Ionic Substances

1. Ions form when the charge imbalance between bonded atoms is so large that one or more electrons are basically, transferred from one atom to another.
2. When this happens ions are formed (both positively charge and negatively charged ions).
3. If you put a bunch of positively charged and negatively charged ions in one place the opposite charges tend to attract strongly to each other forming clusters of ions containing equal amounts of positive charge and negative charge, resulting in a neutral substance.
4. The cluster of ions formed can be of any size as long as there is an equal amount of positive and negative charge. For example, a tiny grain of table salt (NaCl), contains trillions, and trillions of sodium and chlorine ions.
5. We don't call these clusters of ions molecules. Instead they are referred to as crystals. (Any well organized group of ions or even molecules can be referred to as a crystal).
6. Below are some examples of ionic substances:

Aluminum Oxide Al2O3	Calcium Fluoride CaF2
Lead(II) Sulfide PbS	Sodium Chloride NaCl



7. Notice above that the formula for an ionic substance specifies the RATIO of one element to another, not the number of atoms. This ratio depends on the charge of each of the ions.
8. The charge of an ion depends on how many electrons it loses or gains, and the number of electrons lost or gained depends on the number of valence electrons the atoms have.
9. Through experimentation chemists discovered a pattern in which elements lose or gain electrons and how many they lose or gain.
   1. Elements in the first column tend to lose one electron forming +1 charged ions.
   2. Elements in the second column tend to lose two electrons forming +2 charged ions.
   3. Elements in the halogen family (second to last column) tend to gain one electron forming -1 charged ions.
   4. Elements in the Noble Gas family (last column) don't form any charges because they tend not to lose or gain any electrons.
10. The fact that the Noble gasses don't lose or gain electrons indicates that they have the most stable electron configuration with 8 valence electrons.
11. Atoms can lose or gain electrons to achieve these electron configurations.
    1. Metals tend to loose electrons (forming positively charged ions) because they have relatively low ionization energy.
       1. Notice the first column has all atoms with one valence electron.
          Na = 1s²2s²2p⁶3s¹
          K = 1s²2s²2p⁶3s²3p⁶4s¹
       2. If these atoms loose their one loosely held valence electron, then they will have the same electron configurations as nearby Noble Gas elements and will now have 8 valence electrons.
          Na⁺¹ = 1s²2s²2p⁶ = Ne
          K⁺¹ = 1s²2s²2p⁶3s²3p⁶ = Ar
    2. Non-metals tend to gain electrons (forming negatively charged ions) because they have relatively high ionization energy and high electronegativity.
       1. Notice the third to last column has all atoms with 6 valence electrons.
          O = 1s²2s²2p⁴
          S = 1s²2s²2p⁶3s²3p⁴
       2. If these atoms gain two more electrons, then they will have the same electron configurations as nearby Noble Gas elements and will now have 8 valence electrons.
          O^-2 = 1s²2s²2p⁶ = Ne
          S^-2 = 1s²2s²2p⁶3s²3p⁶ = Ar
    3. So, as you can see, elements in the same column (or family) will form the same charge if they lose or gain electrons. By knowing any one element from a column you know the charge that will form on any of the others.
12. By losing and gaining the appropriate amount of electrons ions are formed which then combine with each other in certain proportions to create a neutrally charged compound. For example:
    1. Sodium forms a +1 charged ion (Na⁺¹) and Sulfur forms a -2 charged ion (S^-2), so you would need two atoms of sodium to balance out each atom of sulfur. The formula for this substance would be written as Na₂S.
    2. What would be the ratio of Calcium to Chlorine ions if they were to bond together?
       1. Let's break this down into several steps:
          1. How many valence electrons does each type of atom have when neutral?
             

             Ca
             Cl

             
             
          2. Will they tend to lose or gain electrons?

             Ca
             Cl

             
             
          3. What charge will each of the ions form?

             Ca
             Cl

             
             
          4. What will be the formula for the compound formed by calcium and chlorine ions: