1. 3.1Atomic Theories

2. The stuff you already know!
All matter occupies volume and has mass.
All matter is comprised of particles.
These particles are organized into atoms, molecules & compounds.
Each atom is the fundamental component of an element.
Each element has characteristic physical & chemical properties.

3. The stuff you already know!
The atom has subatomic particles called;
Electrons –responsible for the element’s chemical behaviour.
Protons – responsible for the element’s physical and chemical properties.
Neutron – responsible for the variance in the population of an element’s atoms’ masses. Isotopes of the same element have identical properties.

4. The stuff you already know!
Particle
Mass (u)
Electrical Charge
Location
Electron 1-
Outside nucleus
Proton 1+
Nucleus
Neutron

5. The stuff you already know!
There are about 110 elements of which about 23 are synthetic or man-made.
They are named using conventions adopted by the IUPAC.
They are represented with symbols.
1,2 or 3 letters of which the first is the only one capitalized.
The symbols are internationally recognized as the name varies with the local language.

6. The stuff you already know!
The elements are noted with a “standard notation”.
A  the mass number (protons + neutrons)
Z  the atomic number (protons)
X  the chemical symbol
Isotopes are atoms with the same number of protons but different numbers of neutrons.

7. Stuff you might remember…
Early Greek Theories of Matter
500 BC
Greek philosopher Democrities believed that substances were composed of indivisible particles called atoms (Greek for “indivisible”)
Atoms of different sizes, regular shapes, and are in constant motion.
Empty space between atoms.

8. Stuff you might remember…
Aristotle ( BC)
Criticized Democrities’s theory
All matter is made up of four basic substances:
Earth
Air
Fire
Water
Each basic substance had different combinations of four specific qualities:
Dry, hot, moist & cold
Aristotle’s opinion prevails among scholars!

9. Dalton’s Atomic Theory (1805)
Experimental Work
Theoretical Explanation
Atomic Theory
Law of definite proportions: elements combine in a characteristic mass ratio.
Each atom has a particular combining capacity.
Matter is composed of indestructible, indivisible atoms, which are identical for one element, but different from other elements.
Law of multiple proportions: there may be more than one mass ratio.
Some atoms have more than one combining capacity.
Law of conservation of mass: total mass remains constant
Atoms are neither created nor destroyed in a chemical reaction.

10. Thomson Atomic Theory (1897)
Experimental Work
Theoretical Explanation
Atomic Theory
Arrhenius: the electrical nature of chemical solutions.
Atoms may gain or lose electrons to form ions in solution.
Matter is composed of atoms that contain electrons (negative particles) embedded in a positive material. The kind of element is characterised by the number of electrons in the atom.
“The cookie model for the atom.”
Faraday: quantitative work with electricity & solutions.
Particular atom and ions gain or lose a specific number of electrons.
Crookes: qualitative studies with the cathode ray.
Electricity is composed of negatively charged particles.
Thomson: quantitative studies with the cathode ray.
Electrons are a component of all matter.
Millikan: charged oil drop experiment
Electrons have a specific fixed electric charge.

11. Rutherford Atomic Theory (1911)
Experimental Work
Theoretical Explanation
Atomic Theory
Rutherford: A few positive alpha particles are deflected at large angles when fired at gold foil.
The positive charge in the atom must be concentrated in a very small volume of the atom.
An atom is comprised of a very tiny nucleus which contains positive charges and most of the mass of the atom. Very small negative electrons occupy most of the volume of the atom.
Most materials are very stable and do not self destruct or disintegrate.
A very strong force holds the positive charges together within the nucleus. (Strong nuclear force)
Rutherford: Most alpha particles pass straight through gold foil.
Most of the atom is empty space.

12. The next generation in the knowledge on matter!
Quantum Theory
The next generation in the knowledge on matter!

13. Protons, Neutrons & Isotopes
Experimental Work
Theoretical Explanation
Atomic Theory
Rutherford (1914): The lowest charge on an ionized gas particle is from the hydrogen ion.
The smallest particle of positive charge in the proton.
Atoms are comprised of protons, neutrons and electrons. Atoms of the same element have the same number of protons and electrons, but may have varying number of neutrons, resulting in isotopes of the element.
Soddy (1913): Radioactive decay suggests different atoms of the same element.
Isotopes of an element have fixed number of protons but varying stability and mass.
Aston (1919): Mass spectrometer work indicates different masses for some atoms of the same element.
The nucleus contains neutral particles called neutrons.
Radiation is produced by bombarding elements with alpha particles.

14. A little background . . . . . Enter Max Planck (Plonk not Plank!)
At the turn of the century, Physics and Chemistry become entwined as the study of matter and energy become the focus of the scientific community.
Light energy is of primary interest – does it travel as a particle or a wave?
There is insurmountable evidence to support the wave theory of light and mathematical models supporting the observations.
Maxwell and others define and study the electromagnetic spectrum and the characteristics of its energy. Light is included in this spectrum.
Further investigation of the spectrum uncovers discrepancies that can’t be explained with conventional theories of the time.
Enter Max Planck (Plonk not Plank!)

15. Max Planck ( )
His teacher, Gustav Kirchhoff, investigated the energy emitted from blackbodies. Planck continued in this vein.
Blackbodies -objects that absorb light then radiate energy
– Heat up a piece of metal and it turns “red hot”, then orange, the blue, then “white hot”.
Turn on the stove element and it soon emits heat (IR radiation) and red light (light energy)
The belief of the time was – as you increase the intensity of the incident energy source the emitted energy would increase in energy, as found in the EMS spectrum.

16. Max Planck (1858-1947) Classical Physics prediction
Intensity of incident energy
IR ROYGBV UV
Emitted energy from Blackbody
Observed Results (“The Blackbox Catastrophe”)

17. Max Planck ( )
The results lead to such a revolutionary concept in energy that Planck himself doubted it.
Energy was transmitted and absorbed in “bundles”, “packets” or QUANTA rather than a continuum of energy.
Matter can absorb or emit only discrete quantities of energy called quantum of energy.
(Einstein refines the terminology!)
Energy transfer is like working on a staircase rather than a ramp!

18. More with Max & the Boys!
Energy
Intensity
Quantum of energy
E=hf

19. The Photoelectric Effect
The curiosity around light was how its energy was transmitted – Particle or Wave. This environment lead to much research in the properties of light.
Heinrich Hertz discovered the Photoelectric Effect when a piece of charged zinc was hooked up to an electroscope and then UV light was shone on the zinc. The charge on the electroscope was reduced.
The UV light generated an electric current.
The use of a photosensitive cathode ray tube allowed scientists to study and quantify the photoelectric effect.
Photoelectric effect – light energy releases electrons from a photosensitive surface.
Einstein produces a model for the photoelectric effect that relates the frequency of the photon to the energy of the emitted photoelectron.

20. Creating Quantum Theory
Experimental Work
Theoretical Explanation
Quantum Theory
Kirchhoff (1859): Identifies and investigates blackbody radiation
Planck (1900): The energy from a blackbody is quantized; i.e. emitted energy is restricted to whole number multiples of a finite quantity of certain energy
Electromagnetic energy is not infinitely subdivisible; energy exists as packets or quanta, called photons. A photon is a small packet of energy corresponding to a specific frequency of light. (E=hf )
Hertz (1887): Investigates the photoelectric effect
Einstein (1905): The size of a quantum of electromagnetic energy depends directly on its frequency; one photon of energy ejects one electron