ice) is less dense than its liquid. This is caused by water's H bonds which cause the molecules in ice to be slightly further apart than in liquid water (Expand) & they end up being more symmetrically arranged. The result is that ice floats on/in its liquid.

How does water's chemical structure effect water?

O attracts electrons (e-) more strongly than H does. This causes the electrons in water's O-H bonds to move/be closer to oxygen, making oxygen more negative. O is (slightly) more negative & H is (slightly) more positive. Because of this, electrons are shared unequally between these two different atoms.

What is the cause of most of water properties?

POLARITY

Polar Molecules

Polar molecules are molecules that have a positive charge (+) on one end and a negative charge (-) on the other end.

What happens with the attraction of polar molecules?

Polar molecules attract other polar molecules. This attraction helps to keep some substances together and to pull other substances apart. (Non-polar molecules don't [easily] attract other molecules.)

How are water's characteristics formed?

The properties or characteristics of water are caused by the structure of water. Water's structure causes it to be a polar molecule.

Hydrogen bonding in Water

The slightly negative (-) O atom in one water molecule attracts a slightly positive (+) H atom in a nearby/adjacent water molecule. This type of attraction is referred to as a hydrogen (H) bond. But there are many H bonds b/w adjacent H2O molecules in a volume of water. This creates a network of molecules that are more strongly attracted to each other overall.

Examples of Adhesion

The surface of the water in a container such as a beaker or a graduated cylinder tends to dip slightly in the center. This dip is called a meniscus. More curved the thinner the tube or cylinder. This dip occurs because the adhesion between the water molecules and the glass molecules is stronger than the cohesion between the water molecules.

How many H bonds can water form?

Water can form 4 H bonds around themselves. This is what makes water strong(strength is in numbers not in bonding strength)

Water's chemical formula

Water's chemical formula is H2O.

Adhesion (Microscopic Properties)

Water's polar nature also enables water molecules to attract other non-water polar molecules. This is called adhesion.

Specific Heat of Water and Temperature Moderation

When thermal energy (heat) is added to water, some of this energy goes into the breaking of H bonds and NOT into the increase of KE/Temperature of the water molecules. So...the temperature change in water is less than in other substances. A substance's capacity to absorb heat and change its temperature is called its heat capacity or specific heat. Water can absorb a large amount of heat with a minimal temperature change (ΔT). So...water has a high heat capacity. When thermal energy/heat is removed from water the water cools. When water cools it forms H bonds. This release of thermal energy/heat reduces the drop in the temperature of the water. So... temperature fluctuations in/around water are less extreme.