Chapter 11

1. Chapter 11 Chemical Bonding

2. Section 1: Objectives • Describe chemical bonding. • Identify the number of valence electrons. • Predict whether an atom is likely to form bonds.

3. Combining Atoms • All substances are made up of atoms of one or more of the elements. • Chemical bonding: joining of atoms to form new substances • Chemical bond: an interaction that holds 2 atoms together

4. Combining Atoms • To understand how atoms bond, you need to determine the # of electrons. • Atomic # = # of protons • What else do we know about the atomic #?

5. Combining Atoms • Electrons are arranged in levels. • Not all electrons in an atom make bonds. • Most atoms form bonds with valence electrons.

6. Forming a Compound: Example # 1 (K and F)

7. Combining Atoms • Elements are grouped based on similar properties. • Within a group, atoms have the same number of valence electrons. • Group numbers help you determine the number of valence electrons.

8. Combining Atoms • Not all atoms bond the same way. • The # of electrons in the outermost shell determines if an atom will bond. • What group of atoms is not likely to form bonds? Why? • What group/groups are more likely to form bonds? Why?

9. Forming a Compound: Example # 2 (H, He, C, and Ne)

10. Combining Atoms • Atoms bond by gaining, losing, and sharing electrons. • Their goal is to fill the outermost energy level. • A filled outermost level contains ____ electrons.

11. Combining Atoms • Not all atoms need 8 electrons to have a full outer level. • The outermost energy level of helium only has 2 electrons and it is full. • How is this true for helium?

12. Ch. 11 Section 1: Review Questions • 1) What are all substances made up of? • 2) Why is understanding the number of electrons in an element important? • 3) How are elements grouped? • 4)T/F All atoms bond the same way. • 5) How do atoms bond? • 6)How do most atoms form bonds? • 7) T/F All electrons in an atom can make bonds.

13. Section 2: Objectives • Explain how ionic bonds form. • Describe how positive ions form. • Describe how negative ions form. • Explain why ionic compounds are neutral.

14. Chemical Bonds • Ionic bond: bond that is formed when electrons are transferred from one atom to another • These form so that the outermost energy level is filled. • What does the name of the bond sound like?

15. Chemical Bonds • An atom is neutral because the number of electrons equals the number of protons. • The transfer of electrons causes the number of electrons and the charge to change. • Ion: charged particle that forms when an atom or group of atoms gains or loses one or more electrons

16. Chemical Bonds • Most metals have few valence electrons. • Metal atoms tend to lose their valence electrons and form positive ions.

17. Chemical Bonds • Energy is needed to pull electrons away from atoms. • Only a small amount of energy is needed to take electrons from metal atoms. • That is why elements in Groups 1 and 2 react easily.

18. Chemical Bonds • Some atoms gain electrons from other atoms during chemical changes. • These atoms then have more electrons than protons. • What does this mean for their charge?

19. Chemical Bonds • The outermost energy level of a non-metal is almost full. • They only need a few electrons in order to be full. • Nonmetals tend to gain electrons from other atoms.

20. Chemical Bonds • Energy is given off when non-metals gain electrons. • Group 17 elements give off the most energy when they gain an electron.

21. Chemical Bonds • When ionic compounds form, the # of electrons lost by the metal atoms equals the number gained by the non-metal atoms. • The ions that bond are charged, but the compound is neutral. • Crystal lattice: regular pattern in which a crystal is arranged

22. Chemical Bonds • Most things, such as water and sugar, are held together by covalent bonds. • Low melting and boiling points. • Brittle in solid state.

23. Chemical Bonds • Covalent bond: formed when atoms share one or more pairs of electrons • In non-metals, atoms don’t donate electrons to form a bond with another non-metal because it requires too much energy. • Non-metals share electrons (covalent bonds).

24. Chemical Bonds • A molecule consists of 2 or more atoms combined in a definite ratio. • Most atoms are composed of molecules of 2 or more different elements. • A compound can form from a combination of 2 or more atoms of different elements.

25. Chemical Bonds • An ion is an atom that is no longer neutral because it has gained or lost V.E. • How will changing the V.E. number affect the charge(s) of the atom? • How will changing the V.E. number affect the properties of the atom? (R/U?) • An isotope is a form of an atom that has the same number of protons but a different number of neutrons.

26. Chemical Bonds • One way to represent atoms is to draw a Lewis-Dot Structure. • Lewis-Dot Structures help you predict how atoms might bond. • To draw: write the element symbol and draw dots for every V.E.

27. Chapter 11 Sec. 1-2 Recap • 1) What must we determine to understand how atoms bond? • 2) T/F All electrons in an atom form bonds. • 3) How do you determine the # of valence electrons? • 4) How are elements grouped on the periodic table? • 5) What is needed to pull electrons away from atoms?

28. Chapter 11 Sec. 1-2 Recap • 6) List 2 characteristics of covalent compounds. • 7) An ion will never have a charge of __. • 8) T/F Ionic compounds always have a neutral charge. • 9) Why are Lewis-Dot Structures helpful? • 10) T/F Most metals have few valence electrons.

29. Section 3: Objectives • Explain how covalent bonds form. • Describe molecules. • Explain how metallic bonds form. • Describe the properties of metals.

30. Covalent and Metallic Bonds • Most compounds are held together by covalent bonds • Examples: • Water (H2O) • Sugar • Compounds held together by covalent bonds tend to have low melting and boiling points. • This is why oxygen is a gas at room temperature.

31. Covalent and Metallic Bonds • Substances containing covalent bonds consist of individual particles called molecules. • A molecule usually consists of 2 or more atoms joined in a definite ratio. • However, most molecules are composed of atoms or 2 or more elements.

32. Covalent and Metallic Bonds • A metallic bond is formed by the attraction between positively charged metal ions and the electrons in the metal. • Positively charged metal ions form when metal atoms lose electrons. • Metallic bonding is what gives metals their properties.

33. Covalent and Metallic Bonds • Properties of most metals: • Good conductors of heat/electricity • Ductile • Malleable (ability to be reshaped) • Ex 1) Copper is made into wires for electrical cords. • Ex 2) Aluminum can be pounded in sheets.

34. Covalent and Metallic Bonds • Diatomic molecules are molecules that contain 2 atoms of the same element. • Examples: • O2 (Oxygen) • H2 (Hydrogen) • N2 (Nitrogen) • Cl2 (Chlorine)

35. Chapter 11 Sec. 3 Recap • 1) What type of bond holds most compounds together? • 2) T/F Most molecules are composed of 2 or more of the same element. • 3) When metals lose electrons, what forms? • 4) What is malleability? • 5) List 1 example of a diatomic molecule.

36. Chapter 11 Vocabulary Review • 1) _____: an atom that is no longer neutral because it has lost or gained valence electrons • 2) _____: a bond that is formed when many metal atoms share their pooled valence electrons • 3) _____: an outermost electron of an atom that participates in chemical bonding

37. Chapter 11 Vocabulary Review • 4) ______: a force that holds 2 or more atoms together • 5 _______: a model that represents valence electrons in an atom as dots around the element’s chemical symbol • 6) ______: a group of atoms held together by covelent bonding that acts as an independent unit

38. Chapter 11 Vocabulary Review • 7) _____: a molecule that has a partial positive end because of unequal sharing of electrons • 8) _____: the attraction between positively and negatively charged ions in an ionic compound • 9) _____: a chemical bond formed when 2 atoms share 1 or more pairs of valence electrons • 10) ____: a group of chemical symbols and numbers that represent the elements and the number of atoms of each element in a compound