Ionic and Covalent Bonding & Naming Molecular Compounds

Ionic and Covalent Bonding

Differences Between Ionic and Covalent Bonding

Chemical bonds are the forces that hold atoms together in compounds. The two main types of chemical bonds are ionic bonds and covalent bonds, which differ in how electrons are distributed between atoms.

• Ionic Bonding: Involves the transfer of electrons from a metal atom to a nonmetal atom, resulting in the formation of oppositely charged ions that are held together by electrostatic attraction.

• Covalent Bonding: Involves the sharing of electrons between two nonmetal atoms, resulting in the formation of a molecule.

Example:

• Ionic Compound: Magnesium fluoride ($\mathrm{MgF_2}$) forms when magnesium ($\mathrm{Mg^{2+}}$) transfers electrons to two fluoride ions ($\mathrm{F^-}$).

• Covalent Compound: Water ($\mathrm{H_2O}$) forms when hydrogen and oxygen share electrons.

Naming Covalent (Molecular) Compounds Using the Prefix (IUPAC) System

Introduction to the Prefix System

Unlike ionic compounds, covalent compounds do not contain ions or charges. Therefore, prefixes are used to indicate the number of each type of atom present in the molecule.

Prefixes Used in Naming Molecular Compounds

Number	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

Steps for Naming Molecular Compounds

1. Name the first nonmetal by its element name.

2. Name the second nonmetal by using the root of its element name and adding the suffix -ide.

3. Add prefixes to indicate the number of atoms of each element (subscripts in the formula). The prefix 'mono-' is usually omitted for the first element.

Examples of Naming Covalent Compounds

• $\mathrm{CCl_4}$: Carbon tetrachloride

• $\mathrm{CO}$: Carbon monoxide

• $\mathrm{P_4O_{10}}$: Tetraphosphorus decoxide

• $\mathrm{SF_6}$: Sulfur hexafluoride

• $\mathrm{C_6H_{14}}$: Hexane (common name; systematic name: hexacarbon decahydride)

Examples of Writing Formulas from Names

• Nitrogen tribromide: $\mathrm{NBr_3}$

• Oxygen difluoride: $\mathrm{OF_2}$

• Triselenium octafluoride: $\mathrm{Se_3F_8}$

• Hexafluoro disulfide: $\mathrm{S_2F_6}$

Diatomic Elements

Definition and List of Diatomic Elements

Some elements are more stable as molecules consisting of two atoms of the same element bonded together. These are called diatomic elements.

• Diatomic elements: Nitrogen ($\mathrm{N_2}$), Oxygen ($\mathrm{O_2}$), Hydrogen ($\mathrm{H_2}$), and the Halogens: Fluorine ($\mathrm{F_2}$), Chlorine ($\mathrm{Cl_2}$), Bromine ($\mathrm{Br_2}$), Iodine ($\mathrm{I_2}$).

Any element whose name ends in -gen (e.g., hydrogen, oxygen, nitrogen) or is a halogen (Group 17) will be diatomic in its natural state.

Summary Table: Diatomic Elements

Element	Formula
Nitrogen	N2
Oxygen	O2
Hydrogen	H2
Fluorine	F2
Chlorine	Cl2
Bromine	Br2
Iodine	I2

Additional info: The prefix system is essential for distinguishing between compounds with the same elements but different ratios, such as CO (carbon monoxide) and CO2 (carbon dioxide). The systematic naming ensures clarity in chemical communication.