Periodic Table and Element Properties

Periodic Table Overview

• Elements are arranged by increasing atomic number (protons).
• Groups (vertical columns) determine the number of valence electrons.
• Periods (horizontal rows) indicate the total number of electron shells.

Key Elements in Group and Periods

• Group 4, Period 3: Silicon (Si) with 4 valence electrons.
• Hydrogen and Helium are in Period 1. Carbon is in Period 2.

Valence Electrons and Groups

• Group 1: 1 valence electron (e.g., Li, Na).
• Group 2: 2 valence electrons (Alkaline earth metals, e.g., Mg).
• Group 6: 6 valence electrons (Chalcogens, e.g., O, S).
• Group 7: 7 valence electrons (Halogens, e.g., F, Cl).
• Group 8: Noble gases, full valence shells (e.g., Ne, Ar).

Stability and Reactivity

• Noble gases are unreactive due to full outer shells.
• Elements gain or lose electrons to achieve full shells, forming ions:
  • Cations: positively charged (loss of electrons).
  • Anions: negatively charged (gain of electrons).

Chemical Reactions

• Sodium (Na) loses 1 electron to become Na⁺ (cations); Mg loses 2 to become Mg²⁺.
• Halogens (e.g., Cl) gain 1 electron to become Cl⁻ (anions).
• Nonmetals tend to gain electrons, while metals tend to lose them.

Sharing Electrons and Covalent Bonds

• Group 4 (e.g., C, Si) generally shares electrons.
• Example of covalent bonding: Methane (CH₄) where C shares electrons with H.