Study Guide: Alkali Metals, Alkaline Earth Metals, and Hydrogen

Overview

This study guide covers key concepts and properties of alkali metals, alkaline earth metals, and hydrogen. It discusses trends in reactivity, valence electrons, atomic radius, density, and connects these concepts to Bohr models.

Hydrogen: A Special Case

• Hydrogen is in Group 1 because it has one valence electron.
• Not a metal; lowest density element.
• Atomic number: 1.

Alkali Metals (Group 1)

• Elements: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs).
• Valence Electrons: 1 valence electron.
• Atomic Radius: Increases down the group.
• Density: Increases down the group.
• Reactivity: Increases as atomic radius grows.

Alkaline Earth Metals (Group 2)

• Elements: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba).
• Valence Electrons: 2 valence electrons.
• Atomic Radius: Increases down the group.
• Density: Higher than alkali metals; increases down the group.
• Reactivity: Increases as atomic radius grows.

Comparison of Alkali Metals and Alkaline Earth Metals

• Valence Electrons: 1 vs 2.
• Reactivity: Alkali metals are more reactive.
• Hardness: Alkali metals are softer.
• Density: Alkaline earth metals have higher density.
• Melting Points: Alkaline earth metals have higher melting points.
• Reaction with Water: Alkali metals react more vigorously.
• Common Uses: Batteries, table salt (alkali); building materials, supplements (alkaline earth).

Valence Electrons and Trends

• Trends in Groups:
  • Atomic Radius, Density, Reactivity increase down the group.
• Trends in Periods: Increase for metals as the period increases.

Atomic Mass and Atomic Number

• Atomic mass is the weighted average of all isotopes.
• More isotopes lead to higher atomic mass relative to atomic number.

Bohr Models and Identification

• Identify elements by counting protons and neutrons.
• Use periodic table for identification.

Identifying Isotopes

• Same number of protons, different number of neutrons.

Vocabulary

• Valence Electrons: Outermost shell electrons.
• Atomic Radius: Distance from nucleus to outermost electron.
• Density: Mass in a volume.
• Reactivity: Ease of reaction.
• Atomic Mass: Weighted average of isotopes.
• Isotope: Atom with more neutrons than protons.

Sample Questions

1. Why does density increase as you move down a group?

   • Answer: The nucleus contains more subatomic particles packed into the same space.

2. Which trend is true for metals as you move down a group?

   • Answer: Reactivity and density increase.

3. Explain why the density of elements increases as you move down a group.

   • Answer: More subatomic particles are added, making the nucleus denser.

4. State 2 properties of alkali metals and 2 properties of alkaline earth metals.

   • Answer: Various properties based on notes above.