Unit 1 - Principles of Chemistry: Chapter 4: Periodic Table

The Periodic Table

Learning Objectives

• The Periodic Table displays all known elements, enabling the understanding of property trends and predictions.

• Elements are arranged by atomic number, groups (vertical columns), and periods (horizontal rows).

• Deduce electronic configurations for the first 20 elements.

• Classify elements as metals or non-metals based on electrical conductivity and the acid-base character of their oxides.

• Understand the relationship between electronic configuration and position in the Periodic Table.

• Explain why elements in the same group have similar chemical properties.

• Understand the unreactive nature of noble gases (Group 0).

Arrangement of Elements

• Elements are arranged by atomic number.

Groups

• Vertical columns are groups.

• Groups are numbered 1 to 7, with the last being Group 0.

• Group 1: Alkali metals.

• Group 7: Halogens.

• Group 0: Noble gases.

Periods

• Horizontal rows are periods.

• Hydrogen (H) and helium (He) constitute Period 1.

Lanthanoids and Actinoids

• Placed separately at the bottom to improve readability.

Atomic Number, Neutrons, and Electrons

• Most Periodic Tables list atomic number and mass number.

• Number of protons = atomic number.

• Number of electrons = number of protons in a neutral atom.

• Number of neutrons = mass number - atomic number.

Arrangement of Electrons

• Electrons move around the nucleus in energy levels or shells.

• First level: up to 2 electrons.

• Second level: up to 8 electrons.

• Third level: up to 8 electrons.

Determining Electronic Configuration

• Electronic configuration is the arrangement of electrons in an atom.

• Example: Chlorine (Cl): 2, 8, 7.

• For elements from sodium (Na) to argon (Ar), the third shell is filled similarly; potassium (K) and calcium (Ca) begin to fill the fourth shell.

Electronic Configurations and the Periodic Table

• Electronic configurations for the first 20 elements are shown.

Diagrams of Electronic Configurations

• Represented using circles for shells and dots/crosses for electrons.

Key Points:

• Elements in the same group have the same number of electrons in their outer shell.

• The number of electrons in the outer shell corresponds to the group number for Groups 1 to 7.

• The period number indicates the number of occupied shells.

Elements in the Same Group

• Elements within the same group exhibit similar chemical properties and react similarly.

• Group 1 elements react vigorously with water (e.g., $LiOH$, $NaOH$, $KOH$).

• Group 7 elements react with hydrogen (e.g., $HF$, $HCl$, $HBr$).

• Reactions depend on the number of outer shell electrons.

Noble Gases

• Group 0 elements are the noble gases, known for being unreactive.

Unreactivity

• Due to their full outer shells, they have no tendency to lose, gain, or share electrons.

Metals and Non-Metals

• Metals are on the left, non-metals on the right.

Hydrogen

• Doesn't fit neatly; not in Group 1 due to differing properties.

Properties of Metals and Non-Metals

• Based on electrical conductivity and acid-base character of oxides.

Electrical Conductivity

• Metals conduct electricity due to delocalized electrons; non-metals generally do not.

• Exceptions: Graphite (carbon) and silicon.

Acid-Base Character of Oxides

• Metals form basic oxides that react with acids to form salts (e.g., $CuO + H<em>2SO</em>4 \rightarrow CuSO<em>4 + H</em>2O$).

• Non-metals form acidic oxides that react with bases to form salts (e.g., $CO<em>2 + 2NaOH \rightarrow Na</em>2CO<em>3 + H</em>2O$).

Other Properties of Metals

• Solids with high melting and boiling points and high densities (mercury is an exception).

• Shiny, malleable, ductile, good conductors, form ionic compounds, form positive ions.

Other Properties of Non-Metals

• Low melting and boiling points (carbon and silicon are exceptions).

• Brittle, lack metallic shine, poor conductors (graphite and silicon are exceptions).