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GOB Chemistry: Conversions, Nuclear Stability, and Molecular Polarity

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  • What is the general process for unit conversions in chemistry?

    Use conversion factors based on equivalences, multiply by fractions equal to 1, and cancel units to convert from one unit to another.

  • What determines nuclear stability in an atom?

    The ratio of neutrons to protons and the total number of nucleons affect nuclear stability; too many or too few neutrons cause instability.

  • What is radioactive decay?

    Radioactive decay is the spontaneous transformation of an unstable nucleus into a more stable one, emitting particles or radiation.

  • Name three common types of radioactive decay.

    Alpha decay, beta decay, and gamma decay.

  • How does alpha decay change the nucleus?

    It emits an alpha particle (2 protons and 2 neutrons), decreasing the atomic number by 2 and mass number by 4.

  • What happens during beta decay?

    A neutron converts into a proton and emits a beta particle (electron), increasing the atomic number by 1 without changing mass number.

  • What is the role of lone pairs in molecular shape?

    Lone pairs repel bonding pairs more strongly, affecting bond angles and the overall molecular geometry.

  • How do lone pairs affect bond angles?

    Lone pairs compress bond angles between bonded atoms due to stronger repulsion.

  • What is electronegativity?

    Electronegativity is the tendency of an atom to attract shared electrons in a chemical bond.

  • How does electronegativity difference relate to bond polarity?

    A greater electronegativity difference between atoms leads to a more polar bond.

  • What is a dipole moment?

    A dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating bond polarity.

  • How do molecular shape and dipoles determine molecular polarity?

    Molecular polarity depends on the vector sum of bond dipoles; symmetrical shapes can cancel dipoles, making molecules nonpolar.

  • What molecular shape is associated with a tetrahedral geometry?

    A central atom bonded to four atoms with bond angles of about 109.5°.

  • How does the presence of lone pairs change a tetrahedral shape?

    Lone pairs reduce bond angles and change the shape to trigonal pyramidal or bent.

  • What is the difference between polar and nonpolar molecules?

    Polar molecules have an uneven distribution of charge due to polar bonds and asymmetrical shape; nonpolar molecules have symmetrical charge distribution.

  • How can you predict if a molecule is polar?

    Check for polar bonds and if the molecular geometry allows dipoles to cancel; if not, the molecule is polar.

  • What is the effect of electronegativity on bond type?

    Small electronegativity difference leads to nonpolar covalent bonds; moderate difference leads to polar covalent bonds; large difference leads to ionic bonds.

  • What is the significance of half-life in radioactive decay?

    Half-life is the time required for half of a radioactive sample to decay, indicating the rate of decay.

  • How do you calculate the remaining amount of a radioactive isotope after several half-lives?

    Remaining amount = initial amount × (1/2)^(number of half-lives).

  • What is the VSEPR theory used for?

    Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shapes based on electron pair repulsions.