m2 - Chemical Bonding and Molecules Electron Arrangement...

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Chemical Bonding and Molecules
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Electron Arrangement Determines the Chemical Properties of Atoms
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The Number of Electrons in the Outermost Shell Determines the Chemical Properties of Atoms • Atoms whose shells are not full tend to interact with other atoms. In other words, they participate in chemical reactions. Why? • These atoms of 4 most abundant elements in life participate in many chemical reactions. Electron Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Hydrogen (H) Atomic number = 1
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How do Atoms Complete Their Outer Electron Shells? • Atoms complete their outer shells by: -Gaining Electrons from other atoms, -Losing Electrons to other atoms or -Sharing Electrons with other atoms The sharing of outer shell electrons between 2 atoms results in a covalent bond between those two atoms. Two or more atoms joined together by covalent bonds are called what?
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Covalent Bonds: Sharing of Electrons H O H Before Sharing : Outer Shells Not Full Hydrogen and Oxygen atoms Adapted from Abby Silver After Sharing : Outer Shells of all atoms are filled Water: H 2 O
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• Bond energies (kcal/mol) are determined as the energy required to break a particular type of linkage. • Covalent bonds are 10-100 X stronger than non-covalent interactions. • Covalent bonds are stable because the energy required to break them are much higher than the thermal energy of the environment at normal room temperature (25ºC). Covalent Bonds are Strong
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Adapted from Abby Silver Polarity: Covalent Bonds May be Polar or Non-Polar • Since they are both “covalent” bonds…that means the sharing of electrons occurs in both types of interactions. So how are they different? • Polarity arises with the “unequal” sharing of electrons. Non-Polar bonds : Electrons are shared equally by bonded atoms. Polar bonds : Electrons are shared unequally by bonded atoms.
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Polar or Non-Polar? How do you determine if two atoms share their electrons equally when they are covalently bonded to each other? Compare the electronegativities of the two atoms. Electronegativity is the power of an atom in a molecule to draw electrons to itself.
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Electronegativity Kr Xe Increasing Electronegativity Scale 0-4 Why does electronegativity increase bottom to top/left to right? Why doesn’t He, Ne, Ar, Kr, Xe, Rn have any electronegativity?
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Non-Polar Covalent Bonds: Equal Sharing of Electrons • A bond between atoms with identical or similar electronegativities is said to be non-polar (difference of up to 0.5). • In a non-polar bond, the bonding electrons are essentially “shared” between the two atoms. Kr Xe Examples of non-polar molecules Would a covalent bond between hydrogen and oxygen be polar or non-polar?
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Polar Covalent Bonds: Unequal Sharing of Electrons • A bond between atoms with relatively different electronegativities (0.5 greater) is said to be polar.
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