Chemical Bonds

1. Chemical Bonds

2. Atoms gain or lose electrons through chemical reactions to gain a filled outer shell and therefore a lower energy level. • A chemical reaction forms a chemical bond that is an attractive force that holds atoms together in a compound. • Ionic bonds are formed when an atom transfers an electron to another atom during a chemical reaction • The opposite charges resulting forms an electrostatic attraction between the ions that are formed.

3. Covalent bonds form when atoms share electrons in a chemical bond. • Metallic bonds form in metals. • These new bonds form compounds which can be described in several ways. • Molecular orbital theory describes the electrons as belonging to the whole molecule which gives the orbital its own shape, orientation, and energy levels. • Isolated atom description considers the electrons around the atoms as being isolated from the rest of the molecule.

4. Ionic Bonds • Ionic bonding occurs when one atom transfers an electron to another atom • The difference in electrical charge results in an electrostatic attraction between unlike electrical charges • This occurs when a metal reacts with a nonmetal Na+1 + Cl-1 NaCl (table salt)

5. Energy and Electrons in Ionic Bonding • Example: energy + Na+ Na+ + e- Cl + e-  Cl- + energy Na+ + Cl- NaCl + energy • The energy that is released in steps 2 and 3 is greater that that absorbed in step one and an ionic bond is formed. • This energy is called the heat of formation.

6. Two rules for keeping track of electrons in ionic bonding reactions. • Ions are formed when atoms gain or lose electrons to achieve a noble gas configuration • The number of electrons that are lost must equal the number of electrons that are gained.

7. Ionic Compounds and Formulas • The formula of a compound describes what elements are in the compound and in what proportions. • Compounds that are held together by ionic bonds are called ionic compounds. • The elements in Group IA and IIA tend to lose electrons for form positive ions • The elements in Group VIA and VIIA tend to gain electrons to form negative ions.

8. Covalent Bonds • A covalent bond is a chemical bond that is formed when two atoms share a pair of electrons. • H. + H. H:H • Covalent Compounds and Formulas • Since a pair of electrons is shared in a covalent bond, the electrons move throughout the entire molecular orbital. • In the above example, since both hydrogen share the electron pair, each hydrogen has a filled valence shell, since it has the electron configuration of helium. • Compounds that are held together by covalent bonds are called covalent compounds. • Covalent compounds form from atoms on the right side of the periodic table

9. Multiple Bonds. • In electron dot notations, a pair of electrons can be represented by a pair of dots : . • This can be a bonding pair or a lone pair (non-bonding pair). • Bonding pairs can also be represented by lines connecting atoms. • H:H = H—H • When one pair of electrons is shared, it is called a single bond. • H-H

10. When two pairs of electrons are shared it is called a double bond. H H \ / C C / \ H H • When three pairs of electrons are shared it is called a triple bond. H-C C-H

11. Electronegativity. • Electronegativity is the ability of an atom to attract bonding electrons. • Elements with higher values have the greatest attraction for bonding electrons. • The difference in electronegativity can be used to predict whether a bond will be ionic or covalent. • If the absolute difference is 0.5 or less, the bond will be covalent. • If the absolute difference is 1.7 or more the bond will be ionic.

12. When the absolute difference is between 0.5 and 1.7 a covalent bond is formed, but one in which the electron pair is not shared equally. • This type of bond is called a polar covalent bond. • A polar covalent bond results in areas of partial positive charge and areas of partial negative charge since the electrons spend more time around the more electronegative atom.

13. Naming chemical Compounds

14. Ionic Compound Names • Ionic compounds that are formed from metal ions are named by naming the metal ion (electropositive ion) first, followed by the nonmetal (electronegative ion) • The ending of the nonmetal is changed to end in -ide • When a metal can have various oxidation states the oxidation state is give by roman numerals in parenthesis after the name of the metal.

15. Sr2+strontium ion Na+sodium ion Ba2+barium ion Naming the ions Names of main-group monatomic ions are straightforward. A cation takes the name of the element plus the word "ion." Na Sr Ba

16. Cl-chloride ion N3-nitride ion O2-oxide ion For anions, the element name has its ending replaced with  ide. N O Cl

17. Some transition metals can form more than one ion. Iron, for example, forms both Fe2+ and Fe3+. To name such an ion unambiguously, we use the name of the element, a Roman numeral in parentheses to denote the charge, and the word "ion." Fe2+ and Fe3+ would be iron(II) ion and iron(III) ion, respectively.

18. Ionic Compound Formulas • Rules • The symbol for the positive element is written first, followed by the symbol of the negative element • Subscripts are used to indicate the numbers of ions needed to produce an electrically neutral compound.

19. Example calcium chloride • calcium is Ca2+ and chlorine is Cl- • in order to balance charges there needs to be two negative charges to balance the 2+ on the calcium • the formula is therefore CaCl2

20. Most of the common polyatomic ions are anions, although a few are cations. It is important to know the names, charges, and formulas of all of these ions.

21. Common polyatomic ion names

22. Ammonium fluoride Iron phosphate Silver oxide Anions + Cations = ionic compound name Note: Ag has a charge of +1 and oxide has a charge of –2 sothe chemical formula of silver oxide must be Ag2O

23. What is the correct name for the ionic compound Na2SO4?A. disodium sulfateB. sodium sulfoxideC. sodium sulfateD. sodium sulfide

24. The procedures used for naming binary (two-element) • molecular compounds are similar to those used for • naming ionic compounds: • The name of the element farthest to the left in theperiodic table is usually written first. • If both elements are in the same group in the periodic table, the lower one is named first. • The name of the second element is given an -ide ending. • Greek prefixes (Table 2.6) are used to indicate the number of atoms of each element. The prefix mono- is never used with the first element. When the prefix ends in a or o and the name of the anion begins with a vowel (such as oxide), the a or o is often dropped.

25. CO2 Carbon Dioxide H2O Dihydrogen Monoxide

26. Carbon tetrachloride isA. CCl4B. CClO4C. C2Cl4D. CCl5 TETRA = 4

27. Once you understand chemical names and formulas, you can figure out what chemical compounds are contained in different household products. For example, (A) washing soda is sodium carbonate (Na2CO3) and (B) oven cleaner is sodium hydroxide (NaOH), which is also known as lye.

28. Using Lewis Dot structure to help you move electrons around • The number of valence electrons of any element is the same as the group number of the element in the periodic table. • For example, the Lewis symbol for oxygen, a member of group 6A, shows 6 dots. • A maximum of eight dots can be placed around a symbol, where each dot represents a valence electron. • Dots are placed above, below, to the left, and to the right of the element symbol. • Each position can accommodate two electrons, and electrons are not "paired" until each of the four positions contains a single electron.

29. The Lewis dot structure for Oxygen O Oxygen is in group VIA so it has 6 valence electrons

30. The Lewis dot structure for Chlorine Cl chlorine is in group VIIA so it has 7 valence electrons

31. The Lewis dot structure for calcium Ca calcium is in group IIA so it has 2 valence electrons

32. Ca + Cl Cl Ca( Cl )2 Making calcium chloride

33. Lewis dot structure of a compound NH3 • How many valence electrons does N have? • N is in group VA so it has 5 valence electrons 2) How many valence electrons does H have? H is in group IA so each H has one valence electron 3) How many total valence electrons are there in this molecule? You know it had to be 8 because it has NO CHARGE! 3 x 1 + 5 = 8

34. H H H Lewis dot structure of a compound NH3 N

35. + H H H N H Lewis dot structure and making ammonium ion NH4+ H+

36. Forces.

37. A force is viewed as a push or a pull, something that changes the motion of an object. • Forces can result from two kinds of interactions. • Contact interactions. • Interaction at a distance.

38. The net force is the sum of all forces acting on an object. • When two forces act on an object the forces are cumulative (the are added together. • Net force is called a resultant and can be calculated using geometry.

39. Four important aspects to forces. • The tail of a force arrow is placed on the object that feels the force. • The arrowhead points in the direction of the applied force. • The length of the arrow is proportional to the magnitude of the applied force. • The net force is the sum of all vector forces.

40. The rate of movement and the direction of movement of this ship are determined by a combination of direction and magnitude of force from each of the tugboats. A force is a vector, since it has direction as well as magnitude. Which direction are the two tugboats pushing? What evidence would indicate that one tugboat is pushing with greater magnitude of force? If the tugboat by the numbers is pushing with a greater force and the back tugboat is keeping the ship from moving, what will happen?

41. (A)When two parallel forces are acting on the cart in the same direction, the net force is the two forces added together.

42. (B) When two forces are opposite and of equal magnitude, the net force is zero.

43. (C) When two parallel forces are not of equal magnitude, the net force is the difference in the direction of the larger force.

44. You can find the result of adding two vector forces that are not parallel by drawing thetwo force vectors to scale, then moving one so the tip of one is the tail of the other. A new arrow drawn to close the triangle will tell you the sum of the two individual forces.

45. (A) This shows the resultant of two equal 200 N acting at an angle of 90O, which gives a single resultant arrow proportional to a force of 280 N acting at 45O. (B) Two unequal forces acting at an angle of 60O give a single resultant of about 140 N.

46. Horizontal Motion on Land.

47. It would appear as though Aristotle's theory of motion was correct as objects do tend to stop moving when the force is removed. • Aristotle thought that the natural tendency of objects was to be at rest. • Objects remained at rest until a force acted on it to make it move.

48. Aristotle and Galileo differed in how they viewed motion. • Again, Aristotle thought that the natural tendency of objects was to be at rest. • Galileo thought that it was every bit as natural for an object to be in motion.

49. Inertia. • Galileo explained the behavior of matter to stay in motion by inertia. • Inertia is the tendency of an object to remain in motion in the absence of an unbalanced force such as: • friction • gravity.

50. Galileo (left) challenged the Aristotelian view of motion and focused attention on the concepts of distance, time, velocity, and acceleration.