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Ionic Bonding:
Objectives:
1. Describe the characteristics of an ionic bond.
2. State the octet rule.
3. Draw a Lewis dot diagram to show the valence electrons of an atom.
4. Distinguish between cations, anions, and polyatomic ions.
Key Terms:
ionic bond covalent bond ionic compound cation anion octet rule monatomic ion polyatomic ion binary ionic compound empirical formula
Web Resources:
Notes:
Ionic bonds & Compounds:
Ionic bonding is the result of the attraction of oppositely charged ions (atoms) or polyatomic ions (atom groups). The attraction acts much like the static electricity that holds hair to a comb on a windy day or opposite poles of a magnet. Here are some simple rules for ion formation and naming.
 | Cations - positively charged ions, usually formed from the metallic (IA, IIA, B & Al) groups |
| anions - negatively charged ions, usually formed from the nonmetal (VA, VIA & VIIA) groups |
| Ionic compounds consist of entirely ionic bonds |
| The ionic compound is electronically neutral (positive charges = negative charges) |
| Ions and ionic compounds are frequently more stable than their parent atoms |
(helios.augustana.edu/physics/ 301/periodic-table-fix.jpg)
The properties of ionic compounds are more similar to the nonmetals than the metals and include:
| High melting points |
| Form relatively strong bonds - form a crystalline structure |
| Tend to be brittle - exhibits cleavage or fracture |
| Most dissolve in water to form electrolyte solutions - a solution that is a good conductor of electricity |
| Poor conductors in the solid state |
Octet Rule:
The octet rule was a major breakthrough in the understanding of chemical bonding. What is states is that atoms will gain or loose electrons to fill their valence orbitals. Or more simply stated. The atoms will loose or gain electrons to become more like the nearest noble gas. Here are some simple rules:
(www.mansfieldct.org/schools/ mms/staff/hand/Valence.gif)
| Atoms generally have 8 valence electrons (H & He are the exception with 2 valence electrons) |
| The inner noble gas core is not involved in bonding |
| Most representative (main periodic) elements follow this ionic pattern (most transitional and rare elements do not) |
| Group IA (1) will loose 1 (1+ Charge) |
| Group IIA (2) will loose 2 (2+ Charge) |
| Group VIIA (17) will gain 1 (1- Charge) |
| Group VIA (16) will gain 2 (2- Charge) |
| Group VA (15) will gain 3 (3- Charge) |
Lewis Dot Diagrams:
Lewis Dot diagrams are an easy way to display the 4 valence orbitals involved in bonding. The element name is abbreviated and dots are filled in around the element based on the number of valence electrons present. Here are the simple rules.
| An imaginary box is drawn around the element |
| Dots (electrons) are filled in one side at a time, not doubling up until all 4 sides are full |
| No more than 2 dots can be present on any side |
| Elements with only 2 electrons will have the dots on opposite sides |
(hyperphysics.phy-astr.gsu.edu/ .../imgper/perlewis.gif)
Types of ions: | Monatomic ions - ions formed from a single atom. |
| Some transition metals can form more that one cation (Cu+, Cu2+, Fe2+, Fe3+) |
| Elements that form anions (negative charge) are renamed with the suffix -ide (Cl - chlorine, Cl- - chloride) |
(www.mpcfaculty.net/.../ monatomic_ion_configurations.gif)
| Polyatomic ions - ions formed from multiple
atoms |
(www.iun.edu/.../chemical-nomenclature/ images/polyions.jpg)
| The atoms of a polyatomic ion are bonded by covalent (shared) bonds but form an ion that participates in ionic bonding |
Binary Ionic Compounds
The simplest of the ionic compounds are called binary ionic compounds. They are formed from the union of 2 ions (cation & anion). The bond is relatively strong and the ratios of cations to anions is related to the charge on each ion.
| The ionic compound is named after its components - NaCl is sodium chloride |
The empirical formula (chemical formula) tells us about the exact numbers and ratios in the ionic compounds. The empirical formula only lists elements in their reduced quantities.
| Li+ + O2- a 2Li+O2- a Li2O Lithium sulfide |
| Caa a CaCl2 Calcium chloride |
| Mga a |
| Ka a |
| Baa a |