The Periodic Table

4A: Organizing the elements

Chemical Discoveries

Today we know of 118 elements

• Alchemists: scientists who were interested in turning low-value materials such as lead into into high-value substances like gold

• Robert Boyle: his work solidified the position that matter consisted of indivisible particles of elements, rejecting the Greek concept of matter as mixtures of the five basic elements

• Antoine Lavoisier: played a crucial role in our understanding of the elements; formed a list that included thirty-three elements known in his day

Periodicity

• Triads: a model of periodicity developed by Johann Döbereiner that is based on groups of three elements with similar properties

• Periodicity: the idea that properties of elements repeat in regular patterns in relation to some basic characteristic such as atomic mass or atomic number

• Law of Octaves: the principle published by chemist John Newlands that stated that the properties of the forty-nine then-known elements repeated every eighth element, as in a musical octave

• Periodic Law: the law that states that the properties of the elements vary with their atomic numbers in a regular, repeated pattern

The Modern Periodic Table

• Periodic Table of the Elements: a table of the chemical elements arranged to display their periodic properties in relation to their atomic numbers

• Family: a column of elements in the periodic table having similar valence electron arrangement, resulting in similar valence

4B: Classifying the Elements

Metals

• almost 80% of elements are metals, which have few valence electrons. Metals are found to the left of the heavy stair step line on the periodic table

• Typical Properties:

  • state: exist as a dense, ductile, malleable, lustrous solid

  • conductivity: are are highly conductive, electrically and thermally

  • reactivity: are reactive, especially with nonmetals

Metalloids

• These elements have characteristics between those of metals and nonmetals. Metalloids are located along the stair step one and are also called semiconductors.

• Typical Properties:

  • state: exist as a brittle solid with metallic luster

  • conductivity: are fairly conductive, increasingly so as temperature rises

  • reactivity: varies

Nonmetals

• These elements typically have four or more valence electrons and do not exhibit the general properties of metals. Nonmetals are to the right of, but not touching, the heavy stair step line on the periodic table.

• Typical Properties:

  • state: exist as a gas, liquid, or a dull, brittle solid

  • conductivity: are poorly conductive, electrically and thermally

  • reactivity: varies

Element Families

• Alkali Metals: An element in Group 1 of the periodic table, having one valence electron that it can easily lose to form a 1+ cation, making it extremely reactive; the most reactive of all the metals.

• Alkaline Earth Metal: An element in Group 2 of the periodic table, having two valence electrons that it tends to lose easily to become a 2+ cation, making it very reactive.

• Transitional Metal: Any elements in Group 3-12 of the periodic table, typically having one or two valence electrons, which it easily loses, resulting in cations with charges of 1+ or 2+

• Inner Transitional Metal: An element from either of two rows usually placed below the periodic table; a member of either the ianthahide or actinide series. It typically has two valence electrons

• Mixed Group: Any of Groups 13-16 in the periodic table, so named because they contain metals, nonmetals, metalloids. These groups are often named for the first element in the family

• Noble Gas: An element in Group 18 on the periodic table having eight valence that fill the outer energy level. With a full outer energy level, it is inert

4C Periodic Trends

• Electron Dot Notation: A representation of an atom consisting of its chemical symbol with surrounding dots representing its valence electrons

• Atomic Radius: The distance from the center of an atom’s nucleus to its outermost energy level

• Electronegativity: A measure of an element’s ability to attract and hold electrons when bonded to other atoms