Lecture 31 Ion Formation Ozgur Unal 1

 Calcium carbonate – CaCO3 2  Table salt – NaCl  Aluminum oxide – Al2O3

 The elements in the same group show similar chemical properties.  The chemical properties are determined by the valence electrons.  These valence electrons are involved in the formation of chemical bonds between two atoms.  A chemical bond is the force that holds two atoms together.  Two types of chemical bonds: Ionic bond and Covalent bond. 3  Ionic bonds form by attraction between positive ions and negative ions.

A short review:  Electron-dot structure shows the number of valence electrons of elements. Check out Table 7.1  Ionization energy increases from left to right across a period.  Noble gases (except He) have 8 valence electrons and they have very high ionization energies  chemically stable.  The octet rule states that atoms tend to gain, lose or share electrons in order to acquire a full set of 8 valence electrons. 4

 A positive ion forms when an atoms loses one or more valence electrons in order to attain a noble gas configuration.  A positively charged ion is called a cation.  Example: Na  1s 2 2s 2 2p 6 3s 1 Ne  1s 2 2s 2 2p 6  Sodium has one valence electrons.  According to the octet rule, Na loses its valence electron to have the same electron configuration with Ne.  Therefore, Na forms a sodium cation  Na +  Note that, Na + is still a sodium atom with different chemical properties.  Na + still has 11 protons. It is not a Neon atom! 5

6  Example: Show the electron configuration of Ca and write its electron dot structure. Which noble gas configuration does Ca attain according to the octet rule? Metal Ions:  Metal ions are reactive because they lose valence electrons easily.  The group 1 and 2 metals are most reactive metals on the periodic table.  Some group 13 atoms also form ions.  Check out Table 7.2

Transition Metal Ions:  In general, transition metals have an outer energy level of ns 2.  They also fill their d orbitals.  These metals commonly lose their two valence electrons from s orbital forming +2 cations.  However, they also commonly lose their d electrons forming +3 cations or greater.  Example: Iron, Fe, can form both +2 or +3 ions. Copper, Cu, forms both +2 and +3 ions. 7

Pseudo-noble gas configuration:  According to the octet rule, elements reach chemical stability when they have the electron configuration of noble gases.  However, there are other stable electron configurations.  For example, elements in groups lose electrons to form an outer energy level containing full s, p and d sublevels.  Example: Z  1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 Zinc atom loses 2 electrons in the 4s orbital. Z +2  1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 is called pseudo-noble gas configuration. 8

9  Nonmetals easily gain electrons to attain a stable outer electron configuration.  Example: Cl  1s 2 2s 2 2p 6 3s 2 3p 5 Ar  1s 2 2s 2 2p 6 3s 2 3p 6 Cl -  1s 2 2s 2 2p 6 3s 2 3p 6  An anion is a negatively charged ion. Cl - is an anion.  Check out Figure 7.4  To designate an anion, the ending –ide is added to the root name of the element.  Cl - is called choride.  How is the anion of Nitrogen called?

 Example: Show the electron configuration and electron-dot structure of Oxygen atom. Also show the electron configuration of oxide. 10  Activity: Show the electron-dot structure, electron configuration of each element below. What type of ion(s) do these elements form? State the charge of each ion.  I – Ca – Cu  P – Rb - Cu  Ba – C – Fe  Cl – Ra – Fe