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University of Rhode Island
CHM 103

Electron Structure and the Periodic Law Periodic Law ● this is the statement about the behavior of the elements when they are arranged in a specific order ● in its present form the statement is: Elements with similar chemical properties occur at regular (periodic) intervals when the elements are arranged in order of increasing atomic numbers Periodic Table ● a periodic table is a tabular arrangement of elements based on their properties ● things going across are group/family ● things going down are periods ● these periods/groups have similar chemical properties Group or Family ● a vertical column of elements that have similar properties ● traditionally designated by a Roman numeral and a letter (Either A or B) at the top of the column ● designated only by a number from 1 to 18 ● Group 1A - halogens have same number of outer electrons ○ common anions for acids ○ have same number of outer electrons ● as you go down the periodic table the mass increases Period ● horizontal row of elements arranged according to increasing atomic numbers ● periods are numbered from top to bottom of the periodic table Modern Table ● elements 58-71 and 90-103 are not placed in their correct periods, but are located below the main table ● it is thought that they will be able to make or find element 118 ● most elements are metals ● metalloids have metal and nonmetal properties Examples of Group and Period location for elements ● Calcium, Ca, element 20: group IIA, period 4 ● Silver, Ag, element 47: group IB, period 5 ● Sulfur, S, element 16: group VIA, period 3 The Bohr Theory of Electron Behavior in Hydrogen Atoms ● bohr proposed that the electron in a hydrogen atom moved in any one of a series of circular orbits around the nucleus ● the electron could change orbits only by absorbing or releasing energy ● this model was replaced by a revised model of atomic structure in 1926 ● the seven shells are the same as the periods on the table the Quantum Mechanical Model of Electron behavior in atoms ● according to the qmm of electron behavior, the precise paths of electrons moving around the nucleus cannot be determined accurately ● instead of circular orbits, the location and energy of electrons moving around the nucleus is specified using the three terms shell, subshell, and orbital ● There are 7 shells ○ maximum occupancy is 2 electrons (s) ○ first shell, n=1, only hold 2 electrons ○ second shell, has two subshells, n=2, s and p orbital ○ third shell, 3 subshells, s-p-d, n=3, ○ fourth shell, 4 subshells, s-p-d-f, n=4 Shell ● the location of electrons in a shell is indicated by assigning a number n to the shell and all electrons located in the shell ● the value of n can be 1, 2,3, 4, 5, 6, 7 ● the higher the n value, the higher is the energy of the shell and the contained electrons Subshell ● each shell is made up of 1+ subshells that are designated by a letter from the group s p d f ● the # of the shell to which a subshell belongs is combined with the letter of the subshell to clearly identify subshells ● for ex. a p subshell located in the third shell (n=3) would be designated as a 3p subshell ● every shell does not have a subshell ● the number of subshells located in a shell is the same as the number of the shell. thus, shell number 3 (n=3) contains three subshells, designated 3s, 3p, and 3d ● electrons located in a subshell are often identified by using the same designation as the subshell they occupy. thus, electrons in 3d subshell are called 3d electrons Atomic orbitals ● the description of the location and energy of an electron moving around a nucleus is completed i n the qmm by specifying an atomic orbital in which the electron is located ● each subshell consists of one or more atomic orbitals, which are specific volumes of space around the nucleus in which electrons move ● All s sub consists of 1 s orbital (2 e-) ● all p sub consist of 3 p orbitals (6 e-) ● all d sub consist of 5 d orbitals (10 e-) ● all f sub consist of 7 f orbitals (14 e-) Classifying according to distinguishing electrons ● the distinguishing electron is the last electron listed in the electron configuration of the element Representative, transition, and inner-transition elements ● elements are, again, classified according to the type of distinguishing electron they contain ● groups always have the same charge of ions (ex. alkaline earth metals are all +2) Noble gases are very stable so they do not gain or lose electrons, and thus do not have ions Metals = cations (hydrogen is too) Nonmetals = anions (noble gases are neithe
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