Basic Atomic Structure. Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucippos use the term...
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Transcript of Basic Atomic Structure. Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucippos use the term...
Basic Atomic Structure
Chemistry Timeline #1B.C.400 B.C. Demokritos and Leucippos use the term "atomos”
1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals
1600'sRobert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements
1700s'Georg Stahl: Phlogiston TheoryJoseph Priestly: Discovery of oxygen Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook
2000 years of Alchemy
Chemistry Timeline #2
1800'sJoseph Proust: The law of definite proportion (composition) John Dalton: The Atomic Theory, The law of multiple proportionsJoseph Gay-Lussac: Combining volumes of gases, existence of diatomic moleculesAmadeo Avogadro: Molar volumes of gasesJons Jakob Berzelius: Relative atomic masses, modern symbols for the elements Dmitri Mendeleyev: The periodic table J.J. Thomson: discovery of the electron Henri Becquerel: Discovery of radioactivity
1900's Robert Millikan: Charge and mass of the electron Ernest Rutherford: Existence of the nucleus, and its relative size Meitner & Fermi: Sustained nuclear fission Ernest Lawrence: The cyclotron and trans-uranium elements
Law of Definite Proportion
• Different samples of a pure compound always contain the same elements in the same proportions by mass.
• Water, for example, always has an 8:1 proportion of Oxygen to Hydrogen
16 amu Oxygen2 amu Hydrogen
32 amu Oxygen4 amu Hydrogen
48 amu Oxygen6 amu Hydrogen
Typically, this is written as a mass percent, so we say that water is 88.9% Oxygen (by mass) – what percent by number is this?
Law of Definite ProportionExamples
• What Mass of Oxygen is contained in a 50.0 g sample of water?– 44.5 g O
• What mass of Hydrogen is in a 35.5 g sample of water?– 3.94 g H
• An unknown water like substance was broken down and found to be composed of 58.8 g of Oxygen and 3.7 g Hydrogen. Could this substance be water? Show a calculation to support your answer.– No (shown to be 94.1 % Oxygen)
Law of Multiple Proportion
• If two elements combine to make different compounds, keeping one elements mass constant will always result in a whole number ratio of the second element.
• 50 grams of carbon can combine with 66.5 g of oxygen or 133 g of oxygen. What is the ratio of oxygen to oxygen in each compound?
• 14 grams of Nitrogen can combine with 8, 16, 24, 32 or 40 g of oxygen to form 5 different compounds. What is the ratio of oxygen in each?
Dalton’s Atomic Theory (1808)
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
All matter is composed 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 propertiesJohn Dalton
Modern Atomic TheorySeveral changes have been made to Dalton’s theory.
Dalton said:
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties
Modern theory states:
Atoms of an element have a characteristic average mass which is unique to that element.
Modern Atomic Theory #2
Dalton said:
Modern theory states:
Atoms cannot be subdivided, created, or destroyed
Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions
Discovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.
Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
The rays showed that the charge to mass ratio of the negative particles was always the same, no matter the gas used.
Thomson’s Atomic Model
Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
J.J. Thomson
Mass of the Electron
1909 – Robert Millikan determines the mass of the electron.
The oil drop apparatus
Mass of the electron is 9.109 x 10-31 kg
Conclusions from the Study of the Electron
Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass
Rutherford’s Gold Foil Experiment
Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded
Rutherford’s Findings
The nucleus is small The nucleus is dense The nucleus is positively charged
Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected
“Like howitzer shells bouncing off of tissue paper!”
Conclusions:
Atomic Particles
Particle
RelativeChar
ge
Mass (kg) Location
Electron
-1 9.109 x 10-31 Electron cloud
Proton +1 1.673 x 10-27 Nucleus
Neutron
0 1.675 x 10-27 Nucleus
The Atomic Scale
Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space
Helium-4
Image: User Yzmo Wikimedia Commons.
1 million femtometers = 1 nanometer1 million nanometers = 1 millimeter
About Quarks…
Protons and neutrons are NOT fundamental particles.
Protons are made of two “up” quarks and one “down” quark.
Neutrons are made of one “up” quark and two “down” quarks.
Quarks are held together by “gluons”
Images: Arpad Horvath, Wikimedia Commons.
IsotopesIsotopes are atoms of the same element having different masses due to varying numbers of neutrons.
Isotope Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium)
1 1 0
Hydrogen-2
(deuterium)
1 1 1
Hydrogen-3
(tritium)
1 1 2
Atomic Masses
Isotope Symbol Composition of the nucleus
% in nature
Carbon-12
12C 6 protons6 neutrons
98.89%
Carbon-13
13C 6 protons7 neutrons
1.11%
Carbon-14
14C 6 protons8 neutrons
<0.01%
Atomic mass is the average of all the naturally isotopes of that element.
Carbon = 12.011
Atomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
Element # of protons
Atomic # (Z)
Carbon 6 6
Phosphorus
15 15
Gold 79 79
Mass NumberMass number is the number of protons and neutrons in the nucleus of an isotope.
Mass # = p+ + n0
Nuclide p+ n0 e- Mass #
Oxygen - 10
- 33 42
- 31 15
8 8 1818
Arsenic 75 33 75Phosphorus 15 3116
O188As75
33
P31
Calculating Average Atomic MassCalculate the average atomic mass of Chlorine and Silicon given the following information:
Chlorine Silicon
Mass number
Exact mass
Percent abundance
Mass number
Exact mass Percent abundance
35 34.968852 75.77 28 27.976927 92.23
37 36.965903 24.23 29 28.976495 4.67
30 29.973770 3.10
45.35)2423.0)(5903.36()7577.0)(968852.34( Chlorine: 35.45
Silicon: 28.09