CHAPTER 11-1

WHY ATOMS COMBINE?

COMPOUNDSMost of the matter around you is in the form of compounds.

Like water carbon dioxide and salt

ELEMENTS Some of the matters around you such as iron and oxygen are in the form of elements.

FOR EXAMPLETable salt is composed of the elements sodium and chlorine Sodium is a shiny soft gray metal that reacts with water. chlorine is a greenish yellow gas .

QUESTIONHow are the properties of table salt

different from those of sodium and chlorine?

FORMULASymbols make up a formula, or chemical shorthand, for a compound.For example:Symbols Na and Cl represent sodium and chlorine and NaCl represent sodium chloride.Name more symbols and formulas. (page 270 table 11-1)

The chemical formula for any compound tells what elements it contains and the ratio of the atoms of those elements.

In table 11-1 what is the ratio of atoms in each compound.

An atom is chemically stable if its outer energy level is completely filled with electrons. For the atoms of most elements, the outer energy level is filled when it contains eight electrons.Atoms of the noble gases all contain eight electrons

WHY NOBLE GAS ELEMENTS ARE CHEMICALLY STABLE?Because each noble gas has an outer level that is filled with electrons.

Gaining, losing , or sharing electroms causes chemical changes.

CHEMICAL BONDIs a force that holds together the atoms in a substance.

BY SHARING OR TRANSFERRING ELECTRONS, THE ATOMS ACHIEVE MORE STABLE ARRANGEMENTS OF ELECTRONS.