CHEMICAL BONDINGHISTORICAL DEVELOPMENT

By Moses G. Mabuza

128529

INTRODUCTION

Scientific concepts evolve (Trifiro & Trifiro, n.d)

New ideas take time to be accepted (Hoyningen-Huene, 1996)

Concepts change due to:- discovery of new instruments- flaws / mistakes- new ideas with more expl. power- chance

DEFINITION

Chemical Bond Attraction btn atoms – result to

chemical subst. containing 2 or more atoms.

(Wikipedia, the free encyclopedia)

EARLY IDEAS OF BONDING

DEMOCRITUS (c.460 – 370 B.C)Dates back to 5th century – Greece Atoms differ in size, shape &

arrangement of parts Links btn combined atoms Some atoms had hooks & eyes Some had balls & sockets

(Chemical Bonding, n.d)

EARLY IDEAS OF BONDING CONT.

ASCLEPIADES (c.130 – 40 B.C)Built on ideas of Epicurus – Grk phil. Discussed ‘clusters of atoms’ – did not

know what force bonded them

LUCRETIUS (c.95 – 55 B.C) Atoms attached by

- fishhook-like appendages

EARLY IDEAS OF BONDING CONT.

DESCARTES (1596 – 1650)Concurred wt Lucretius: Atoms held together

by tiny hooks & barbs

NEWTON Particles attract at a

distance due to force

BOYLE (1627 – 1691)Rejected Newton’s ideas Particles arranged

themselves in grps Chemical change

result from rearrangements within the grps

EARLY MODERN ADVANCES

JOHN DALTON (1766 – 1844)Birth of modern atomic theory in 1803 All elements composed of tiny

indestructible particles (atoms acc. to Democritus)

All substances are a combination of atoms

Atoms sit next to each other without forming true bonds

EARLY MODERN ADVANCES CONT.

AMEDEO AVOGADRO (1776 – 1856) Helped distinguish btn atoms &

molecules

BOLTZMANN (1844 – 1906) Proposed atoms had ‘sensitive

regions’

(Chemical Bonding, n.d)

MODERN ADVANCES

AUGUST KEKULE (1829 – 1896)First attempted using modern terminology Defined valency Represented bonds with symbols Dvlped a system of showing

arrangement of bonds in space

MODERN ADVANCES CONT.

SCOTT COUPER (1831 – 1892) Dvlped a system of short dashed lines

for bondse.g

H–O–H

MODERN ADVANCES CONT.

JOSEPH THOMSON (1856 – 1940)In 1904 – First to explain chem. bonding in terms of electrons Proposed transfer of corpuscles to form

cpds Atoms oppositely charged, therefore,

form cpds

MODERN ADVANCES CONT.

Ionic bond theory stood for 2 decades as the only way of bonding

Problem – nonpolar subst. lacked polarity

e.g. H2

Therefore, another explanatory power needed

MODERN ADVANCES CONT.

GILBERT LEWIS (1875 – 1946)In 1916, Presented covalent bonding to

explain nonpolar molecules Introduced idea – shared pair of

electrons Molecules with unpaired

electron – ‘odd’(Estabrooks,

1998)

MODERN ADVANCES CONT.

LEWIS (1875 – 1946) Began with Cubical Model

of the Atom

MODERN ADVANCES CONT.

Thought no diff. btn ionic & covalent bonding

Electron pair not equally shared by atoms (unless same element)

Many organic cpds – not explained by ionic bonding

After demonstrations – covalent bond was accepted alongside the ionic bond

MODERN ADVANCES CONT.

IRVING LANGMUIR (1881 – 1957)In 1919, Took Lewis’ ideas Called shared-e- pair bond, covalent

bond Named the ‘octet rule’

(Langmuir, n.d)

MODERN ADVANCES CONT.

DRUDE & LORENTZDid early work in metallic bonding Realised metals contained weakly

bound e-s (conduct electricity)Therefore, Lewis – there were 3 types of bonding

- polar (ionic), nonpolar (covalent) & metallic

MODERN ADVANCES CONT.

OTHER CHEM. BONDING MODELSLatimer & Rodebush Introduced H – bond to explain bonding

in water & ethanoic acidSidgwick Proposed the coordinate bond

MODERN ADVANCES CONT.

Quantum mechanics – probability of finding an electron in region of spaceTwo main approaches – VBT & MOTLINUS PAULING (1901 – 1994) Dvlped VBT Learnt from the work of Lewis &

Langmuir Showed that ionic and covalent

bonding were merely extremes

MODERN ADVANCES CONT.

ROBERT MULLIKEN (1896 – 1986) Dvlped MOT, & Ligand field theory

(together with others) MOT explained the absorption spectra

of molecules

CONCLUSION

IMPORTANT FEATURES Understanding the atom (composition

& structure) New ideas based on old ones Ancient philosophers were speculating

– no experimentation

- THE END -

THANK YOU!

Babe Mabuza