Chemistry Chapter 2
Describe what atoms are, their structure, and how they bond. • Understand water’s features that help it support all life. • Describe carbohydrates—their structure and function.
Describe lipids—their structure and function. • Describe proteins—their structure and function. • Describe nucleic acids—their structure and function.
element - substance that cannot be broken down chemically into any other substances • atom - matter that cannot be subdivided any further without losing its essential properties
the number of protons • the number of neutrons • the number of electrons • the number of electrons in its outer orbital
Chemical BONDS • Covalent • Ionic • Polar Covalent • Hydrogen • Metallic
A sodium ion is positively charged (+1). How many electrons did it originally have in its outer orbital as a sodium atom? • 1 • 2 • 3 • 7 • 6
A chloride ion is negatively charged (1). How many electrons did it originally have in its outer orbital as a chlorine atom? • 1 • 2 • 3 • 7 • 6
Potassium chloride (KCl) is formed using ionic bonding. Potassium ions have a net positive charge (+1). Chloride ions have a net negative charge (1). How many electrons were in the outer orbital of the potassium (K) and chloride (Cl) atoms? • K=7; Cl=7 • K=1; Cl=6 • K=7; Cl=6 • K=1; Cl=7
electrons shared by the atoms spend a greater amount of time, on average, closer to one nucleus than the other • due to geometry of molecule and electronegativity differences • result is a charge separation in the molecule, where one part of the molecule has a partial negative charge and one part has a partial positive charge
molecule is not an ion (no excess of protons or electrons) • water is the most common but not the only molecule that can have polar covalent bonds • other molecules that have polar covalent bonds are peptide bonds and amines • the biological consequence of polar covalent bonds is that these kinds of bonds can lead to the formation of a weak bond called a hydrogen bond
formed when a charged part of a molecule having polar covalent bonds forms an electrostatic interaction with a substance of opposite charge • molecules that have nonpolar covalent bonds do not form hydrogen bondsclassified as weak bonds because they are easily and rapidly formed and broken under normal biological conditions • under the right environmental conditions, any compound that has polar covalent bonds can form hydrogen bonds
important in biological systems • explains many of the properties of water • used to stabilize and determine the structure of large macromolecules like proteins and nucleic acids • involved in the mechanism of enzyme catalysis
often determines the molecule’s function • enables physical properties such as taste and smell
All life on earth depends on water; organisms are made up mostly from water and require it more than any other molecule. • Hydrogen bonding among water molecules gives water several important properties that contribute to its important role in the biology of all organisms.
Cohesion – wateris attracted to other water • Adhesion – wateris attracted to other materials • oxygen end of water has a negative charge • hydrogen end has a positive charge • hydrogens of one water molecule are attracted to oxygen of another water molecule • this attractive force is what gives water its cohesive and adhesive properties
cohesion of water molecules at the surface of a body of water • all the water molecules on the surface of a quantity of water (a bead, cup, pond, etc.) are 'holding' each other together, creating surface tension
Surface tension allows water striders to 'skate' across the top of a pond. • Many objects are heavier than water, but because of surface tension, the water is able to hold up the metal. • Surface tension is not the force that keeps boats floating.
an object is immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object • applies to object of all densities • density of object > density of fluid object will sink • density of object = density of fluid object will neither sink nor float • density of object < density of fluid object will float • note: buoyant force does not depend on weight or shape of submerged object, only on weight of displaced fluid
related to adhesive properties of water • click here for demonstration • water 'climbs' up the straw as the water molecules are attracted to the straw molecules • when one water molecule moves closer to the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. • limited by gravity and size of straw; thinner straw/tube the higher up capillary action will pull the water means water will travel higher
Large bodies of water, especially oceans, can absorb huge amounts of heat from the sun during warm times of the year, reducing temperature increases on the land. • Similarly, during cold times of year the ocean slowly cools, giving off heat that reduces the temperature drop on shore.
Because there is so much salt dissolved in oceans, many of the water molecules have their positively charged sides all facing the Cl ions. • Simultaneously, many molecules of water are turned the other way: with their negatively charged sides facing the Na+ ions. • Consequently, the orderly lattices of hydrogen bonds cannot form in salt water, and it does not freeze well.
Fish live in water. What property of water is important for the survival of fish during the winter? Cohesion Heat capacity Ice floats Water is a good solvent
Cohesion Adhesion Surface tension Capillary Attraction Archimedes’ Principle High heat capacity Low density as a solid