Structure of the Atom

To be able to understand and change matter we need to know what matter is made of (Composition) and How it is put together (Structure).

Put yourself in the shoes of early scientists So what is matter? Put yourself in the shoes of early scientists

~ 400 BCE Democritus proposes the atom “Nothing exists but atoms and empty space, everything else is opinion.”

Alchemy becomes Chemistry and the Idea of the Atom is Reborn Around 1800, Lavosier realized that to advance chemistry mathematics and the concept of the atom would be needed.

The Rediscovery of the Atom & Injection of Math Lead to Law of Conservation of Matter - Atoms are not created or destroyed. Conservation Law depended on a theory of gasses. Relative weights of elements - Avogadro Law of Constant Composition - Compounds are made up of exact ratios of atoms.

 Dalton's Atomic Theory Elements are made of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

Electrical Nature of the Atom Franklin discovers charges which he calls positive and negative. He believes that these two charges are cloud-like fields have opposite natures. FARADAY describes the atom as being made of these charges

Thomson discovers that the negative charge is a subatomic particle.

Thomson’s Cathode Ray Tube Experiments

Rutherford’s Alpha Scattering Experiment Shoots radioactive particles at a very thin gold foil. Wants to know if the radioactive particles will be deflected.

Rutherford expects the radioactive particles to pass thru the gold foil without much resistance because the radioactive particles are small & the atom is basically a positive charge cloud with very small negative particles.

Rutherford’s Atom

ATOMIC NUMBER Moseley around 1913 discovered a unique positive charge on nucleus which starts to explain why element behaves differently.   The number of protons in the nucleus is called “atomic number”.

Spectrometer

Discovery of Particles of Light Ejection of electrons depended on Frequency first. After minimum frequency to eject particles was achieved, increasing brightness ejected more particles. Discovery of Particles of Light PHOTONS

Bohr was trying to figure out why different elements will give off different colors when placed into a flame.

Bohr’s Model Electrons are in orbitals Each “orbital” has a unique energy. Electrons can move between orbitals by absorbing or releasing energy. When electrons release energy it is always in the form of electromagnetic radiation (packets of light). Light Metallurgists

Other Uses for Emission Spectra Composition of the stars Metallurgists and Chemists use spectroscopy to identify elements within a substance

James Chadwick discovers the NEUTRON allowing for a later Neutrons add to the atom’s mass Neutron exert the strong force which keeps protons together

Character of Subatomic Particles Robert Millikan is important for the discovery of the size of electron

Contemporary Model of the Atom Nucleus can be changed Radioactivity Atoms can be split apart (Fission) Larger atoms can be made from smaller atoms (Fusion) E = MC2

Electron clouds based on probability an electron exists in a certain region of space around the atom

9/17/2004 ORNL Electron Microscope Images (0 9/17/2004 ORNL Electron Microscope Images (0.6 angstroms resolution or 0.00000000006 meters) of Silicon Crystal Dumbbell-shaped electron clouds!!!

Scanning Tunneling Microscope

Protons & neutrons are not fundamental. Protons and neutrons are made of Quarks

END

Answer these questions Draw an atom Include subatomic particles, charges, size and locations Answer these questions What makes elements different? Define atoms, elements, compounds, mixtures, ions, isotopes?