History of the Atomic ModelHistory of the Atomic Model

How the model of the atom has How the model of the atom has changed or evolved over timechanged or evolved over time

Definition of an AtomDefinition of an Atom

The smallest particle The smallest particle of an elementof an element There are 2,000 billion There are 2,000 billion

billion atoms of oxygen billion atoms of oxygen in one drop of waterin one drop of water

Atomic StructureAtomic Structure

Atoms are made up of three basic Atoms are made up of three basic particlesparticlesProtonsProtons: Carry a : Carry a positivepositive charge chargeNeutronsNeutrons: Carry : Carry nono charge charge

Protons and neutrons join together to form the Protons and neutrons join together to form the nucleusnucleus- the central part of the atom- the central part of the atom

ElectronsElectrons: carry a : carry a negative negative charge and circle charge and circle around the nucleusaround the nucleus

Atomic StructureAtomic StructureElectronsElectrons

Electrons travel around the nucleus in Electrons travel around the nucleus in energy shells or orbitals.energy shells or orbitals.

Each orbital can only hold a certain Each orbital can only hold a certain amount of electrons.amount of electrons.

Atomic StructureAtomic Structure

Atomic StructureAtomic Structure

Protons and neutrons have the same mass and Protons and neutrons have the same mass and are the heaviest part of the atomare the heaviest part of the atom

Electrons are much smaller, move faster, and Electrons are much smaller, move faster, and give the atom its volumegive the atom its volume

How have scientists figured this How have scientists figured this out ????out ????

The Greek Model (460-440 BC)The Greek Model (460-440 BC)

Democritus was a Greek philosopherDemocritus was a Greek philosopherMatter cannot be divided into smaller Matter cannot be divided into smaller

and smaller pieces forever. and smaller pieces forever.

The smallest piece called an “atom”The smallest piece called an “atom”

Dalton (1790-1807)Dalton (1790-1807)

Atoms are indivisible and indestructibleAtoms are indivisible and indestructible

Atoms of the same element are exactly Atoms of the same element are exactly alike, atoms of different elements are notalike, atoms of different elements are not

Atoms can combine to form more complex Atoms can combine to form more complex compoundscompounds

Thomson (1887-1898)Thomson (1887-1898)

Called the “Plum Pudding” ModelCalled the “Plum Pudding” ModelAtoms Atoms areare divisible. divisible.

Discovered negatively charged Discovered negatively charged particles, called electrons.particles, called electrons.

Believed atom was like a positive Believed atom was like a positive pudding with negative electrons stuck inpudding with negative electrons stuck in it.it.

Rutherford (1909-1919)Rutherford (1909-1919)

Conducted the Gold Foil ExperimentConducted the Gold Foil Experiment

Found that atom was mostly empty space Found that atom was mostly empty space with very dense, positive centerwith very dense, positive center

Electrons on the edge of the atom.Electrons on the edge of the atom.

Bohr (1913 - 1920)Bohr (1913 - 1920)

Found that electrons did not move Found that electrons did not move randomly around nucleus, they had randomly around nucleus, they had definite paths or “orbits”definite paths or “orbits”

Each orbit only holds a certain number of Each orbit only holds a certain number of electronselectrons

Electrons can jump from one orbit to Electrons can jump from one orbit to another (quantum jump)another (quantum jump)

Electron Cloud Model (current)Electron Cloud Model (current)

Dense nucleus is surrounded by a cloud Dense nucleus is surrounded by a cloud where the electrons arewhere the electrons are

The cloud has energy levels.The cloud has energy levels.

Electrons may “jump” back and forth Electrons may “jump” back and forth between energy levels.between energy levels.

Whose model is represented by the Whose model is represented by the pictures?pictures?

Whose model is represented by the Whose model is represented by the pictures?pictures?