PS.4 The periodic table is a model used to organize elements based on their atomic structure. Key uses include
1. symbols, atomic numbers, atomic mass, chemical groups (families), and periods are identified on the periodic table;
2. elements are classified as metals, metalloids, and nonmetals.

Symbols, Atomic numbers, Atomic Mass, Chemical groups (families), and Periods

• Predictable properties emerge when elements are arranged according to the number of protons.
• The periodic table models these patterns and can be used to predict properties of elements.
• All atoms of an element contain the same number of protons and cannot be broken down into simpler substances using chemical reactions.

• Each element is distinguished by the number of protons in the nuclei of its atoms (atomic number).
• The number of protons never changes in an atom during chemical or physical changes.
• There are more than 118 known elements.
• Elements with an atomic number greater than 92 are not found naturally in measurable quantities on Earth.
• These elements are artificially produced in a laboratory setting.
• The periodic table is a tool used to organize information about the elements.
• The boxes in the periodic table are arranged in increasing order of atomic number.

Atomic Mass, Isotopes, Ions

• Although an element's atoms all have the same number of protons, they can have different numbers of neutrons.
• Atomic mass is equivalent to the number of protons and neutrons in the atom of an element.

• Atoms of an element with differing numbers of neutrons are known as isotopes, which leads to a different atomic mass; however, the chemical properties of the isotopes are the same.
• The atomic mass presented in the periodic table represents a population-weighted average of naturally occurring isotopes.

• Gaining or losing electrons makes an atom an ion.
• An ion has different chemical properties than the original atom.

Chemical groups (families), and Periods

• Elements in the same column (group or family) of the periodic table have similar properties because they contain the same number of electrons in their outer energy level (valence).

• The horizontal rows of the periodic table are called periods.
• The vertical columns in the table are called groups.
• They are also commonly referred to as families.
• Elements in the same group share many physical and chemical properties because they contain the same number of electrons in their outer energy level (valence).

Metals, Metalloids, and Nonmetals

• Elements on the left side of the periodic table are metals .
• Elements have fewer metallic properties as one reads from left to right across the periodic table.
• The nonmetals are located to the right of the stair-step line on the periodic table .
• Metalloids, which occur along the stair-step line, have both metallic and non-metallic properties .

You should know the following
• compare the location, charge, and relative mass of protons, neutrons, and electrons in a single atom
• differentiate between atoms of an element and its isotopes
• an atom's identity is related to the number of protons in its nucleus
• use the periodic table to obtain the following information about the atom of an element: symbol, atomic number, and atomic mass
• organization of the periodic table in terms of atomic number, metals vs. nonmetals, and groups vs. periods
• use basic information provided for an element (atomic mass, atomic number, symbol, and name) to determine its place on the periodic table
• the number of electrons in the outermost energy level determines an element's chemical properties or chemical reactivity
• classify a given element as metal, nonmetal, or metalloid based on its position in the periodic table
• given a chemical formula of a compound, identify the elements and the number of atoms of each that comprise the compound