Ikatan Kovalen Polar Dan Asam Basa - Kimor 2
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Transcript of Ikatan Kovalen Polar Dan Asam Basa - Kimor 2
IKATAN KOVALEN POLAR dan ASAM BASA
Oleh : Alvan Febrian Shalas, S. Farm., Apt
TUJUAN PEMBELAJARAN
• Mahasiswa dapat memahami reaktifitas kimia suatu senyawa dengan:1. Memahami konsep elektronegatifitas2. Memahami konsep momen dipol3. Memahami konsep muatan formal4. Memahami resonansi struktur5. Memahami konsep asam basa
“Most bonds are neither fully ionic nor fully covalent but are somewhere between the two extremes”
Such bonds are called polar covalent bonds, meaning that the bonding electrons are attracted more strongly by one atom than the other so that the electron distribution
between atoms is not symmetrical
ELEKTRONEGATIFITASBond polarity is due to differences in ELECTRONEGATIVITY (EN),
the intrinsic ability of an atom to attract the shared electrons in a covalent bond
ELEKTRONEGATIFITAS
ELEK
TRO
NEG
ATIF
ITAS
ELEKTRONEGATIFITAS
> 2 Ionik
0,5-2 Kovalen Polar
< 0,5 Kovalen Non Polar
JENIS IKATAN ATOM BERDASARKAN BEDA ELEKTRONEGATIFITAS
ELEKTRONEGATIFITAS
δ : Muatan Parsial
used to indicate the direction of bond polarityelectrostatic potential maps
ELEKTRONEGATIFITAS
INDUCTIVE EFFECT is the shifting of electrons in a σ bond in response to the electronegativity of nearby atoms.
• Metals, such as lithium and magnesium, inductively donate electrons
• Reactive nonmetals, such as oxygen and nitrogen, inductively withdraw electrons
MOMEN DIPOL
“Just as individual bonds, molecules as a whole are often polar”
• Molecular polarity results from the vector summation of all individual bond polarities and lone-pair contributions in the molecule
• Net molecular polarity is measured by a quantity called the dipole moment (µ)
MOMEN DIPOL
MOMEN DIPOL
• Contain strongly electronegative atoms (oxygen and nitrogen)
• All three molecules have lone-pair electrons
MOMEN DIPOL
Molecules such as carbon dioxide, methane, and ethane have zero dipole moments. Because of the symmetrical structures of these molecules, the individual bond polarities and lone-pair contributions exactly cancel.
MUATAN FORMAL
12
VS VSmetana dimetilsulfoksida sulfat
MUATAN FORMAL
Carbon valence electrons : 4 Carbon bonding electrons : 8Carbon nonbonding electrons : 0For carbon :Formal charge = 4 − 8/2 − 0 = 0
Hydrogen valence electrons : 1Hydrogen bonding electrons : 2Hydrogen nonbonding electrons : 0For Hydrogen :Formal charge = 1 − 2/2 − 0 = 0
Total Formal Charge = 0 + (4 x 0) = 0
MUATAN FORMAL
Sulfur valence electrons : 6 Sulfur bonding electrons : 6Sulfur nonbonding electrons : 2For sulfur :Formal charge = 6 − 6/2 − 2 = +1
Oxygen valence electrons : 6Oxygen bonding electrons : 2Oxygen nonbonding electrons : 6For Oxygen :Formal charge = 6 − 2/2 − 6 = -1
MUATAN FORMAL
15
Sulfur valence electrons : 6 Sulfur bonding electrons : 8Sulfur nonbonding electrons : 0For sulfur :Formal charge = 6 − 8/2 − 0 = +2
Oxygen valence electrons : 6Oxygen bonding electrons : 2Oxygen nonbonding electrons : 6For Oxygen :Formal charge = 6 − 2/2 − 6 = -1
Total Formal Charge = = +2 + (4 x (-1)) = -2
MUATAN FORMAL
16
Calculate formal charges for the nonhydrogen atoms in the following molecules !!
EXERCISES......
RESONANSI
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The two oxygen atoms in the acetate ion appear different in linebond structures, experiments show that they are equivalentNeither of the two structures for acetate is correct by itself
RESONANSI
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The true structure is intermediate between the two
ASAM BASA
Brønsted–Lowry acid is a substance that donates a hydrogen ion (H+)Brønsted–Lowry base is a substance that accepts a hydrogen ion (H+)
Brønsted–Lowry
ASAM BASA
• Acid strengths are normally expressed using pKa values
• A stronger acid has a smaller pKa• Weaker acid has a larger pKa• A strong acid loses H+ easily, meaning that its
conjugate base holds the H+ weakly and is therefore a weak base.
• A weak acid loses H+ with difficulty, meaning that its conjugate base holds the proton tightly and is therefore a strong base
ACID and BASE STRENGTH
ASAM BASARelative Strengths of Some Common Acids and Their Conjugate Bases
ASAM BASAPREDICTING ACID and BASE REACTION FROM pKa VALUES
• H+ will always go from the stronger acid to the stronger base.
• An acid will donate a proton to the conjugate base of a weaker acid
• The conjugate base of a weaker acid will remove the proton from a stronger acid
ASAM BASA
Lewis acid is a substance that accepts an electron pairLewis base is a substance that donates an electron pair.
LEWIS
ASAM BASA
“Lewis acid must have either a vacant, low-energy orbital or a polar bond to
hydrogen so that it can donate H+ (which has an empty 1s orbital)”
ASAM BASA
ASAM BASA
“The Lewis base is a compound with a pair of nonbonding electrons
that it can use to bond to a Lewis acid”
ASAM BASA
ASAM BASA
• Using curved arrows, show how acetaldehyde(CH3CHO), can act as a Lewis base!!
EXERCISES......
ASAM BASAEXERCISES......