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Periodic Trends The Periodic Law The Periodic Law states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements. What is a periodic trend? Periodic trend… properties of the elements change in a predictable way as you move through the periodic table Atomic Radius The textbook definition is: Atomic radius is the distance from the center of an atom’s nucleus to its outermost electron. I will show you a visual of the property. Atomic Radius Do you have an atomic radius graph? If you turned yours in, does someone near you have a graph that you can look at? Atomic Radius Atomic Radius What is the trend for the atomic radius going down a group? Do the data points generally show an increasing pattern or a decreasing pattern? Atomic Radius When you look at the atomic radius graphs, what is the trend for atomic radius across a period? Do the data points generally show an increasing pattern or a decreasing pattern? Atomic radius • Atoms get smaller moving from the left to the right across each period • Why? • Going from the left to the right across a period, the atom’s outer electrons are increasingly attracted to the nucleus because they stay within the same principal energy level. Atomic Radius Trend for atomic radius • Atoms get larger going down a group • Why? • As you move down a group, the principal quantum number of the outermost electrons increases Atomic Radius http://www.shodor.org/chemviz/ionization/students/background.html Atomic Radius – Think of a Snowman http://www.shodor.org/chemviz/ionization/students/background.html Round 1 Larger Atomic Radius • K or Cs • K or Br • C or Pb Round 1 Smaller Atomic Radius • Pb or Os • Mg or Ar • Ar or He Ionization Energy (IE) Ionization energy this is the energy needed to remove one of the atom’s outermost electrons. Chemical Equation: Li (g) ---> Li+ (g) + e– IE = 8.64 X 10-19 J/atom I will show you a visual of the property. Ionization Energy When you look at the ionization energy graph, what is the trend for ionization energy across a period? Do the data points generally show an increasing pattern or a decreasing pattern? Trend for IE IE’s increase as you move from the left to the right across a period. • Why? • The valence shell fills moving across a period, so the number of electrons gets closer to a full valence shell of 8 electrons. It becomes harder and harder to remove an electron as the valence shell fills. Ionization Energy What is the trend for ionization energy as you move down a group? Do the data points generally show an increasing pattern or a decreasing pattern? Trend for IE IE’s decrease as you move down a group • Why? • The principal energy level increases moving down a group, so the outermost electrons are farther away from the pull of the nucleus. Ionization Energy http://www.shodor.org/chemviz/ionization/students/background.html Round 1 Smaller Ionization Energy • V or Ta • Ta or Au • Be or Sr Round 1 Larger Ionization Energy • I or Sr • Pt or Ni • Pt or At Successive Ionization Energy What do you think the term successive ionization energy means? Successive IE’s The energy required to remove a second electron from an atom is called its second IE, and so on… Ionization Energy Do you think that it takes more or less energy to remove a second or third electron? Take a look at the Ionization Energy graph with both first and second ionization energies plotted to answer this question. Successive Ionization Energies Electronegativity An atom’s electronegativity reflects its ability to attract electrons in a chemical bond. • It is NOT an amount of energy • It is NOT a property of an atom that can be directly measured Electronegativity Electronegativity The highest electronegativity values are located in the upper-right hand corner of the periodic table • Fluorine has the highest electronegativity value of 4.0 The lowest electronegativity values are located in the lower-left hand corner of the periodic table Round 1 Smaller Electronegativity • F or I • Mn or Zn • Hg or Zn Round 1 Larger Electronegativity • Bi or As • Y or In • Te or S Enjoy Periodic Trends !!!
