Electronic Structure of Atoms: Valency and Ion Formation

Definitions of Valency and Valence Electrons

• VALENCY: Defined as the number of electrons in an atom’s outermost shell that must be gained or lost in order to achieve a full shell.
• VALENCE ELECTRONS: Defined as an electron located in the outer electron shell of an atom.
• Group Relationships: In the periodic table, elements categorized within the same group possess the same number of valence electrons.

The Principles of Stable Electron Configuration

• Stability Criteria: Atoms achieve chemical stability by possessing a full outermost energy level. This state is mathematically and structurally similar to the nearest noble gas, as noble gases possess completely filled outer energy levels.
• Mechanisms of Stability: Atoms work toward stability through three primary processes:
  • Gaining electrons.
  • Losing electrons.
  • Sharing electrons to obtain a full outer shell.
• Ion Formation: Atoms that undergo the process of gaining or losing electrons are transformed into ions.

The Process of Gaining Electrons and Anion Formation

• Non-metal Behavior: Non-metal elements typically exhibit a tendency to gain electrons to achieve a noble gas electron configuration.
• ANIONS: When an atom gains electrons, the total number of electrons exceeds the number of protons, resulting in the formation of a negative ion known as an anion.
• Case Study: Chlorine (Cl):
  • Periodic Placement: Chlorine is located in Group $17$.
  • Neutral Configuration: Its neutral electron configuration is $2, 8, 7$.
  • Process: Chlorine gains $1$ electron to achieve a stable noble gas electron configuration of $2, 8, 8$.
  • Charge Calculation: Because it has gained $1$ electron, it possesses one more electron than it does protons. This results in a net charge of $-1$, denoted as $Cl^-$.
• Visual Representation (Figure 6.1.5): When a neutral Chlorine atom gains an electron ($e$), it becomes a Chloride negative ion with a full outermost energy level.

The Process of Losing Electrons and Cation Formation

• Metal Behavior: Metal elements typically exhibit a tendency to lose electrons to achieve a noble gas electron configuration.
• CATIONS: when an atom loses electrons, it then possesses fewer electrons than protons, resulting in the formation of a positive ion known as a cation.
• Case Study: Sodium (Na):
  • Periodic Placement: Sodium is located in Group $1$.
  • Neutral Configuration: Its neutral electron configuration is $2, 8, 1$.
  • Process: Sodium loses $1$ electron to achieve a stable electron configuration of $2, 8$.
  • Charge Calculation: Because it has lost $1$ electron, it possesses one less electron than it does protons. This results in a net charge of $+1$, denoted as $Na^+$.
• Visual Representation (Figure 6.1.6): A neutral Sodium atom loses an electron to reach a noble gas configuration, transforming into a Sodium positive ion.