TOPIC 18 ACIDS AND BASES 18.1 Lewis Acids and Bases

ESSENTIAL IDEA The acid-base concept can be extended to reactions that do not involve proton transfer. NATURE OF SCIENCE (2.5) Theories can be supported, falsified or replaced by new theories – acid-base theories can be extended to a wider field of applications by considering lone pairs of electrons. Lewis theory doesn’t falsify Bronsted-Lowry but extends it.

INTERNATIONAL-MINDEDNESS Acid-base theory has developed from the ideas of people from different parts of the world through collaboration and competition..

THEORY OF KNOWLEDGE The same phenomenon can sometimes be explored from different perspectives, and explained by different theories. For example, do we judge competing theories by their universality, simplicity or elegance?

UNDERSTANDING/KEY IDEA 18.1.A A Lewis acid is an electron lone pair acceptor and a Lewis base is an electron lone pair donor.

THREE MAIN TYPES Arrhenius Acid – produces H+ ions Arrhenius Base – produces OH- ions This is an early theory. Bronsted-Lowry Acid – proton donor Bronsted-Lowry Base – proton acceptor Lewis Acid – electron pair acceptor Lewis Base – electron pair donor

GUIDANCE Know the relationship between Bronsted-Lowry and Lewis acids and bases.

All Bronsted-Lowry acids are Lewis acids because they can accept a lone pair of electrons. However, not all Lewis acids are Bronsted- Lowry acids because they may not have an H + to donate.

All Bronsted-Lowry bases are Lewis bases because they have a lone pair of electrons to donate. Not all Lewis bases are Bronsted-Lowry bases because they don’t have to accept a proton to be a Lewis base. Bronsted-Lowry acids and bases are subsets of Lewis acids and bases so the Lewis definition is a broader definition.

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UNDERSTANDING/KEY IDEA 18.1.B When a Lewis base reacts with a Lewis acid a coordinate bond is formed.

BF 3 + NH 3 ↔ F 3 BNH 3 BF 3 is trigonal planar with no lone pairs of electrons. NH 3 is trigonal pyramidal with one lone pair of electrons. NH 3 donates both of its electrons to BF 3. The bond formed is a “dative” or coordinate covalent bond because both electrons came from nitrogen. NH 3 is the Lewis base because it donates a pair of electrons making BF 3 the Lewis acid because it accepts the lone pair of electrons.

APPLICATION/SKILLS Be able to apply the Lewis theory to inorganic and organic chemistry to identify the role of the reacting species.

dlt.ncssm.edu dlt.ncssm.edu Fe H 2 O → [Fe(H 2 O) 6 ] 3+ Fe 3+ is the Lewis acid and H 2 O is the Lewis base.

 dlt.ncssm.edu Cu NH 3 → [Cu(NH 3 ) 4 ] 2+ Cu 2+ is the Lewis acid and NH 3 is the Lewis base.

UNDERSTANDING/KEY IDEA 18.1.C A nucleophile is a Lewis base and an electrophile is a Lewis acid.

A nucleophile is an electron-rich species that donates a lone pair to form a new covalent bond in a reaction. (Lewis base) An electrophile is an electron-deficient species that accepts a lone pair from another reactant to form a new covalent bond. (Lewis acid) The reactions are depicted using curly arrows.

Examples of nucleophiles (Lewis bases): OH -, NH 3, Cl - Examples of electrophiles (Lewis acids): BF 3, Cu 2+, Br +, NO 2+, (CH 3 )C + 

Citations International Baccalaureate Organization. Chemistry Guide, First assessment Updated Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd ed. N.p.: Pearson Baccalaureate, Print. Most of the information found in this power point comes directly from this textbook. The power point has been made to directly complement the Higher Level Chemistry textbook by Catrin and Brown and is used for direct instructional purposes only.