Dive in! Chemistry Review and Properties of Water!

The Atom The atom has three parts: 1) Protons 2) Neutrons 3) Electrons

Lewis Dot Diagrams

Chemical Bonds Compounds are stable combinations of different elements held together by chemical bonds. Two of the most common are ionic and covalent. When atom loses electron(s) and become positive, called cations, when they gain electron(s) and become negatively charged, called anions. Covalent bond – formed when two atoms share one or more pairs of valence electrons. H-H, O=O, N N

Differences between Ionic & Covalent bonds Ionic BondsCovalent Bonds Bond between metals and non-metals Bond between non- metals Metal loses its valence electrons to the non- metal (stolen!) Atoms share their valence electrons The atoms are held together by the attraction between (+) & (-) The atoms are bonded by the shared electrons

Water! Our bodies are 70% water Vital for Transport – carries substances in and out of cells Maintains body temperature Acts as a solvent

Covalent bonding Polar covalent bond – unequal sharing of electrons Why is water considered a polar molecule? What is a partial positive and partial negative charge? Hydrogen Bonds – Intermolecular bonds!!

Covalent bonding vs. Hydrogen bonding Covalent Bond Hydrogen Bond

Intermolecular Bonds There are three types of intermolecular bonds (collectively referred to as van der Waals forces) London Forces – exist between all atoms, very weak, unequal distribution of electrons Dipole-Dipole forces – hold molecules together (+-+-) Hydrogen Bonds – H of one molecule and N, O, F of a nearby polar molecule

Water is the solvent of Life! Solute – substance dissolved in a solvent to form a solution Solvent – fluid that dissolves solutes Example: Ice Tea – water is the solvent and tea and sugar the solutes Universal Solvent

11 Water-soluble protein

Properties of Water cohesion = water attracted to other water molecules because of polar properties adhesion = water attracted to other materials surface tension = water is pulled together creating the smallest surface area possible Cohesion, Adhesion and Surface Tension

Properties of Water Capillary Action Because water has both adhesive and cohesive properties, capillary action is present. Capillary Action = water’s adhesive property is the cause of capillary action. Water is attracted to some other material and then through cohesion, other water molecules move too as a result of the original adhesion. Ex: Think water in a straw Ex: Water moves through trees this way

14 Surface tension

Properties of Water In order to raise the temperature of water, the average molecular speed has to increase. It takes much more energy to raise the temperature of water compared to other solvents because hydrogen bonds hold the water molecules together! Water has a high heat capacity. “The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.” High Heat Capacity

Properties of Water Density Water is less dense as a solid! This is because the hydrogen bonds are stable in ice – each molecule of water is bound to four of its neighbors. Solid – water molecules are bonded together – space between fixed Liquid – water molecules are constantly bonding and rebonding – space is always changing

Ice, water, vapor

Properties of Water So, can you name all of the properties of water? Adhesion Cohesion Capillary action High surface tension Holds heat to regulate temperature (High heat capacity) Less dense as a solid than a liquid

Acids and Bases Strength compared using pH scale Ranges from 0 – 14 Logarithmic Scale (gets 10x bigger/smaller) Acid – donates H+ when added to aqueous solutions Ranges from pH Base – breaks up into hydroxide (OH-) ions and another compound when placed in an aqueous solution Ranges from pH 7.1 – 14 Distilled water is pH 7.0 or neutral. Why? H 2 O H+ + OH-

Acids and Bases Buffers – compounds used to maintain a contant pH within a system H 2 CO 3 H + + HCO 3 - Carbonic acid bicarbonate ion

22 Buffers resist changes to the pH of a solution when H + or OH - is added to the solution. Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted.

Acids and Bases

Making Biological Molecules Condensation Reaction Hydrolysis Reaction and H 2 O H2OH2O