Remember ions and the relation between the charges of many ions and their position in the periodic table:
Ionic Compounds - Ions form ionic compounds that are electrically neutral
Na+ + Cl- --> NaCl ionic compound
Held together by ionic bonds - the force of attraction between positively and negatively charged ions.
Ionic compounds are generally made from metals and nonmetals since cations typically form from metals and anions from non-metals.
Chemical formula for ionic compounds:
Write the metal first followed by the nonmetal
Why two chlorines? Need to maintain charge neutrality - equal number of positive and negative charges
Ca2+ = +2
2Cl- =2( -1) = -2
Total sum of charges = 0
Note: we indicate the charge as a superscript after the element. Also note that in the above example it is written as 2+ and not +2.
Remember: the charge on an ion can often be rationalized by its electronic configuration and the idea that a noble gas configuration is particularly stable.
What is the chemical formula of the compound formed from Na+ and S2-?
Naming Ionic Compounds
"cation" name + "anion" name (with different suffix if a single atom)
For simple ionic compounds between a metallic element and a nonmetallic element this is of the form:
metal name + nonmetal name (with different suffix)
Some metals form cations with different charges. For these or whenever we want to emphasize the charge on the cation, a roman numeral is used. Some ions also have "common" names.
Polyatomic ions: Many common ions are made of several atoms
Some of the most important are:
Structure of ionic compounds:
Ionic bonds are strong and ionic compounds are usually solids that melt at high temperatures.
The structure of solid ionic compounds, in the most simplistic sense, can be thought of as a bunch of hard spheres packing tightly with negative ions near positive ions. Basically, the atoms are trying to fill space tightly.
See a small representative unit of sodium chloride. This structure repeats itself many many many times in a macroscopic sample such as a salt crystal in your salt shaker.
Making ionic compounds: Can't just put Na+ in a bottle because of charge neutrality. Can make ionic compounds by reacting a nonmetal (which prefers to give up its electrons) with a metal (which prefers to gain an electron).
Electron Dot Structures - Helpful tools in thinking about bonding.
Pictorial representation of the valence electron configuration around an atom. We will only consider s and p block elements (main group) and consequently only be concerned with s and p orbitals.
Carbon - 1s22s22p2 - four valence electrons
Electron dot structure - valence electrons are represented by dots placed around the chemical symbol. Electrons are placed up to two on each side of the elemental symbol for a maximum of eight, which is the number of electrons in a filled s and p shell. We place a single electron on each side before pairing them up (this is related to Hund's rule)