Atomic Structure/ Periodic Table

The Structure of the Atom In the beginning all that was known was that matter was made of something Dalton: One part of his atomic theory named the small neutral particle that everything was made of an “atom” It was represented as a sphere J. J. Thomson used a cathode ray tube to prove that atoms could be made to release negative particles.

A New Atomic model Rationale: If the atom contains negative particles and the entire atom is neutral then it must also contain something positive to counterbalance the electron charges… The atom was therefore thought to be a positive mass with negative particles imbedded in it. The Plum Pudding Model

The Plum Pudding Model Equal # of protons and electrons Overall charge is neutral First to identify protons and electrons JJ Thomson

Rutherford set out to test Thomson’s hypothesis Alpha Particles are positively charged particles that are released from radioactive material (like uranium, plutonium, etc…) Rutherford’s experiment was to shoot alpha particles at a piece of gold foil. He thought that the alpha particles would go straight through and maybe occasionally be deflected a tiny bit by the positive mass of the atoms.

Rutherford’s Gold Foil Experiment

Rutherford was surprised! Most of the particles went straight through, a few of them bounced back.

Rutherford proposed the nuclear model of the atom. 1. Atoms are mostly empty space. 2. Atoms have a small, massive nucleus. 3. The nucleus is positively charged. 4. Surrounding the nucleus are electrons, which have very little mass. Note: Rutherford’s experiment does NOT say what the nucleus is made of or what the electrons are doing around the nucleus.

Bohr’s model: Orbits Bohr realized that atoms could be made to emit light. His explanation was that electrons are assigned to energy levels outside the nucleus The electrons within these energy levels orbit at certain distinct distances from the nucleus. In order to change it’s orbital pattern the electron must loss or gain energy. This happens in the form of light.

Bohr’s model

Bohr Atom & Light Photon The ground state of an electron is the lowest state of energy for that electron. Photons contain radiant energy or “packets of light”.

Bohr Atom & Light The excited state occurs when an electron absorbs the energy. Electron jumps to a higher energy level. Electrons do not stay in the excited state for very long.

Bohr Atom & Light The electron falls down to the ground state and emits energy in the form of light.

Atoms and Light When an atom absorbs energy - in the form of heat, light- it re-emits that energy as light. Every atom emits light in different colors (wavelength).

Continuous Spectrum

Emission Spectrum If we separate the light by passing it through a prism, we can observe the atom’s emission spectrum. No two elements have the same emission spectrum because the spacing of energy levels is different for each atom.

Spectroscopy Lab

Light measured… C = ν  Speed of light (3 x 108 m/s) = frequency x wavelength Hertz (Hz) or Wave/sec Meters

Energy E = h ν E: Enery in joules h: Plank’s constant = 6.626 x 10-34 J*s ν: Frequency

Electromagnetic Spectrum Diagram showing the total range of electromagnetic radiation. Energy (radiant energy) moves in waves. Radio waves have lowest energy and lowest frequency. Gamma waves have highest energy and highest frequency.

Light Equations Speed of light equation: Speed of light = Frequency x Wavelength

Different Theories of the Atom Model we will use Current Model 90%probability

Atoms, Ions, and Isotopes Made of electrons, protons, & neutrons Smallest unit of an element Neutral charge Ion: Atom that has lost or gained electrons Has a + or - charge Isotope: Atoms of the same element that have differing numbers of neutrons

Isotopic Nomenclature X = elemental symbol A = Mass # (p + n) Z = atomic # (p)

Isotopic Nomenclature Practice Write the following in isotopic form: Cl with 20 neutrons C with 8 neutrons How many neutrons do each of the following elements have? 2016S 1713Al

Isotopic Shorthand C with 8 neutrons is Cl with 20 neutrons is

Average Atomic Mass The atomic mass is the weighted average of all isotopes of that element. | A Weighted average reflects: 1) Mass (p + n) 2) Relative Abundance (%) The mass on the periodic table is known as the average atomic mass.

Calculating Average Atomic Mass If chlorine has 2 isotopes: Cl-37 at 20% and Cl-35 at 80%, then average atomic mass is