The Atomic Structure The Atomic Structure of Atomsof Atoms

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Democritus: Hypothesizing the Democritus: Hypothesizing the AtomAtom

Around 460 B.C., Around 460 B.C., Democritus Democritus first first developed the developed the ideaidea of of atomsatoms as the smallest as the smallest possible bit of matter. possible bit of matter.

The word “atom” came The word “atom” came from the Greek word from the Greek word atomosatomos meaning meaning indivisibleindivisible

Greek philosophers laid Greek philosophers laid the ground work for the the ground work for the modern atomic theorymodern atomic theory

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Dalton: The Atomic TheoryDalton: The Atomic Theory

John Dalton, in the early John Dalton, in the early 1800’s, developed the 1800’s, developed the “atomic theory” “atomic theory” from from observations gathered observations gathered from many experimentsfrom many experiments..

Fun Fact: Dalton was a Fun Fact: Dalton was a school teacher and school teacher and chemist! chemist!

Dalton’s Atomic Theory:Dalton’s Atomic Theory: 1. 1. All elements are composed of atoms. All elements are composed of atoms.

Atoms cannot be divided or destroyed. Atoms cannot be divided or destroyed. – (Now we know atoms (Now we know atoms cancan be divided) be divided)

2. 2. Atoms of the same element are Atoms of the same element are exactly alike. Atoms of different exactly alike. Atoms of different elements are different. elements are different. – (Now we know that atoms of the same element (Now we know that atoms of the same element

that are that are notnot exactly alike are called exactly alike are called isotopes – isotopes – they have a diff. # of neutronsthey have a diff. # of neutrons))

3. 3. The atoms of two or more elements The atoms of two or more elements can join together to form compounds.can join together to form compounds.

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J.J. Thomson: 1856-1940J.J. Thomson: 1856-1940

Discovered the Discovered the electron.   electron.  

He was awarded He was awarded with the Nobel with the Nobel Prize in Physics in Prize in Physics in 1906. 1906.          

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Lord Ernest Rutherford: 1871-1937Lord Ernest Rutherford: 1871-1937

Ernest Rutherford was Ernest Rutherford was once a student of JJ once a student of JJ Thomson Thomson

Discovered that most of Discovered that most of the atom is made up of the atom is made up of "empty space” where "empty space” where the electrons movethe electrons move

He discovered and He discovered and named both the named both the nucleusnucleus  and   and protonsprotons

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James Chadwick: 1891-1974James Chadwick: 1891-1974

James Chadwick was a James Chadwick was a student of Rutherford student of Rutherford

Discovered the Discovered the neutronneutron

He found neutrons to He found neutrons to have essentially the have essentially the same mass as protonssame mass as protons

He was awarded the He was awarded the Nobel Prize in physics Nobel Prize in physics in 1935in 1935

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Niels Bohr: early 1900’sNiels Bohr: early 1900’s

Discovered electrons Discovered electrons traveled in energy levels traveled in energy levels around the nucleus. around the nucleus. 

The lowest energy level The lowest energy level is closest to the nucleus is closest to the nucleus and holds up to 2 and holds up to 2 electrons. electrons.

Higher energy levels are Higher energy levels are father from the nucleus father from the nucleus and can contain more and can contain more electronselectrons

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REVIEW: Early Atomic ChemistsREVIEW: Early Atomic Chemists

DemocritusDemocritus Named the atomNamed the atom

DaltonDalton Atomic TheoryAtomic Theory

ThomsonThomson Discovered electronDiscovered electron

RutherfordRutherford Named the nucleus, proton, and described the Named the nucleus, proton, and described the

“empty space” where electrons travel“empty space” where electrons travel ChadwickChadwick

Discovered neutronDiscovered neutron BohrBohr

Discovered electron energy levelsDiscovered electron energy levels

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Parts of an AtomParts of an Atom Locations Locations

NucleusNucleus Electron CloudElectron Cloud

Subatomic Subatomic ParticlesParticles ProtonsProtons NeutronsNeutrons ElectronsElectrons

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NucleusNucleus

Is the Is the positively positively chargedcharged, central , central part of an atom.part of an atom.

Contains Contains protonsprotons and and neutronsneutrons. .

Contains almost Contains almost ALL ALL of the of the atom’s massatom’s mass

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Inside the NucleusInside the Nucleus

ProtonsProtons are are positively (+) positively (+) charged particlescharged particles

NeutronsNeutrons are are uncharged uncharged particles (Ø) particles (Ø) – ““neutrons are neutrons are

neutral”neutral”

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Outside the NucleusOutside the Nucleus

ElectronsElectrons are are negatively (-) negatively (-) charged particles charged particles located in the located in the electron cloud. electron cloud.

The The electron cloudelectron cloud is arranged in is arranged in energy levelsenergy levels and and travels around the travels around the atom’s nucleus. atom’s nucleus.

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Neutral AtomsNeutral Atoms

An atom has an An atom has an

overall neutral charge overall neutral charge

when:when:

the # of electrons (-) = the # of electrons (-) =

the # of protons (+)the # of protons (+)

Remember, neutrons are neutral!

electron

neutron

proton

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