7.5 and 7.6 Narrated Notes

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Chapter Seven – Part 3 : 

Chapter Seven – Part 3 7.5 – Electron Affinities 7.6 – Metals, Nonmetals, and Metalloids

Ionization Energy : 

Ionization Energy The positive value of ionization energy means that energy must be put into the atom in order to remove the electron 7.5

Electron Affinity : 

Electron Affinity The energy change that occurs when an electron is added to a gaseous atom or ion For most atoms, energy is released when an electron is added 7.5

Ionization Energy Versus Electron Affinity : 

Ionization Energy Versus Electron Affinity Ionization energy measures the ease with which an atom loses an electron, whereas electron affinity measures the ease with which an atom gains an electron 7.5

Electron Affinity : 

Electron Affinity Why are the electron affinities for the noble gases positive numbers? The anion is higher in energy than are the separated atom and electrons When you add an electron to a noble gas, the electron has to occupy a previously unoccupied higher energy level 7.5

Electron Affinity : 

Electron Affinity Why are the electron affinities for Be and Mg positive? The added electrons would reside in a previously empty p subshell that is higher in energy 7.5

Electron Affinity : 

Electron Affinity Why is the electron affinity for N a positive value? Nitrogen (and the rest of the group) have a half-filled p subshell The added electron must be put in an orbital that is already occupied, resulting in larger electron-electron repulsion 7.5

Electron Affinity : 

Electron Affinity What is the general trend for electron affinity as you move across a period? In general, the electron affinity becomes more negative as you move across a period There are many exceptions to this rule! There is no real group trend for electron affinity 7.5

Electron Affinity : 

Electron Affinity 7.5

Metals, Nonmetals, and Metalloids : 

Metals, Nonmetals, and Metalloids Metallic character generally increases as we proceed down a column of the periodic table 7.6

Characteristics of Metallic Elements : 

Characteristics of Metallic Elements Have a shiny luster; various colors, although most are silvery Solids are malleable and ductile Good conductors of heat and electricity 7.6

Characteristics of Metallic Elements : 

Characteristics of Metallic Elements Most metal oxides are ionic solids that are basic Write a reaction for a metal oxide with an acid MgO + 2 HCl MgCl2 + H2O 7.6

Characteristics of Metallic Elements : 

Characteristics of Metallic Elements Tend to form cations in aqueous solution Metals tend to have low ionization energies and therefore tend to form positive ions relatively easily 7.6

Characteristics of Metallic Elements : 

Characteristics of Metallic Elements The alkali metals tend to form cations with a charge of +1 The alkaline earth metals tend to form cations with a charge of +2 Many transition metals form cations with variable charge 7.6

Characteristics of Metallic Elements : 

Characteristics of Metallic Elements Compounds of metals with nonmetals tend to be ionic substances Most metal oxides tend to be basic Write the reaction of a metal oxide combining with water CaO + H2O Ca(OH)2 7.6

Practice Exercise : 

Practice Exercise Write the balanced chemical equation for the reaction between copper (II) oxide and sulfuric acid CuO + H2SO4 CuSO4 + H2O 7.6

Characteristics of Nonmetallic Elements : 

Characteristics of Nonmetallic Elements Do not have a luster; various colors Solids are usually brittle; some are hard, some are soft Poor conductors of heat and electricity 7.6

Characteristics of Nonmetallic Elements : 

Characteristics of Nonmetallic Elements Most nonmetal oxides are molecular substances that form acidic solutions Write a reaction for a nonmetal oxide with an acid P4O10 + 6 H2O 4 H3PO4 7.6

Characteristics of Nonmetallic Elements : 

Characteristics of Nonmetallic Elements Tend to form anions or oxyanions in aqueous solutions. Because of their electron affinities, nonmetals tend to gain electrons when they react with metals 7.6

Characteristics of Nonmetallic Elements : 

Characteristics of Nonmetallic Elements Compounds composed entirely of nonmetals are molecular substances 7.6

Practice Exercise : 

Practice Exercise Write the balanced chemical equation for the reaction of solid tetraphosphorus hexoxide with water P4O6 + 6 H2O 4 H3PO3 7.6

Metalloids : 

Metalloids Metalloids have properties intermediate between those of metals and those of nonmetals 7.6