Tabla Periódica y Clasicación de Elementos

General Information

• The periodic table is a system for organizing elements
• It's arranged by increasing atomic number
• Similar properties are grouped together
• Elements with similar properties are in the same column (group)
• Elements with similar properties appear at regular intervals (periods)

Dobereiner's Triads

• Scientists tried to classify elements based on properties
• Dobereiner grouped elements into triads
• The atomic mass of the middle element was approximately the average of the other two elements in a triad

Newland's Law of Octaves

• Newland arranged elements in increasing atomic mass
• Properties repeated every eighth element, similar to musical octaves
• This system was not widely accepted

Mendeleev's Periodic Table

• Dmitri Mendeleev arranged elements by increasing atomic mass
• Similar properties grouped together in columns (groups)
• Left gaps for undiscovered elements
• Predicted properties of undiscovered elements correctly
• Mendeleev's periodic law states that physical and chemical properties of elements are a periodic function of their atomic masses

Modern Periodic Law

• The modern periodic law states that physical and chemical properties of elements are a periodic function of their atomic numbers
• This replaced Mendeleev's law
• Atomic number is a more accurate basis for organization than atomic mass

Periodic Table Organization

• Groups/families: Vertical columns
• Periods: Horizontal rows
• Representative elements (main group elements): Groups 1, 2, 13-18
• Transition elements: Groups 3-12
• Inner transition elements: Lanthanides (57-71) and Actinides (89-103)
• Metals: Generally on the left side of the periodic table
• Nonmetals: Generally on the right side of the periodic table
• Metalloids: Have properties intermediate between metals and nonmetals

Trends in the Periodic Table

• Atomic size: Generally increases down a group and decreases across a period
• Metallic character: Decreases across a period, and increases down a group
• Electronegativity: Increases across a period and decreases down a group
• Ionization energy: Increases across a period, and decreases down a group
• Reactivity: Varies across a period and down a group.

Groups

• Alkali metals (Group 1): Very reactive metals
• Alkaline earth metals (Group 2): Reactive metals
• Halogens (Group 17): Reactive nonmetals
• Noble gases (Group 18): Nonreactive, stable elements

Modern Periodic Table Improvements

• Use of atomic number instead of atomic mass
• More accurate organization of elements due to atomic number
• Accurate prediction of properties of undiscovered elements
• Better understanding of periodicity

Isotopes

• Atoms of the same element with different numbers of neutrons, but the same number of protons.
• Isotopes have the same chemical properties.