The Periodic Table Chapter 4

Section 1: Introduction to the Periodic Table

By 1830 fifty-five different elements had been isolated and named. In 1869 Mendeleev arranged elements in order of increasing atomic mass and found that elements with similar properties fell into groups.

Moseley improved the periodic table by arranging the elements according to atomic number instead of atomic mass.

The modern periodic table contains seven periods or rows of elements whose properties change gradually and eighteen groups or columns, each with a family of elements having similar properties.

Groups 1 and 2 along with groups 13 to 18 are called the representative elements. Groups 3 to 12 are called the transition elements

A metal has luster, conducts heat and electricity, is malleable and ductile. Nonmetals are usually gases or brittle solids at room temperature. A metalloid shares properties with metals and nonmetals. Symbols are abbreviations usually based on the element’s name.

Section 2: Representative Elements

Groups 1 and 2 are active metals found in nature combined with other elements; although hydrogen is placed in Group 1, it is not a metal and it shares properties with Groups 1 and 17.

Why is hydrogen a different color? Alkali metals – silvery solids with low densities and low melting points; they increase in reactivity from top to bottom of the periodic table. Why is hydrogen a different color?

Alkaline earth metals – are denser, harder, have higher melting points, and are slightly less active than alkali metals in the same period.

Group 13 through 18 may contain metals, nonmetals, or metalloids in solid, liquid, or gas form. The boron family elements in group 13 are all metals except boron, which is a metalloid; these elements are used in a variety of products.

The carbon group elements are all metalloids or metals, except for carbon itself. Carbon is found in all living things and exists in several forms. Silicon and germanium are used in electronics as semiconductors. Tin and lead are used in many products.

The nitrogen group contains nitrogen and phosphorus, which are required by living things and which are used in industry.

The oxygen family contains oxygen and sulfur, which are essential for life and used to manufacture many products.

The halogen group elements form salts with sodium and with other alkali metals.

The noble gases rarely combine with other elements; they are often used in lighting and inflating balloons.

Section 3: Transition Elements

Groups 3 to 12 are metals; most are combined with other elements in ores. The iron triad is composed of iron, cobalt, and nickel; they are used in many applications. Several transition elements can be used as catalysts, substances that make a reaction occur faster.

The inner transition elements are called lanthanides and actinides. The lanthanides are soft metals and were once thought to be rare. All the actinides are radioactive; several are synthetic elements that do not occur naturally. Dental materials are sometimes made of new composites, resins, and porcelains.