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.
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