Atomic Structure and Theory

Atomic Structure and Theory - Transcript

Ch 4 Atomic Structure

4 1 Early Atomic Theory
Joseph Proust Law of Definite Proportions
Specific substances always contain elements in the same ratio by mass Water made of hydrogen and oxygen
Ratio is 1 8 Hydrogen mass to Oxygen mass

Salt is made of sodium and chlorine
Ratio in salt is always 1 1 54 sodium to chlorine

4 1 Dalton s Hypothesis
First atomic theory
Atoms are smallest particle of matter Atoms are indivisible

Law of Multiple Proportions The ratio of masses of one element that combine with a constant mass of another element can be expressed in small whole numbers
Relates to different compounds made from the same elements Each compound contains a different amount of one element

4 1 Early Research on Atomic Particles
Cathode Ray tube
Electrodes metal pieces at each end of tube
Cathode negatively charged electrode Anode positively charged electrode

Cathode rays beam of particles from cathode

Called particles Electrons e
Have negative charge Very small in comparison to size of atom negligible mass

4 1 Early Research on Atomic Particles
Canal ray beam of light electricity generated at anode
Called particles Protons 1 positive charge 1836 times the mass of an electron

4 1 Early Research on Atomic Particles
Nucleus 1911 Ernest Rutherford
Massive center of atom Nucleons Particles found in the center of the atom nucleus
Protons and Neutrons Considered to make up the entire mass of the atom

Neutrons 1932 James Chadwick
Neutral particles No charge Same mass as a proton

4 1 Isotopes and Atomic Number
Atoms
differentiated by number of protons Atomic number Z total of protons in an atom
Determines which element an atom is Top number in box on periodic table

Mass number A total number of protons and neutrons in an atom
Tells number of nucleons in an atom Bottom number in box on periodic table

4 1 Isotopes and Atomic Number
Isotopes atoms that are the same element but have different atomic masses
Same of protons differ by of neutrons Nuclide a specific isotope of an element

4 1 Radioactivity
rays being spontaneously produced by unstable nuclei Results in nuclear reactions
Energy released is much greater than in chemical changes or reactions

4 2 Radiation
Rays
can be made of particles and or energy radiant ejected until nucleus becomes less massive more stable

3 Naturally Occuring Types
Alpha particle 2 protons and 2 neutrons He nucleus Beta particle high speed electron emitted from radioactive nuclei Gamma rays very high energy electromagnetic waves massless particles

4 2 The Rutherford Bohr Atom
Electrons are in orbit around the nucleus
Prevents electrons from being pulled into the nucleus

Based on light given off by atoms
Electromagnetic energy Radiant

4 2 The Rutherford Bohr Atom
Properties of Electromagnetic Waves
Frequency cycles per second number of up and down motions of a wave per second wavelength distance covered by a single wave and are inversely proportional speed of electromagnetic radiation is constant
Same as light c light is a form of electromagnetic radiation Calculated from c

Planck s Hypothesis
Quantum Theory 1900 Max Planck Light is made of packets of energy
Called Quanta Each quantum is a tiny burst of energy Defined Energy of 1 quantum as E hv
h Planck s Constant 6 626 x 10 34 J hz v frequency

Einstein showed that quanta are actually light particles made of pure energy photons

4 2 The Hydrogen Atom and Quantum Theory
Quantum Theory explained the size of the electron orbits Electrons with more energy have larger orbits Ground state Smallest orbit of an electron
Least amount of energy Closest to the nucleus

Energy practice problem
What is the energy of a quantum of light of frequency 8 2 x 1014 Hz

Energy practice problem
What is the frequency of a photon with energy of 600 J

4 2 Atomic Mass
The mass of a single atom Measured in atomic mass units u
Based on the mass of an isotope of carbon
Carbon 12 Has 12 nucleons 6 protons and 6 neutrons

1 12 the mass of carbon 12 Approximately the mass of 1 proton

Very similar to mass number

4 2 Average Atomic Mass
Accounts for existence of different isotopes of the same element
Different isotopes have different masses

Averages the masses of most common isotopes Multiply each isotope atomic mass by its found in nature Add the atomic masses together Divide by 100

Practice Problem p 103
Neon has 2 isotopes Neon 20 has an atomic mass of 19 992u and Neon 22 has a mass of 21 991 u In an average sample of 100 neon atoms 90 will be neon 20 and 10 will be neon 22 Calculate the avg atomic mass of neon