chem

Charge and Ions

• Charges in chemistry are not inherently real; they are useful for bookkeeping.
• Using charges, predictions can be made about which compounds are likely to form.

Atoms vs. Ions

• Atoms: No charge (neutral).
• Ions: Charged species, which can be cations (positively charged) or anions (negatively charged).

Specific Elements: Sodium and Sulfur

• Sodium (Na):

  • State: Atom (zero charge).
  • Group: 1.
  • Behavior: Wants to lose one electron to form a sodium cation ($Na^+$).

• Sulfur (S):

  • State: Atom (zero charge).
  • Group: 6.
  • Behavior: Wants to gain two electrons to form a sulfide anion ($S^{2-}$).

Electronegativity (EN) and Ionic Compounds

• Electronegativity (EN): Ability to attract electrons between atoms.
  • Sodium EN: 0.9
  • Sulfur EN: 2.5
  • Difference: $2.5 - 0.9 = 1.6$ (large enough for ionic bond).

Electro Neutrality

• The overall charge of a compound must equal zero.
• Example: For $Na^+$ (1) and $S^{2-}$ (2), the formula requires 2 sodium atoms and 1 sulfur atom:
  • Resulting formula: $Na_2S$.

Common Element Behaviors

• Calcium (Ca):

  • Charge: $Ca^{2+}$ (wants to lose 2 electrons).

• Oxygen (O):

  • Charge: $O^{2-}$ (wants to gain 2 electrons).

• For calcium and oxygen:

  • Common factor: 1
  • Resulting formula: $CaO$.

Aluminum and Variations

• Aluminum (Al):

  • Charge: $Al^{3+}$ (wants to lose 3 electrons).

• Cation Naming:

  • Cation with a single oxidation state uses only the name of the metal:
  • $Li^+$: lithium cation.
  • $K^+$: potassium cation.
  • $Ca^{2+}$: calcium cation.

Naming Multiple State Cations

• Metals with multiple oxidation states (like Iron $Fe$):
  • Name includes a Roman numeral indicating the charge.
  • Example: $Fe^{2+}$: iron(II) cation and $Fe^{3+}$: iron(III) cation.

Common Anions and Their Naming

• To name anions, modify the elemental name:
  • $Cl^-$: chlorine → chloride.
  • $P^{3-}$: phosphorus → phosphide.
  • $N^{3-}$: nitrogen → nitride.
  • $O^{2-}$: oxygen → oxide.

Nomencalature for Compound Naming

• Combine names of cations and anions for compounds:
  • Example: $NaCl$: sodium chloride.
  • Example: $CuCl_2$: copper(II) chloride.
  • Total charge balance for naming compounds correctly is essential.

Common Oxidation States and Naming Rules

• Common polyatomic ions must be memorized:
• Systems using Roman numerals are not applicable for anions as they can represent different elemental forms.

Ionic vs Covalent Compounds

Ionic Compounds

• Formed by the transfer of electrons between metals (cations) and nonmetals (anions).
• Strong ionic bonds established through electrostatic forces lead to forming extended structures, contrasting with discrete molecules.

Covalent Compounds

• Formed from sharing of electrons between atoms of similar electronegativities, creating molecules.
• Example: Hydrogen ($H2$), Chlorine ($Cl2$), Oxygen ($O_2$).
• These elements exist in elemental states as diatomic molecules due to their high electronegativity.

Properties and Naming of Covalent Compounds

• Use prefixes to indicate the number of atoms in covalent compounds:
  • Mono- (1), Di- (2), Tri- (3), Tetra- (4), Penta- (5), Hexa- (6), Hepta- (7), Octa- (8), Nona- (9), Deca- (10).
• Example Names:
  • $N2O5$: dinitrogen pentoxide.
  • $CO$: carbon monoxide.

Diatomic Elements

• Certain elements are naturally diatomic in their elemental state:
  • Hydrogen ($H2$), Nitrogen ($N2$), Oxygen ($O2$), Fluorine ($F2$), Chlorine ($Cl2$), Bromine ($Br2$), Iodine ($I_2$).
  • These must be recognized as pairs when naming them accordingly.

Key Takeaways

• Naming ionic compounds includes correctly identifying oxidation states, while naming covalent compounds requires knowledge of the prefixes and their corresponding compounds.
• Extensive practice is required to master naming conventions and chemical formulas, as they are fundamental to chemistry communication.

Practice and Memorization

• Polyatomic ions and naming conventions will be significant in upcoming quizzes/tests.
• Consistent practice is needed to achieve proficiency, especially as these concepts build foundational skills for further chemistry studies.