Science Csdgdsghapter 6 Notes

Elements, Compounds, Bonds I) All Organisms are composed of matter =anything that takes up space and has mass Mass= Amount of matter in an object Weight = How strongly it is pulled by gravity A) Element= Substance that can’t be broken down into other substances 1. Around 25 of the 92 elements are essential to life 2. Only 4 make up 96% of living matter: Carbon, Hydrogen, Oxygen and Nitrogen B) Compound= Substance made of two or more elements combined in a fixed ratio Example: NaCl=1:1 H2O- 2:1 C) Energy= Ability to do work 1. Potential energy = Energy stored by matter a. Is there more energy in a candy bar or a piece of wood? A loaf of bread? 2. Electrons store energy due to their position in relation to the nucleus 3. When electrons move from an orbital to another that’s further from the nucleus energy is released II) 4 chemical bonds important in biology A) 2 relatively strong ones: 1. Covalent= 2 atoms sharing valence electrons 2. Ionic= 2 atoms with a strongly unequal attraction end up with one stripping the electron from another a. Sodium Chloride (NaCl): Sodium has 1 electron in its outer shell and Chlorine has 7. The Chlorine takes the e- from Sodium B) Two comparatively weak bonds 1. Hydrogen: A Hydrogen atom covalently bonded to an electronegative atom is also attracted to another 2. Van der Waals: ‘Hot spots’ of positive and negative charge due to non-symmetrical distribution of electrons. Allows atoms and molecules to stick together.

a. Allows gecko to climb ‘smooth’ surfaces. Inside ridges are hairs with tiny projections at tip (increases surface area) so many contacts that van der waal attractions between surface and hairs will support gecko. III) Molecular shape A. Determined by position of atom’s orbitals and a combination of molecular attractions and repulsions Example: O2 is linear H2O is not B. Shape is important- Determines how molecules recognize and respond with specificity 1. Only complementary shapes will bind to each other with weak bonds Example: Endorphins (natural signal molecules) bind to specific receptors on the surface of the brain cells- (have complementary shape)- produces Euphoria and pain relief. Other molecules with a similar shape will do the same thing. It’s why morphine and heroin work – they mimic endorphins

Properties of Water I) Water - Life began in water and evolved there for 3 billion years before moving onto land A. Polar Molecule 1. Because oxygen is more electronegative than hydrogen, the espends more time close to the oxygen. Result: Oxygen has a partial negative charge and hydrogen has a partial positive charge. 2. The partial charges mean that the hydrogen of one molecule will be attracted to the oxygen on another (hydrogen bond). Each water molecule can form bonds to four neighbors B. Water is cohesive; hydrogen bonds hold water molecules together 1. Water also has strong surface tension a. At interface between liquid water and air is an ordered arrangement of hydrogen bonded molecules b. Holds together fairly strongly 2. Water is also adhesive, it sticks to other things 3. Cohesion/ adhesion allows plants to move water against gravity (more later)

C. Water has a high specific heat 2. High specific heat means that water resists temperature change when it absorbs or loses heat 4. Water also has a high heat of vaporization a. As a liquid evaporates, the surface of the liquid cools down. ’Hottest’ molecules (with most kinetic energy) most likely to leave as a gas b. Solar heat is absorbed near equator, water evaporates, Tropical air circulated toward poles, releases heat as it condenses (rain) D. Water is the solvent of life 1. Versatile solvent due to its polarity a. The partial charges will be attracted to the opposite charges on any polar molecule and pull that molecule apart. E. Ice Floats 1. Therefore, oceans and lakes don’t freeze solid a. Water reaches it maximum density at 4oC. As temp approaches 0oC the water becomes locked in a crystalline lattice. Hydrogen bonds keep molecules apart > less dense > ice floats

Acids and Bases A) Water dissociates (comes apart) B) Acids and Bases 1) Acid is a substance that increases the hydrogen ion concentration of a solution 2) A base is a substance that reduces the hydrogen ion concentration C) pH scale 1) The pH scale goes from 1 (acidic) to 14 (basic) and each level is 10 times the previous level. For example, a ph of 5 is 10 times more acidic than a ph of 6 D) Acid rain (rain, snow, or fog with a pH lower than 5.6) 1) Caused by Sulfur and Nitrogen oxides in atmosphere a. Mostly from burning of fossil fuels; coal, oil, and gas b. Common in East to burn coal to produce electricity/ heat (lots of sulfur in coal)

2) Wind carries pollutants so acid rain may fall hundreds of miles from source a. In some parts of East rain fall averaged pH 4,3 3) Most of damage is to life in streams and lakes a. Also affects plants due to leaching of soil buffers essential to growth and increasing the concentrations of acid soluble minerals poisonous to plant life