Water's Polarity, Hydrogen Bonding, and Its Unique Properties in Biology

[TOPIC] Why is water polar?

Oxygen is more electronegative than hydrogen, so electrons are shared unequally. Oxygen is partially negative and the hydrogens are partially positive.

[TOPIC] What is a hydrogen bond?

A weak intermolecular attraction between a partially positive hydrogen on one polar molecule and an electronegative atom on another.

[TOPIC] Why do hydrogen bonds form between water molecules?

The partially positive H of one water molecule is attracted to the partially negative O of another.

[TOPIC] What happens to hydrogen bonds in liquid water?

They form, break, and re-form frequently as water molecules move.

[TOPIC] How would you label 5 water molecules in a diagram showing polarity?

Label O as partial negative (δ−), each H as partial positive (δ+), and draw hydrogen bonds between the H of one molecule and O of another.

[TOPIC] What is cohesion?

Attraction of water molecules to other water molecules.

[TOPIC] What causes cohesion in water?

Hydrogen bonding.

[TOPIC] Give examples of cohesion.

Transpiration, surface tension, and water striders.

[TOPIC] What is adhesion?

Attraction of water molecules to other polar molecules or surfaces.

[TOPIC] What causes adhesion?

Water's polarity and hydrogen bonding.

[TOPIC] Give examples of adhesion.

Water sticking to xylem walls, capillary action, and transpiration.

[TOPIC] What is surface tension?

Resistance of a liquid surface to external force or stretching because water molecules attract one another.

[TOPIC] What causes surface tension?

Cohesion from hydrogen bonding.

[TOPIC] Give examples of surface tension.

Water striders walking on water and water held by soil particles.

[TOPIC] What is capillary action?

Upward movement of water caused by cohesion, adhesion, and surface tension.

[TOPIC] Why is capillary action important in plants?

It helps move water and nutrients upward against gravity.

[TOPIC] What is high specific heat?

Water resists changes in temperature and changes temperature slowly.

[TOPIC] Why does water have high specific heat?

Heat must be absorbed to break hydrogen bonds, and heat is released when hydrogen bonds form.

[TOPIC] How does high specific heat contribute to life?

It moderates environmental temperature, stabilizes aquatic environments, and helps organisms resist rapid temperature changes.

[TOPIC] What is evaporative cooling?

The highest-energy water molecules leave as gas, carrying heat away.

[TOPIC] How does evaporative cooling help organisms?

It helps prevent overheating, such as sweating in humans and transpiration in plants.

[TOPIC] What is high heat of vaporization?

A large amount of energy is required to change water from liquid to gas.

[TOPIC] Why does ice float?

Hydrogen bonds hold water molecules in a crystal structure that spaces them farther apart, making ice less dense than liquid water.

[TOPIC] Why is floating ice important to life?

It insulates the water below and helps aquatic organisms survive.

[TOPIC] How many hydrogen bonds can one water molecule form with neighboring water molecules in ice?

Four.

[TOPIC] Why is water a versatile solvent?

Because its polarity lets it interact with ions and other polar molecules.

[TOPIC] What does 'like dissolves like' mean for water?

Polar water dissolves ionic and polar substances more easily than nonpolar substances.

[TOPIC] What is a solution?

A homogeneous mixture of two or more substances.

[TOPIC] What is a solvent?

The substance that does the dissolving.

[TOPIC] What is a solute?

The substance that is dissolved.

[TOPIC] How does water interact with positive ions?

The partially negative oxygen is attracted to the positive ion.

[TOPIC] How does water interact with negative ions?

The partially positive hydrogens are attracted to the negative ion.

[TOPIC] What are four major unique properties of water to know?

Cohesion/adhesion, temperature regulation, lower density of ice, and ability to act as a solvent.

[TOPIC] Why are hydrogen bonds important to the properties of water?

They cause cohesion, surface tension, high specific heat, high heat of vaporization, and the open structure of ice.

[TOPIC] What two ions form when water dissociates?

Hydronium (H3O+) and hydroxide (OH−).

[TOPIC] What is the pH of pure water?

7, neutral.

[TOPIC] What does a pH below 7 indicate?

An acidic solution.

[TOPIC] What does a pH above 7 indicate?

A basic solution.

[TOPIC] What happens to H+ concentration as pH decreases?

H+ concentration increases.

[TOPIC] What happens to H+ concentration as pH increases?

H+ concentration decreases.

[TOPIC] How large is the change in H+ concentration for each 1-unit change in pH?

A 10-fold change.

[TOPIC] What is an acid?

A substance that increases hydrogen/hydronium ion concentration in solution.

[TOPIC] What is a base?

A substance that reduces hydrogen ion concentration in solution.

[TOPIC] Why can changes in pH affect biological systems?

Changes in H+ concentration can change molecular interactions and protein shape/function.

[TOPIC] What is a buffer?

A substance/system that resists sudden changes in pH.

[TOPIC] How do buffers moderate pH changes?

They accept excess H+ when there is too much and can donate H+ when needed.

[TOPIC] Why are buffers important in biological systems?

They help keep pH within a range where proteins and other cell processes can function properly.

[TOPIC] What are the six major elements of life?

CHONPS: carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.

[TOPIC] Which elements are found in carbohydrates?

C, H, O.

[TOPIC] Which elements are found in lipids?

Mostly C, H, O; phospholipids also contain P.

[TOPIC] Which elements are found in proteins?

C, H, O, N, S.

[TOPIC] Which elements are found in nucleic acids?

C, H, O, N, P.

[TOPIC] What is carbon used to build in living organisms?

Carbohydrates, proteins, lipids, and nucleic acids.

[TOPIC] What is nitrogen used to build?

Proteins and nucleic acids.

[TOPIC] What is phosphorus used to build?

Nucleic acids and certain lipids.

[TOPIC] What are the three main subatomic particles?

Protons, neutrons, and electrons.

[TOPIC] What charge does a proton have?

Positive.

[TOPIC] What charge does a neutron have?

No charge.

[TOPIC] What charge does an electron have?

Negative.

[TOPIC] Which subatomic particle is directly involved in chemical reactions?

Electrons.

[TOPIC] What is atomic number?

The number of protons.

[TOPIC] What is atomic mass?

Approximately the number of protons plus neutrons; atomic mass on the periodic table reflects isotopes.

[TOPIC] What are valence electrons?

Electrons in the outermost electron shell that participate in bonding.

[TOPIC] How many valence electrons does carbon have?

Four.

[TOPIC] Why is carbon such a versatile element?

It has four valence electrons and can form up to four covalent bonds with many atoms, including other carbons.

[TOPIC] What kinds of covalent bonds can carbon form?

Single, double, and triple bonds.

[TOPIC] What shapes can carbon skeletons form?

Chains, branched structures, and rings.

[TOPIC] What is a Lewis dot model?

A diagram that shows an element's valence electrons around its symbol.

[TOPIC] How would carbon be shown in a Lewis dot model?

C with four dots around it, representing four valence electrons.

[TOPIC] What is organic chemistry?

The study of carbon compounds.

[TOPIC] What are organic compounds?

Compounds that contain carbon and hydrogen.

[TOPIC] What are hydrocarbons?

Organic molecules made only of carbon and hydrogen.

[TOPIC] How are hydrocarbons different from many other organic molecules?

Hydrocarbons contain only C and H and are generally nonpolar/hydrophobic; other organic molecules can contain additional functional groups and elements.

[TOPIC] What is a chemical bond?

An attraction between atoms caused by sharing or transferring valence electrons.

[TOPIC] What is electronegativity?

An atom's ability to attract electrons toward itself.

[TOPIC] What is a covalent bond?

A bond in which atoms share electrons.

[TOPIC] What is a nonpolar covalent bond?

A covalent bond in which electrons are shared equally.

[TOPIC] Give an example of a nonpolar covalent molecule.

O2.

[TOPIC] What is a polar covalent bond?

A covalent bond in which electrons are shared unequally.

[TOPIC] Give an example of a polar covalent molecule.

H2O.

[TOPIC] What is an ionic bond?

Attraction between oppositely charged ions after electrons are transferred.

[TOPIC] What is a cation?

A positively charged ion.

[TOPIC] What is an anion?

A negatively charged ion.

[TOPIC] What are van der Waals interactions?

Very weak attractions that occur when atoms or molecules are very close together.

[TOPIC] Rank these from strongest to weakest according to the notes: covalent, ionic, hydrogen, van der Waals.

Covalent → ionic → hydrogen → van der Waals.

[TOPIC] What is a functional group?

A chemical group attached to a carbon skeleton that affects the molecule's chemical properties and reactions.

[TOPIC] How do functional groups affect organic molecules?

They affect polarity, charge, reactivity, solubility, and interactions with other molecules.

[TOPIC] What are the seven functional groups to know?

Hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl.

[TOPIC] What is the formula of the hydroxyl group?

-OH.

[TOPIC] What does a hydroxyl group do to a molecule?

Makes it more polar and able to hydrogen-bond, increasing hydrophilicity.

[TOPIC] What type of compound commonly contains a hydroxyl group?

Alcohol.

[TOPIC] Give an example of a hydroxyl-containing molecule.

Ethanol.

[TOPIC] What is the formula of the carbonyl group?

C=O.

[TOPIC] What does a carbonyl group do to a molecule?

Makes it polar and reactive.

[TOPIC] What are the two common types of carbonyl-containing compounds?

Aldehydes and ketones.

[TOPIC] Where is the carbonyl in an aldehyde?

At the end of the carbon skeleton.

[TOPIC] Where is the carbonyl in a ketone?

Within the carbon skeleton.

[TOPIC] What is the formula of the carboxyl group?

-COOH.

[TOPIC] Why is the carboxyl group acidic?

It can lose H+.

[TOPIC] What charge can a carboxyl group have after losing H+?

Negative.