Unit 5 - Periodic Law

Introduction:

Unit 5 focuses on the history of the periodic table, the structure of the table and trends as determined by periodic law. Understanding that effective nuclear charge explains period trends and that shielding and the shell model explain group trends is crucial to understanding this chapter.

Student Objectives - Unit 5:

5.1

a. The periodic law states that the physical and chemical properties of the elements are periodic functions of their atomic numbers.

b. The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column.

c. The columns in the periodic table are referred to as groups.

5.2

a. The rows in the periodic table are called periods.

b. Many chemical properties of the elements can be explained by the configurations of the elements’ outermost electrons.

c. The noble gases exhibit unique chemical stability because their highest occupied levels have an octet of electrons ns2np6 (with the exception of helium, whose stability arises from its highest occupied level being completely filled with two electrons, 1s2).

d. Based on the electron configurations of the elements, the periodic table can be divided into four blocks: the s block, the p block, the d block and the f block.

5.3

a. The groups and periods of the periodic table display general trends in the following properties of the elements: electron affinity, electronegativity, ionization energy, atomic radius and ionic radius.

b. The electrons in an atom that are available to be lost, gained or shared in the formation of chemical compounds are referred to as valence electrons.

c. In determining the electron configuration of an ion, the order in which electrons are removed from the atom is the reverse of the order given by the atom’s electron-configuration notation.

Ohio Department of Education Standards

Periodic Table:

In the physical science syllabus, elements are placed in order of increasing atomic number in the periodic table such that elements with similar properties are placed in the same column. How the periodic table is divided into groups, families, periods, metals, nonmetals and metalloids was also in the physical science syllabus. In chemistry, with more information about the electron configuration of elements, similarities in the configuration of the valence electrons for a particular group can be observed. The electron configuration of an atom can be written from the position on the periodic table. The repeating pattern in the electron configurations for elements on the periodic table explain many of the trends in properties across periods or down columns including atomic radii, ionic radii, first ionization energies, electronegativities and whether the element is a solid or gas at room temperature. Additional ionization energies, electron affinities and periodic properties of the transition elements, lanthanide and actinide series is reserved for more advanced study.

Note: Quantum numbers and equations of de Broglie, Schrödinger and Plank are beyond the scope of this course.

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