Modern Chemistry Chapter 3

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law of conservation of mass
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States that matter can be neither destroyed nor created during ordinary chemical reactions or physical changes
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law of definite proportions
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The fact that a chemical compounds contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
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law of multiple proportions
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if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers
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atom
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the smallest particle of an element that retains the chemical properties of that element
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nucleus
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very small region located near the center of an atom. made of protons and neutrons
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Proton
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positively charged particle
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neutron
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neutral particle
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electron
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negatively charged particle
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atomic number
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the number of protons in the nucleus of each atom of an element
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isotope
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atom of the same element with a different mass
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mass number
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total number of protons and neutrons in the nucleus of an isotope
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atomic mass unit
atomic mass unit
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exactly 1/12 the mass of a carbon-12 atom
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average atomic mass
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the weighted average of the atomic masses of naturally occurring isotopes of an element
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Avogadro’s number
Avogadro's number
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6.022 x 10^23 The number of particles in exactly one mole of a pure substance
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molar mass
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the mass of one mole of a pure substance
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Dalton
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Early 1800’s, chemist who was a pioneer in discovery of the atom. Thought atoms were indivisible.
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Thompson
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English physicist accredited with the discovery and identification of the electron and isotopes.
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Rutherford
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New Zealander physicist known as the Father of Nuclear Physics. Discovered the nucleus and radioactive substances.
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Cathode Ray Tube Experiment
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This was JJ Thomson’s experiment that led to the discovery of the electron and the development of the plum pudding model of the atom. showed cathode rays were composed of negatively charged particles.
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Plum Pudding Model
Plum Pudding Model
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model which Thomson thought electrons were randomly distributed within a positively charged cloud
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Gold Foil Experiment
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This was Ernest Rutherford’s experiment that led to the discovery of the nucleus as the small, dense, positively charged center of the atom and the development of the nuclear theory of the atom.
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Nucleus
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contains the protons and neutrons of the atom
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Milikan
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Used the oil drop experiment to determine the charge of an electron4red
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Chadwick
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Discovered the neutron
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alpha particle
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positively charged particles
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ion
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A charged atom that has unequal numbers of electrons and protons
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percent abundance
percent abundance
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the naturally occurring amount of a certain isotope of an element, out a of a 100
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Avogadro
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scientist who worked with and determined the proportion of particles in 1 mole
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relative abundance
relative abundance
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the naturally occurring amount of a certain isotope of an element, out a of 1.00
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mol
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abbreviation for moles
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Dalton’s Atomic Theory
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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. 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.
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Modern Atomic Theory
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All matter is composed of extremely small particles called atoms. A given element can have atoms with different masses; atoms of different elements differ in size, mass, and other properties. Atoms can be subdivided, but Law of Conservation of Mass holds. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.
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nuclear forces
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The short-range proton-neutron, proton- proton, and neutron-neutron forces that hold the nuclear particles together
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Atomic Number
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the number of protons of each atom of that element.
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Neutral atom
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# protons = # electrons Therefore, the atomic number is also equal to the number of electrons in a neutral atom.
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Isotopes
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atoms of the same element that have different masses. all have the same number of protons and electrons, but different number of neutrons
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Nuclide
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a general term for a specific isotope of an element.
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The mass number
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is the total number of protons and neutrons that make up the nucleus of an isotope. A = #protons + #neutrons (under symbol)
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Hyphen notation:
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The mass number is written with a hyphen after the name of the element. uranium-235
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Average Atomic Mass
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is the weighted average of the atomic masses of the naturally occurring isotopes of an element. What is the atomic mass of chlorine if a naturally occurring sample contains 75.5% 35Cl and 24.5% 37Cl? 35 x (0.755) + 37 x (0.245) = 35.5 amu

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