Ionic Compounds
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Explain limitations of diagrams and models
Work out the empirical formula from models and diagrams
Identify ionic compounds from structures
Ionic compounds are neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions.
Ionic substances form giant ionic lattices containing positive and negatively charged ions.
They have high melting and boiling points, and conduct electricity when melted or dissolved in water.
An ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding
Ionic compounds often form crystals when they are arranged in giant ionic lattices. The illustration shows part of a sodium chloride (NaCl) ionic lattice.
Positively charged Na ions and negatively charged Cl ions
The empirical formula of a compound is the simplest whole number ratio of each type of atom in a compound
An empirical formula can be calculated from information about the mass of each element in a compound or from the percentage composition.
How to:
Start with the number of grams of each element, given in the problem.
Convert the mass of each element to moles using the molar mass from the periodic table.
Divide each mole value by the smallest number of moles calculated.
Round to the nearest whole number. This is the mole ratio of the elements and is.
Dot and Cross
Pros:
Cons:
Suggests electrons from different atoms are different
Does not show the structure formed
Shows how electrons are shared in bonds or lossed or gained
Ball and Stick
Pros:
Cons:
Shows the structure of a molecule
Show how many bonds there actually are
Shows that the atoms are 3D
Suggests bonds are physical "sticks"
Shows atoms too far apart from each other
Metallic Bonding
Pros:
Cons:
Shows lattice structure
Helps explain properties such as conductivity and malleability
Does not show that ions would be constantly vibrating
Doesn't show that the electrons move
3D Space Filled Model
Pros:
Cons:
3D space filled models are very useful to see the shapes of molecules or structures
They do not show how atoms are bonded
They do not allow all atoms to be seen
You cannot determine a formula from them