The Periodic Table of Elements

Page numbers are provided on your note sheet, copy

what is seen in red.

Modeling AtomsO Because atoms are so small,

scientists use models to study them.

O The modern atomic model explains why most elements react with other elements, while a few elements hardly react at all.

The First Periodic Table (p. 82)

O In 1869 a Russian chemist, Dimitri Mendeleev made a chart trying to organize the 63 elements known at that time.

O Mendeleev’s chart is known as the periodic table.

O He arranged his table by atomic mass.

Groups or Families (pg. 87)

O The elements that fall into the same vertical column have similar (but not identical) characteristics or properties.

O There are a total of 18 groups. O The vertical columns are groups or families.O Atoms in the same column have a similar number of

electrons in their outermost electron shells (known as their Valence electrons) and therefore behave similarly. (Review your chart of family characteristics!)

Periods (pg. 86)

O The horizontal rows are known as periods.

O There are a total of 7 periods.

O Elements in a period are not identical in their properties, and those properties change according to a pattern.

O The first element in the period (on the left) is usually a highly reactive metal.

O

O The last element in the period (on the right) is always an unreactive gas known as a noble gas.

Organization of the Periodic Table (pp. 82-83)

O Today, modern Periodic Tables are arranged in order of atomic number, not by atomic mass.

O The atomic number tells how many protons are in the nucleus of the atom and this number is equal to the number of electrons in the electron cloud.

O Each box on the Periodic Table represents a different element. Each element box includes:

O Atomic numberO Chemical symbolO Element nameO Average atomic mass

O The bottom number is the element’s average atomic mass measured in atomic mass units (amu).

O The average atomic mass is determined from the combined percentages of all the element’s isotopes.

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Fe Iron 55.847

O An isotope for an element has the same number of protons, but a different number of neutrons.

Metals and Nonmetals (pp. 88, 99, 105)

O Elements to the left of the zig-zag line are metals. Metals are good conductors of electricity and heat; they can be hammered into thin sheets (malleable) and be stretched into wire (ductile). Most are also able to combine with other elements (reactive) and some are magnetic.

O The elements to the right of the zig-zag line (with exception of hydrogen) are nonmetals. Nonmetals are dull, are poor conductors of heat and electricity and they are brittle (not malleable or ductile), and may be reactive or non-reactive.

O The elements along the zig-zag line are known as metalloids. They may have some characteristics of metals and nonmetals. O Metalloids are used as semiconductors.O Semiconductors can be a conductor or an insulator

(electricity does not flow through insulators), and are also used in electronic devices and computers.