Chemistry: Valence Electrons, Ionic and Covalent Compounds

Valence Electrons and Group Number

• Group number corresponds to the number of valence electrons in an atom.

• Example: Neutral nitrogen has five valence electrons.

Noble Gases Behavior

• Helium, a noble gas, won’t lose valence electrons due to its nonmetal status.

• Noble gases like helium aim to achieve stability (the 'king or queen' analogy).

• Helium has a maximum of two electrons in the first energy level, n=1, making it stable and incapable of engaging in bonding like other nonmetals.

Compounds and Chemical Formulas

• A compound is defined as a chemical entity containing at least two different elements combined in a fixed ratio (Section 6.2).

• Chemical formulas convey the composition of compounds; they can use 1 to 3 different atoms.

• Example: The structural formula of acetate is represented as C2H3O_2^−.

• Chemical compounds need to maintain overall electrical neutrality, balancing positive and negative charges.

Ionic Compounds

• Ionic compounds form as a result of the strong attraction between oppositely charged ions.

• They possess unique properties due to their structure, often forming crystal lattices.

• Example: Demonstrated through the simple case of the hydrogen molecule consisting of two hydrogen atoms, showcasing basic atomic interaction.

Example of Charge Neutrality

• When dealing with compound charges, such as Ca^{2+}, the formula must balance to achieve a neutral charge overall.

• Calculation example: For a compound needing a neutral charge with Ca^{2+}, if the charge is +2, we must find a negative charge, x, such that: 2 + x = 0 (thus, x = -2).

Covalent vs Ionic Bonds

• Some compounds consist of nonmetal atoms bonded covalently, meaning no ions are formed.

• Example given: Compounds that are not ionic cannot showcase properties derived from ionic bonding; instead, they utilize covalent bonds.

Application in Learning

• Understanding these chemical principles requires connecting concepts and principles across different sections (e.g., the relationship between chemistry and biology in a course like Bio 160).

• Active engagement in learning processes, through discussion or asking questions, enhances comprehension and retention of material.