Ch. 4.2 - Atomic Structure I. Subatomic Particles (p.113-114)
Subatomic Particle Properties Particle Symbol Location Charge Relative Mass (amu) Actual Mass (g) electron e - Electron cloud 1/1840 approx 0 9.11 x 10-28 proton p + nucleus + 1 1.67 x 10-24 neutron n 0 nucleus 0 1 1.67 x 10-24
Symbols Elements are listed by their chemical symbols Symbols are usually either one capital letter like C for Carbon, or one capital and one lowercase letter like Ne for Neon
Periodic Table The periodic table gives much information we need to learn more about the atom of each element
Atomic Number Atomic number = # of protons in an atom Whole number shown on periodic table Periodic table is arranged by atomic number
Atomic Mass The average atomic mass is the number at the bottom of this square Found by averaging the natural abundances of its isotopes
Atom Math Protons Electrons Protons Neutrons # n 0 = Atomic mass Atomic
Subatomic Particles ATOM NUCLEUS ELECTRONS PROTONS NEUTRONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE Atomic Most of Number the atom s #n 0 = mass. Atomic equal mass in a equals the # of... - Atomic neutral # atom
Ch. 4.3 - Atomic Structure II. How Atoms Differ (p. 114-121) Mass Number Isotopes Relative Atomic Mass Average Atomic Mass
A. Mass Number mass # = protons + neutrons always a whole number NOT on the Periodic Table! Addison-Wesley Publishing Company, Inc.
B. Isotopes Atoms of the same element with different numbers of neutrons Isotope notation: Mass # Atomic # 12 6 C Element name Mass # Isotope name: carbon-12
B. Isotopes Chlorine-37 atomic #: mass #: # of protons: # of electrons: # of neutrons: Isotope notation: 17 37 17 37 Cl 17 17 20
Natural Abundances of Isotopes Most elements are found as mixtures of isotopes Relative abundance of each isotope is the same in each source
an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative charge. Cation: has a positive charge, due to the loss of electrons Anion: has a negative charge, due to the gain of electrons
Addison-Wesley Publishing Company, Inc. C. Relative Atomic Mass 12 C atom = 1.992 10-23 g atomic mass unit (amu) 1 amu = 1 / 12 the mass of a 12 C atom 1 p = 1.007276 amu 1 n = 1.008665 amu 1 e - = 0.0005486 amu
D. Average Atomic Mass weighted average of all isotopes on the Periodic Table Avg. Atomic Mass (mass)(%) (mass )(%) 100
D. Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O. Avg. Atomic Mass (16)(99.76 ) (17)(0.04) (18)(0.20) 16.00 100 amu
D. Average Atomic Mass EX: Find chlorine s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass (35)(80) (37)(20) 100 35.40 amu
Atomic Theory Development of our understanding of the atom
Early Models Battle of Philosophers Aristotle -Matter is infinite vs. Democritus - Matter is composed of extremely small particles -4 Basic elements - Called these particles atoms - Earth (From atmos meaning invisible) -Air -Fire *Eventually after many years -Water Democritus is proven right
Early Models Dalton s model was the Billiard Ball Published an Atomic Theory 1. All matter is composed of atoms that are indivisible (did not know about protons, electrons, or neturons) 2. Atoms of a given element have same size, mass and chemical properties and are different from those of another element (no longer true, b/c of isotopes) 3. Different atoms combine in whole number ratios to form compounds and are separated, combined and rearranged in chemical reactions 4. In chemical reactions atoms can combine or separate, but are neither created or destroyed
Law of Definite Proportions Each compound has a specific ratio of elements It is a ratio by mass Water is always 8 grams of oxygen for each gram of hydrogen
Law of Multiple Proportions if two elements form more than one compound, the ratio of the second element that combines with 1 gram of the first element in each is a simple whole number.
What? Water is 8 grams of oxygen per gram of hydrogen. Hydrogen Peroxide is 16 grams of oxygen per gram of hydrogen. 16 to 8 is a 2 to 1 ratio True because you have to add a whole atom, you can t add a piece of an atom.
Parts of Atoms J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. It is a vacuum tube - all the air has been pumped out.
Thomson s Experiment - Voltage source + Vacuum tube Metal Disks
Thomson s Experiment - Voltage source +
Thomson s Experiment - Voltage source +
Thomson s Experiment - Voltage source +
Thomson s Experiment - Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson s Experiment - Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson s Experiment - Voltage source + Passing an electric current makes a beam appear to move from the negative (cathode) to the positive end (anode)
Thomson s Experiment - Voltage source + Passing an electric current makes a beam appear to move from the negative (cathode) to the positive end (anode)
Thomson s Experiment Voltage source By adding an electric field
Thomson s Experiment Voltage source + By adding an electric field -
Thomson s Experiment Voltage source + By adding an electric field -
Thomson s Experiment Voltage source + By adding an electric field -
Thomson s Experiment Voltage source + By adding an electric field -
Thomson s Experiment Voltage source + By adding an electric field -
Thomson s Experiment Voltage source + - By adding an electric field he found the ratio of electrical charge to mass (e/m) for an electron The e/m ratio is (negative) 1.76 x 10 8 coulombs per gram (or C/g in SI units).
Thomsom s Model Thomson always found the same value for the e/m ratio no matter what the tube materials or the gas inside. Reinforced the notion that the electrons are a fundamental component of matter. Plum Pudding model: a thin positive fluid, which contains most of the mass, w/ negative electrons embedded to balance the charge
Other pieces Proton - positively charged pieces 1840 times heavier than the electron Neutron - no charge but the same mass as a proton. Where are the pieces?
Millikan used oil drop experiment Would spray a fine mist of oil droplets above a pair of parallel plates. Some of the oil drops would pass through the hole in the top plate. He then used X-rays to knock electrons off of the air molecules in the barrel and some of those electrons attached themselves to the oil drops. The oil drops, which were now negative, could now be affected by the electrical field. He then could now measure the charge of the oil drops.
Millikan found that all the values he obtained were whole-number multiples of -1.60 x 10-19 coulomb. This value must be the charge of an electron. The electron s charge was -1.60 x 10-19 coulombs Using two values and solving for m - 1.60 x 10-19 coul = - 1.76 x 10 8 coul/g m m = 9.11 x 10-28 grams (a negligible mass even in the smallest atom) Confirmed the negative charge of an electron Determined mass of the electron
Rutherford s experiment Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the atom. Wanted to see how big they are using radioactivity Alpha particles - positively charged pieces given off by uranium Shot them at gold foil which can be made a few atoms thick
Lead block Uranium Florescent Screen Gold Foil
He Expected The alpha particles to pass through without changing direction very much Because The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles
What he expected
Because, he thought the charge was evenly distributed in the atom
What he got
+
How he explained it Atom is mostly empty Small dense, positive piece at center (nucleus) Refined the concept of the nucleus & concluded it was composed of positively charged particles called protons James Chadwick: discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. +
Moving Forward Neils Bohr said electrons move in orbits Found in energy levels Explains bright-line spectrum Called Solar System Model where Electrons move in orbits around the nucleus
What we believe now Heisenberg/Schrodinger Heisenber Uncertainty Principle: You can know either the eˉ position or velocity but not both Schrodinger said the eˉ are located in orbitals, (regions of probability) around the nucleus not orbits Electron Cloud model