Chemistry Chapter: Ions and Bonds

1.3 lons and Octet Rule

• The octet rule describes the tendency of atoms to gain, lose, or share electrons to achieve a stable electron configuration similar to a noble gas (8 valence electrons).
• Helium is an exception, achieving stability with 2 valence electrons.
• Atoms can achieve stability by forming ions.
• Metals typically lose valence electrons to form positive ions (cations).
• Nonmetals typically gain valence electrons to form negative ions (anions).

Ionic and Covalent Bonds

• Atoms form octets to become more stable.
• This can be achieved by losing, gaining or sharing valence electrons.
• These processes form either ionic bonds or covalent bonds.
• When a metal (M) loses electrons and combines with a nonmetal (Nm) it forms positive and negative ions, resulting in an ionic bond.
• The sharing of electrons between nonmetals forms a covalent bond.

Metals Form Positive lons (Cations)

• Metals lose valence electrons to form positive ions.
• The resulting configuration matches the nearest noble gas' electron arrangement.
• The number of positive charges on the ion is related to the group number.

Formation of a Sodium Ion (Na⁺)

• Sodium (Na) needs to lose one valence electron to achieve an octet.
• Sodium losing this electron becomes a positively charged sodium ion.
• The sodium ion (Na⁺) has the same electronic structure as the noble gas neon (Ne).

Charge of Sodium Ion (Na⁺)

• A sodium ion has a +1 charge.
• This is because it has one less electron than the number of protons.

Formation of Magnesium Ion (Mg²⁺)

• Magnesium (Mg) needs to lose two valence electrons to achieve an octet.
• Magnesium losing these electrons forms a positively charged magnesium ion.
• The magnesium ion (Mg²⁺) has the same electronic structure as the noble gas neon (Ne).

Learning Check

• Aluminum has three valence electrons.
• To achieve an octet, aluminum loses three electrons.
• Aluminum's ionic charge is +3.
• The symbol for the aluminum ion is Al³⁺.

Formation of Negative lons (Anions)

• Nonmetals achieve octets by gaining valence electrons.
• This results in negatively charged ions known as anions.
• Anions have a charge equivalent to a small whole number (-3, -2, or -1).

Formation of a Chloride Ion (Cl^-)

• Chlorine (Cl) gains one electron to complete its octet.
• The resulting ion, chloride, has a -1 charge (Cl^-).
• The chloride ion (Cl^-) has the same electronic configuration as the noble gas argon (Ar).

Charge of Chloride Ion (Cl^-)

• A chloride ion has a -1 charge.
• This is because it has one more electron than the number of protons.

Some Ionic Charges

• This section details the charge that elements will have in their ionic state depending on their group. (Metals are on the left side of the periodic table and Nonmetals are on the right).

Polyatomic lons

• Polyatomic ions are groups of atoms acting as a single unit and carrying an overall ion charge.
• Common polyatomic ions include nitrate (NO₃^-), ammonium (NH₄⁺), hydroxide (OH^-), carbonate (CO₃^2-), nitrite (NO₂^-), phosphate (PO₄^3-), and others.

Names and Formulas of Common Polyatomic lons

• This section provides a table listing the formulas of common polyatomic ions along with their names.