Basic Chemical Bonding

Introduction to Compounds and Molecules

Chemical bonding is fundamental to understanding how atoms combine to form the substances that make up all matter. This section introduces the basic concepts of compounds, molecules, and the role of valence electrons in chemical behavior.

• Compound: A general term for a group of atoms of two or more different elements joined together in a fixed ratio.

• Molecule: A specific term for compounds in which atoms are held together by shared electrons (covalent bonds).

• Valence Electrons: The outermost electrons of an atom, responsible for the chemical behavior of elements.

• Understanding valence electrons allows prediction of how elements will bond and what types of compounds they will form.

Chemical Formulas

Chemical formulas represent the composition of compounds, indicating the types and numbers of atoms present.

• Compound: Formed from atoms of two or more elements joined by chemical bonds.

• Chemical Formula: Shows which elements are present and the number of atoms of each element (e.g., CO2, H2O, NH3).

• Subscript: Indicates the number of atoms of each element in the compound.

• Elements are typically listed from most metallic to least metallic.

Example: In H2O, the subscript '2' indicates two hydrogen atoms for every one oxygen atom.

Order of Elements in Formulas

• Elements are listed from most metallic (left and lower on the periodic table) to least metallic (right and upper).

• Hydrogen is listed before oxygen (e.g., H2O), sulfur (H2S), but after boron (BH3), carbon (CH4), and nitrogen (NH3).

Ionic and Covalent Compounds

When different elements bond, they form either ionic or covalent compounds, depending on the nature of the elements involved.

• Ionic Compounds: Composed of a metal and a nonmetal. Metals lose electrons to form positive ions (cations), while nonmetals gain electrons to form negative ions (anions).

• Covalent Compounds: Composed of two or more nonmetals. Atoms share electrons to achieve a stable electron configuration.

Example: Sodium (Na) loses an electron to become Na+, and chlorine (Cl) gains an electron to become Cl−. Together, they form NaCl (table salt).

Formula Unit

• The formula unit is the simplest ratio of ions in an ionic compound that results in a net zero charge.

• Example: NaCl (1 Na+ and 1 Cl−), MgBr2 (1 Mg2+ and 2 Br−).

Summary Table: Types of Chemical Bonds

Key Concepts in Chemical Bonding

• Octet Rule: Most main group elements tend to gain, lose, or share electrons to achieve a full valence shell of eight electrons.

• Lewis Dot Structures: Diagrams that represent valence electrons as dots around the chemical symbol of an element.

• Electronegativity: A measure of the tendency of an atom to attract electrons in a chemical bond. Differences in electronegativity determine bond polarity.

Applications and Examples

• Water (H2O): A covalent compound where oxygen shares electrons with two hydrogen atoms.

• Sodium Chloride (NaCl): An ionic compound formed by the transfer of an electron from sodium to chlorine.

Additional info: The images provided illustrate the formation of ionic and covalent compounds, the use of chemical formulas, and the order of elements in formulas. The concepts covered are foundational for understanding chemical reactions, molecular structure, and the properties of substances in biology and chemistry.