Trends in the redox properties of compounds in periods and groups. You will:be able to predict the patterns of changes in the properties of compounds of chemical elements by period and groupbe able to predict the properties of chemical elements and their compounds by position in the periodic system Periodicity of oxidation-reduction properties The oxidation-reduction properties of the elements also exhibit periodic changes. The periodicity of these changes is as follows: the elements occupying the left part of the periodic table, that is, the alkali and alkaline-earth metals are strong reducing agents. Then, as you move to the right along each period, reducing properties decreases and oxidizing properties increases.Finally, group 17 are strong oxidizers. Let us now consider this pattern in somewhat more detail.The reducing properties of the metals are characterized by low ionization energy, low electron affinity and low electronegativity.Examples of reducing properties of metals:React with oxygen and oxygen 2Mg(s) + O2(s) ? 2MgO(s)2. React with halogens 2Na(s) + Cl2(g) ? 2NaCl(s) Reactions which are given above are examples of reducing properties of metals since in each case metals easily loses electrons: Mg ? Mg+2 + 2e- Na ? Na+1 + e- Oxidizing properties of elements of the 17th group, which are placed on the right side of the table, are characterized by high ionization energy, high electron affinity and high electronegativity.For instance, chlorine element has properties of a strong oxidizer. It reacts violently with hydrogen in the sunlight, forming hydrogen chloride.p-Elements, which are closer to the middle part of the periods, show weak reducing and (or) weak oxidizing properties. For example, the silicon belonging to 14th group reacts slowly with oxygen, forming an oxide. Si(s) + O2(g) ? SiO2 The nitrogen belonging to the 15th group can act both as a weak reducer and as a weak oxidizer. For example, it behaves as a weak reducing agent in reaction with oxygen: N2(g) + O2(g) ? 2NO(g)In contrast, in a reaction with hydrogen, nitrogen behaves as a weak oxidizer: N2(g) + H2(g) ? NH3(g)The transition elements have the properties of weak reducing agents. For example, hot iron reacts with water vapor to form hydrogen: Fe(s) + H2O(g) ? FeO(s) + H2(g) Oxidizing and reducing strength of elements by groupsGroup12Groups (3-12) Transition metals1314151617Strengthstrong oxidizersstrong oxidizersweak oxidizersweak oxidizers or weak reducersweak oxidizers or weak reducersweak reducer or weak oxidizerstrong oxidizer or weak reducerstrong oxidizer ???? ????? Identifying the properties of chemical elements according to place in the Periodic tableExample:For example, let’s describe of the chemical element with the atomic number 15 by position in the periodic system of elements and the structure of the atom.Solution:1. First, we find the chemical element #15 and write down its symbol and name.Chemical element number 15 is phosphorus. His symbol is P. 2. We characterize the position of the element (number of periods, group).Phosphorus is placed in the 3rd period and 15th group. 3. Let us give a general characteristic of the composition of the atom of a chemical element (nuclear charge, atomic mass, number of protons, neutrons, electrons and electron configuration). The charge of the nucleus of the phosphorus atom is +15. The relative atomic mass of phosphorus is 31. The nucleus of the atom contains 15 protons and 16 neutrons (31-15 = 16). The phosphorus atom has three energy levels, on which there are 15 electrons.Electron configuration: 15P: 1s2 2s2 2p6 3s2 3p34. We determine the maximum and minimum degree of oxidation of the phosphorus atom.Phosphorus is the main group of the 15th group, therefore the maximum degree of oxidation of phosphorus +5. The minimum degree of oxidation for non-metals is in most cases equal to the difference between the group number and the number eight. So, the minimum degree of oxidation of phosphorus -3.5. Determine the type of chemical element (metal or nonmetal, s-, p-, d- or f-element).Phosphorus is a nonmetal. Since the last subshell in the phosphorus atom, which is filled with electrons, is the p-subshell, Phosphorus belongs to the family of p-elements.5. We compose the formulas of higher oxide and phosphorus hydroxide and characterize their properties (basic, acidic or amphoteric).The highest phosphorus oxide, P2O5, exhibits the properties of an acid oxide. The hydroxide corresponding to the higher oxide, H3PO4, exhibits the properties of the acid. Let us confirm these properties by the equations of chemical reactions:P2O5 + 3Na2O = 2Na3PO4H3PO4 + 3NaOH = Na3PO4 + 3H2O6. Let’s compare the non-metallic properties of phosphorus with the properties of the neighboring elements by period and group.The neighbor of phosphorus in the subgroup is nitrogen. Neighbors of phosphorus over a period is silicon and sulfur. The non-metallic properties of the atoms of the chemical elements of the main groups increase with the increase in the ordinal number in the periods and decrease in the groups. Therefore, the nonmetallic properties of phosphorus are more shown than in silicon and less shown than in nitrogen and sulfur.