6.1 Ion Formation

Lesson 1: Ion Formation

Focus Question

  • Why do elements form compounds?

New Vocabulary

  • Chemical bond: A force that holds atoms together.

  • Cation: A positively charged ion formed by losing electrons.

  • Anion: A negatively charged ion formed by gaining electrons.

Review Vocabulary

  • Octet Rule: Atoms gain, lose, or share electrons to acquire eight valence electrons, achieving stability.

Valence Electrons

  • Definition:

    • Electrons responsible for the chemical properties of atoms.

    • Located in the outer energy level.

    • Includes s and p electrons in the outermost energy level.

    • Highest occupied energy level.

Core Electrons

  • Definition:

    • Electrons in energy levels below the outer shell.

    • Present in shells below the outer shell and not involved in bonding.

Electron Dot Diagrams

  • Also Known As: Lewis Dot Diagrams.

  • Purpose:

    • A way to represent and keep track of valence electrons.

  • Construction:

    • Write the symbol for the element to represent the nucleus and core electrons.

    • Use one dot for each valence electron, with a maximum of eight.

    • Electrons do not pair until necessary (Hund's rule).

Valence Electrons and Chemical Bonds

  • Chemical Bonds:

    • Forces that hold two atoms together.

    • Form through attraction between positive nuclei and negative electrons, or between positive and negative ions.

  • Illustration:

    • Electron-dot structures depict how chemical bonds form.

  • Ionization Energy:

    • Indicates how easily an atom loses an electron.

  • Electron Affinity:

    • Measures how much attraction an atom has for electrons.

  • Noble Gases:

    • Have high ionization energies and low electron affinities, resulting in low reactivity.

    • Possess full outermost energy levels.

  • Reactiveness:

    • Atoms react to achieve the stable electron configuration of noble gases, trying to form an octet by gaining or losing valence electrons.

Positive Ion Formation

  • Definition:

    • A positive ion forms when an atom loses valence electrons to achieve a noble gas configuration.

    • A positively charged ion is called a cation.

  • Example:

    • Sodium (Na) loses a valence electron to become a sodium cation (Na+), obtaining the stable electron configuration of neon.

  • Reactivity of Metals:

    • Metals, especially in groups 1 and 2, are reactive due to their tendency to lose valence electrons easily.

  • Transition Metals:

    • Commonly form +2 or +3 ions but can also form higher ions.

    • Stable electron arrangements can include pseudo-noble gas configurations.

Negative Ion Formation

  • Definition:

    • Nonmetals tend to gain electrons to achieve a stable outer electron configuration.

    • A negatively charged ion is an anion.

  • Example:

    • Chlorine (Cl) gains an electron to become a chloride anion (Cl-).

  • Nonmetal Ions:

    • Gain electrons to fill their octet and achieve a noble-gas configuration.

    • Some nonmetals may gain or lose varying numbers of electrons to complete their octet.