CHEMICAL BONDS & pH SCIE 203 SPRING 2008

CHEMICAL BONDS Atom - smallest part of an element that can take part in reactions. Molecule - a stable arrangement of atoms chemically bonded together that can exist independently. Element - contains atoms all of one sort. Compound - two or more different elements chemically combined

CHEMICAL BONDS ◦Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells.  These interactions usually result in atoms staying close together.  The atoms are held together by chemical bonds. 3 types of chemical bonds ◦Ionic Bonds—weakest ◦Hydrogen Bonds— ◦Covalent Bonds— strongest

IONIC BONDS ◦When an atom loses or gains electrons, it becomes electrically charged.  Charged atoms are called ions.  Ionic bonds are formed between oppositely charged ions.

HYDROGEN BONDS ◦Water is a compound in which the electrons in its covalent bonds are shared unequally.  This causes it to be a polar molecule, one with opposite charges on opposite ends.

COVALENT BONDS A covalent bond forms when two atoms share one or more pairs of outer- shell electrons

pH pH is a measures the concentration of Hydrogen ions (H + ) in a solution If concentration of H+ is high then pH is low, if concentration is low pH s high A substance added to a solution that increases H+ concentration is called an acid If it reduces the number of H+ it is a base

pH To describe the acidity of a solution, we use the pH scale. pH scale runs from 0-14 ◦Between 0 and less then 7 is acidic ◦Over 7 to 14 is basic ◦7 in neutral ◦Each unit of change represents a tenfold change in acidity

pH Acids are corrosive and taste sour ◦Reacts w/ bases to form salt and water Bases are corrosive and have a ‘soapy’ feel and tastes bitter ◦Accepts protons

pH Positive charges from H+ alter the environment of other molecules in solution. The forces cause molecules to change shape. Shape changes in molecules affect their effectiveness