Chapter6 Chemical Bonding بالل عبدهللا الروزي فهد حمد آل سعيد مسعود شبير احمد
Chemical Bonding Chemical bonds: are the attraction between atoms that hold compounds together. Chemical bonds divided by two categories: ionic bonds. Covalent bonds.
Bonding in ionic compounds Ionic compound: is a compound consisting of cations and anions held together by electrostatic attraction into crystal structure for example : LiF, NaCl, CaO,CaCl2, Li2O Na (1S 2 2S 2 3S 1 ) Na + (1S 2 2S 2 2P 6 3S 0 )+e - Cl ( 1S 2 2S 2 2P 6 3S 2 3P 5 )+e - Cl - (1S 2 2S 2 2P 6 3S 2 3P 6 ) Na + +cl - Na + cl -
Factors Law ionization energy and high electron affinity The lattice energy of the resulting compound is very large Two factor (1)+(2). According to the above factors most compounds formed between metals and non metals are ionic
Lewis symbols Lewis symbols are used to describe valence electron configurations of atoms and non-atomic ions. These symbols consist of the symbol for the element and one dot each valence electron present. When two dots written adjacent to each other, as in
The covalent bond: The covalent bond is a bond formed between two atoms by electrons sharing. In a single bond, one electron pair is shared. Double and triple covalent bonds are called multiple bonds. In a double bond, two electron pairs are shared, and in a triple bond, three electron pairs are shared For example: Single bond :
Double bond: Triple bond:
The covalent bond Note that, the atoms in polyatomic ions, such as OH -, NO 3 - and NH 4 + are held together by covalent bonds. Thus, compounds containing polyatomic ions are stabilized by both covalent bonds and ionic bonds. For example KNO 3 has ionic bonds resulting from the electrostatic attraction between ions K + and NO 3 - and covalent bonds between the nitrogen and oxygen atoms in NO 3-.
Lewis structures: Lewis structures: Lewis structures utilize Lewis symbols to show electrons in molecules and ions For example : Lewis structures shown above for Cl 2 indicates that Cl atom has three pairs of electrons that are not used in bonding (called unshared pairs, or lone pairs) and one shared pair of electrons.
OCTET RULE The tendency of the ions of many of the representative elements to have a noble gas configuration with 8 electrons in the outer shell, is the basis of the Octet rule. When metals and non metals of A groups react they often tend to gain or lose electrons until there are eight electrons in the outer shell The central atoms in the following example obey octet rule.
Bond order and some bond properties : Bond order : is the number of covalent bonds that exist between a pair of atoms Some bond properties : 1- Average bond length : the bond length decreases as the bond order increases 2-Average bond energy : the bond energy increases as the bond order increases 3- Average vibrational frequency : for a given pair of atoms, as the bond order increases. So dose the vibrational frequency.
Multiple choice questions: 1.Which of the following compounds dose not obey the octet rule: 1) PCl 3 2) PCl 5 3) SF 6 4) CCl 4 a)1,2 b)2,4 c)1.3 d)2.3 2. Which of the compounds, the central atom dose not obey the octet rule: a)pcl 3 b) H 2 o c) IF 7 d) CCl 4 3.Consider the following compounds: The largest carbon nitrogen vibrational frequency is: a) b) c) d)
4.The c-c bond order, bond length and bond energy in the following compounds H3C-CH3, H2C= CH2 and HC = CH are respectively : bond order bond length bond energy A) Increases Increases decreases b) Increases decreases Increases c) Increases Increases decreases d) Decreases Increases Increases 5. In one of the following compounds, the central atom obeys the octet rule: a) PCl 5 b) ClF 3 c) IF - 4 d) PF 3
6. One of the following statement is incorrect: a)the largest the bond order the stronger the bond b) The weaker the bond the smaller the vibrational frequency c) The shorter the bond the smaller the bond order d) The higher the vibrational frequency the stronger the bond 7. The value of bond energy is an indication of: 1) Bond strength 2) bond length 3) polarity 4) solubility a) 1,3 b)1,2 c)2,3 d)3,4
8. Which of the following increase(s) by increasing bond order: 1)Bond length 2)vibrational frequency 3)Bond energy 4) non of the above a)1,2 b)2,3 c)1,3 d)3,4 9. Which of the following compounds do(es) not obey octet rule: 1)NaF 2) PF 5 3) CCl 4 4) CO 2 a)1,2 b)2,3 c)3,4 d)2 10.In one if the following, the central atom(s) do(es) not obey octet rule: 1) H 3 O + 2) NH + 4 3) SCl 4 4) PF 5 a)1,2 b)3 c)2 d)3,4
11. The type of bond between two similar non-metallic atom is: a) A pure ionic bond b) A pure covalent bond c) 50% ionic and 50% covalent d) No bond is formed 12. The factors that lead to ionic bond formation are: a) High ionization energy and low electron affinity b) High ionization energy and high electron affinity c) High ionization energy only d) Low ionization energy and high electron affinity