CHM 1045 STUDGY GUIDE CHPTS 8 9 and 10 CHAPTER 8 Valence electrons Core electrons Noble gas Transition metal characteristics Isoelectronic Cations derived from transition metals Effective nuclear charge Zeff Shielding Effective nuclear charge TREND PERIODIC RELATIONSHIPS AMONG ELEMENTS Outermost electrons reactivity of elements depend on this in the highest occupied n shell all elements in a given group have the same number and type of valence e Non valence electrons in an atom Filled orbit and chemically inert Resemble one another and are set apart from other elements because they all have incompletely filled d sub shells Have the same number of electrons and therefore the same ground state electron configuration Ex H and He When a cation is formed from an atom of a transition metals electrons are always removed first from the ns orbital and then from the n 1 d orbitals The nuclear charge felt by an electron when both the actual nuclear charge Z and the repulsive effects shielding of the other electrons are taken into account Zeff Z Sigma is the shielding constant which is greater than 0 but smaller than Z Core electrons are on average closer to the nucleus than valence electrons therefore core electrons shield valence e much more than valence e shield one another Increase in effective nuclear charge from left to right across a period and from top to bottom in a group Atomic radius Atomic radius trend We define the size of an atom in terms of this which is one half the distance between the two nuclei in two adjacent metal atoms or in a diatomic molecule Because the effective nuclear charge increases from left to right the added valence e at each step is more strongly attracted by the nucleus than the one before therefore the atomic radius decreases from Li to Ne or INCREASES FROM RIGHT TO LEFT and INCREASES FROM TOP TO BOTTOM CHM 1045 STUDGY GUIDE CHPTS 8 9 and 10 Ionic radius Atom to anion size Atom to cation size Isoelectronic ions size Isoelectronic cations Isoelectronic anions Variation of physical properties Metallic property Ionization energy First ionization energy Second third IE Ionization energy TREND The radius of a cation or anion Size radius increases Because the nuclear charge is the same but the repulsion resulting from the additional e enlarges the domain of the e cloud Radius decreases Removing an e reduces electron electron repulsion but nuclear charge remains the same so e cloud shrinks Cations are smaller than anions Ex Na is smaller than F Radii of tripositive ions 3 positive charges are smaller than dipositive ions which are smaller than unipositive ions Ex Al3 Mg2 Na Radius increases as we go from ions with uninegative charge to those with dinegative charge 2 and so on From left to right across a period there is a transition from metals to metalloids to nonmetals Metallic character decreases from left to right and increases from top to bottom The minimum energy in KJ mol required to remove an electron from a gaseous atom in ground state the amount of energy in KJ needed to strip 1 mole of electrons from 1 mole of gaseous atoms measured by how tightly the electron is held in the atom Higher the IE the more difficult it is to remove the e When an e is removed from an atom the repulsion among the remaining electrons decreases Because the nuclear charge remains constant more energy is needed to remove another e from the positively charged ion thus IE s increase in this order IE1 IE2 IE3 endothermic process always positive The amount of energy in a many electron atom required to remove the first electron from the atom in its ground state Energy X g X g e X is an atom of any element Energy X g X2 g e second ionization Energy X2 g X3 g e third ionization Increase from left to right increase from bottom to top The trend is due to the increase in effective nuclear charge from left to right a larger effective nuclear charge means a more tightly held valence CHM 1045 STUDGY GUIDE CHPTS 8 9 and 10 e and thus a higher first IE Electron affinity Electron affinity TREND Ability to accept one or more electrons The negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion X g e X g Nobel gases have extremely low EA s General trends in chemical properties Diagonal relationship Hydrogen 1s1 trend Group 1A elements ns1 n 2 Same as ionization energy Increases from left to right and from bottom to top The first member in each group the element in the second period from Li to F differs from the rest of the members of the same group Ex Li exhibits many but not all the properties characteristic of the alkali metals this is because of the unusually small size of the 1st element Diagonal relationships Greater variations in properties among group 3A to 6A because elements are changing from non metals to metals or from nonmetals to metalloids Similarities between pairs of elements in different groups and periods of the periodic table first three members of second period Li Be B exhibit many similarities to those elements located diagonally below them Shown in A but can be a class of itself Like the alkali metals is has a single s valence e and forms a unipositive ion H but can also form the hydride ion H in ionic compounds In this respect H resembles the halogens Alkali metals Low ionization energies great tendency to lose the single valence e Very reactive never found in pure state CHM 1045 STUDGY GUIDE CHPTS 8 9 and 10 Group 2A elements ns2 n 2 Group 3A elements ns1np1 n 2 Group 4A elements ns2np2 n 2 Group 5A elements ns2np3 n 2 Group 6A elements ns2np4 n 2 Group 7A elements ns2np5 n 2 Group 8A elements ns2np6 n 2 Create metal hydroxides oxides peroxides or superoxides difference has to do with stability of the oxides in solid state Alkaline earth Less reactive than 1A Form M2 ions Boron is a metalloid the rest are metals B doesn t form binary ionic compounds and is unreactive toward oxygen gas and water Other group 3A form both unipositive and tripositive ions Carbon is a nonmetal and the next two members Si and Ge are metalloids The metallic elements Sn and Pb don t react with water but do react with acids Form compounds in both 2 and 4 oxidation states C and Si 4 more stable as you go down 2 becomes more stable ex in lead Nitrogen and phosphorus are nonmetals arsenic and antimony are metalloids and bismuth is a metal Greater variation of properties within the group First 3 members are non metals and the last two are
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