Periodic Table and Group Properties

Based on Source 1, titled 'Properties of Groups and Mendeleev's Periodic Table', the document explains Dmitri Mendeleev's development of the periodic table in 1869 as a foundational achievement in chemistry. The source highlights that his work provided a systematic framework to organize chemical elements, predict the properties of missing elements, and establish essential periodic laws and chemical trends.

Based on Source 1, titled 'Properties of Groups and Mendeleev's Periodic Table', Dmitri Mendeleev's development of the periodic table in 1869 established a foundational framework for chemistry by organizing elements by atomic mass and predicting missing elements. Expanding on these fundamentals provides a comprehensive overview of periodic table structure, element classifications, and periodic trends.

1. Structure of the Modern Periodic Table

The modern periodic table organizes elements by increasing atomic number ( $Z$ ), which represents the number of protons in an atom's nucleus.

Periods (Horizontal Rows)
- Represent elements with the same highest principal energy level ( $n = 1$ to $n = 7$ ).
- Atomic radius decreases across a period due to increasing nuclear charge without additional inner-shell shielding.
Groups (Vertical Columns)
- Comprise 18 numbered columns containing elements with identical outer shell electron configurations.
- Elements in the same group exhibit similar chemical properties and reactivity patterns.

2. Major Element Groups

Group 1 (Alkali Metals): Highly reactive metals with an $ns^1$ valence electron configuration, forming $+1$ cations via $M(s) \rightarrow M^+(aq) + e^-$ .
Group 2 (Alkaline Earth Metals): Reactive metals with an $ns^2$ valence electron configuration, forming $+2$ cations.
Groups 3–12 (Transition Elements): Metals characterized by partially filled d-subshells, variable oxidation states, and colored compounds.
Group 17 (Halogens): Reactive non-metals with an $ns^2\,np^5$ valence configuration, forming $-1$ halide anions.
Group 18 (Noble Gases): Unreactive non-metals with full valence energy shells ( $ns^2\,np^6$ ).

3. Essential Periodic Trends

Atomic Radius: Decreases left-to-right across a period due to effective nuclear charge; increases top-to-bottom down a group as new electron shells are added.
First Ionization Energy: The energy required to remove one mole of electrons from one mole of gaseous atoms:
$X(g) \rightarrow X^+(g) + e^-$
Increases across a period and decreases down a group.
Electronegativity: The measure of an atom's ability to attract a shared pair of electrons in a covalent bond. Increases across a period and decreases down a group.