Biology Unit 1 Topic 1: Structure of Water and Hydrogen Bonding

Matter

Anything that takes up space and has mass (rocks, metal, oil, gases, organisms, etc. are all forms of matter).

Element

a substance that cannot be broken down into other substances by chemical reactions (92 elements occur in nature, periodic table).

Electronegativity

the measure of an atom’s ability to attract electrons to itself.

Atomic Number

the number of protons in an element (seen above the element symbol).

Atomic Mass

number of protons plus neutrons averaged over all isotopes.

Octet Rule

elements will gain, lose, or share electrons to complete their valence shell and become stable (like noble gases).

Chemical Bonds

an attraction between two atoms, resulting from the sharing or transferring of valence electrons.

Compounds

a substance consisting of two or more different elements combined in a fixed ratio (H2O and NaCl).

Covalent Bonds

when two or more atoms share electrons (usually between two nonmetals), forms molecules and compounds. (two types: nonpolar and polar)

Nonpolar Covalent Bonds

electrons are shared equally between two atoms (ex. O2)

Polar Covalent Bonds

electrons are not shared equally between two atoms (ex. H2O)

Ionic Bonds

the attraction between oppositely charged atoms (ions); usually metal and nonmetal (metal transfers electrons to nonmetal). Forms ionic compounds and salts (example: NaCl and LiF). (Cation: pos, Anion: neg)

Adhesion

the attraction to other molecules that are polar or have charge (H2O to other molecules).

Cohesion

attraction of molecules for other molecules of the same kind (H2O sticks together)

Capillary Action

the upward movement of water due to the forces of cohesion, adhesion, and surface tension (occurs when adhesion is greater than cohesion).

Solvent

dissolving agent in a solution

pH

a measure of how acidic or basic (alkaline) a solution is.

Acid

substance that releases hydrogen ions (H+) when dissolved in water.

Base

substance that accepts H+ or releases hydroxide ions (OH-)

Buffer

a solution that resists changes in pH when an acid or base is added (they maintain pH stability in biological systems).

Identify the elements that make up nearly all living matter.

Carbon, Hydrogen, Oxygen, Phosphorus, and Nitrogen (CHOPN)

How are hydrogen bonds different from other types of bonds?

The partially positive hydrogen atom in one polar covalent molecule is attracted to an electronegative atom in another polar covalent molecule.

Draw a few water molecules. Label the types of bonds found in and between the molecules.

How does electronegativity affect the interactions between water molecules?

Causes hydrogen to have a partial positive charge and electronegative atom partial negative charge.

Imagine if O and H had the same electronegativity, what would that do to the properties of water?

O and H would not be attracted to each other in an intermolecular bond through the hydrogen bond and water would not be as structured.

Describe the properties of water; give an example of each.

Polarity: polar covalent bonds created by unequal sharing of electrons between oxygen & hydrogen within the molecule of water

• H2O

Cohesion: hydrogen bonds between H2O molecules held together & increase cohesive forces

• allows for transport of water & nutrients against gravity in plants

Adhesion: attraction of other molecules that are polar or have a charge

• water can cling to the stiff walls of plants to resist the downward pull of gravity

Capillary action:upward movement of water due to cohesion, adhesion and surface tension

• transport of water and nutrients in plants as water movies upwards

Temp Control: has high specific heat to resist changes in temp, high vaporization water requires large amt. of energy to evaporate

• stabilizes ocean temp as water absorbs heat in daytime and releases it at night

Density (floating ice): water solidifies, expands, and becomes less dense

• keeps environmental climate stable as it reflects the rays of the sun with the brightness of the ice

Solvent: polar molecules are attracted to ions and other polar molecules (form hydrogen bonds)

• .

pH and buffering: water dissociates into hydrogen and hydroxide ions

• acid substances release hydrogen ions when dissolved

• bases accepts hydrogen or releases hydroxide

• buffer resists changes in pH when acid or base is added

  • maintains pH stability in biological systems

Describe two ways in which the properties of water benefit organisms.

• temperature control: evaporative cooling stabilizes earth’s climate & allows them to resist changes in on internal temp & overheating (sweating)

• Density (floating ice): allows marine life to survive under floating ice sheets