Two exceptions are removing the first p electron and

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Chemistry & Chemical Reactivity
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Chapter 20 / Exercise 13
Chemistry & Chemical Reactivity
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•Two exceptions are removing the first p electron and removing the fourth p electron. •The s electrons are more effective at shielding than p electrons. So, forming the s 2 p 0 configuration is more favorable. •When a second electron is placed in a p orbital, the electron-electron repulsion increases. When this electron is removed, the resulting s 2 p 3 configuration is more stable than the starting s 2 p 4 configuration. Therefore, there is a decrease in ionization energy. •Ionization energy decreases down a group.
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Chemistry & Chemical Reactivity
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Chapter 20 / Exercise 13
Chemistry & Chemical Reactivity
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•This means that the outermost electron is more readily removed as we go down a group. •As the atom gets bigger, it becomes easier to remove an electron from the larger orbital. •Example: for the noble gases, the ionization energies follow the order He > Ne > Ar > Kr > Xe •The representative elements exhibit a larger range of values for I 1 than transition metals. Electron Configurations of Ions •These are derived from the electron configurations of elements with the required number of electrons added or removed from the most accessible orbital. Li: [He]2 s 1 becomes Li + : [He] F: [He]2s 2 2 p 5 becomes F - : [He]2 s 2 2 p 6 = [Ar] •Transition metals tend to lose the valence shell electrons first and then as many d electrons as are required to reach the desired charge on the ion. •Thus electrons are removed from 4 s before the 3 d , etc. 7.5 Electron Affinities Electron affinity is the energy change when a gaseous atom gains an electron to form a gaseous ion. •Electron affinity and ionization energy measure the energy changes of opposite processes. •Electron affinity: Cl( g ) + e Cl ( g ) E = –349 kJ/mol •Ionization energy: Cl( g ) Cl + ( g ) + e E = 1251 kJ/mol •Electron affinity can either be exothermic (as the above example) or endothermic: Ar( g ) + e Ar ( g ) E > 0 •Look at electron configurations to determine whether electron affinity is positive or negative. •The extra electron in Ar needs to be placed in the 4 s orbital which is significantly higher in energy than the 3 p orbital. •The added electron in Cl is placed in the 3 p orbital to form the stable 3 p 6 electron configuration. •Electron affinities do not change greatly as we move down in a group. 7.6 Metals, Nonmetals and Metalloids Metallic character refers to how much an element exhibits the physical and chemical properties of metals. •Metallic character increases down a group. •Metallic character decreases from left to right across a period. Metals •Metals are shiny and lustrous, as well as malleable and ductile. •Metals are solids at room temperature and have very high melting temperatures (exceptions: mercury is liquid at room temperature; gallium and cesium melt just above room temperature). •Metals tend to have low ionization energies and tend to form cations easily. •Metals tend to be oxidized when they react. •Compounds of metals with nonmetals tend to be ionic substances. •Metal oxides form basic ionic solids. •Most metal oxides are basic: •Metal oxides react with acids to form salts and water: Nonmetals •Nonmetals are more diverse in their behavior than metals.

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