Prelims - Lec 1 - Evolution of Atom

Atomos

smallest piece of matter, not to be cut, indivisible

Atom

The element’s smallest part containing all its properties. Tiny particle that defines an element. It makes up all matter (any that takes space & has mass).

0.1-0.5 nm

Diameter of an atom.

Democritus (460-370 BC)

Who believed that matter could not be divided indefinitely?

Aristotle (384-322 BC)

Believed that matter could be divided into smaller and smaller pieces forever.

Earth, Fire, Water, and Air

What are the 4 elements Aristotle believed at?

John Dalton

Proposed the hook and eye model of atom based on experimentation and not on pure reason; There are elements that can be easily combined/separated; Also believed that atom is the smallest unit

Law of Conservation of Mass

Atoms cannot be created nor destroyed.

Law of Multiple Proportions

It states that when chemical elements combine, they do so in a ratio of small whole numbers.

Atomic Theory (1808)

All matter is made of atoms.

Hook and Eye Model of Atom

It is crucial for the successful interaction of two atoms.

Joseph John Thomson (1856-1940 BC)

First proposed that atoms are divisible; Found that atoms could sometimes eject a far smaller negative particle, the electron, while working with a cathode ray tube.

1897

When was electron discovered?

Corpuscles

The term before for electrons

The Plum Pudding Model of Atom

JJ Thomson developed this model of atom.

negative electric charges (electrons)

The plums represented what?

shapeless mass of uniform positive electrification

The pudding represented what?

Ernest Rutherford (1871-1937)

He introduced that the positive electrification mentioned by Thomson is a small dense center he named nucleus; He is considered the Father of Nuclear Physics; He also discovered the proton.

1911

When was nucleus discovered?

1919

When was proton discovered?

Nuclear Model of Atom

A model by Rutherford that describes the atoms as containing a small, dense, + charged center, known as the nucleus, with - electrons orbiting a nucleus in set, predictable paths

Niels Bohr (1766-1844)

A Danish scientist that proposed an improvement in Rutherford’s Theory by placing each electron in a specific energy level.

1913

When did Niels Bohr proposed an improvement by placing each electron in a specific energy level?

Energy Quantum

Electrons can move up a level if given enough energy. What is the so-called energy?

Quantum Leap

Electrons can move up a level if given enough energy. What is the so-called movement of electrons?

The Planetary Model of Atom

An atomic model by Bohr wherein electrons move in definite orbits around the nucleus, much like planets circle the sun . These orbits, or energy levels, are located at certain distances from the nucleus.

Erwin Schrödinger

An Austrian physicist that used mathematical equations to describe the likelihood of finding an electron in a certain position; Also introduced the concept of sub-energy levels (s,p,d,f...)

Quantum Mechanical Model

An atomic model by Schrodinger that describes the likelihood of finding an electron in a certain position. It portrays a nucleus surrounded by an electron cloud.

Electron Cloud Model

Other term for Quantum Mechanical Model

1926

When was Quantum Mechanical Model proposed?

James Chadwick

Who discovered the neutron? He was also awarded a nobel prize in physics for this discovery.

Ernest Rutherford

Mentor of James Chadwick