Ikatan Kimia Konsep dalam Ikatan Kimia Simbol LewisIkatan ionik dan Struktur LewisIkatan kovalen dan struktur LewisJenis-jenis ikatan kovalen : tulen, datif dan berkutub

Apabila suatu atom berinteraksi bagi membentuk ikatan kimia, hanya elektron valens sahaja yg berhubung.

Ahli kimia menggunakan sistem titik untuk menunjukkan yang jumlah elektron bagi atom tidak berubah. 1 titik untuk 1 elektron valens.

Elektron Valens adalah elektron terluar (elektron di petala terluar) suatu atom. Hanya e valens yg terlibat dalam pembentukan ikatan.

Tulis simbol Lewis bagi atom natrium dan ion natrium. Answer : atom Na, Z = 11konfigurasi e : 2.8.1 elektron valens : 1 atom natrium : Na ion natrium : [ Na ]+

Tulis simbol Lewis bagi atom oksigen dan ion oksida.Answer : atom oksigen O, Z = 8konfigurasi e : 2.6 elektron valens : 6 Atom oksigen : ion oksida : [ ]2-

Suatu sebatian ionik terbentuk drpd gabungan ion positif dan negatif. Ion-ion dalam sebatian ionik dipegang oleh daya elektrostatikPembentukan kation Atom logam, M menyingkir elektron bagi membentuk ion positif (kation)M M+ + e Pembentukan anionAtom bukan logam, X menerima e valens bagi membentuk ion negatif (anion)X + e X-

Kation M+ dan anion X- bergabung dengan ikatan ionik bg membentuk sebatian ionik. M+ + X- MXIkatan kimia dalam MX adalah tarikan antara cas positif ion M dengan cas negatif ion X. Sebatian MX secara elektriknya neutral.

2.12.722.8[He][Ne]contohTbls antara litium dan florin bagi membentuk litium florida. ( kation )( Anion )

2Ca(p) + O2(g) 2CaO(p)contohkalsium terbakar dalam oksigen dan membentuk kalsium oksida.2.8.8.22.6[Ar][Ne]LatihanGunakan simbol titik Lewis utk menunjukkan pembentukan : (i) Magnesium nitrida, Mg3N2(ii) Aluminium oksida, Al2O3

Ik kovalen ialah ik kimia di mana 2 atau lebih elektron dikongsikan.Struktur Lewis F2Ikatan kovalenPsgn e sendiriPsgn e sendiriPsgn e sendiriIk. Kovalen tunggal

++Str Lewis airIk. berganda 2 atom berkongsi 2 pasang eorIk ganda 3 2 atom berkongsi 3 pasang eor

*Lukis str kerangka sebatian dengan atom jum minimum (atau paling elektropositif)) di tengah (atom pusat). Letak atom2 lain di keliling atom pusat (atom hujung).Hitung jum e valens. Tambah 1 pd setiap 1 cas negatif dan tolak 1 bagi setiap cas positif.Lengkapkan oktet semua atom hujung terlebih dahulu, Oktet bg H ialah 2!Jika struktur mengandungi lebihan e, bentukkan ik dubel atau tripel dgn atom pusat sebgmn perlu.Melukis str Lewis sebat kovalen9.6

*Step 1 N is less electronegative than F, put N in centerStep 2 Count valence electrons N - 5 (2s22p3) and F - 7 (2s22p5) 5 + (3 7) = 26 valence electronsStep 3 Draw single bonds between N and F atoms and complete octets on N and F atoms.Step 4 - Check, are # of e- in structure equal to number of valence e- ?3 single bonds (32) + 10 lone pairs (102) = 26 valence electrons

*Step 1 C is less electronegative than O, put C in centerStep 2 Count valence electrons C - 4 (2s22p2) and O - 6 (2s22p4) -2 charge 2e- 4 + (3 x 6) + 2 = 24 valence electronsStep 3 Draw single bonds between C and O atoms and complete octet on C and O atoms.Step 4 - Check, are # of e- in structure equal to number of valence e- ?3 single bonds (3x2) + 10 lone pairs (10x2) = 26 valence electrons9.6Step 5 - Too many electrons, form double bond and re-check # of e-

*Formal Charge and Lewis Structures9.7For neutral molecules, a Lewis structure in which there are no formal charges is preferable to one in which formal charges are present.Lewis structures with large formal charges are less plausible than those with small formal charges.Among Lewis structures having similar distributions of formal charges, the most plausible structure is the one in which negative formal charges are placed on the more electronegative atoms.

*9.7Two possible skeletal structures of formaldehyde (CH2O)An atoms formal charge is the difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a Lewis structure.The sum of the formal charges of the atoms in a molecule or ion must equal the charge on the molecule or ion.

*formal charge on C= 4 -2 - x 6 = -1formal charge on O= 6 -2 - x 6 = +1-1+19.7

*formal charge on C= 4 -0 - x 8 = 0formal charge on O= 6 -4 - x 4 = 0009.7

*A resonance structure is one of two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure.9.8

*Ik kovalen berkutub adalah ik kovalen dengan ketumpatan elektron yang tidak sekata antara 2 atom.electron richregionelectron poorregione- riche- poord+d-9.5

*Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond.Electron Affinity - measurable, Cl is highestElectronegativity - relative, F is highest9.5

*9.5

*9.5

*9.4

*Klasifikasi ikatan yang bergantung kpd perbezaan keelektronegatifanperbezaanJenis ikatan0kovalen 2Ionik0 < dan

*Cs 0.7Cl 3.03.0 0.7 = 2.3IonicH 2.1S 2.52.5 2.1 = 0.4Polar CovalentN 3.0N 3.03.0 3.0 = 0Covalent9.5

*Lengths of Covalent BondsBond LengthsTriple bond < Double Bond < Single Bond9.4

Bond TypeBond Length(pm)C-C154CC133CC120C-N143CN138CN116

*Dative Covalent Bond or Coordinate Covalent BondCovalent bond forms between two atoms that donate an electron each.However, it is possible for both electrons to come from the same atom. This is known as a dative covalent bond or a coordinate covalent bond.The atom that donate the electrons is known as the donor and it must have at least one lone pair of electrons.The other atom that shares the electrons is known as the acceptor and it must have an incomplete octet.

*Example 1Example 2

*Exceptions to the Octet RuleThe Incomplete OctetBeH2BF39.9

*Exceptions to the Octet RuleOdd-Electron MoleculesNOThe Expanded Octet (central atom with principal quantum number n > 2)SF69.9

*Hydrogen BondingA hydrogen atom in a polar bond (e.g. H-F, H-O or H-N) can experience an attractive force with a neighboring electronegative molecule or ion which has an unshared pair of electrons (usually an F, O or N atom on another molecule) Hydrogen bonds are considered to be dipole-dipole type interactions A bond between hydrogen and an electronegative atom such as F, O or N is quite polar:

* The hydrogen atom has no inner core of electrons, so the side of the atom facing away from the bond represents a virtually naked nucleus This positive charge is attracted to the negative charge of an electronegative atom in a nearby molecule Because the hydrogen atom in a polar bond is electron-deficient on one side (i.e. the side opposite from the covalent polar bond) this side of the hydrogen atom can get quite close to a neighboring electronegative atom (with a partial negative charge) and interact strongly with it (remember, the closer it can get, the stronger the electrostatic attraction) Hydrogen bonds vary from about 4 kJ/mol to 25 kJ/mol so they are still weaker than typical covalent bonds. But they are stronger than dipole-dipole and or dispersion forces. They are very important in the organization of biological molecules, especially in influencing the structure of proteins

*Water is unusual in its ability to form an extensive hydrogen bonding network As a liquid the kinetic energy of the molecules prevents an extensive ordered network of hydrogen bonds When cooled to a solid the water molecules organize into an arrangement which maximizes the attractive interactions of the hydrogen bonds This arrangement of molecules has greater volume (is less dense) than liquid water, thus water expands when frozen The arrangement has a hexagonal geometry (involving six molecules in a ring structure) which is the structural basis of the six-sidedness seen in snow flakes Each water molecule can participate in four hydrogen bonds

- One with each non-bonding pair of electrons - One with each H atom

*Metallic BondAssume that a metallic lattice is composed of closely packed positive ions surrounded by an electron cloud. This happen when metal atoms lose their valence electrons, forming metal cations, and the valence electrons then make up the electron cloud. The attractive force between the electron cloud and the positive ions called the metallic bond.The strength of the metallic bond is inversely proportional to the size of the ion and directly proportional to the number of valence electrons on the metal atom. The smaller the size of the cation and/or the more electrons supplied by the atoms to electron cloud, the stronger is the attractive force between the positively charged ion and the electron cloud. Hence, the stronger is the metallic bond formed.

*Intermolecular ForcesIntermolecular forces are generally much weaker than covalent bonds. Only 16 kJ/mol of energy is required to overcome the intermolecular attraction between HCl molecules in the liquid state (i.e. the energy required to vaporize the sample) However, 431 kJ/mol of energy is required to break the covalent bond between the H and Cl atoms in the HCl molecule Thus, when a molecular substance changes states the atoms within the molecule are unchangedThe temperature at which a liquid boils reflects the kinetic energy needed to overcome the attractive intermolecular forces (likewise, the temperature at which a solid melts). Thus, the strength of the intermolecular forces determines the physical properties of the substance

*Attractive forces between neutral molecules Attractive forces between neutral and charged (ionic) molecules ion - dipole forces Note that all of these forces will be electrostatic in natureTypically, dipole-dipole and dispersion forces are grouped together and termed van der Waals forces (sometimes the hydrogen bonding forces are also included with this group) Dipole - dipole forces London dispersion forces Hydrogen bonding forces

*Ion-dipoleInvolves an interaction between a charged ion and a polar molecule (i.e. a molecule with a dipole) Cations are attracted to the negative end of a dipole Anions are attracted to the positive end of a dipole Ion-dipole forces are important in solutions of ionic substances in polar solvents (e.g. a salt in aqueous solvent)

*Dipole-Dipole ForcesA dipole-dipole force exists between neutral polar molecules Polar molecules attract one another when the partial positive charge on one molecule is near the partial negative charge on the other molecule. The polar molecules must be in close proximity for the dipole-dipole forces to be significant. Dipole-dipole forces are characteristically weaker than ion-dipole forces. Dipole-dipole forces increase with an increase in the polarity of the molecule.

*Nonpolar molecules would not seem to have any basis for attractive interactions. However, gases of nonpolar molecules can be liquefied indicating that if the kinetic energy is reduced, some type of attractive force can predominate. Fritz London (1930) suggested that the motion of electrons within an atom or non-polar molecule can result in a transient dipole moment. London Dispersion ForcesA Model To Explain London Dispersion Forces: Helium atoms (2e) Consider the particle nature of electrons. The average distribution of electrons around each nucleus is spherically symmetrical. The atoms are non-polar and posses no dipole moment. The distribution of electrons around an individual atom, at a given instant in time, may not be perfectly symmetrical.

* Both electrons may be on one side of the nucleus The atom would have an apparent dipole moment at that instant in time (i.e. a transient dipole) A close neighboring atom would be influenced by this apparent dipole - the electrons of the neighboring atom would move away from the negative region of the dipole Due to electron repulsion, a temporary dipole on one atom can induce a similar dipole on a neighboring atom This will cause the neighboring atoms to be attracted to one another This is called the London dispersion force (or just dispersion force) It is significant only when the atoms are close together

*The ease with which an external electric field can induce a dipole (alter the electron distribution) with a molecule is referred to as the "polarizability" of that molecule.The greater the polarizability of a molecule the easier it is to induce a momentary dipole and the stronger the dispersion forces Larger molecules tend to have greater polarizability Their electrons are further away from the nucleus (any asymmetric distribution produces a larger dipole due to larger charge separation) The number of electrons is greater (higher probability of asymmetric distribution) thus, dispersion forces tend to increase with increasing molecular massDispersion forces are also present between polar/non-polar and polar/polar molecules (i.e. between all molecules)

2. Use the octet rule and draw the Lewis structure of each of the following substances or ions, keeping in mind that one H atom in a compound cannot be bonded to another H atom.(a) OH -(b) H3O+(c) NH4+(d) NH2-(e) SH -(f) H3S+*1. Write Lewis symbols for the following: (a) P(b) Te(c) Br(d) B (e) Mn2+(f) Mn3+(g) Pb2+(h) Pb4+

*4. Determine the formal charges for the following compounds, considering all possible Lewis structures if there are more than one. (a) SO2(b) NH3(c) H2SO43. Write Lewis structures for the following covalent molecules: (a) HNNN ( hydrazoic acid ) (b) H2NCN ( cyanamide ) (c) CH3NH2 ( methylamine )5. Draw the possible structures of HNO2 and use formal charge to pick the most likely. The order of atoms is HONO.

*7. What happens to the valence shells of Rb and Cl when these elements react to form an ionic compound. What is the formula of this compound?. 6. Write the Lewis structure for acetate ion ( CH3COO- ), including resonance structures if appropriate.8. Give the empirical formulas and names of the compounds formed from the following pairs of ions: (a) Rb+ and I-(b) Cs+ and SO42- (c) Sr2+ and N3-(d) Al3+ and S2-9. Write the Lewis dot symbols of the reactants and products in the following reactions. ( First balance the equations.) (a) Sr + Se SrSe(b) Li + N2 Li3N

*10. The atom of element A has a nuclear charge of +11. Atom B requires two electrons to achieve an octet ( A and B are not the actual symbols of the elements). (a) By using Lewis structures, show the formation of the compound formed when element A combine with element B. (b) Can the solid compound formed conduct electricity?. Explain briefly. Phosphonium ion, PH4+ is formed when phosphene, PH3 combine with H+ ion via a type of bond. By using the Lewis structure show the formation of the PH4+ ion and label this new bond.

* Using Lewis structures, show the formation of a dative covalent bond between (i) NH3 molecule and H+ ion (ii) phosphorus chloride, PCl3 and oxygen, O.13. With the aid of a suitable diagram, describe a metallic bond according to the electron cloud model. Arrange the following substances, NaF, HF, F2 and CF4 in order of increasing boiling points. Explain briefly your answer.

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