Atoms

Greek Atomic Greek Atomic ModelModel

•Democritus (400 BC)Democritus (400 BC)•Named the atomNamed the atom•Atom cannot be Atom cannot be divideddivided

Dalton’s Dalton’s AtomicAtomic Theory Theory•18031803

•All elements are composed All elements are composed of atoms (not divisible)of atoms (not divisible)

•Atoms of same element are Atoms of same element are the samethe same

•Atoms of different Atoms of different elements are differentelements are different

Thomson’s Thomson’s ModelModel

•18971897•Atom has smaller parts, Atom has smaller parts, like electronslike electrons

•Atom made of a positive Atom made of a positive pudding-like material with pudding-like material with negatively charged negatively charged electrons scattered electrons scattered throughoutthroughout

Rutherford’s Rutherford’s ModelModel

•19111911•Positive-charged Positive-charged particles in the nucleusparticles in the nucleus

•Negative scattered Negative scattered around edgesaround edges

•Gold foil experimentGold foil experiment

Rutherford’s Rutherford’s ExperimentExperiment

Bohr’s Bohr’s ModelModel

•19131913•Electrons move in definite Electrons move in definite orbits around the nucleus orbits around the nucleus (like the planets move (like the planets move around the sun)around the sun)

•Energy levels located a Energy levels located a certain distance from the certain distance from the nucleusnucleus

Compare the Compare the Thomson to the Thomson to the Rutherford/BohrRutherford/Bohr

Wave Wave TheoryTheory

•Modern modelModern model•Electrons do not travel Electrons do not travel in definite pathsin definite paths

•Think electron cloudThink electron cloud

Atomic StructureAtomic Structure

Subatomic Subatomic ParticlesParticles

• protons = positive charge (+)protons = positive charge (+)• electrons = negative charge (-)electrons = negative charge (-)• neutrons = neutral (0 charge)neutrons = neutral (0 charge)

Subatomic Subatomic ParticlesParticles

Lithium AtomLithium Atom

•How many How many protons?protons?

•How many How many electrons?electrons?

•How many How many neutrons?neutrons?

Atomic NumberAtomic Number

• identifies the element on the identifies the element on the periodic tableperiodic table

• equals the # of protons in the equals the # of protons in the nucleusnucleus

Atomic MassAtomic Mass

• sum of the # of protons + # of sum of the # of protons + # of neutrons in the nucleusneutrons in the nucleus

• changes with isotopeschanges with isotopes

IsotopesIsotopes• atoms of the same elementatoms of the same element• same # of protonssame # of protons• different # of neutronsdifferent # of neutrons• different atomic mass different atomic mass • examples = hydrogen, carbon, examples = hydrogen, carbon,

uraniumuranium

IsotopesIsotopes

Electron Electron CloudCloud• electrons move electrons move

about the about the nucleus locked nucleus locked in a certain in a certain area of the area of the electron cloudelectron cloud

• location called location called energy levelsenergy levels

Electron ShellsElectron Shells

# of electrons in # of electrons in each orbital shelleach orbital shell• electrons electrons

with low with low energy energy are found are found in the in the energy energy level level closest to closest to the the nucleusnucleus