Element and Compound Properties: Bonding, Nomenclature, and Periodic Trends

Element and Compound Properties

Introduction

This unit explores the predictable patterns of properties that emerge when elements are arranged according to the periodic table, the nature of chemical bonds, and the systematic naming of compounds. Understanding these foundational concepts is essential for predicting chemical behavior and mastering chemical nomenclature.

Periodic Table and Periodic Trends

The Periodic Table

• Periodic Law: Properties of elements are periodic functions of their atomic numbers.

• Groups/Families: Vertical columns with similar chemical properties due to similar valence electron configurations.

• Periods: Horizontal rows indicating increasing atomic number.

Periodic Trends

• Atomic Radius: Decreases across a period, increases down a group.

• Ionization Energy: Increases across a period, decreases down a group.

• Electronegativity: Increases across a period, decreases down a group.

• Electron Affinity: Generally becomes more negative across a period.

Example: Fluorine has the highest electronegativity, while cesium has one of the lowest.

Chemical Bonding

Types of Bonds

• Ionic Bonds: Formed by the transfer of electrons from metals to nonmetals, resulting in oppositely charged ions held together by electrostatic attraction.

• Covalent Bonds: Formed by the sharing of electrons between nonmetals.

• Metallic Bonds: Involve a 'sea' of delocalized electrons shared among metal atoms.

Electronegativity and Bond Type

• The difference in electronegativity ($\Delta EN$) between two atoms determines bond type:

Bond Type	$\Delta EN$ Range	Example
Ionic	High ($>1.7$)	NaCl
Polar Covalent	Medium ($0.4-1.7$)	HCl
Nonpolar Covalent	Low ($<0.4$)	Cl2

Lewis Structures

• Lewis dot diagrams represent valence electrons as dots around element symbols.

• Used to predict bonding and molecular structure.

Bond Polarity

• Polar Covalent Bonds: Unequal sharing of electrons due to differences in electronegativity.

• Nonpolar Covalent Bonds: Equal sharing of electrons.

Naming Compounds (Nomenclature)

Naming Ionic Compounds

• Name the cation (metal or ammonium) first, then the anion (nonmetal or polyatomic ion).

• For transition metals, indicate the charge with Roman numerals (e.g., FeCl2: iron(II) chloride).

• Polyatomic ions retain their names (e.g., Na2SO4: sodium sulfate).

Naming Molecular (Covalent) Compounds

• Use prefixes to indicate the number of each atom (mono-, di-, tri-, etc.).

• Name the more metallic element first, then the less metallic element with an -ide ending.

• Example: CO2 is carbon dioxide, PCl3 is phosphorus trichloride.

# of Atoms	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-

Naming Acids

• Binary Acids: Contain hydrogen and one other nonmetal. Named as "hydro-" + base name + "-ic acid" (e.g., HCl: hydrochloric acid).

• Oxyacids: Contain hydrogen, oxygen, and another element (usually a nonmetal). If the polyatomic ion ends in "-ate," the acid ends in "-ic acid" (e.g., H2SO4: sulfuric acid); if "-ite," the acid ends in "-ous acid" (e.g., H2SO3: sulfurous acid).

Writing Chemical Formulas

Ionic Compounds

• Balance charges to ensure the compound is neutral.

• Use the criss-cross method to determine subscripts.

• Example: For calcium chloride, Ca2+ and Cl- combine to form CaCl2.

Molecular Compounds

• Use prefixes to determine the number of each atom in the formula.

• Example: Dinitrogen tetroxide is N2O4.

Polyatomic Ions to Know

Formula	Name
NO3-	Nitrate
SO42-	Sulfate
CO32-	Carbonate
PO43-	Phosphate
NH4+	Ammonium
OH-	Hydroxide
ClO3-	Chlorate
NO2-	Nitrite
SO32-	Sulfite

Summary Table: Types of Bonds

Type of Bond	Between	What Happens
Ionic	Metal & Nonmetal	Transfer of electrons
Covalent	Nonmetal & Nonmetal	Sharing of electrons
Metallic	Metal & Metal	Delocalized electrons

Key Equations and Concepts

• Electronegativity Difference:

$\Delta EN = |EN_1 - EN_2|$

• Criss-Cross Method for Ionic Compounds: Use the magnitude of the charge on one ion as the subscript for the other ion.

Essential Skills

• Predict properties using the periodic table.

• Write and name chemical formulas for ionic, covalent, and acidic compounds.

• Draw Lewis structures for molecules and polyatomic ions.

• Classify bonds as ionic, covalent, or metallic based on electronegativity differences.

• Identify and name polyatomic ions and common acids.

Additional info:

• These notes integrate content from periodic trends, chemical bonding, and nomenclature, as outlined in General Chemistry chapters on atoms, elements, molecules, compounds, and chemical bonding.