Topic 2

Periods and Groups in the Periodic Table

Periods:


·         Short Period (Period 1): 

                                                Contains only two elements: hydrogen and helium.

·         Normal Periods (Periods 2 and 3): 

                                                Each contains eight elements. Examples:

o    Period 2: 

                 Lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon.

o    Period 3: 

                Sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon.  

·         Long Periods (Periods 4 and 5): 

                 Each contains eighteen elements.

·         Very Long Periods (Periods 6 and 7): 

                   These periods are longer due to the presence of the Lanthanides (elements 57-71) and Actinides (elements 89-103), which are typically placed separately at the bottom of the periodic table to maintain a manageable format.

Groups

·         Group 1 (Alkali Metals): 

                    Hydrogen, lithium, sodium, potassium, rubidium, cesium, francium. These elements have one valence electron.

·         Group 2 (Alkaline Earth Metals): 

                    Beryllium, magnesium, calcium, strontium, barium, radium. These elements have two valence electrons.

·         Groups 3-12 (Transition Metals): 

                    These elements are characterized by partially filled d orbitals in their outer electron shells. Examples include iron, copper, zinc, and gold.

·         Groups 13-17 (Representative Elements): 

                    These elements have varying numbers of valence electrons and exhibit a wide range of properties. Examples include boron, carbon, nitrogen, oxygen, fluorine, aluminum, silicon, phosphorus, sulfur, chlorine.

·         Group 18 (Noble Gases): 

                    Helium, neon, argon, krypton, xenon, radon. These elements have completely filled outer electron shells and are generally unreactive.

Key Points:

·         The number of elements in a period is determined by the maximum number of electrons that can occupy a particular energy level (valence shell).

·         Elements within a group share similar chemical properties due to having the same number of valence electrons.

·         The placement of Lanthanides and Actinides at the bottom of the periodic table is a convention to maintain a compact format.

Example:

·         Period 3: The elements in this period have 3 electron shells. The number of valence electrons increases from left to right, from sodium (1 valence electron) to argon (8 valence electrons).

·         Group 1: All alkali metals have 1 valence electron, giving them similar properties such as reactivity with water and formation of ionic compounds.