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Elements, Water and pH Chemistry of Life All matter is composed of tiny particles called atoms. There are 109 types of atoms. A substance made up of one kind of atom is called an element. An atom is the smallest part of an element that still has the properties of that element. A is for Atom https://www.youtube.com/watch?v=Oc2s9q 2nh48 CHNOPS Molecules and Compounds When two or more atoms bond, they form a molecule. A compound is a substance made of 2 or more different elements In Your Notes… How is it that two atoms can make a molecule but not a compound? Why do elements bond? • Elements bond(stick together) because of the structure of their electrons. • If the outer ring of electrons is not full with 8 total electrons, the atom will bond to complete it’s outer ring. (Hydrogen’s outer ring is full with 2) Ionic Bonds Ionic Bonds are formed when atoms lose or gain electrons and become electrically positive or negative. The resulting opposite charges a drawn to each other. Covalent Bonds Formed when atoms “share electrons” How many drops of water fit on a Penny? Have every person in your lab group estimate how many drops of water can fit on the top of a penny before it spills over the edge and gets the paper towel wet. Test it to see who was the closest to the correct answer. Polar Molecules Water is a “Polar Molecule” because it has a positive and a negative side to it. Because the electrons from the Hydrogen atoms are stuck in bonds with the Oxygen, the Hydrogen side becomes positive and the Oxygen side becomes negative. Water is the “Solvent of Life” Because of water’s polarity, it breaks ionic bonds to form solutions. Characteristics of Water Because water is “polar” it has the following 2 characteristics. Cohesion-water molecules stick to each other Adhesion- water molecules stick to other substances. Non-polar Molecules Non-polar molecules have the same charge all the way around. There are no “poles” All lipids are non-polar Oil and Water do not mix! The cell membrane forms because phospholipid molecules are polar(hydrophilic) on one end and nonpolar(hydrophobic) on the other end. pH or Hydrogen Ion to Hydroxide Ion ratio The pH scale is a scale from 1 to 14. a pH of 7 is “balanced” or neutral. A pH below 7 is acidic and above 7 is alkaline or basic. Acids have more hydrogen Ions than Hydroxide ions. Bases have more Hydroxide ions than Hydrogen Ions. The pH Scale pH explained http://www.youtube.com/watch?v=Xeuyc55 LqiY