The Atomic ModelThe Atomic Model

Define: AtomDefine: Atom

An atom is the smallest component An atom is the smallest component of an element that retains the of an element that retains the characteristics of the elementcharacteristics of the element

What atoms are made What atoms are made of ?of ?

If you broke apart any one atom, it If you broke apart any one atom, it would be made of three parts- and would be made of three parts- and it wouldn’t be the atom anymore.it wouldn’t be the atom anymore.

Atoms are made from three Atoms are made from three different different sub-atomic sub-atomic particles:particles:

•Protons

•Protons

•Electrons

•Electrons

•Neutrons

•Neutrons

A brief history of A brief history of AtomsAtoms

460 B.C. Democritus: pounded stuff into itty-bitty pieces460 B.C. Democritus: pounded stuff into itty-bitty pieces 1808 Dalton: small solid spheres1808 Dalton: small solid spheres 1898 Thompson: atoms eject tiny negative particles!!!!1898 Thompson: atoms eject tiny negative particles!!!! 1904 Thompson: Plum pudding model1904 Thompson: Plum pudding model 1910 Rutherford: Gold foil expt1910 Rutherford: Gold foil expt 1913 Bohr: Electrons in ORBITS! 1913 Bohr: Electrons in ORBITS! Modern Theory (Wave Theory): electrons are wavelike, Modern Theory (Wave Theory): electrons are wavelike,

NOT arranged in neat orbits, but can be discussed only by NOT arranged in neat orbits, but can be discussed only by the probability of where they are. (Electron Cloud)the probability of where they are. (Electron Cloud)

DemocritusDemocritus (460 – 370 BC) (460 – 370 BC) Eventually reach Eventually reach

matter that cannot be matter that cannot be divided: which he divided: which he called an “atom”. called an “atom”.

John Dalton (1766-John Dalton (1766-1844)1844)

Elements combine in Elements combine in certain ratioscertain ratios

1803: Dalton proposes1803: Dalton proposes“Atomic Theory”“Atomic Theory”

All Matter is composed of tiny, indivisible All Matter is composed of tiny, indivisible particles called atoms.particles called atoms.

Atoms of a given element possess unique Atoms of a given element possess unique characteristics and masscharacteristics and mass

Atoms of different elements can join to Atoms of different elements can join to form compounds.form compounds.

Discovered electrons Discovered electrons Proposed “Plum Pudding” modelProposed “Plum Pudding” model

Joseph John Joseph John Thomson Thomson

(1897)(1897)

RutherfordRutherford

Discovered the nucleusDiscovered the nucleus According to his According to his

model, an atom is model, an atom is mostly empty space.mostly empty space.

Stadium AnalogyStadium Analogy

If a football is placed on the 50 yard line (in the middle) of a football field then the If a football is placed on the 50 yard line (in the middle) of a football field then the outer seats are the edge of the electron cloud and the football is the nucleus. outer seats are the edge of the electron cloud and the football is the nucleus. Everything in the stadium (atom) other than the football is empty space.Everything in the stadium (atom) other than the football is empty space.

Niels BohrNiels Bohr

Proposed that each Proposed that each electron is in a specific electron is in a specific energy level.energy level.

BohrBohr’’s model is also s model is also called the “planetary called the “planetary model”model”

Bohr ModelBohr Model Write the number of Write the number of

protons and neutrons in protons and neutrons in the centerthe center

Up to 2 electrons on the Up to 2 electrons on the inner ring, and up to eight inner ring, and up to eight on the second ring. The on the second ring. The third ring can have up to third ring can have up to 16 electrons.16 electrons.

P=N=

Cloud ModelCloud Model Erwin Schrödinger The cloud model represents a sort of

history of where the electron has probably been and where it is likely to be going. 

It utilizes Heisenberg’s uncertainty Principle

The structure of an atomThe structure of an atom

Bohr Model

“Planetary Model”

Schrödinger Model

“Electron Cloud Model”

Lewis Dot ModelLewis Dot Model

Dots are drawn Dots are drawn for each for each OUTER OUTER electronelectron

Not all Not all electrons are electrons are drawndrawn

Valence ElectronsValence Electrons

Electrons located on the Electrons located on the outermost energy level.outermost energy level.

Use the columns on Use the columns on periodic table!!!periodic table!!!

Dmitri MendeleevRussian scientist/professor

History of the Atom Timeline: http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm

CitationsCitations