CHEMICAL BONDS & pHCHEMICAL BONDS & pHSCIE 203

SPRING 2008

CHEMICAL BONDSCHEMICAL 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 BONDSCHEMICAL 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 BONDSIONIC 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 BONDSHYDROGEN 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 BONDSCOVALENT BONDS

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

pHpH

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

pHpH

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

pHpH

Acids are corrosive and taste sour◦Reacts w/ bases to

form salt and waterBases are corrosive

and have a ‘soapy’ feel and tastes bitter◦Accepts protons

pHpH

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