Topic

Ch. 8.1 Ionic Compounds

Name

Essential Question

What similarities do ionic compounds share?

Class

Chemistry - 4th block

Date

Questions

Notes

Write down questions that occur while you work.

Ionic substances have very similar properties

1. hard & brittle
   
2. solid at room temperature
   
3. very high melting points
   
4. conduct electricity if heated to liquid state
   
5. conduct electricity if dissolved in water or other solvent
   

These properties can be traced back to underlying properties and atomic level structures of the ionic substances

• ionic substance is formed when a positively charged ion (resulting from the loss of one or more electrons) is attracted to a negatively charged ion (resulting from the gain of one or more electrons).
• ions will attract each other forming ionic bonds with all neighboring atoms.

In any ionic crystal, the ratio of positive ions to negative ions must allow for all of the positive charge to cancel out the negative charge. Otherwise the ions in the crystal will not be able to hold together.

Examples:

sodium chloride (NaCl)

lead(II) sulfide (PbS)

aluminum oxide (AI2O3)

copper(II) sulfate (CuSO4)

Connecting Ionic Structure to Properties

How ionic structure leads to physical properties

1. hardness:
   each ion is attracted to and is bonded with all of its neighbors, so the ions have an interconnected network of bonds holding the entire crystal together, which gives the crystal overall strength making it hard.
2. melting point:
   This also makes it difficult to melt.
3. state of matter:
   To be in a liquid state, the ions have to have enough kinetic energy (a high enough temperature: melting point) to continually break free of the attractions, allowing them to flow together.
4. brittle:
   Putting pressure along 1 edge causes ions to shift in place so the positive & negative ions from 1 layer are not properly aligned with the oppositely charged ions in the next layer. If this happens, there’s a repulsion btw the layers and the crystal will break.
5. electric current:
   the movement of many electric charges, either ions or electrons, in a particular direction.

Polyatomic Ions

polyatomic ion: A thing (atom, molecule, etc.) becomes charged when there is an unequal number of protons and electrons.

Example: carbonate

Similarities to single atomic ions

1. pack together in a regular pattern (crystal)
2. most are negative ions, but there a few positive ions

Writing Formulas for Ionic Compounds

For ionic compounds the chemical formula tells the ratio of positive to negative ions in the entire substance. The ratio must be just right so the total positive charge from all positive ions = total negative charge from all negative ions.

Example

Writing Formulas with Polyatomic Ions
The strategy is the same as for single atomic ions, the only difference is how you show you want more than 1 polyatomic ion, which is to add parentheses:

single molecule nitrate ion = NO2-

polyatomic: three nitrate ions = (NO2-)3

Example

Writing Names for Ionic Compounds

Write the names of the ions as they appear in the formula, then add a suffix from table on p. 235:

binary ionic compound NaF = sodium fluorine = sodium fluoride (generally suffix -ide )

sodium hydroxide

polyatomic ionic compound MgCO3 = magnesium carbonate (generally suffix -ate )

aluminum phosphate

Ionic Naming with Transition Metals

On p. 235 you’ll see some positive ions followed by a Roman numeral, which describes the charge on that ion. Most transition metals can have multiple charges, so it’s specified with a Roman numeral.

• check the common ion table when writing the name of the ionic compound
• silver almost always forms +1 ion so no Roman numeral
• zinc almost always forms +2 ion so no Roman numeral

Summary

Describe what you learned, something you found interesting, any questions you have.