Structure of Water and Hydrogen Bonding

Matter Element Anything that takes up space and has mass ● Rocks, metals, oils, gases, organisms, etc. are all forms of matter A substance that cannot be broken down into other substances by chemical reactions ● 92 elements occur in nature ● Periodic table Compound A substance consisting of two or more different elements combined in a fixed ratio ● H2O ● NaCl Essential elements: of the 92 naturally occurring elements 2025% are essential to survive and reproduce. CHOPN make up 96% of living matter Trace elements: of the 92 naturally occurring elements, these are required by an organism in very small quantities © Getting Down with Science 2020 Research, Pair, Share ● Search up the essential elements. Why are they essential? (i.e. what major roles do these elements play in the human body? ● Search up trace elements. What are a few examples of trace elements and their purpose in the human body? © Getting Down with Science 2020 Chemistry Review Atomic number: number of protons Element symbol Atomic mass: number of protons plus neutrons averaged over all isotopes © Getting Down with Science 2020 Chemistry Review Elements in the same vertical column have the same number of valence electrons Elements in the same horizontal row have the same total number of electron shells © Getting Down with Science 2020 Think, Pair, Share ● What else do you remember about the periodic table? © Getting Down with Science 2020 Types of Bonds Elements want to be stable ● Achieve this by forming chemical bonds with other elements ● Octet rule: elements will gain, lose, or share electrons to complete their valence shell and become stable (like noble gases) ○ Valence shell: outermost layer of electrons in an atom © Getting Down with Science 2020 Types of Bonds Chemical Bonds: an attraction between two atoms, resulting from the sharing or transferring of valence electrons Electronegativity: the measure of an atom’s ability to attract electrons to itself Electronegativity decreases Electronegativity increases © Getting Down with Science 2020 Types of Bonds Covalent bonds: when two or more atoms share electrons (usually between two nonmetals) ● Forms molecules and compounds o Single bond: 1 pair of shared eo Double bond: 2 pairs of shared eo Triple bond: 3 pairs of shared e● There are two types of covalent bonds: nonpolar covalent and polar covalent © Getting Down with Science 2020 Types of Bonds Nonpolar covalent: Electrons are shared equally between two atoms ● Example: O2 Double bond: 2 pairs shared e© Getting Down with Science 2020 Types of Bonds Polar covalent: Electrons are not shared equally between two atoms ■ Example: H2O Unequal sharing of e- results in partial charges on oxygen and hydrogen © Getting Down with Science 2020 Types of Bonds Ionic bonds: The attraction between oppositely charged atoms (ions) ● Usually between a metal and nonmetal (metal transfers electrons to nonmetal) ● Forms ionic compounds and salts o NaCl o LiF ● Occurs when there is a transfer of electrons from one atom to another atom forming ions o Cation: positively charged ion o Anion: negatively charged ion © Getting Down with Science 2020 Types of Bonds Hydrogen bonds: the partially positive hydrogen atom in one polar covalent molecule will be attracted to an electronegative atom in another polar covalent molecule ● Intermolecular bond: bond that forms between molecules © Getting Down with Science 2020 Types of Bonds ● Why does this happen? ○ When a hydrogen atom is bonded to an electronegative atom (usually O, N, or F) the electrons are not being shared equally between atoms (remember: this is a polar covalent bond) ■ This causes the hydrogen to have a partial positive charge and the electronegative atom to have a partial negative charge © Getting Down with Science 2020 Hydrogen Bonding Example: hydrogen bonds between water molecules Polar covalent bond Hydrogen bond Water molecules move a lot! Hydrogen bonds form, break, and re-form with great frequency The hydrogen bonds between water make it more structured than most liquids © Getting Down with Science 2020 © Getting Down with Science 2020 Properties of Water Overview of the properties of water:  Polarity  Cohesion  Adhesion  Capillary action  Temperature control  High specific heat  High Heat of Vaporization;Evaporative cooling  Density  Solvent  pH and Buffering © Getting Down with Science 2020 Properties of Water 1. Polarity: polar covalent bonds created by unequal sharing of electrons between oxygen and hydrogen within the molecule of water © Getting Down with Science 2020 Properties of Water 2. Cohesion: attraction of molecules for other molecules of the same kind (H2O to H2O) ● Hydrogen bonds between H2O ● molecules hold them together and increase cohesive ● forces Property allows water to resist external force Xylem of leaf Allows for the transport of H2O and nutrients against gravity in plants Responsible for surface tension o Surface H2O molecules experience greater inward pull because there are no molecules above them to balance the forces © Getting Down with Science 2020 Properties of Water 3. Adhesion: the Xylem of leaf attraction to other molecules that are polar or have charge (H2O to other molecules) Adhesion: H2O molecules ● Due to the stick to the xylem wall polarity of H2O ○ In plants, this allows water to cling to the cell walls to resist the downward pull of gravity © Getting Down with Science 2020 © Getting Down with Science 2020 Properties of Water 4. Capillary Action: the upward movement of water due to the forces of cohesion, adhesion, and surface tension Xylem of leaf ● Occurs when adhesion is Capillary action occurs moving greater than cohesion water upwards ○ Important for transport of water and nutrients in plants © Getting Down with Science 2020 Properties of Water 5. Temperature Control High Specific Heat: H2O resists changes in temperature ● How? ● Hydrogen bonds! ○ Heat must be absorbed to break hydrogen bonds, but heat is released when hydrogen bonds form © Getting Down with Science 2020 Properties of Water Temp control properties of H2O stem from these hydrogen bonds Importance of high specific heat: ● Moderates air temperature ○ Large bodies of water can absorb heat in the daytime and release heat at night ● Stabilizes ocean temp ○ Benefits marine life ● Organisms can resist changes in their own internal temp © Getting Down with Science 2020 Properties of Water ● High heat of vaporization ○ Water requires a large amount of energy to evaporate due to strong hydrogen bonds ○ Evaporative cooling: as water molecules evaporate, the surface they evaporate from gets cooler © Getting Down with Science 2020 Properties of Water Importance of evaporative cooling: ● Moderates Earth’s climate ● Stabilizes temp in lakes and ponds ● Prevents terrestrial organisms from overheating (think sweating in humans) ● Prevents leaves from becoming too warm in the sun © Getting Down with Science 2020 Properties of Water 6. Density (floating ice): as water solidifies it expands and becomes less dense ● Due to the hydrogen bonds ● When cooled, H2O molecules move too slowly to break the bonds ○ Allows marine life to survive under floating ice sheets © Getting Down with Science 2020 Properties of Water Hydrogen bonds cause water molecules to form a crystalline structure © Getting Down with Science 2020 Properties of Water Quick! Think, Pair, Share Imagine the 3D crystalline structure of ice. How many hydrogen bonds can one molecule of water make with its neighboring water molecules? Answer: four © Getting Down with Science 2020 Properties of Water 7. Solvent: dissolving agent in a solution ● Water is a versatile solvent ○ Its polar molecules are attracted to ions and other polar molecules it can form hydrogen bonds with Solution: homogenous mix of 2+ substances Solvent: dissolving agent in a solution Solute: substance that is dissolved © Getting Down with Science 2020 Properties of Water ● Remember: “like dissolves like” ● Water can interact with sugars or proteins containing many oxygen and hydrogen ● Water will form hydrogen bonds with the sugar or protein to dissolve it © Getting Down with Science 2020 Properties of Water Ionic compounds ● The partially negative oxygen in water will interact with a positive atom ● The partially positive hydrogen in water will interact with a negative atom ● Dissolves ions ClNa+ Na+ surrounded by oxygen Cl- surrounded by hydrogen © Getting Down with Science 2020 Properties of Water 8. pH and Buffering ● 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-) when dissolved in water  Water can dissociate into hydrogen (H+) and hydroxide ions (OH-) © Getting Down with Science 2020 Properties of Water ● Buffer: a solution that resists changes in pH when an acid or base is added  Buffers help maintain pH stability in biological systems © Getting Down with Science 2020 © Getting Down with Science 2020