Chapter 02 - CHEMISTRY The Molecular Science Chapter Two...

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CHEMISTRY The Molecular Science Chapter Two Atoms and Elements
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Atomic Structure Atomic structure refers to the identity and arrangement of subatomic particles in the atom. Two types of electrical charge exist: positive (+) and negative (–) Electrical charges of the same type repel, and opposite charges attract each other.
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Atomic Structure Atoms of radioactive elements emit three types of radiation: beta: - 1 charge, has mass (particle) alpha: +2 charge, has mass (particle), heavier than beta particles gamma: no charge (neutral), massless, behaves like light Atoms are made up of smaller components
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Alpha, beta and gamma radiation behave differently when passed in between electrically charged plates – determined their relative charge.
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Experiments with Cathode Ray Tubes Thomson: High voltage was applied to metal electrodes which produced a cathode ray – composed of electrons, the carriers of electricity. Negatively charged particles were generated at the negative electrode (cathode) and were attracted to the positive electrode (anode). A variety of metals produced cathode rays electrons are components of all atoms.
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Thomson cathode ray experiment Thomson calculated mass to charge ratio (m/Z) for electrons in a cathode beam: 5.60x10 –9 g/C C = coulomb, unit of charge
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Millikan’s Experiment
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Millikan’s Experiment Determined: The charge of an electron: –1.60x10 –19 C This value was considered to be a fundamental unit of charge electron has a –1 charge. From Thomson’s mass/charge ratio: (5.60x10 –9 g/C)x1.60x10 –19 C –28
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Experiments ionizing atoms: When atoms lose electrons (–), atoms become positively (+) charged ions. Atoms contain (+) charged particles = protons. Different elements contain a different number of protons. Hydrogen has the smallest mass/charge contains a fundamental mass unit, the mass of one proton. Mass of proton = 1.672x10 –24 g = 1800 x mass of electron –19
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Rutherford’s Experiment (1910-1911)
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Rutherford’s Model of the Atom An atom is composed mainly of vacant space. All the positive charge and most of the mass is in a small area called the nucleus which had to be sufficiently dense and highly charged to repel alpha particles (+2 charge, mass of He). Electrons are in an electron cloud surrounding the nucleus. Most of the atom’s volume is occupied by electrons.
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Chadwick detects neutrons All atoms are neutral they must contain an equal number of electrons and protons. Mass of atoms was determined to be greater than the sum of the mass of all electrons and protons there is another type of particle present in the nucleus. Neutrons are neutral subatomic particles with - no charge - mass equivalent to a proton
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Structure of the Atom Outside the nucleus: electrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu Atoms are neutral # electrons = # protons amu = atomic mass units 1amu = 1.66056x10 -27 kg Nucleus:
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Chapter 02 - CHEMISTRY The Molecular Science Chapter Two...

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