Herrera Lecture3 - Covalent bonds where electrons are...

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Covalent bonds – where electrons are shared Typically the strongest bonds in biological systems. Can be polar (where electrons are not equally shared) or non-polar (electrons are equally shared).
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Figure 2.10 Formation of a covalent bond Hydrogen atoms (2 H) Hydrogen molecule (H 2 ) + + + + + + In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. 1 When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton in the other nucleus. 2 The two electrons become shared in a covalent bond, forming an H 2 molecule. 3
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A molecule Consists of two or more atoms held together by covalent bonds A single bond Is the sharing of one pair of valence electrons A double bond Is the sharing of two pairs of valence electrons
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(a) (b) Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Hydrogen (H 2 ). Two hydrogen atoms can form a single bond. Oxygen (O 2 ). Two oxygen atoms share two pairs of electrons to form a double bond. H H O O Figure 2.11 A, B Single and double covalent bonds
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Name (molecular formula) Electron- shell diagram Structural formula Space- filling model (c) Methane (CH 4 ). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Water (H 2 O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) H O H H H H H C Figure 2.11 C, D Covalent bonding in compounds
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Electronegativity Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom The more strongly it pulls shared electrons toward itself
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A nonpolar covalent bond The atoms have similar electronegativities Share the electron equally Common in hydrocarbons
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Figure 2.12 This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. H 2 O δ O H H δ + δ + Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. The atoms have differing electronegativities Share the electrons unequally A polar covalent bond
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Ionic Bonds Electron transfer between two atoms creates ions Ions Are atoms with more or fewer electrons than usual Are charged atoms An anion Is negatively charged ions A cation Is positively charged
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Herrera Lecture3 - Covalent bonds where electrons are...

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