Concepts of Chemical Bonding

Chemical Bonds Three types: Ionic Electrostatic attraction between ions Gaya tarik menarik antar ion-ion Covalent Sharing of electrons Pemakaian elektron bersama Metallic Metal atoms bonded to several other atoms atom2 logam terikat pada beberapa atom lain

Lewis symbols A convenient way to keep track of the valence electrons in an atom or molecule cara yang mudah untuk menelusur elektron valensi dlm atom/molekul Lewis dot symbol Each dot is one valence electron tiap titik = elektron valensi

Covalent Bonding ikatan kovalen There are several electrostatic interactions in these bonds: beberapa interaksi elektrostatis dlm ikatan ini: Attractions between electrons and nuclei tarik-menarik antara elektron-inti Repulsions between electrons tolak-menolak antara elektron Repulsions between nuclei tolak-menolak antara inti

Polar Covalent Bonds Although atoms often form compounds by sharing electrons, the electrons are not always shared equally. Meski atom2 membentuk senyawa dgn pemakaian elektron bersama, tetapi elektron tidak dibagi dengan sama tepat. Fluorine pulls harder on the shared electrons than hydrogen does. Fluor menarik lebih kuat elektron yg dipakai bersama drpd hidrogen Therefore, the fluorine end has more electron density than the hydrogen end. Fluor memiliki rapat elektron drpd hidrogen (dlm molekul H-F) But how do you know who pulls hardest?

Electronegativity: skala Pauli increases Electronegativity increases The ability of atoms in a molecule to attract electrons to itself. Kemampuan atom dlm molekul untuk menarik elektron On the periodic chart, electronegativity increases as you go… …from left to right across a row. …from the bottom to the top of a column.

Polar Covalent Bonds ikatan kovalen polar When two atoms share electrons unequally, a bond dipole results. 2 atom berbagi-pakai elektron dgn tidak setara  dipole ikatan The dipole moment, , produced by two equal but opposite charges separated by a distance, r, is calculated: momen dipole, , yg dihasilkan 2 muatan yg berlawan dan terpisah dgn jarak r, dihitung sbg:  = Qr It is measured in debyes (D).

Polar Covalent Bonds The greater the difference in electronegativity, the more polar is the bond. Semakin besar beda elektronegatifitas  semakin polar ikatan

Menuliskan Struktur Lewis G.N. Lewis

Lewis Structures Lines correspond to 2 electrons in bond Lewis structures are representations of molecules showing all valence electrons, bonding and nonbonding. Struktur Lewis menggambarkan molekul dgn menunjukkan seluruh elektron, baik yang dipakai berikatan dan tdk.

Writing Lewis Structures Find the sum of valence electrons of all atoms in the polyatomic ion or molecule. Jumlahkan seluruh elektron valensi dari seluruh atom dalam molekul / ion banyak atom If it is an anion, add one electron for each negative charge. Jika anion  +1elektron utk tiap muatan negatif If it is a cation, subtract one electron for each positive charge. Jika kation  -1elektron utk tiap muatan positif PCl3 5 + 3(7) = 26

Writing Lewis Structures The central atom is the least electronegative element that isn’t hydrogen. Atom “pusat”  atom dgn elektronegatifitas terendah kecuali Hidrogen Connect the outer atoms to it by single bonds. Hubungkan atom “luar” ke atom “pusat” dgn ikatan tunggal Keep track of the electrons: hitunglah jumlah elektron 26  6 = 20

Writing Lewis Structures Fill the octets of the outer atoms. Penuhi aturan “oktet” bagi atom2 “luar” Keep track of the electrons: 26  6 = 20  18 = 2

Writing Lewis Structures Fill the octet of the central atom. Penuhi aturan oktet bagi atom “pusat” Keep track of the electrons: 26  6 = 20  18 = 2  2 = 0

Writing Lewis Structures If you run out of electrons before the central atom has an octet… jika kehabisan elektron sebelum atom pusat memenuhi “oktet” …form multiple bonds until it does. Bentuklah ikatan rangkap hingga aturan oktet terpenuhi...

Writing Lewis Structures Then assign formal charges. Tandailah “muatan formal” For each atom, count the electrons in lone pairs and half the electrons it shares with other atoms.= A Tiap atom, hitung elektron PEB dan separuh jika berbagi-pakai dng atom lain = A Subtract that from the number of valence electrons for that atom: The difference is its formal charge. Eleketron valensi tiap atom = B. Muatan formal = B-A

Writing Lewis Structures The best Lewis structure… …is the one with the fewest charges. ... muatan paling rendah …puts a negative charge on the most electronegative atom. ...meletakkan muatan negatif pada atom yg paling elektronegatif -2 0 +1 -1 0 0 0 0 -1

Latihan Tuliskan struktur Lewis untuk molekul berikut: CH4, CHCl3, CH3COOH

Resonance Draw the Lewis structure for ozone, O3.

Resonance Draw the Lewis structure for ozone, O3. But why should one O be different from the other? + -

Resonance It is at odds with the true, observed structure of ozone, tidak sesuai dgn struktur ozone yg teramati …both O—O bonds are the same length. O-O = sama panjang …both outer oxygens have a charge of 1/2. muatan O “luar” = -1/2

Resonance One Lewis structure cannot accurately depict a molecule such as ozone. Satu struktur Lewis tdk bisa menggambarkan dgn akurat molekul seperti ozone We use multiple structures, resonance structures, to describe the molecule. Multi struktur, struktur resonansi  digunakan + + - -

Resonance Just as green is a synthesis of blue and yellow… semisal warna hijau = hasil perpaduan warna biru dan kuning …ozone is a synthesis of these two resonance structures. It is not jumping between the two.

Resonance Draw resonance structure for: HCO2-

Resonance - .. O C O H Draw resonance structure for: HCO2- But why would the two oxygens be different?

Resonance In truth the electrons that make up the double bond are not localized, but rather are delocalized. Elektron yang membuat ikatan rangkap dua tidak terlokalisasi  delokalisasi O C O H .. - .. - .. .. .. O C O H ..

Resonance Draw the Lewis structure of NO3-

Resonance Draw the Lewis structure of NO3- .. .. .. .. .. .. .. O O O + + + N N N .. .. .. .. .. .. .. .. O - - .. .. .. .. O - - .. .. .. .. O - .. O O O

Resonance The organic compound benzene, C6H6 is a hexagon of carbon atoms with 6 H/s Draw the Lewis structure for benzene.

Resonance The organic compound benzene, C6H6, has two resonance structures. Bensen memiliki dua struktur resonansi It is commonly depicted as a hexagon with a circle inside to signify the delocalized electrons in the ring. Lazim digambarkan sbg segienam dgn lingkaran di dalamnya  elektron terdelokalisasi