6.2 – NOTES Ions

The theme or societal issue for the second quarter is water. What questions can you think of that municapalites, states and countries think of when dealing with water? How do we make sure we have enough water? How do we make sure that water is clean? How do we test what is in the water?

Ions in the Water One consideration that we need to think about with water is what substances are dissolved in the water. Most municipalities have ions dissolved into the public water system. If we are going to understand ions, we need to understand valence electrons…

Valence Electrons The stability of an atom is dependent on the atoms electron configuration and the number of valence electrons. Valence Electron - an electron in the outer most energy level.

The number of an elements valence electrons corresponds to family number of the Group A elements. Valence Electron diagrams are generally represented by electron dot diagrams that shows an atoms correct number valence electrons.

When an atom has a "full valence shell" which is 8 electrons, it is considered unreactive and will not bond. Which family on the periodic table is represented by these atoms? Noble Gases

All other atoms on the periodic table are trying to become stable by gaining, losing or sharing electrons to acquire a full outer valence of 8 electrons. The different types of ways that atoms gain this full outer valence is how we classify the different types of bonds. In this course we will be studying ionic and covalent bonds

Ionic compounds: substances composed of positive and negative ions Ions: electrically charged atoms or groups of atoms

Sodium atom Sodium ion  11 protons +11 11 protons 11 electrons -11 10 electrons -10 X 0 charge +1 charge, Na+

Chlorine atom Chlorine ion  17 protons +17 17 protons 17 electrons -17 18 electrons -18   0 charge -1 charge, Cl-

Ion Formation Some atoms tend to donate or accept electrons to gain a full outer valence.

Cations and Anions Metals like Sodium and Magnesium will lose electrons to become a positively charged cations. Left side of the perioidic table. Non-Metals like Oxygen and Fluorine will gain electrons to become negatively charged anions. Right side of the periodic table.

Forming Ion Practice Element Electrons Gain or Lost Ion Created Cation or Anion? S Ca K Br

Other Terminology Ionic compounds are neutral, because positive and negative charges offset each other Crystal: the 3D network of positive and negative charges Formula Unit: the simplest unit of an ionic compound

Ionic compounds dissolve in water because water has regions with partial positive and partial negative charges.

Hexane (C6H14) does not contain positive or negative regions, therefore it cannot dissolve ionic compounds. But it will dissolve the halogens (Cl2, Br2 and I2) because they also do not contain positive and negative regions. Like dissolves like!