9/26/14 1 Chapter 2: The Chemistry of Life Chapter 2: The Chemistry of Life 2–2 Properties of Water Mr. M. Varco St. Joseph High School • Like other molecules, water is considered electrically neutral – Its 10 protons (+) balance of its 10 electrons (-) • With 8 protons, water’s oxygen nucleus attracts electrons more strongly that the 1 proton of water’s two Hydrogen atoms • As a result, water’s shared electrons are more likely to be found near the oxygen atom 2.2: The Water Molecule
Transcript
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Chapter 2: The Chemistry of Life
Chapter 2: The Chemistry of Life
2–2 Properties of Water
Mr. M. Varco St. Joseph High School
• Like other molecules, water is considered electrically neutral – Its 10 protons (+) balance of its 10 electrons (-)
• With 8 protons, water’s oxygen nucleus attracts electrons more strongly that the 1 proton of water’s two Hydrogen atoms
• As a result, water’s shared electrons are more likely to be found near the oxygen atom
2.2: The Water Molecule
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• Because the oxygen nucleus is at one end of the molecule, water has a partial negative charge on one end, and positive charge on the other.
• A molecule in which the charges are unevenly distributed is said to be polar
• Water molecules are polar
2.2: The Water Molecule
2.2: The Water Molecule
Hydrogen Bond: • The attraction between a hydrogen atom with a partial (+) charge
and another atom with a partial (-) charge is a hydrogen bond
• Hydrogen Bonds are weaker than both Ionic and Covalent Bonds
• Because water is polar, it can form many hydrogen bonds
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• Cohesion: An attraction between molecules of the same substance – Water is cohesive. Why? – Because a single water molecule can be involved with up to four hydrogen
bonds at once
• Adhesion: An attraction between molecules of a different substance
2.2: The Water Molecule
• A mixture is a material composed of two or more elements or compounds that are physically mixed together, but not chemically combined
• Two types of mixtures are solutions and suspensions
2.2: Solution and Suspensions
+ = Mixture
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• Solutions:
– Solutions form when all of the components in a substance are uniformly distributed throughout.
2.2: Solution and Suspensions
Cl-
Water
Cl- Na+
Water Na+
• Solutions: – In a saltwater solution, table salt is the solute, and water is the solvent
– A solute is the substance that is dissolved – A solvent is the substance in which the solute is dissolved
2.2: Solution and Suspensions
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• Solutions:
– Water’s polarity allows it to dissolve both ionic compounds and other polar molecules.
– When a given amount of water has dissolved all of the solute, it is said to be saturated
2.2: Solution and Suspensions
• Suspensions:
– Mixtures composed of water and non-dissolved material, where the movement of water molecules keeps the small particles suspended
– Example: Blood in our body
2.2: Solution and Suspensions
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• pH Scale: – The purpose of the pH scale is to determine the concentration of H+ ions
in a solution
– The pH scale ranges from 0 – 14:
• Acidic (pH below 7): Solutions with more H+ ions than OH- ions • Neutral (pH = 7) : Solutions with equal H+ ions and OH- ions • Basic (pH above 7) : Solutions with less H+ ions than OH- ions
2.2: The pH Scale
• pH Scale:
– Each step on the pH scale represents a factor of 10 • pH of 4 has 10 times as many H+ ions as pH of 5
2.2: The pH Scale
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• Where do the extra H+ ions in a low pH solution come from? – Acids: any compound that forms H+ ions in a solution
• Base: a compound that produces hydroxide (OH-) ions – Strong bases have pH between 11-14
• Water is considered neutral (pH = 7). Why? – When water molecules split, H+ ions and OH- ions are released – But…the number of H+ ions and OH- ions are equal
2.2: Acids, Bases, and Buffers
• How does our body regulate the pH of the fluids within our body to stay between 6.5 and 7.5?
– Buffers: weak acids or bases that can react with strong acids or bases to
