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Basic Atomic Structure

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Presentation on theme: "Basic Atomic Structure"— Presentation transcript:

1 Basic Atomic Structure

2 Chemistry Timeline #1  2000 years of Alchemy B.C.
400 B.C. Demokritos and Leucippos use the term "atomos”  years of Alchemy 1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals 1600's Robert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements 1700s' Georg Stahl: Phlogiston Theory Joseph Priestly: Discovery of oxygen Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook

3 Chemistry Timeline #2 1800's Joseph Proust: The law of definite proportion (composition) John Dalton: The Atomic Theory, The law of multiple proportions Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules Amadeo Avogadro: Molar volumes of gases Jons 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

4 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 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? 16 amu Oxygen 2 amu Hydrogen 32 amu Oxygen 4 amu Hydrogen 48 amu Oxygen 6 amu Hydrogen

5 Law of Definite Proportion Examples
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)

6 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?

7 Dalton’s Atomic Theory (1808)
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 properties John Dalton 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

8 Modern Atomic Theory Several 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.

9 Modern Atomic Theory #2 Dalton said:
Atoms cannot be subdivided, created, or destroyed Modern theory states: Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions

10 Discovery of the Electron
In 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.

11 Thomson’s Atomic Model
J.J. Thomson Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

12 Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. Mass of the electron is 9.109 x kg The oil drop apparatus

13 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

14 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

15 Rutherford’s Findings
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: The nucleus is small The nucleus is dense The nucleus is positively charged

16 Atomic Particles Particle RelativeCharge Mass (kg) Location Electron
-1 9.109 x 10-31 Electron cloud Proton +1 1.673 x 10-27 Nucleus Neutron 1.675 x 10-27

17 The Atomic Scale Helium-4 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 1 million femtometers = 1 nanometer 1 million nanometers = 1 millimeter Image: User Yzmo Wikimedia Commons.

18 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.

19 Isotopes Isotopes are atoms of the same element having different masses due to varying numbers of neutrons. Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

20 Composition of the nucleus
Atomic Masses Atomic mass is the average of all the naturally isotopes of that element. Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.89% Carbon-13 13C 7 neutrons 1.11% Carbon-14 14C 8 neutrons <0.01% Carbon =

21 Atomic Number Atomic 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 Phosphorus 15 Gold 79

22 Mass Number Mass 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 18 8 8 18 Arsenic 75 33 75 Phosphorus 16 15 31

23 Calculating Average Atomic Mass
Calculate the average atomic mass of Chlorine and Silicon given the following information: Chlorine Silicon Mass number Exact mass Percent abundance 35 75.77 28 92.23 37 24.23 29 4.67 30 3.10 Chlorine: 35.45 Silicon: 28.09

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