3.2.1 Periodic Trends: Oxides Across a Period

Oxides Across a Period

• Oxide = a binary compound that contains oxygen and another element

  • ex. Carbon dioxide CO₂

• Since oxides are acid-base they show their chemical trend: they change from basic to amphoteric to acidic as you move across a period

• Amphoteric = having the ability to react chemically as either an acid or a base

• ex. Aluminum oxide (so it can react with an acid like HCl or with a base like NaOH)
  

Period 3 Oxides

• The reason for the different acidic or basic natures is because of their structure, bonding, and electronegativity

• Electrons will be transferred to oxygen when forming oxides and providing an ionic bond because of the highest difference in electronegativity between oxygen and Na/Mg/Al

• On the other hand, Si, P, and S (elements with the least difference in EN) will share the electrons with oxygen to form covalently bonded oxides

3.2.2 Periodic Trends: Group 1 - The Alkali Metals

• Group 1 Metals = “Alkali Metals” = metals that form alkaline solutions with high pH when they react with water

• All elements in group 1 end with the electron configuration: ns¹

Physical Properties

• Soft and easy to cut (more so as you move down the group)

• Shiny

• Conduct heat/electricity

• Low melting points (decreases more going down the group since atomic radius increases so metallic bonding gets weaker)

• Low Density

Chemical Properties

• Reactive with oxygen and water in the air

  • Often kept under oil to prevent reactions

• Highly reactive with water

  • And produces an alkaline metal hydroxide solution and hydrogen gas

3.2.3 Periodic Trends: Group 17 - The Halogens

The Halogens

• Group 17 non-metals

• Poisonous

• Diatomic = forming molecules of 2 atoms

• Have 7 valence electrons

• Form halide ions by gaining one more electron to complete the octet rule

Physical Properties Trends (Down the Group)

• Density, Melting/Boiling Points of the halogens increase going down the group

• Reactivity decreases down the group

  • Why?

    • Halogens electron configurations all end in ns²np⁵

    • When the 7 valence electrons react, they need one more to have a full shell

    • Electron Affinity decreases

    • Atomic Radius increases

      • → # of Shells increases

      • → Shielding increases

      • → Distance to nucleus increases

      • → Weaker electrostatic forces to attract the 8th electron

      • Therefore, as you go down the group, the reactivity decreases (because it is harder to attract the 8th electron)

Reaction of Halogens with Halid Ions in Displacement Reactions

• Halogen Displacement = When a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide

Halogen Displacement Reactions

Chlorine and Bromine

• Chlorine + colorless potassium bromide = bromine (Orange Solution)

• Since chlorine is above bromine in group 17, it is more reactive

  • So chlorine will displace bromine

2KBr (aq)       +    Cl₂ (aq)  →     2KCl (aq)     +       Br₂(aq)

potassium bromide + chlorine → potassium chloride + bromine

Bromine and Iodine

• Since bromine is higher than iodine in group 17, it is more reactive

• Thus, bromine will displace iodine

  Br₂ (l) +      2NaI (aq)    →    2NaBr (aq)     +    I₂ (aq)

bromine +  sodium Iodide → sodium bromide + iodine