Ionic BondsChapter 13 Section 2

Objectives:

•Explain how ionic bonds form

•Describe how positive ions form

•Describe how negative ions form

•Explain why ionic compounds are neutral

Forming Ionic Bonds:

•Ionic bond: a bond that forms when electrons are transferred from one atom to another

•One or more valence electrons get transferred

•These bonds form so that the outermost energy level gets filled

Ionic Bond animation:

http://facstaff.gpc.edu/~pgore/PhysicalScience/ionic_bond_animation.gif

Charged Particles:

•Atoms are neutral (protons = electrons)

•When electrons are transferred, ions form

•Ion = charged particles that form when atoms gain or lose electrons

•Atoms need to be nearby for this to happen

Forming Positive Ions:

•Ionic bonds form during chemical changes when atoms pull electrons away from other atoms

•If electrons are lost, the atom becomes more positive

•The ion then has a positive charge (protons outnumber electrons)

Example: Sodium & Chlorine

http://www.revisionworld.com/files/ionic%20bonding.jpg

Metal Atoms & the Loss of Electrons:•Atoms of most metals have few valence

electrons

•Metals tend to lose their valence electrons and become positive ions

•Sodium in the previous example has a 1+ charge

•The chemical symbol becomes: Na+

Another example: Aluminum•Can you write the chemical symbol for this ion?

http://images.suite101.com/319550_com_558pxelectron_shell_013_aluminium_svg.png

The Energy Needed to Lose Electrons:•Energy is needed to pull electrons away

from atoms

•Metals only require a little bit of energy to lose their electrons

•Groups 1 & 2 lose electrons very easily (reactive!)

Forming Negative Ions:

•These atoms gain electrons

•They have more electrons than protons

•These ions have a negative charge

Example: Fluorine

http://www.jirvine.co.uk/Chemistry_GCSE/C3A/Fluorine.JPG

Nonmetal Atoms Gain Electrons:•The outer energy level of a nonmetal is

almost full

•They tend to gain electrons easily

•Oxygen is a good example

•An oxide ion has a charge of 2-

•Negative ions always end in -ide

Example: Oxygen

http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_oxygen_2_ion.gif

The Energy of Gaining Electrons:• Energy is given off by nonmetal atoms when

they gain electrons

• Atoms of Group 17 give off the most energy when they gain electrons (very reactive!)

• Ionic bonds form between metals & nonmetals

• This bond will form if the nonmetal releases more energy than is needed to take electrons from the metal

Ionic Compounds:

•The # of electrons lost by the metal atoms = the # gained by the nonmetal atoms

•The ions that bond are charged, but the compound is neutral

•The charges of the ions cancel each other

•They form a 3-D repeating pattern: crystal lattice

Properties of Ionic Compounds:

•Brittleness

•High melting points

•High boiling points

•Ex: NaCl (table salt)

NaCl – crystal lattice structure

http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/PublicWaterSupply/images/nacl.jpg

Quick Quiz:

•How does an atom develop charge?

•What is a crystal lattice?

Reference:

•Holt Science and Technology: Physical Science. New York: Henry Holt & Co, 2007. Print.