Ions and Ionic Compounds PDF

TOPIC 2: Atoms, Molecules and Ions ❖ L 3: Atoms - Atomic structure, -Atomic Weights, Atomic Number, Isotope ❖ L 4-L7: The Periodic Table (PT) - Electron Configuration - Groups and Periods...

TOPIC 2: Atoms, Molecules and Ions ❖ L 3: Atoms - Atomic structure, -Atomic Weights, Atomic Number, Isotope ❖ L 4-L7: The Periodic Table (PT) - Electron Configuration - Groups and Periods - Trends in the Periodic Table ❖ L 8: Molecules and Molecular Compounds (Covalent Bonding) ❖ L 9: Ions and Ionic Compounds (Ionic Bonding) 1 IONIC COMPOUNDS When a metal combines with a non-metal = the valence electrons of the metal are transferred to the valence shell of the non-metal E.g Ca [noble gas] 2s2 Cl [noble gas] 2s22p5  NB: Ions are formed the atom attains the same number of electrons as the nearest noble gas. For example, each one of N,O,F, (period 2) gains And each one of Na, Mg and Al (period 3) loses electrons to attain noble gas electronic structure for Ne. Ion formation All of the following species therefore are isoelectronic; N3- ,O2- ,F- , Ne, Na+ ,Mg2+ , Al3+ Ion formation For an atom, number of electrons = number of protons, hence net charge is zero. When an atom loses or gains valence electron == ion. 4  Cation formation. Each electron lost from an atom increases the overall positive charge of the atom by one unit, e.g. Ca atom 2 electrons lost > 2e- + Ca2+ Al atom 3 electrons lost > 3e- + Al3+ Metallic elements typically form cations, and their charges are often related to the group to which they belong in the Periodic Table. 5  anion formation. Each electron gained by an atom increases the atom’s negative charge by one unit, e.g. Cl atom + e- 1 electron gained > Cl- O atom + 2e- 2 electrons gained > O2- N atom + 3e- 3 electrons gained > N3- non-metallic elements form anions, and their charges are often related to the group to which they belong in the periodic table. 6  Inorganic Compounds Summary of ion formation by Group Group 1,2 : M+ , M2+ (e.g. Na+ , Ca2+) Group 13 : M3+ (e.g. Al3+, Ga3+) Group 15 : X3- (e.g. N3-, P3-) Group 16 : X2- (e.g. O2-, S2-) Group 3-12 (Transition Metals) variable/multiple (e.g. Cu+ , Cu2+ , Cu3+ )  Process Ion produced Ca → Ca2+ + 2e- Ca2+ Ion Al → Al3+ + 3e- Al3+ formation summary N + 3e- → N3- N3- O + 2e- → O2- O2- Exercise: Write an equation for the formation of each of the ions in the list below: N3- O2- F- Ne Na+ Mg2+ Al3+  Ionic Compounds After losing the n electrons, the metal atom becomes positively charged (now has more protons than electrons), n+ charge and the non-metal, having gained the n electrons, becomes negatively charged (now has more electrons than protons), n- charge Ionic compounds consist of positive and negative ions held together by the attraction between their opposite charges (electrostatic forces)  Conceptualization of the (stepwise) formation of an ionic compound Formation of cations by loss of e- e.g1. When a Ca atom loses two electrons to form a cation with a charge of 2+ Ca → Ca2+ + 2e- Ionic (conventionally, not Ca - 2e- → Ca2+) e.g 2 Al loses three electrons to form a cation with charge of 3+ Compounds Al → Al3+ + 3e- Formation of anions by gain of e- e.g. An oxygen and nitrogen atom, respectively gain two and three electrons to produce anions with 2- and 3- , respectively O + 2e- → O2- N + 3e- → N3- Ionic Compounds The metal (M) is now a cation, Mn+ , while the non- metal (X) has become an anion, Xn- The cation and anion are attracted to each other by an electrostatic force of attraction since they have opposite charges They form a geometric array of ions called a crystal lattice.  The formation of the crystal lattice from the attraction of the ions can be generally represented as below, where n usually ranges from 1 to 3; Ionic Compounds M n+ + Xn- → MX crystal lattice (A familiar example is NaCl: Na+ + Cl- → NaCl)  Ionic Compounds Each one of the cations A helpful principle in determining formed above can combine the formula of an ionic compound: with either one of the anions The total charge supplied by each ion in such proportions as would in the formula of an ionic compound ensure that the overall charge is the lowest common multiple of the ionic compound is (LCM) of the charges of the neutral. combining cation and anion Ions Charge LCM # of Cations # of anions to Therefore combining to give LCM give LCM formula is; Ca2+ and O2- 2 1 1 CaO Ca2+ and N3- 6 3 2 Ca3N2 Al3+ and O2- 6 2 3 Al2O3 Al3+ and N3- 3 1 1 AlN  ▪ Three-dimensional array of of ions, each surrounded by oppositely charged counter- ion, eg NaCl Physical Properties of Ionic Compounds ▪ Mostly solids at room temp ▪ High m.p and b.p due to strong electrostatic attraction between anions and cations  Electrical conductivity Physical Properties of Ionic Compounds