PERIODIC TABLE AND PERIODICITY

 

Al D. Deacon 

Founder: Gold'N Geniuz 

Physicist and Educator 

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1. Explain the Basis for the Arrangement of Elements in the Periodic Table

• Elements are arranged in increasing atomic number (Z).
• Groups (Vertical Columns, 1–18): Elements in the same group have similar chemical properties due to the same number of valence electrons.
• Periods (Horizontal Rows, 1–7): Elements in the same period have the same number of electron shells but increasing proton numbers and different properties.
• Blocks (s, p, d, f): Based on electron configurations.
• Periodic Law: Properties of elements repeat periodically when arranged by atomic number.

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2. Explain Trends in Group II (Alkaline Earth Metals: Be, Mg, Ca, Sr, Ba, Ra)

• Atomic Radius: Increases down the group as new electron shells are added.
• Ionization Energy: Decreases down the group as outer electrons are further from the nucleus.
• Reactivity: Increases down the group as it is easier to lose electrons.
• Melting & Boiling Points: Generally decrease down the group.
• Reaction with Water: Be does not react, Mg reacts slowly, but Ca, Sr, Ba react more vigorously forming hydroxides and hydrogen gas.
  • Example: $$Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2$$

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3. Explain Trends in Group VII (Halogens: F, Cl, Br, I, At)

• Atomic Radius: Increases down the group as more electron shells are added.
• Electronegativity: Decreases down the group as the attraction for electrons weakens.
• Reactivity: Decreases down the group because the ability to gain electrons decreases.
• Melting & Boiling Points: Increase down the group due to stronger Van der Waals forces.
• State at Room Temperature:
  • Fluorine (F₂) – Gas
  • Chlorine (Cl₂) – Gas
  • Bromine (Br₂) – Liquid
  • Iodine (I₂) – Solid
  • Astatine (At₂) – Solid (radioactive, rare)
• Displacement Reactions: More reactive halogens displace less reactive ones from compounds.
  • Example: $$Cl_2 + 2KBr \rightarrow 2KCl + Br_2$$

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4. Identify Trends in Period 3 (Na to Ar)

Property	Trend Across Period 3 (Na → Ar)
Atomic Radius	Decreases (more nuclear charge pulling electrons in)
Ionization Energy	Increases (harder to remove electrons)
Electronegativity	Increases (stronger attraction for electrons)
Metallic Character	Decreases (left are metals, right are nonmetals)
Electrical Conductivity	Decreases (Na, Mg, Al conduct, nonmetals do not)
Melting Point	Varies: Peaks at Si (strong covalent network), then drops

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5. Predict Properties of Unknown Elements Based on the Position in the Periodic Table

• Example: Suppose we discover "Element X" in Group 2, Period 5.
  • It would have two valence electrons.
  • It would be reactive with water, forming a hydroxide and hydrogen gas.
  • It would have a lower ionization energy than Ca but higher than Ba.
  • It would likely form 2+ ions in compounds (e.g., XO, XCl₂).
• If in Group 17, Period 4:
  • It would be a halogen.
  • It would form X₂ molecules.
  • It would react with Group 1 metals to form salts (e.g., NaX).

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