IB MYP 4-5 Chemistry -Periodic table layout — groups and periods- Study Notes - New Syllabus

Periodic Table and Group Trends

The Periodic Table is a systematic arrangement of all known elements based on their atomic number, electron configuration, and recurring chemical properties. It helps predict how elements will behave and react chemically.

Structure of the Periodic Table

• Each horizontal row is called a period.
• Each vertical column is called a group.
• Elements in the same group have the same number of valence electrons.
• Elements in the same period have the same number of electron shells.

Modern Periodic Law

“The chemical properties of elements are a periodic function of their atomic numbers.”

This means that when elements are arranged by increasing atomic number, their properties repeat at regular intervals (periodically).

Importance of the Periodic Table

• Shows relationships between elements.
• Predicts properties of unknown elements.
• Explains trends in reactivity, metallic character, and valency.
• Provides a framework for studying chemical bonding and reactions.

Group Trends in the Periodic Table

Valence Electrons and Valency:

• All elements in a group have the same number of valence electrons.
• This gives them similar chemical properties and reactivity.
• Valency remains the same across a group.

Examples:

Atomic Size (Atomic Radius):

• Down a Group: Atomic size increases because new electron shells are added.
• Across a Period: Atomic size decreases because the number of protons increases, pulling electrons closer to the nucleus.

Trend: \( \mathrm{Size\ ↑\ down\ a\ group,\ ↓\ across\ a\ period} \)

Metallic and Non-metallic Character:

• Metallic character: Tendency to lose electrons.
• Non-metallic character: Tendency to gain electrons.
• Down a group: Metallic character increases.
• Across a period: Metallic character decreases; non-metallic character increases.

Trend: \( \mathrm{Metallic\ ↑\ down,\ ↓\ across;\ Nonmetallic\ ↓\ down,\ ↑\ across} \)

Reactivity:

• In metals (Groups 1 and 2): Reactivity increases down a group because electrons are more easily lost.
• In non-metals (Group 17): Reactivity decreases down a group because electrons are less easily gained.

 Ion Formation:

• Metals form positive ions (cations) by losing electrons.
• Non-metals form negative ions (anions) by gaining electrons.
• Elements in the same group form ions with the same charge.

Examples:
\( \mathrm{Na \rightarrow Na^+ + e^-} \)
\( \mathrm{Cl + e^- \rightarrow Cl^-} \)

Trends Summary