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Arrhenius Acids

Arrhenius Acids. Arrhenius acids are substances that dissociate in water to give H 3 O + ions. Stronger acids dissociate to a greater degree than weaker acids. Arrhenius Bases. Arrhenius bases are substances that dissociate in water to give hydroxide ions.

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Arrhenius Acids

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  1. Arrhenius Acids • Arrhenius acids are substances that dissociate in water to give H3O+ ions. • Stronger acids dissociate to a greater degree than weaker acids. Chapter 1

  2. Arrhenius Bases • Arrhenius bases are substances that dissociate in water to give hydroxide ions. • Stronger bases (NaOH) dissociate more than weaker bases (Mg(OH)2). Chapter 1

  3. Conjugate Acids and Bases • Conjugate acid: when a base accepts a proton, it becomes an acid capable of returning that proton. • Conjugate base: when an acid donates its proton, it becomes capable of accepting that proton back. Chapter 1

  4. Effect of Electronegativity on pKa • As the bond to H becomes more polarized, H becomes more positive and the bond is easier to break. Chapter 1

  5. Effect of Size on pKa • As size increases, the H is more loosely held and the bond is easier to break. • A larger size also stabilizes the anion. Chapter 1

  6. Effect of Resonance on pKa • If the negative charge on an atom can be delocalized over two or more atoms, the acidity of that compound will be greater than when the negative charge cannot be delocalized. • The ethoxide anion is less acidic than the acetate ion simply because the acetate ion can delocalize the negative charge. • Methanesulfonic acid can delocalize the charge in three different resonance forms, making it more acidic than the acetate ion. Chapter 1

  7. Lewis Acids and Lewis Bases • Lewis bases are species with available electrons than can be donated to form a new bond. • Lewis acids are species that can accept these electrons to form new bonds. • Since a Lewis acid accepts a pair of electrons, it is called an electrophile. Chapter 1

  8. Nucleophiles and Electrophiles • Nucleophile: Donates electrons to a nucleus with an empty orbital. • Electrophile: Accepts a pair of electrons. • When forming a bond, the nucleophile attacks the electrophile, so the arrow goes from negative to positive. • When breaking a bond, the more electronegative atom receives the electrons. Chapter 1

  9. Nucleophiles and Electrophiles Chapter 1

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