Chemical Elements and Water Honors Biology 2011-12

What you will learn… 1. Levels of organization 2. Why Chemistry? 3. Life’s elements 4. Chemical Bonding 5. Polar Covalent Bond 6. Electronegativity and Water 7. Thee Hydrogen Bond 8. Properties of Water/Structural Explanation/Significance For Life 9. Solutions 10. Acids/Bases/pH/Buffers

1. How do we organize living things? Biosphere Ecosystem Community Population Organism Organ System Organ Tissue Cell Organelle Macromolecule Molecule Atom

2. Why Chemistry? To understand the structures and functions of living organisms, it’s essential to know the basis of all living things. The properties of life emerge from the arrangement of its chemical parts into higher and higher levels of biological organization. At the base of the hierarchy of living things: atoms, elements, and molecules

3. Life requires elements! There are about 25 chemical elements required for life. Oxygen, Carbon, Hydrogen, and Nitrogen make up about 96% of the human body Essential ingredients of the major biological macromolecules: fats, proteins, and sugars Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, and Magnesium account for the remaining 4%. Involved in functions such as bone formation, nerve signaling, and DNA synthesis

3. What makes up an element? Each element consists of one kind of atom Atoms consists of three subatomic particles: Protons are positive and located in the nucleus of the atom (represents atomic number) Neutrons are neutral and located in the nucleus (add to protons to determine mass number) Electrons are negative and found on orbitals around the nucleus

4. Chemical Bonds Atoms can bind with each other to form more complex forms of matter called compounds. There are two basic types of bonds: Covalent bond – electrons are shared between atoms forming a molecule Ionic bond – electrons are lost or gained by atoms and the oppositely charged ions are held together by electrostatic attraction.

5. Covalent Bond- Polarity Some molecules with covalent bonds share the electrons equally or the molecule is symmetrical – nonpolar molecules (Ex. Oil) Some molecules have an uneven electron sharing. One atom attracts the electrons more in the bond than the other – polar molecules (Ex. Water)

5. Water!

6. Electronegativity Electronegativity An atom’s attraction for its electrons, including shared electrons.

6. Electronegativity and Water Unequal sharing of electrons produces what is called a polar covalent bond. The pulling of shared electrons closer to the more electronegative atom makes that atom partially negative and the other atom partially positive. Oxygen is one of the most electronegative elements, and thus attracts the shared electrons in H2O much more strongly than H does. the O atom has a slight negative charge and each H atom a slight positive charge. The V shape and its polar covalent bonds make water a polar molecule

7. Hydrogen bonding in Water!

7. Thee Hydrogen Bond In addition to strong polar covalent bonds, water also forms bonds with other water molecules. This bond, called a Hydrogen Bond, attaches the H+ from one molecule to the O- of another molecule One water molecule can have up to four hydrogen bonds. The molecules of water are constantly moving in relation to each other, and the hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds.[13] However, this bond is sufficiently strong to create many of the peculiar properties of water The hydrogen bond, and the polar nature of water, are essential properties allowing for many unique features of water.

8. WATER!! 

Property of Water 1 1. Property: 1. Structural Explanation: Water as ice is less dense than liquid water 1. Structural Explanation: Ice takes on a more regular, tetrahedral structure so the molecules are further from each other. Significance for Life: Life can exist under ice

Property of Water 2 2. Property: 2. Structural Explanation: Water has a low viscosity 2. Structural Explanation: Small molecules 2. Significance for Life: Water can for through very small spaces, capillaries

Property of Water 3 3. Property: 3. Structural Explanation: Water is liquid at room temperature 3. Structural Explanation: Hydrogen bonds 3. Signifance For Life: Water is a medium aquatic life, water is found inside cells

Property of Water 4 4. Property: 4. Structural Explanation: Water is colorless with a high transmission of visible light 4. Structural Explanation: Small, stable molecule, no excitable electrons 4. Significance For Life:

Property of Water 5 5.Property: 5. Stuctural Explanation: Water has strong adhesive (water sticks (adheres) to other molecules or surfaces) and cohesive (water sticks together) forces. 5. Stuctural Explanation: Polarity- adhesion/ Hydrogen bonds- cohesion 5. Significance For Life: Adhesive (water can stick to plant tissue during transpiration)/ Cohesive (water can stick to other water molecules during transpiration)

Property of Water 6 6. Property: 6. Structural Explanation: Water is classified as a universal solvent because many substances can dissolve in water. 6. Structural Explanation: 6. Significance For Life: Water is a medium for the chemical reactions of life/ main transport medium (dissolved minerals and ions in water for plants)

Property of Water 7 7. Property: 7. Structural Explanation: High heat of fusion- a significant amount of energy is required before water can change state 7. Structural Explanation: Hydrogen bonds 7. Significance For Life: Contents of cells are unlikely to freeze

Property of Water 8 8. Property: 8. Structural Explanation: Water has a high heat of vaporization. 8. Structural Explanation: Hydrogen bonds 8. Significance For Life: Heat is lost by evaporation of water. Sweating causes rapid cooling.

Property of Water 9 9. Property: 9. Structural Explanation: Water has a high specific heat capacity (water can absorb a large amount of energy for only a small rise in temperature). 9. Structural Explanation: Hydrogen bonds 9. Significance For Life: Aquatic environments are thermally stable. Organisms have stable internal temperatures when external temperature fluctuate.

Property of Water 10 10. Property: 10. Structural Explanation: Water has a high surface tension (caused by cohesion). 10. Structural Explanation: Close attraction between water molecules, H-bonds 10. Significance For Life: water forms droplets on surfaces and runoffs

8. Properties of Water (refer to chart) 1. Water as ice is less dense than liquid water 2. Water has a low viscosity 3. Water is liquid at room temperature 4. Water is colorless with a high transmission of visible light 5. Water has strong adhesive (water sticks (adheres) to other molecules or surfaces) and cohesive (water sticks together) forces. 6. Water is classified as a universal solvent because many substances can dissolve in water. 7. High heat of fusion- a significant amount of energy is required before water can change state 8. Water has a high heat of vaporization. 9. Water has a high specific heat capacity (water can absorb a large amount of energy for only a small rise in temperature). 10. Water has a high surface tension (caused by cohesion).

8. Structural Explanations (refer to chart) 1. Ice takes on a more regular, tetrahedral structure so the molecules are further from each other. 2. Small molecules 3. Hydrogen bonds 4. Small, stable molecule, no excitable electrons 5. Polarity- adhesion/ Hydrogen bonds- cohesion 6. Hydrogen bonds, polar, small molecules 7. Hydrogen bonds 8. Hydrogen bonds 9. Hydrogen bonds 10. Close attraction between water molecules, H-bonds

8. Significance For Life (refer to chart) 1. Life can exist under ice 2. Water can for through very small spaces, capillaries 3. Water is a medium aquatic life, water is found inside cells 4. light can penetrate tissues in plants and also aquatic environments 5. Adhesive (water can stick to plant tissue during transpiration)/ Cohesive (water can stick to other water molecules during transpiration) 6. Water is a medium for the chemical reactions of life/ main transport medium (dissolved minerals and ions in water for plants) 7. Contents of cells are unlikely to freeze 8. Heat is lost by evaporation of water. Sweating causes rapid cooling. 9. Aquatic environments are thermally stable. Organisms have stable internal temperatures when external temperature fluctuate. 10. water forms droplets on surfaces and runoffs

9. Solutions A solution is a liquid consisting of a uniform mixture of two or more substances. The dissolving agent is the solvent and the solute is the substance dissolved. When water is the solvent, the result is an aqueous solution. For example, water is the solvent in blood and in plant sap.

10. Acids and bases In aqueous solutions, water molecules can break apart (dissociate) into ions. The ions formed are H+ (hydrogen ion) and OH- (hydroxide ion). Some chemical compounds contribute additional H+ to an aqueous solution, while others remove H+ from it.

10. Acids Acids are compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution.  Increase the concentration of hydrogen ions For example, hydrochloric acid (HCl) dissolves in water as follows: HCl H + (aq ) +  Cl-(aq)

10. Bases Bases as substances that dissolve in water to release hydroxide ions (OH-) into solution and removes H+. decrease the concentration of hydrogen ions (by accepting them).  For example, a typical base according to the Arrhenius definition is sodium hydroxide (NaOH): NaOH   Na+ (aq)  +  OH- (aq)

10. pH scale The acidity or basicity of something, therefore, can be measured by its hydrogen ion concentration. pH is a measure of the balance between hydrogen ions (H+) and hydroxide ions (OH-) in an aqueous solution. Solutions with pH = 7 are neutral (for example, pure water)  Solutions with pH < 7 are acidic  Solutions with pH > 7 are basic (or “alkaline”)

10. Buffers Buffers: A buffer solution is one which resists changes in pH when small quantities of an acid or a base are added to it. They can resists changes in pH by accepting H+ when it is in excess and donating H+ when it is depleted. For example, your blood has buffers that help to ensure an optimal pH is maintained in your body.

10. pH Indicators Chemical compound added to a solution to determine the pH visually. Example: Red cabbage juice contains a pigment molecule that will change color based on pH: Very acidic solutions will turn a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow