Periodic Table and Trends

• Periodic Table of Elements


  Tabular display of elements and their chemical properties
• Periodic Table


  • Elements are arranged by the atomic number
• Key Information of elements

  • Chemical Symbol
  • Atomic Number
  • Mass Number
  • Atomic Weight
• Chemical Symbol


  Notation of one or two letters representing an element
• Atomic Number


  Number of protons in the nucleus and number of electrons in the electron cloud
• Mass Number


  Sum of the number of protons and neutrons in an isotope
• Atomic Weight


  Weighted average of the masses of the element's isotope. Rounding it to the nearest whole number yields the mass number
• By 1800, 31 elements were known
• By 1865, 63 elements were identified
• In recent years, 118 elements have been identified, 94 of these are naturally occurring and 24 are synthetic (elements 95-118)
• Acquired knowledge regarding these elements are organized by scientists by classifying the elements
• Periodic Law


  • When elements are arranged based on their atomic mass, certain sets of properties repeat periodically
  • The physical and chemical properties of elements are a periodic function of their atomic masses
• Moseley's Observation


  Observed regularities in the characteristic X-ray spectra of the elements, showed that the atomic number is more important than the mass
• Modern Periodic Law


  "The physical and chemical properties of the elements are periodic functions of their atomic numbers"
• Period


  Horizontal row of elements in the periodic table, indicates the number of principal energy levels in the atoms of each element
• Group


  Vertical column, elements in the same group has the same number of electrons in their outer orbital level, the number of electrons in the outer shell increases from one group to another, there are exceptions in the transition elements
• Ways of numbering the groups

  • IUPAC (Group 1-18)
  • US (I-VIII) and letters A and B Families
• Periods and Groups


  Elements in the vertical column constitute a group or family and exhibit similar chemical behavior because they have the same number and distribution of electrons
• Classification of groups and periods

  • s-block
  • p-block
  • d-block
  • f-block
• Properties of Metal Elements

  • Solid at room temp except for liquid mercury
  • good conductors of electricity
  • ductile and malleable
  • Lustrous/ shiny
  • Tends to lose electrons
  • Reacts with water to form basic oxides
  • Nonmetal reacts with water to form acidic oxides
• Families of the Periodic Table

  • Alkali Metals
  • Alkaline Earth Metals
  • Transition metals
  • Basic/Poor Metals
  • Lanthanides and Actinide Metals
  • Metalloids
  • Non-Metals
  • Halogens
  • Noble Gases
• Alkali Metals


  • Reactive, do not occur freely in nature, a malleable, ductile, good conductor, readily lose 1 electron to form cations with charge 1+
• Alkaline Earth Metals


  • Somewhat reactive, do not occur freely in nature, shiny, silvery -white, readily lose 2 electrons to form cations with charge 2+
• Transition Metals


  • Bridge between metal and non-metal properties, unfilled d orbital thus tends to gain electrons, ductile, malleable, and good conductor
• Basic/Poor Metals


  • Most electronegative, least reactive, melting and boiling point are generally lower
• Lanthanides and Actinide Metals


  • Ductile and malleable, have a high-density
• Metalloids


  • Have properties of metal and nonmetal, semi-conductors, can carry electrical charge under special conditions, useful in computers and calculators
• Non-metals


  • Low density, melting and boiling point, tend to gain or share electrons, not a good conductor, brittle, not reflective
• Atomic Radius


  Size of an atom measured as the distance from the nucleus to the outermost shell, measured in Angstroms (1A=10^-10) or picometer (1pm=10^12m), measured using x-ray and electron diffraction method
• Covalent Radius


  Half the distance between two nuclei in a covalent bond (non-metallic radius), if the atom is metal, one-half of the distance between nuclei of two adjacent atoms in the metallic crystal is measured
• Van der Waals Radius


  If the atom does not bond, one-half of the distance between the nuclei of two adjacent atoms when they are closest is measured as its radius, noble gases are monoatomic, their non-bonded radii values are very large
• Atomic Size Trend


  • In a given group or family, atomic size increases from top to bottom, as the atomic number increases, the energy level also increases thus making the atom bigger
• Atomic Size Trend


  • Atomic size decreases from left to right with increase in the atomic number, increase in atomic number means increase in protons causing a stronger and effective nuclear charge thus pulling in electrons towards the nucleus resulting in shorter radius between the nucleus and the outermost shell
• Electronegativity


  Ability of an atom to attract electrons in a chemical bond, electronegative elements attract electrons (non metal), electropositive elements releases electrons (metals)
• Electronegativity Trend


  • Increases from left to right, the effective nuclear charge which is proportional to the atomic number charge increases causing a stronger attraction for the shared electrons
• Electronegativity Trend


  • Decreases as it goes down, the number of shielding electrons increases and the effective nuclear charge lessens with distance causing less attraction for the shared electrons
• Ionization Energy


  Energy needed to remove an atom's most loosely held electron, measured in kilojoule per mole
• Ion


  Group of atoms with nonzero charge
• Ionization Energy Trend


  • Increases from left to right with the increasing atomic number, increase in atomic number means an additional proton causing attraction to electrons which requires more energy to be removed
• Ionization Energy Trend


  • Decreases as the atomic number increases from top to bottom, every increase in the atomic number an a step downward means an additional energy level farther from the nucleus thus attraction between electron and proton is lower