Organizing the Elements

 How do you organize a collection of different things?  Elements are organized into groups based upon their chemical properties  Elements that have similar chemical behavior are grouped together

 Mendeleev is the father of the modern periodic table (1869)  Organized elements by ◦ increasing atomic mass ◦ Repeating pattern of properties  Was able to predict unknown elements using his table

 Reorganized periodic table based upon increasing atomic number  Resolved inconsistencies of Mendeleev’s table

 When elements are arranged by increasing atomic number….  Their physical and chemical properties repeat in a periodic fashion (repeating pattern)  Properties of elements within a group are very similar. Why?  Properties of elements vary in a regular way across a period

 Most elements are metals (~ 80%)  Properties of metals ◦ Solid at RT (except for Hg) ◦ Good conductors of heat ◦ Electrical conductivity ◦ Luster ◦ Ductile ◦ Malleable

 Most nonmetals are gases at RT  Some solids, one liquid (Br)  Properties of Nonmetals ◦ Poor conductors of heat ◦ Poor electrical conductivity (except C) ◦ Brittle

 Metalloids sometimes called “semi-metals”  What does this tell you about metalloids?  Seven Metalloids  Properties of Metalloids ◦ Intermediate between metals and nonmetals ◦ Often depends upon conditions ◦ Example: Si is a poor electrical conductor, but is a good conductor when mixed with small amounts of boron.

 Groups ◦ vertical columns ◦ 1-18 ◦ IA – VIII A are “representative elements”  Periods ◦ horizontal rows ◦ 1-7  Squares ◦ element symbol and other information ◦ ~115

Inner Transition Metals

 Group 1:___________________?  Group 2:___________________?  Groups 3-12: ___________________?  Group 17: ___________________?  Group 18: ___________________?

 Elements are within a group have the same ending electron configurations  This is why elements within a group have similar chemical properties

 Atomic Radius: half the distance between nuclei of two like atoms joined together

 Increases from top to bottom down a group  Decreases from left to right across a period Arrow points toward increase

 Down a group, added energy levels increase radius  Because atomic number increases across a period, there is greater nuclear (+) charge  No energy levels are added across a period  This tends to draw electrons closer to nucleus, decreasing atomic radius

 Ions are atoms which have gained or lost electrons  Cations are positively charged because they have lost electrons (negative charges)  Anions are negatively charged because they have gained electrons (negative charges). Na 0 → Na + + e - Cl 0 + e - → Cl -

 Positive and negative ions form when electrons are transferred between atoms. 6.3

 Positive and negative ions form when electrons are transferred between atoms. 6.3

Cations and AnionsRelative Sizes  Cations are smaller than their parent atoms  Anions are larger than their parent atoms

 Ionic radius follows the same pattern as atomic radius but remember…  Cations are smaller than their parent atoms  Anions are larger than their parent atoms  This is because of a change in the relative strength of the nucleus, i.e…. ◦ The ratio of protons to electrons changes  In the case of cations, an energy level is lost

 Energy required to remove an e - from an atom  Decreases from top to bottom down a group  Increases from left for right across a period A 0 + E i → A + + e - Na 0 + E i → Na + + e -

 Energy required to remove 1 st, 2 nd, & 3 rd e - Al 0 → Al + + e - E i1 = 578 kJ/mol Al + → Al 2+ + e - E i2 = 1816 kJ/mol Al 2+ → Al 3+ e - E i3 = 2744 kJ/mol  Why would it require more energy to remove the 2nd electron?  The 3 rd electron?

 Why are these important? ◦ These explain trends in atomic size, ionic size, and ionization energy  Nuclear charge ◦ tends to draw e - s toward nucleus (reducing atomic radius) ◦ The bigger the atomic number, the more positive it is ◦ Increases across a period

 Electron Shielding: ◦ Inner (core) electrons “screen” outer electrons from attractive force of the nucleus ◦ Allows outer e - s to move further from nucleus (increasing atomic radius) ◦ Decreases down a group ◦ Does not change across a period

 Tendency of an atom to attract electrons to itself when bonded to another atom  A very important property!

Increases left to right across a period Decreases down a group