Evolutions of Atomic Theory

By Denyse Briggs and George Osnaya

Definition of Atomism

• Any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles

• The ancient Greek philosophers Democritus and Epicurus held atomic theories of the universe.

Earth, Air, Wind and Fire Model

• Western chemistry grew up around alchemical ideas of Earth, Air, Fire, and Water.

• They’re called Aristotelian elements originated from a Sicilian aristocrat, Empedocles of Acragas.

• Empedocles is best known for claiming that all matter is formed when the opposing forces of Love and Hate act upon the four elements; Earth, Air, Fire, and Water.

Atomism

• Atomism was developed prior to the time of Socrates (399 B.C.)

• It’s the belief that all matter of the universe is made up of tiny particles that are indivisible, called atoms.

• The word atom comes from the Greek word atomos meaning invisible.

Solid Sphere Model

• The solid sphere model was proposed by John Dalton.

• John Dalton was an English chemist, meteorologist, and physicist.

• He is best known for his pioneering work in the development of modern atomic theory, and his research into color blindness (sometimes referred to as Daltonism, in his honor).

Solid Sphere Model (Cont.)• The atoms of a given element are different from those of any

other element• The atoms of different elements can be distinguished from

one another by their respective relative atomic weights. • All atoms of a given element are identical.• Atoms of one element can combine with atoms of other

elements to form chemical compounds• A given compound always has the same relative numbers of

types of atoms. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process

• A chemical reaction simply changes the way atoms are grouped together.

• Atoms combine in whole number ratios to form compounds.

Solid Sphere Model (Cont.)

Plum Pudding Model

• The Plum pudding model was proposed by J.J. Thompson.

• J.J. Thompson was a physicist who is most famous for his discovery of the electron.

• In this model, the atom is composed of electrons surrounded by a group of positively charged particles to balance the electron's negative charge, like negatively-charged "plums" surrounded by positively-charged "pudding".

Plum Pudding Model (Cont.)

• The electrons were thought to be positioned throughout the atom, but there are many structures possible for positioning multiple electrons, like rotating rings of electrons.

• In this model, the electrons were free to rotate within the blob or cloud of positive substance.

• In this model, the electrons were free to rotate within the blob or cloud of positive substance.

Plum Pudding Model (Cont.)

The Nuclear Model

• The nuclear model was proposed by Ernest Rutherford.

• The nuclear model was based on Rutherford's analysis that the Plum pudding model of J. J. Thomson of the atom was incorrect.

• Rutherford devised an experiment to test the Thomson model of the atom.

The Nuclear Model (Cont.)• Rutherford came up a new model of the atom in

which all of the positive charged particles were crammed inside a tiny nucleus about ten thousand times smaller than the atom as a whole.

• Since the nucleus and its electrons are oppositely charged, and therefore attract one another, there wasn’t anything to stop the electrons from being pulled immediately into the nucleus.

• Alpha particles were shot through the atom and some of the particles bounced back, which led to the discovery of the nucleus.

The Nuclear Model (Cont.)

The Nuclear Model (Cont.)

• http://www.youtube.com/watch?v=5pZj0u_XMbc