NIS – CHEMISTRY

Lecture 31Ion Formation

Ozgur Unal

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Ion FormationCalcium carbonate – CaCO3

Table salt – NaCl

Aluminum oxide – Al2O3

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Valence Electrons and Chemical BondsThe 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.Ionic bonds form by attraction between positive ions and negative ions.

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Valence Electrons and Chemical BondsA short review:Electron-dot structure shows the number of valence electrons of elements. Check out Table 7.1Ionization 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.

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Positive Ion FormationA 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 1s2 2s2 2p6 3s1

Ne 1s2 2s2 2p6 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!

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Positive Ion FormationExample: 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

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Positive Ion FormationTransition Metal Ions:In general, transition metals have an outer energy level of ns2.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.

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Positive Ion FormationPseudo-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 11-14 lose electrons to form an outer energy level containing full s, p and d sublevels.Example: Z 1s2 2s2 2p6 3s2 3p6 4s2 3d10

Zinc atom loses 2 electrons in the 4s orbital.Z+2 1s2 2s2 2p6 3s2 3p6 3d10 is called pseudo-

noble gas configuration.

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Negative Ion FormationNonmetals easily gain electrons to attain a stable outer electron configuration.Example: Cl 1s2 2s2 2p6 3s2 3p5

Ar 1s2 2s2 2p6 3s2 3p6 Cl- 1s2 2s2 2p6 3s2 3p6

An anion is a negatively charged ion. Cl- is an anion.Check out Figure 7.4To 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?

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Negative Ion FormationExample: Show the electron configuration and electron-dot structure of Oxygen atom. Also show the electron configuration of oxide.

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 – CuP – Rb - CuBa – C – Fe Cl – Ra – Fe