Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 5. (L15)-Chemical Bonds Today’s Outline..From atoms to molecules..Some basic questions about molecules..Electron-dot structures..Concept of stable electron configuration..Octet rule..How atoms combine together to form molecules: Ionic bonds..Ionic compounds or molecules

Chapter 5. (L15)-Chemical Bonds Building Your Chemical Vocabulary Iron ore: Fe 2 O 3, Fe 3 O 4, other Fe oxides Iodine: I 2 (brown color) Salt substitute: KCl, potassium chloride Sulfur: S

Chapter 5. (L15)-Chemical Bonds From atoms to molecules..A demo example: 2Hg(l)+ O 2 (g)= 2HgO(s) Hg: silvery liquid metal O 2 : invisible gas HgO: orange red solid Hg, O 2, and HgO are different substances.

Chapter 5. (L15)-Chemical Bonds From atoms to molecules..A demo example: Hg + O = HgO Questions: Why is HgO a stable molecule? What holds Hg and O atoms together? What is the nature of this bonding? Is there any relationship between the chemical bonding and the physical and chemical properties of a molecule (e.g., HgO here)?

Chapter 5. (L15)-Chemical Bonds Some basic questions about molecules..Molecules: Atoms of the same or different kinds combined together by a certain chemical bond staying stably as new chemical entities. -homoatomic molecules: O 2, H 2, Cl 2, etc. -heteroatomic molecules: HgO, NaCl, etc. Questions: Is the chemical bonding the same for all kinds of molecules? Is the strength of the chemical bonding the same for all kinds of molecules? How can I tell what kind of chemical bonding a specific molecule would have?

Chapter 5. (L15)-Chemical Bonds Review of electron configurations..Electron configurations of Na and Cl Na(11)2, 8, 1 Na(11)1s 2 2s 2 2p 6 3s 1 Valence shell: 3(1), or 3s 1 Inner shell: 2(8), or 2s 2 2p 6 Cl(17)2, 8, 7 Cl(17)1s 2 2s 2 2p 6 3s 2 3p 5 Valence shell: 3(7), or 3s 2 3p 5 Inner shell: 2(8), or 2s 2 2p 6

Chapter 5. (L15)-Chemical Bonds Review of electron configurations..Electron configurations of He and Ne He(2)2 Na(2)1s 2 Valence shell: 1(2), or 1s 2 Ne(10) 2, 8 Ne(10) 1s 2 2s 2 2p 6 Valence shell: 2(8), or 2s 2 2p 6 Ar(18) 2, 8, 8 Ar(18) 1s 2 2s 2 2p 6 3s 2 3p 6 Valence shell: 3(8), or 3s 2 3p 6

Chapter 5. (L15)-Chemical Bonds Electron-dot structures..Electron configurations of Na and Cl Na(11)2, 8, 1 Valence shell: 3(1) Dot structure: Na Cl(17)2, 8, 7 Valence shell: 3(7).. Dot structure: :Cl...

Chapter 5. (L15)-Chemical Bonds Electron-dot symbols and periodic table..Main group number = valence shell electron number = dots of an atom See textbook, pp.123, Table 5.1 for a detailed list of the dot-structures of various atoms.

Chapter 5. (L15)-Chemical Bonds Concept of stable electron configuration..Question: Why are noble gases chemically stable? Theory: This is because their valence shells are all completely filled or filled to full; in other words, their valence shells have eight electrons (2 as full for He) The octet valence electron configuration is the most stable configuration. Octet: meaning eight

Chapter 5. (L15)-Chemical Bonds Octet rule..The stable electron configuration theory leads to the following octet rules: -for metal atoms: Each atom of metal tends to give up the valence electrons in its outer shell to achieve the octet electron configuration like the valence shell of noble gas atoms -for non-metal atoms: Each atom of non-metal tends to obtain enough electrons to fill its valence shell to full to achieve the octet electron configuration like the valence shell of noble gas atoms

Chapter 5. (L15)-Chemical Bonds Octet rule.. Examples: Na(11)2, 8, 1 or 1s 2 2s 2 2p 6 3s 1 Na· = Na + + e - Na, 11p e - ; valence shell: 3(1), or 3s 1 Na +, 11p e - ; outer shell: 2(8), or 2s 2 2p 6 Cl(17) 2, 8, 7 or 1s 2 2s 2 2p 6 3s 2 3p :Cl. + e - = :Cl: Cl, 17p e - ; valence shell: 3(7) or 3s 2 3p 5 Cl -, 17p e - ; outer shell: 3(8) or 3s 2 3p 6

Chapter 5. (L15)-Chemical Bonds Ions: Special forms of molecules or atoms, charged molecules or charged atoms.. Cations: The atoms or molecules with positive charges after they give up electrons Examples: H +, Na +, Ca 2+, Al 3+, NH 4 +..Anions: The atoms or molecules with negative charges after they gain electrons Examples: Cl -, S 2-, SO 4 2-, NO 3 -..Symbols and names for some simple (monatomic) ions: Textbook, pp.128, Table 5.2.

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules..Na reacts with Cl: Na: soft metal, highly reactive in air and water Cl 2 : greenish-yellow gas. Disinfectant for drinking water.... Na· + ·Cl: = Na + + :Cl: Na atom + Cl atom = sodium cation + chlorine anion Cl - is called chloride

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules..K reacts with Br: K(19), 2, 8, 8, 1, or 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Br(35), 2, 8, 18, 7, or 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p K· + ·Br: = K + + :Br: -.. K atom + Br atom = potessium cation + bromine anion Br - is called bromide

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules..Mg reacts with O: Mg(12), 2, 8, 2, or 1s 2 2s 2 2p 6 3s 2 O(8), 2, 6, or 1s 2 2s 2 2p ·Mg· + ·O· = Mg 2+ + :O: Mg atom + O atom = magnesium oxide

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules..K reacts with O: K(19), 2, 8, 8, 1 O(8), 2, 6,.... ·K + K· + ·O· = K + + K + + :O: K atom + O atom = potassium oxide

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules: Ionic bonds..In the previous reactions forming cations and anions, the ions carry opposite charges by cations and anions, and thus, the cations and anions are held together by strong electrostatic attraction. This electrostatic attraction between cations and anions to hold them together is called ionic bond. Ionic bonds are strong chemical bonding.

Chapter 5. (L15)-Chemical Bonds How atoms combine together to form molecules: Ionic bonds..Na + and Cl - form a crystal structure containing many octahedral units with each Na + cation surrounded by six Cl - anions and each Cl - anion surrounded by six Na + cations The NaCl crystal, see textbook, pp125, Fig. 5.2.

Chapter 5. (L15)-Chemical Bonds Ionic compounds or molecules..Names of simple cations: Atom name + ion Na + : sodium ion or sodium cation K + : potassium ion or potassium cation Mg 2+ : magnesium ion or magnesium cation..Names of simple anions: ending by –ide + ion Cl - : chloride Br - : bromide S 2- : sulfide..Binary (two-components) ionic bonding compounds or molecules: NaCl, MgCl 2, AlCl 3 Na 2 O, MgO, Al 2 O 3

Chapter 5. (L15)-Chemical Bonds Ionic compounds or molecules..How to write chemical formula for ionic compounds or molecules (binary ionic bonding compounds or molecules) Valence electron number and charges of ions Group 1A: 1+ (giving up 1 electron) Group 2A: 2+ (giving up 2 electron) Group 6A: 2- (gaining 2 electrons, = 8) Group 7A: 1- (gaining 1 electron, = 8) The rule of charge balance: The whole molecule has no charge, which means the overall charge of cations = overall charge of anion

Chapter 5. (L15)-Chemical Bonds Ionic compounds or molecules..How to write chemical formula binary ionic bonding compounds or molecules NaCl, Na + & Cl -, 1+ vs. 1-; total charge = 0 MgCl 2, Mg 2+ & Cl -, 2+ vs. 2- (=(1-)×2); total charge = 0 AlCl 3, Al 3+ & Cl -, 3+ vs. 3- (=(1-)×3); total charge = 0 Na 2 O, Na + & O 2-, ((1+)×2 =) 2+ vs. 2-;total charge = 0 MgO, Mg 2+ & O 2-, 2+ vs. 2-; total charge = 0 Al 2 O 3, Al 3+ & O 2-, ((3+)×2 =) 6+ vs. 6- (= (2-)×3); total charge = 0 Tip: Find out the charge for each cation and anion involved, then apply the rule below to decide the number of cation(s) and anion(s) for the molecule. Rule: Overall charge of the cation(s) = overall charge of anion(s), so the whole molecule has no net charge.

Chapter 5. (L15)-Chemical Bonds Quiz Time What are the numbers of valence electron for Na and Cl, respectively? Is it (a) 7 and 1; (b) 1 and 7; (c) 11 and 17; (d) 17 and 11. Tip: Write down the complete electron configuration for each atom first and then go from there to either remove electron(s) or add electron(s).

Chapter 5. (L15)-Chemical Bonds Quiz Time Which are the outer shell electron configurations for Mg and O after Mg gives up its valence electrons and O gains 2 electrons, respectively: (a) 2, or 2s 2 and 8, or 2s 2 2p 6 (b) 8, or 2s 2 2p 6 and 6, or 2s 2 2p 4 ; (c) 8, or 2s 2 2p 6 and 8, or 2s 2 2p 6 ; (d) 6, or 2s 2 2p 4 and 8, or 2s 2 2p 6. Tip: Write down the complete electron configuration for each atom first and then go from there to either remove electron(s) or add electron(s).

Chapter 5. (L15)-Chemical Bonds Quiz Time Which are the right dot-structures for O atom and O anion, respectively: (a) :O: and :O: - ; (b) :O. and :O: 2- ;... (c) :O: and :O: 2- ; (d) :O: and :O: -..

Chapter 5. (L15)-Chemical Bonds Quiz Time Why is Neon very stable? Is it because (a) its valence shell is not full; (b) it has no valence shell for its electrons; (c) its most outer shell (its valence shell in this case) is full, with 8 electrons, that is, the octet configuration; (d) its protons are very special.

Chapter 5. (L15)-Chemical Bonds Quiz Time The Octet Rule states that (a) a metal atom tends to gain electron(s) to achieve octet outer electron shell and a non-metal atom tends to give up electron(s) to achieve octet outer electron shell; (b) a metal atom tends to gain electron(s) to achieve non-octet outer electron shell and a non-metal atom tends to give up electron(s) to achieve non-octet outer electron shell; (c) a metal atom tends to give up electron(s) to achieve octet outer electron shell and a non-metal atom tends to gain electron(s) to achieve octet outer electron shell; (d) a metal atom tends to give up electron(s) to achieve non-octet outer electron shell and a non-metal atom tends to gain electron(s) to achieve octet non-outer electron shell.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which of the following are ions: (a) Cl 2 and CO 2 ; (b) Ar and Hg; (c) N 2 and Na; (d) Cl - and Fe 3+.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which of the following is an anion: (a) O 2 ; (b) Ag; (c) I - ; (d) Zn 2+.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which of the following is a cation: (a) F 2 ; (b) Pt; (c) F - ; (d) Ca 2+.

Chapter 5. (L15)-Chemical Bonds Quiz Time The ionic bond is (a) electrostatic attraction between anions; (b) electrostatic attraction between cations; (c) electrostatic repulsion between cations and anions; (d) electrostatic attraction between anions and cations.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which is the right molecular formula for the binary ionic molecule, sodium sulfide? Is it (a) NaS; (b) NaS 2 ; (c) Na 2 S; (d) NaCl.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which is the right molecular formula for the binary ionic molecule, calcium chloride? Is it (a) CaCl; (b) CaCl 2 ; (c) Ca 2 Cl; (d) Ca 2 Cl 3.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which is the right molecular formula for the binary ionic molecule, aluminum oxide? Is it (a) AlO; (b) AlO 2 ; (c) Al 2 O; (d) Al 2 O 3.

Chapter 5. (L15)-Chemical Bonds Quiz Time Which is the right molecular formula for the binary ionic molecule, calcium sulfide? Is it (a) CaS; (b) CaS 2 ; (c) Ca 2 S; (d) Ca 2 S 3.