covalent bonding IGCSE chemistry, topic 4

IGCSE chemistry topic 4, covalent bonding describes the formation of covalent bonds by the sharing of electrons. It describes the properties of covalent compounds. Some relevant examples and dot and cross diagram helps students to understand the concept behind the topic

1. Formation of Chemical Bondings K (WALT): The naming system covalent Compounds/ molecules U (TIB): The concept of forming covalent compound by sharing of electrons D (WILF): Use criss -cross diagram to form ionic compound and covalent compounds Properties, naming and Formation of covalent compound

2. When atoms of the same or different types chemically joined together, it is known as chemical bonding. Atoms bond together in order to achieve stable electronic configuration of noble gases. According to octet rule atoms will lose, gain or share electrons to achieve full valence shell K (WALT): The naming system covalent compounds U (TIB): The concept of forming covalent compound by sharing of electrons D (WILF): Use criss-cross diagram to form ionic compound and covalent compounds Chemical Bonding

3. Formation of Covalent Bonding

4. K (WALT): The naming system covalent compounds U (TIB): The concept of forming covalent compound by sharing of electrons D (WILF): Use criss-cross diagram to form ionic compound and covalent compounds CO VALENT BOND Bond formed by the sharing of electrons between non-metallic elements in group 14-17. Think about the word Co valent share Valence electron

5. What are the types of covalent bonds? Single Triple Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence. Double

6. What are the types of covalent bonds? Single Triple Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence. Double

7. Formation of covalent compound Positive end of a magnet attracted to negative end of another magnet. Same principle is applied in formation of covalent bond

8. Formation of covalent compound K (WALT): The naming system covalent compounds U (TIB): The concept of forming covalent compound by sharing of electrons D (WILF): Use criss-cross diagram to form ionic compound and covalent compounds

9. The two chlorine shared electrons to form a covalent bond. The shared electrons are concentrated between two nucleus of chlorine atoms.

10. The two chlorine shared electrons to form a covalent bond. The shared electrons are concentrated between two nucleus of chlorine atoms. Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence

11. M4 Bonding: Covalent Bonding Single Covalent Bond Other elements that share two electrons between themselves and form a diatomic molecule are: The rest of the halogens (Chlorine, Bromine, and Iodine) Oxygen Nitrogen Hydrogen and halogens (fluorine, chlorine, bromine and iodine) share only two electrons between the atoms bonded together. A covalent bond consisting of only two shared electrons it is referred to as a single bond . Oxygen and nitrogen however share 4 and 6 electrons respectively. Can you guess why? (Hint: How many electrons do oxygen and nitrogen atoms need to have a full valence shell?)

12. M4 Bonding: Covalent Bonding Multi p le covalent bonds : Double Bond Electronic configuration: 2 , ( 6 + 2 = 8 ) 2 , ( 6 + 2 = 8 ) outer shell full outer shell full energetically stable energetically stable Since the oxygen atoms share 2 pairs of electrons (4 electrons), a molecule of oxygen therefore has a double bond . Determine the bonding situation in nitrogen. (Hint: It has a triple bond.) Determine the bonding situation in diatomic molecules of chlorine, bromine and iodine as well. Additionally, draw structural formula for all the molecules considered thus far. O 2

13. M4 Bonding: Covalent Bonding Multi p le covalent bonds: Triple Bond Nitrogen is another non-metal. A structure for nitrogen is given to the right. How many electrons does it need to have a completely filled outer shell and become energetically stable? If two nitrogen atoms are to combine and form a diatomic molecule , and become stable, how many electrons must they each contribute to the bond then? How many electrons must they share between them? 2, 5 5 3 6 3 What is the electronic configuration of nitrogen? How many electrons does its outer shell have?

14. What is electronegativity?? The atoms with higher tendency to gain electrons to attain full valence shell

15. What is electronegativity?? If the attraction is between more electronegative atoms and less electrogative atom, the electrons will not be shared evenly. Uneven charge distribution causes the formation of dipole

16. What is DIPOLE?? Separation of the charges between two covalently bonded atoms The more electronegative atom attract electrons of bonded atom more strongly . The resulting bonding is described as ‘polar’- unequal sharing of electrons gives it ‘direction’

17. Simple concept behind polar and non-polar covalent bond Non-polar

18. Simple concept behind polar and polar covalent bond Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence. Polar

19. Probability representations of the electron sharing in HF. (a) What the probability map would look like if the two electrons in the H–F bond were shared equally. (b) The actual situation, where the shared pair spends more time close to the fluorine atom than to the hydrogen atom. Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence

20. Lewis Structures The formation of a bond between H and Cl to give an HCl molecule can be represented in a similar way. Thus, hydrogen has two valence electrons about it (as in He) and Cl has eight valence electrons about it (as in Ar). : H : : : Cl H . . : : Cl : +

21. Lewis Structures Formulas such as these are referred to as Lewis electron-dot formulas or Lewis structures . : : H Cl : : An electron pair is either a bonding pair (shared between two atoms) or a lone pair (an electron pair that is not shared). bonding pair lone pair Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence.

22. Inorganic examples C : : : O .. : O .. : : C : O .. O .. : : : : N : C : H : N C H Carbon dioxide Hydrogen cyanide Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence.

23. Organic examples Ethylene ethene Acetylene ethylene : : : C : C : H H C C H H C : : C .. H : : .. H H H C C H H H H Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence.

24. Predicting the Molecular Formula of Covalent Compounds We can predict the formula of a covalent compound by referring to the valency of the elements in the compound, if we know which group in periodic table the element is located. The valency of an atom is the number of electrons receive of release to achieve octet electrons arrangement. Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence.

25. Predicting the Molecular Formula of Covalent Compounds Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence.

26. Low melting/boiling point (Volatile) Molecules held by weak intermolecular forces in a simple molecular structure , requires little energy to overcome. 1 Low density Molecules held by weak intermolecular forces , hence they are usually not packed. 2 Does not conduct electricity in any state They do not have any free moving ions to carry electrical charges . 4 Properties of Covalent Compound Usually insoluble in water Soluble in organic compounds (eg oil) 3 Simple Molecular Structure Intermolecular Forces (Weak) Covalent Bond (Strong) Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

27. Properties of covalent compounds Global Context: Personal and cultural expressions Key Concept: systems Related concept: Models and evidence Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence. Most covalent compounds are made up of independent molecular units, as shown in figure above. The attraction force between molecules is the weak Van der Waals’ force.

28. Statement of Inquiry: The development of systems roots from the expression and discovery of ideas through models and evidence. Properties of Simple Covalent Molecular Substances – Small Molecules! The intermolecular force between the simple covalent molecules is very weak. Therefore, covalent compounds have low melting and boiling point. They are also poor conductors of electricity because there are no free electrons or ions in any state to carry electric charge. Most small molecules will dissolve in organic solvent to form a solution . Examples – CO 2 , CO, NH 3

29. Activity 1 Draw dot and cross diagrams to illustrate the bonding in the following covalent compounds. If you wish you need only draw the outer shell electrons; 1. Water, H 2 O 2. Carbon dioxide, CO 2 3. Ethyne, C 2 H 2

30. Post-Lesson Task Group 1: Define giant molecules How the structure of giant molecules are different from simple covalent structures Provide examples of giant molecules List down the properties of simple molecules and giant molecules.

31. Quiz 1

32. Quiz 2

33. Quiz 3

34. Quiz 4

35. Quiz 5

36. WEEK 5 LESSON 1   Molecules and covalent bonds Hydrogen bond (Brief)*  Macromolecules (giant covalent ) Metallic bond formation MYP Criteria:  Criterion: A Strand(s): apply scientific knowledge and understanding to solve problems set in familiar and unfamiliar situations In this session, students will learn K: State the basis behind formation of ions U: Describe how different group elements loses/gain electrons D: Draw Dot and cross diagrams for various ionic compounds

37. Covalent BONDing 1 Sharing of Electrons Ionic bonding cannot be formed when: Atom has 4 valence electrons Metals are absent (no electron donor) To obtain noble configuration, non-metals will: Share electrons with another atom of the same element Share electrons with another non-metal Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

38. F F O C O 2 Dot & Cross Diagrams and Lewis Structure Example 1: Fluorine Example 2: Carbon Dioxide Chemical Formula: F 2 Chemical Formula: CO 2 2 pairs of electrons (double bond) 1 pair of electrons (single bond) Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

39. Low melting/boiling point (Volatile) Molecules held by weak intermolecular forces in a simple molecular structure , requires little energy to overcome. 1 Low density Molecules held by weak intermolecular forces , hence they are usually not packed. 2 Does not conduct electricity in any state They do not have any free moving ions to carry electrical charges . 4 Properties of Covalent Compound Usually insoluble in water Soluble in organic compounds (eg oil) 3 Simple Molecular Structure Intermolecular Forces (Weak) Covalent Bond (Strong) Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

40. Metallic bonding 1 Sea of delocalised electrons Metals always lose electrons to form positive ions (cations) When there is no available atoms to take in the electrons lost, the electrons will stay ’floating’ around the positive ion. In a bigger picture, many electrons will ‘float’ around their corresponding positive ions, forming a sea of delocalised electrons Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

41. 2 Metallic Bonding Electrostatic attraction between positively charged ions and sea of delocalised electrons Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

42. Special covalent bonding a) Diamond What it is? Diamond is made up of carbon elements held together in a strong lattice. It is an element . 1 What does it look like? 2 Each carbon is bonded to 4 other carbons What does it mean? The giant covalent structure is extremely strong. Therefore, diamond: is the hardest substance has a high m.p of 3550 o C 3 All valence electrons of a carbon atom are used up to form bonding. Therefore, diamond cannot conduct electricity . Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

43. b) Graphite What it is? Graphite is made up of carbon elements held together in layers. It is an element . 1 What does it look like? 2 What does it mean? The layers can slide over each other easily. Therefore, graphite is soft and slippery . 3 Each carbon is bonded to 3 other carbons The layers are held together by weak forces Only 3 electrons of a carbon atom are used to form bonding. The remaining electron are free to move. Therefore, graphite can conduct electricity . Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion

44. c) Silicon (IV) Oxide What it is? Silicon (IV) oxide is made up of silicon and oxygen atoms held together in a strong lattice . It is a compound. 1 What does it look like? 2 What does it mean? The giant covalent structure is extremely strong. Therefore, sand: is a hard substance has a high m.p of 1710 o C 3 All valence electrons silicon and oxygen atoms are used up to form bonding. Therefore, sand cannot conduct electricity . Each silicon is bonded to 4 oxygen atoms Each oxygen is bonded to 2 silicon atoms Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion Tuning in Sorting Out Going Further Making Conclusion