Bonds. Covalent Bonds Atoms share a pair of electrons. Occur between atoms whose outer shells are...
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Transcript of Bonds. Covalent Bonds Atoms share a pair of electrons. Occur between atoms whose outer shells are...
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Bonds
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Covalent Bonds• Atoms share a pair of electrons.• Occur between atoms whose outer shells are
not full. • Covalent bonds are strong chemical bonds,
because the shared electrons behave as if they belong to each atom.
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Electrons are not always evenly shared between atoms…
• Some atoms attract shared electrons more readily than do other atoms.
• The electronegativity of an atom is the measure of its ability to attract electrons in a bond.
• Polar Covalent bonds: the distribution of electrons around the nuclei creates polarity or a difference in electric charge across the molecule.
• Nonpolar Covalent bonds: a strong bond is formed between two atoms with similar electronegativities and no polarity exists
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Hydrogen Bonds• An important result of certain polar covalent bonds
is the ability of one molecule to loosely associate with another molecule through a hydrogen bond.
• This bond forms when a hydrogen atom from one polar molecule is attracted to an electronegative atom, in another polar molecule.
• An example is the attraction between two water molecules.
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Ionic Bonds• Atoms are electrically neutral because they
contain equal numbers of electrons and protons.• If an atom loses or gains an electron it becomes
charged (ion) • An ionic bond forms when an ion with a positive
charge is attracted to an ion with a negative charge
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SHAPE
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Molecules may change their shape
• When atoms combine, they can form various 3-D shapes, depending on their bonds.
• These shapes are flexible and rotate without breaking any of the covalent bonds.
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Shape Affects Life• The 3-D flexible shape of a molecule
contributes to their biological properties. • Ex: Taste, food molecules interact with protein
receptors on our tongues, the two molecules recognize each other by their unique shape, and fit together like a key.
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Common Functional Groups• Groups of atoms with characteristic chemical
features and properties attached to a molecule.
• Each functional group exhibits similar properties in all molecules it occurs.
Amino – NH2
Hydroxyl- OHMethyl- CH3
Carboxyl- COOH