Chemical Bonds

1. Chemical Bonds Chapter 20

2. Chemical Bonds • Section 1 Stability in Bonding slides 3-22 • Section 2 Types of Bonds slides 23-48 • Section 3 Writing Formulas & Naming Compounds slides 49-84

3. 1- Stability in Bonding • What You’ll Learn: • About elements in a compound • Chemical formulas • How electric forces help form compounds • Why a chemical bond forms

4. Do compounds look like their elements? • Elements can combine with others in a chemical reaction to form compounds.

5. Do compounds look like their elements? • Elements can combine with others in a chemical reaction to form compounds. • When Cu, S & O combine, they produce a blue solid, copper sulfate.

6. Do compounds look like their elements? • Elements can combine with others in a chemical reaction to form compounds. • When Cu, S & O combine, they produce a blue solid, copper sulfate. • Cu shiny, copper metal, S yellow solid, O colorless, odorless gas

7. Do compounds look like their elements? • Cu shiny, copper metal, S yellow solid, O colorless, odorless gas • When elements combine they produce compounds with their own special properties.

8. Formulas • A chemical formula tells what elements are in a compound & how many atoms of each element are in one unit of the compound.

9. Atomic Stability • Protons positive & electrons negative charge. • These opposite electric forces attract each other pulling the atoms together to form compounds.

10. Electron Distributions Into Shells for the First Three Periods

11. Why do atoms form compounds? • Look at your periodic table. Notice the six elements in Group 18, the noble gases. • Atoms of the noble gases almost never combine to form compounds because they are so stable (full). • Their compounds are less stable than the original atoms.

12. Why are the noble gases different? Lewis Dot Diagrams of Selected Elements

13. Why are the noble gases different? • The number of electrons in the outer energy level of an atom determines if that atom will combine to form a compound.

14. What makes an atom stable? • An atom is chemically stable when it has a complete outer energy level. • If an atom is chemically stable. It does not easily form compounds with other atoms.

15. What elements have incomplete outer energy levels? • None of the elements in Groups 1 through 17 have full outer energy levels. These elements are more stable when they form compounds.

16. How do atoms become more stable? • Atoms without a stable outer energy level can do one of three things to complete their outer level: • Gain electrons • Lose electrons • Or Share electrons with other atoms that have incomplete outer levels. This way, each atom becomes more stable.

17. How do atoms become more stable?

18. How do atoms become more stable? • Sodium has one outer electron & chlorine has seven. • When these two elements combine, sodium gives its outer electron to chlorine which now has eight electrons in its outer level. • The next energy level of sodium is also full & completely stable.

19. What is another way atoms can become stable? • For the compound water, H2O, each hydrogen shares an electron from an oxygen to complete its outer level. • Oxygen shares each of the H atoms’ electrons to complete its outer level. • The compound water is more stable than either a hydrogen atom or an oxygen atom.

20. What is another way atoms can become stable? • An attractive force forms when atoms gain, lose, or share electrons to make a compound. • A chemical bond is the force that holds atoms together in a compound.

21. Atoms Become more stable by: They can do this by:

22. Atoms Become more stable by: Completing their outer energy level They can do this by: Gaining electrons Losing electrons Sharing electrons

23. 2- Types of Bonds • What You’ll Learn: • What ionic bonds are • What covalent bonds are • What particles are produced by ionic & covalent bonding • About polar & nonpolar covalent bonds

24. Gain or Loss of Electrons • Atoms gain or lose electrons to meet the standard of a full energy level.

25. Gain or Loss of Electrons • Atoms gain or lose electrons to meet the standard of a full energy level. • When an atom gains or loses an electron, it becomes an ion.

26. Gain or Loss of Electrons • Atoms gain or lose electrons to meet the standard of a full energy level. • When an atom gains or loses an electron, it becomes an ion. • An ion is a charged particle because it has either more or fewer electrons than protons • More electrons than protons, ion is negative • More protons than electrons, ion is positive

27. What are some common compounds? • The electric forces between + and – particles hold compounds together.

28. What are some common compounds? • The electric forces between + and – particles hold compounds together. • Many common compounds form by gaining or losing just one electron from Group 1 & Group 17 elements.

29. What are some common compounds? • The electric forces between + and – particles hold compounds together. • Many common compounds form by gaining or losing just one electron from Group 1 & Group 17 elements. • Examples: sodium chloride, sodium fluoride, potassium iodide

30. How is potassium iodide formed? K I [K]+ [ I ] • An atom of potassium has one electron in its outer level which it loses becoming a positive (K+) ion.

31. How is potassium iodide formed? K I [K]+ [ I ] • An atom of potassium has one electron in its outer level which it loses becoming a positive (K+) ion. • When iodine reacts with potassium it becomes a negative iodide ion (I-).

32. How is potassium iodide formed? K I [K]+ [ I ] • An atom of potassium has one electron in its outer level which it loses becoming a positive (K+) ion. • When iodine reacts with potassium it becomes a negative iodide ion (I-). • An ionic compound forms when two or more ions combine to become neutrally charged.

33. The Ionic Bond • An ionic bond is the force of attraction between a positive ion & a negative ion in an ionic compound. • In an ionic compound, one atom gives up electrons & the other atom takes them so that the compound stays neutral. Cl Cl Mg [ Cl ]-Mg+2[ Cl ]- Magnesium+2 chlorine atoms =Magnesium Chloride

34. The Ionic Bond • In this case, the magnesium atom has 2 electrons to give; however, a chlorine atom can only use 1 so it takes 2 chlorine atoms to rake the two electrons from Mg & combine to form the ionic compound magnesium chloride. Cl Cl Mg [ Cl ]-Mg+2[ Cl ]- Magnesium+2 chlorine atoms =Magnesium Chloride

35. Does an ionic compound have a charge? • It’s neutral because the sum of the charges on the ions is zero. • The total number of electrons and protons stays the same. • Ionic bonds usually form when a metal bonds with a nonmetal. • Elements on the far left of the PT tend to form ionic bonds with elements on the far right.

36. Sharing Electrons • Some atoms of nonmetal elements become more stable when they share electrons. • Group 14 elements have 4 outer electrons • Must gain or lose 4 e- to be stable • Requires lots of energy for that many • Ions hold remaining e- more tightly after each loss so even more energy needed to remove another---meaning it’s easier to share e-

37. Sharing Electrons • Some atoms of nonmetal elements become more stable when they share electrons. • A covalent bond is the force of attraction between two atoms that share electrons.

38. Sharing Electrons • Some atoms of nonmetal elements become more stable when they share electrons. • A covalent bond is the force of attraction between two atoms that share electrons. • Amolecule is the neutral particle that forms when atoms share electrons.

39. How are single covalent bonds formed? • When 2 atoms share 2 e-, 1 from each atom in the covalent bond www.school-for-champions.com

40. How are single covalent bonds formed? • When 2 atoms share 2 e-, 1 from each atom in the covalent bond • There are 2 single covalent bonds in water. www.school-for-champions.com

41. How are single covalent bonds formed? • When 2 atoms share 2 e-, 1 from each atom in the covalent bond • There are 2 single covalent bonds in water. • In each single bond, a H atom & an O atom each give 1 e- which the atoms share becoming more stable. www.school-for-champions.com

42. What are multiple bonds? • A covalent bond can have more than 2 electrons. • Each N atom has 5 e- in outer energy level; needs 3 to be stable. • Share 3 pairs of e- to form triple bond making 8 e- in outer energy level. N2 www.chem.lsu.edu/ grandinetti.org/.../LewisDot/assets/N2.gif

43. What are multiple bonds? • A double bond is 2 pairs of electrons shared between 2 atoms. In CO2 the C atom shares 2 e- with 1 O atom & 2 e- with the other O atom. In return each O shares 2 e- with the C so that all 3 have 8 e- in outer energy level. Space filling model of carbon dioxide

44. Recognize covalent compounds • Covalent bonds form between nonmetals. • Nonmetals are found in the upper right-hand corner of the PT. • Many covalent compounds are liquids or gases at room temperature.

45. Are electrons always shared equally? • Not always because the positive charge in one nucleus can be stronger than that of another smaller atom. • If a shared electron is closer to one nuclei it may be held more strongly. • Nuclei with a greater positive charge attract electrons more strongly.

46. What is an example of unequal electron sharing? • Hydrogen chloride HCl is an example of unequal e- sharing. When mixed with water it becomes hydrochloric acid. Cl atom attracts e- in the bond more strongly than the H atom. Cl has partial negative charge δ_ & H has a partial positive charge δ+. www.elmhurst.edu

47. What are polar & nonpolar molecules? • In water, oxygen has a stronger attraction for the bonding e- giving the O a partial negative charge & the H a partial negative charge. A polar molecule has a slightly + end & a slightly – end, but the molecule is neutral

48. What are polar & nonpolar molecules? • In a nonpolar molecule, electrons are shared equally with no partial charges or oppositely charges ends.

49. 3- Writing Formulas & Naming Compounds • What You’ll Learn: • How to determine oxidation numbers • How to write formulas & names for ionic compounds • How to write formulas & names for covalent compounds

50. Binary Ionic Compounds • A binary compound is a compound made of two elements; for example, potassium iodide, a compound added to table salt. www.webelements.com