10 Chem Chapter 3 Atomic Structure

Atomic Structure Early Models of Atoms -

The atom is the smallest particle of an element that retains the chemical identity of the element

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Law of Constant Composition states that any given compound always contains the same elements in the same proportions by mass.

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Dalton’s Atomic Theory: Each element is composed of extremely small particles called atoms All atoms of a given element are identical, but they differ from those of any other element A given compound always has the same relative numbers and kinds of atoms

Discovering Atomic Structure -Electrons are particles in an atom with negative charges -Protons are particles with positive charges -Neutrons are particles with no charge - Masses of atoms are expressed in atomic mass units (amu) - Atomic Number is the number of protons in an atom Ions -

The charge of an ion is the number of protons minus the number of electrons

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An ion is a net electrical charge that an atoms have when it loses or gains electrons

Isotopes -

Isotopes are atoms that have the same number of protons but different number of neutrons

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Isotopes can differ between their mass: Isotopes with more neutrons have a higher mass, Isotopes with less neutrons have a lower mass

Changes in the Nucleus

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All changes are produced by nuclear reactions. Nuclear reactions can produce alpha, beta, or gamma radiation

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A stable nucleus depends on the combinations of protons and neutrons in that nucleus.

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All atoms in an atom need to be held together by a strong nuclear force

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All stable nuclei follow patterns. From elements 1 – 20 (Hydrogen to Calcium), the elements all have about equal numbers of protons and neutrons.

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All elements with atomic numbers greater than 83 are considered radioactive

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Nuclei can be unstable if they have too little or too many neutrons

Types of Radiation -

Alpha Radiation: Can only travel a few cm through the air Easily stopped by paper or clothing Not a hazard to humans unless it enters the body

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Beta Radiation: Propels out of the nucleus at a high speed Can penetrate through 2 mm of solid material Can pass through clothing and damage skin

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Gamma Radiation: Can penetrate deeply through solid material, including body tissue Can only be stopped by heavy shielding of lead or concrete

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Radioactive Decay is when an atom emits one kind of the three types of radiation

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Nuclear Equations is an equation that keeps track of radioactive decay

Solving Nuclear Equations 1. The mass numbers and atomic numbers in a nuclear equation must balance 2. If the Nuclear equation was in the following form

Where M represents the mass number of the new atom, Z represents the atomic number, and X represents the element symbol. 3. The sum of the mass numbers must be equal so write the algebraic equation: 185 = M + 4 Solve to find that M = 185 – 4, or M = 181. For the atomic numbers, write the equation: 79 = X + 2 Solving gives Z = 77. From the periodic table, the element with atomic number 77 is Ir (Iridium). Therefore, the symbol of the produce is , and the nuclear equation is 4. Double check your math