Radioactivity
Henri Becquerel was a French physicist, who discovered in 1896, while doing experiments with Uranium, that all the pictures on his photographic film were overexposed.
Marie Curie and her husband Pierre found out that Uranium and Radium gave off rays of radiation due to an unstable nuclei.
· In the early 1900's Albert Einstein came up with a equation that explained why these energy rays were produced during nuclear changes.: E = mc2
Radioactivity is the process of spontaneously emitted radiation due to atom's nuclei being unstable.
· The rays and particles emitted by the radioactive atoms are called radiation.
· Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay.
· Uranium and Radium both occur in nature in the form of the ore called pitchblende.
Types of Radiation
1. Alpha radiation is radiation that was deflected toward the negatively charged plate alpha radiation.
· Made up of 2 alpha (a) particles
Ø Each alpha particle contains 2 protons and 2 neutrons
Ø Has a 2+ charge
Ø Has a mass of 4 amu
§ Ex.: Ra- 88 (Radium-226) ®86 Rn (radon-222) + 4 He (alpha particle) (Exact model will be shown in class)
2. Beta radiation is radiation deflected toward the positively charged plate beta radiation.
· Consist of fast moving electrons known as beta (b) particles.
Ø Each beta particle contains an electron with a -1 charge.
§ Ex.: Carbon 14 results in the creation of Nitrogen. (Exact model will be shown in class)
3. Gamma radiation is the third common type and uses gamma rays.
· Gamma rays (g) are high-energy radiation that possesses no mass.
Ø Because they possess no electrical charge, gamma rays are not deflected by electric or magnetic fields.
Ø Usually will accompany alpha and beta radiation.
Ø Accounts for most of the energy lost during the radioactive decay process.
§ Ex.: 238 U (Uranium-238) ®234 Th (Thorium-234) + 4 He (alpha particle) + 2 gamma rays
§ Since gamma rays have no mass, the emission of gamma rays by themselves can't result in the formation of a new atom.
§ Must be accompanied by either an alpha or beta particle to form a new atom.
Half Life Formula
Amount Remaining= Original Amount of parent ÷ 2n n=half-life
(See examples in class)
Quantum Theory
In 1900, the German physicist Max Planck searched for clues to why light energy is emitted from heated objects.
· He realized the following: Matter can gain or lose energy only in small, specific amounts called quanta.
· A Quantum is the minimum amount of energy that can be gained or lost by an atom.
· Planck proposed that this emitted light energy was quantized, where E is energy, h is Planck constant, and v is frequency.
ü Formula: E quantum = hv
ü Planck's constant: 6.626 x 10-34 J x s
Quantum Mechanical Model of the Atom
The size of the smallest orbit an electron can occupy is known as ground state.
Bohr calculated the ground state of H.
· The atomic model in which electrons are treated as waves is called the wave mechanical model of the atom or, more commonly, the quantum mechanical model of the atom.
· Principal quantum numbers (n) indicate the relative sizes and energies of atomic orbitals.
ü As n increases, the orbital becomes larger
ü Principal energy levels: An atom's lowest principal energy level is assigned a principal energy quantum number of one.
Ø s is circle shaped
Ø p is dumbbell shaped
Electron Configuration
· The arrangement of electrons in an atom are known as electron configuration.
ü The order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s
3 Rules, or principles apply:
1. The aufbau principle states that each electron occupies the lowest energy orbital available
· All orbitals related to an energy sublevel are of equal energy.
· In a multi-electrons atom, the energy sublevels within a principal energy level have different energies.
· In order of increasing energy, the sequence of energy sublevels within a principal energy level is s, p, d, and f.
· Orbital related to energy sublevels, within one principal energy level can overlap orbitals related to energy sublevels within another principal
2. The Pauli exclusion principal states that a maximum to 2 electrons may occupy a single atomic orbital, but only if the electrons have opposite spins.
ü Represented as ↑↓
3. Hund's rule states that single electrons with the same spin must occupy each equal-energy orbital that same orbital.
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