Logic or Scientific Madness? The Periodic Table and Trends

Alkali Metals (1A) Transition Metals Other Metals Halogens (7A) Alkali Earth Metals (2A) Rare Earth Metals Nonmetals Nobel Gases (8A) Classification of the Elements

PROPERTIES MetalsNonmetalsMetalloids Shiny when smooth and clean Solids at room temperature (except Hg) Good conductors of heat and electricity Ductile Malleable All elements on left side of table (except H) Groups 1A and 2A, highly reactive Dull looking solids OR Gases Poor conductors of heat and electricity Brittle solids Br only liquid at room temperature Upper right side of table Group 7A highly reactive Group 8A extremely unreactive Semimetals Properties of both metals and nonmetals Stairsteps separating metals on right from nonmetals on left Si and Ge most important

Atomic Radii Definition: For metals, half the distance between adjacent nuclei in a crystal of the element. For nonmetals, half the distance between nuclei of identical atoms chemically bonded together. Units of picometer (1 х meters). radius

Atomic Radii Trend--Groups TREND: INCREASES down a GROUP CAUSE: Nuclear charge increases with each step down the group. Electrons added to higher principal energy level. Outer most orbital size increases with increase principal energy level causing electrons to be farther from nucleus. Additional orbitals “shield” the outer electrons from the nucleus.

Atomic Radii--Groups Which atom is larger? Na or Cs Which atom is smaller? S or Po

Atomic Radii--Periods TREND: DECREASES from left to right in a period CAUSE: Increasing positive charge in nucleus across a period but principal energy level remains the same. Increase in nuclear- electron attraction pulls electrons closer to nucleus.

Atomic Radii--Periods Which atom is larger? Rb or I Which atom is smaller? Mg or P

Ionic Radii Metal ions form cations ***metal ions are smaller than their corresponding atomic radii Nonmetal ions form anions ***nonmetal ions are larger than their corresponding atomic radii

Ionic Radii Trend -- Groups TREND -- Both positive and negative ions increase in size down a group. CAUSE – An ion’s outer electrons are in a higher energy level as you move down a group.

Ionic Radii Trend--Periods Metal ions—generally decrease in size from left to right (not much change in d block) Cause—loss of valence electrons. ---number of protons > number of electrons, so increased electrostatic attraction between nucleus and electrons (belt tightening) Nonmetal ions—generally decrease in size from left to right. Cause---distance between nucleus and outer energy level does not change; as number of valence electrons increases the stability increases as it approaches the octet (going to the next notch on your belt)

Ionization Energy Definition: Energy required to remove an electron from its gaseous atom. Units: kJ/mole Note: The required ionization energy increases with each successive electron removal. The huge increase in ionization energy between removal of electrons in successive energy levels indicates the relationship to the “octet rule”. Low ionization energy  likely to form + ions. Large ionization energy  likely to form – ions.

Ionization Energy Trend--Groups Trend: DECREASES down a GROUP Cause: As atomic size increases, the attraction between nucleus and valence electrons decreases (shielding increases).

Ionization Energy--Groups Which has the higher ionization energy? Na or Cs Which has the lower ionization energy? O or Se

Ionization Energy Trend--Periods Trend: INCREASES from left to right in a period Cause: Going across the table, the increased nuclear charge increases the attraction for the valence electrons.

Ionization Energy--Periods Which has the higher ionization energy? K or Br Which has the lower ionization energy? C or F

Ionization Energy Period 1 Period 2 Period 3 Period 4 Period 5 Period 6 Period 7 a

Electronegativity Definition: Relative ability of atoms to attract electrons in a chemical bond. Values: 4.0 or less (always look at F) Units: Paulings (honorary only) Notes: Atom with greater electronegativity attracts bond’s electrons. Electronegativities of bonding atoms help determine type of bond formed. The most electronegative atoms are very small, nonmetals.

Electronegativity Trends--Groups Trend: DECREASES down a group. Cause: The electrostatic attraction between the nucleus and the outer electrons decreases with increasing atomic size (shielding). The ability to attract another electron is decreased by the increasing electron repulsion.

Electronegativity--Groups Which has the higher electronegativity? Al or Tl Which has the lower electronegativity? Li or Rb

Electronegativity Trends--Periods Trend: Electronegativity increases from left to right across a period. Cause: Electronegativity increases with decreasing atomic size. The attraction between the nucleus and the outer shell electrons increases (more protons in the nucleus to attract other atom’s electrons).

Electronegativity---Periods Which has the higher electronegativity? P or Cl Which has the lower electronegativity? K or As

And a Final Note on Reactivity Reactivity is determined by how easily a metal atom loses its electrons (low ionization energy) and by how easily a nonmetal atom gains electrons (high electron affinity).

Reactivity -- Metals Trends Groups: Increases as you move down a column. – Cause: Increasing atomic size; increasing number of orbits; increased shielding  easier to to remove electrons. Periods: Decreases as you move left to right across a period. – Cause: Decreasing atomic size ; increasing nonmetallic character  harder to lose an electron.

Reactivity -- Nonmetals Trends Groups: Decreases as you move down a column. – Cause: Increasing atomic size with increasing number of orbitals; increased shielding  harder to gain electrons in the outer orbital. Periods: Increases as you move left to right across a period. – Cause: Decreasing atomic size with more protons in the nucleus to attract electrons into the outer orbit  easier to gain electrons.

Periodic Table Review

Bibliography Dingrando, Laurel, et al. Chemistry Matter and Change. New York: Glencoe McGraw-Hill, Winter, Mark. “The Periodic Table of the WebElements – (July, August 2003). Hill, Wilma. “Unit 9: The Periodic Table and Trends.” Pre-AP Chemistry. Arlington, TX, July 2003