Where Does Water Come From? What is an atom? • Simplest part of an element. • Protons = + charges • Neutrons = no charge • Electrons = - charge Atoms form molecules by bonding covalently. Hydrogen and Oxygen atoms covalently bond to form a water molecule. Properties of Water Molecular Structure & Polarity • Water is a "polar" molecule, meaning that there is an uneven distribution of electrons resulting in a molecule with a both a positively and negatively charged region. • In other words, the electrons are not shared equally. Covalent Bond NEXT Hydrogen Bond • Positive charges on one molecule and negative charges on another molecule attract each other and form hydrogen bonds. View the video on Polarity and H Bonding! • Click on the bucket of water below to watch the short animation on water. Click on “NEXT” when you are finished. NEXT Cohesion • Due to water’s polarity, water molecules stick to each other forming hydrogen bonds! Adhesion • Due to polarity, water sticks to other surfaces as well (unlike substances, opposites attract). Meniscus Capillary action/Low Viscosity • Due to polarity, water is able to move through small spaces, against gravity. • Cohesion and adhesion are also seen in this property. • This helps move water to the tops of tall trees and through veins in humans. Surface tension • Due to polarity, hydrogen bonds form at the surface of water, forming an “elastic film”. • Things that are light enough like water bugs can live and exist in an ecosystem on top of the water. Density • Unlike most substances, water becomes less dense when it freezes. • H bonds first condense when water is cold but then expands when water freezes leaving air pockets between the water molecules. • Ice floating acts as an insulator to water in a body of water so fish don’t die in the winter. Density •Cold water is more dense then hot water. •Cold water sinks (H bonds condense) •Hot water floats (H bonds expand) •Cause of currents in ocean; different life found at bottom of ocean compared to top. Solubility/Universal Solvent • Because of water’s polarity, it is a universal solvent (can dissolve many things) • Solute is the material being dissolved in a solution. Animation of a solution forming Due to polarity, water’s opposite charges attract to the opposite charged ions in salt. Dissolving (solvent and solute forms a solution) • The slight positively charged areas of the water, surround the Cl- parts of the salt. • The slight negatively charged areas of the water, surround the Na+ parts of the salt. • This property aides in the process of digestion. High Specific Heat Capacity (Temperature Moderation) • Water takes a long time to heat up and cool down. • This is because heat energy is first used to break H bonds, leaving less heat energy to increase movement of the molecules which is necessary to increase temperature. • This property helps maintain homeostasis (body temperature) and prevents bodies of water form changing drastically, effect life in it. pH (potential hydrogen) • Solutions are either an acid (below 7), base (above 7) or neutral (7). • Due to the dissociation of water, H2O can break apart in a solution and become H+ (making a solution acidic) or OH- (making a solution basic) • If there is an equal amount of each ion, the solution is neutral. • Water being neutral prevents tissue from being damaged in living things.