Unit 4. Bonding and Nomenclature

Transcription

1 Unit 4 Bonding and Nomenclature

2 A. Vocabulary Chemical Bond attractive force between atoms or ions that binds them together as a unit bonds form in order to decrease potential energy (PE) increase stability

3 ** properties of individual elements differ from the compounds they form COMPOUND 2 elements more than 2 elements Binary Compound NaCl Ternary Compound NaNO 3

4 Name Symbol PHYSICAL STATE at room temp properties sodium Na solid 1) metal 2) silver-white 3) soft 4) reacts violently with H 2 O and O 2 chlorine Cl 2 gas 1) nonmetal 2) greenish 3) poisonous 4) stinging odor sodium chloride NaCl solid 1) white crystals 2) soluble in water 3) important to cells 4) stable

5 carbon + oxygen = carbon dioxide (CO 2 )

6 Noble Gases Noble gases are chemically inert (unreactive) because they have a full valence shell of 8 electrons

7 Octet Rule reactivity of atoms is based on achieving a complete octet of valence electrons(8/8) Everybody wants to be like a noble gas! Ne

8 atoms in compounds tend to have a stable Noble Gas configuration exceptions to the Octet Rule 1)atoms of transition metals 2)examples: Ag+, Cu+, Au+, Cd 2+, Hg 2+

9 Octet Rule Most atoms form bonds (compounds) in order to obtain 8 valence e - Bonds form when atoms collide and there is enough energy

10 Part I - Ionic Bonds

11 Types of Bonds Covalent bond = sharing e - Ionic bond = transfer of e -

12 Ionic Bonds Ionic Bonds occur between a metal and a nonmetal **** In chemistry A salt refers to any compound made from a metal + nonmetal It does not refer to the stuff you put on food!

13 Ionic Bonding Sodium is in Group 1, so it has 1 valence electron. Chlorine is in Group 17 (7A) and has 7 valence electrons.

14 Ionic Bonding the one valence electron of sodium is transferred to the chlorine atom, both chlorine and sodium become stable with an octet of electrons.

15 Ionic Bonding An ion is an atom or group of atoms that has a charge because of the loss or gain of electrons. A compound that is composed of ions is called an ionic compound.

16 Ionic Bonding sodium lost an e -, it now has an unbalanced proton in the nucleus and therefore has a positive (+) charge. Sodium is now a positive ion Positive ions are called CATIONS

17 Ionic Bonding Because the chlorine atom now has an extra e - it now has a negative charge. chlorine is now a negative ion negative ions are called ANIONS

18 Cations Positive, Anions Negative Cat People Are Nice

19 Ionic compounds 1+ Common Ion Charges aka oxidation number NA

20 GROUP # VALENCE # WHEN OXIDATION # FORMING IONS: Group IA 1 loses 1 e Group IIA 2 loses 2 e Group IIIA 3 loses 3 e Group IVA 4 can lose or gain Group VA 5 gains 3 e Group VIA 6 gains 2 e Group VIIA 7 gains 1 e Group VIIIA 8 does not form ions 0

21 Compounds must be neutral aluminum atom chlorine atom aluminum ion chloride ions (three chlorines are needed to balance the charges)

22 Ionic compound formulas A formula unit is the lowest ratio of ions in an ionic compound Aluminum forms ions with a +3 charge Al 3+ Chlorine forms ions with a -1 charge Cl - 3 chlorines are needed for every 1 aluminum The formula unit is: AlCl 3

23 Question 2 How many valence electrons must an atom have in its outer energy level in order to be considered stable? Answer The answer is 8.

24 Naming Binary Ionic compounds 1. Write each ion, cation first. 2. Change ending of anions to ide Chlorine atom becomes chloride ion

25 Naming Ionic compounds sodium bromide Na + Br - NaBr magnesium fluoride Mg +2 F - MgF 2

26 Naming ionic compounds potassium chloride K + Cl - KCl magnesium oxide Mg 2+ O -2 MgO

27 Naming ionic compounds with transition metals: copper (I) bromide Cu + Br - CuBr copper (II) chloride Cu 2+ Cl - CuCl 2 ****** many transition metals have more than one oxidation state. The roman numeral designates which ion is in the compound

28 NAMING IONIC COMPOUNDS CONTAINING POLYATOMIC IONS 1 atom 2 or more atoms Monatomic Polyatomic Ion Ion Na + NO 3 - Compounds that contain polyatomic ions have an -ate or -ite at the end of the compound name

29 Compounds With Polyatomic Write the cation first, then the polyatomic anion. Balance the charge by adding subscripts. Sodium Carbonate Na +1 CO 3-2 Na 2 CO 3 IONS If you need to add a subscript to balance a polyatomic ion, use parentheses around the ion and place the subscript outside. Calcium nitrate Ca +2 Nitrate NO 3-1 Ca (NO 3 ) 2

30 Examples Write the formula from the name. Write the name from the formula Iron III carbonate Fe +3 CO 3-2 Fe 2 (CO3) 3 FeSO 4 Sulfate has a -2 charge. Iron has no subscript. Iron II sulfate

31 Part II Covalent Bonds

32 Covalent Compounds covalent bond = sharing pairs of electrons. Notice that in a covalent bond, atoms share electrons and neither atom has a charge.

33 Covalent compounds occur between 2 or more NONMETALS in a water molecule the eight valence electrons (six from oxygen and one each from two hydrogens) are distributed among the three atoms.

34 Covalent Compounds A compound whose atoms are held together by covalent bonds is a covalent compound. Water is a covalent compound.

35 Covalent compound A molecule is an uncharged group of two or more atoms held together by covalent bonds.

36 Covalent Compounds The 7 diatomic (composed of two atoms) molecules H Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 N O F Cl Br I

37 single boron atom with three fluorines OR boron trifluoride

38 Multiple Covalent Bonds: double covalent bond sharing two pairs of electrons single O atom single O atom OR diatomic oxygen molecule

39 Multiple Covalent Bonds: B. triple covalent bond sharing three pairs of electrons 2 nitrogen atoms OR diatomic nitrogen molecule

40 Naming Covalent Compounds 1. Less electronegative atom comes first. 2. Use prefixes to indicate # of atoms. Omit mono- prefix on first element. 3. Change the ending of the second element to -ide.

41 Naming Covalent Compounds PREFIX monoditritetrapentahexaheptaoctanonadeca- NUMBER

42 Naming Covalent Compounds CCl 4 carbon tetrachloride N 2 O dinitrogen monoxide CO = carbon monoxide CO 2 = carbon dioxide SF 6 sulfur hexafluoride

43 Naming Covalent Compounds arsenic trichloride AsCl 3 dinitrogen pentoxide N 2 O 5 tetraphosphorus decoxide P 4 O 10

44 Properties of Ionic Compounds Ionic compounds are composed of wellorganized, tightly bound ions. These ions form a strong, threedimensional crystal structure.

45 Electrolytes Any compound that conducts electricity when melted or dissolved in water is an electrolyte. Ionic compounds are electrolytes.

46 Comparison of ionic and molecular compounds Covalent compounds Ionic compounds Particles molecules formula units Elements nonmetals metals & nonmetals Conductivity low nonelectrolytes high (when molten or in aqueous solution) electrolytes State at room temp. solid, liquid, or gas solid only Type of Bond covalent ionic Misc. also called salts

47 Part III Carbon & Other Bonds

48 there really is no clear-cut division between ionic and covalent compounds A compound may be partly covalent and partly ionic. A more realistic view of bonding is to consider that all chemical bonds involve a sharing of electrons

49 Electrons may be shared equally, but they also may be shared only slightly almost not at all. The properties of any compound, are related to how equally the electrons are shared.

50 Bonding is measured by differences in electronegativity three main classes of bonds ionic, polar covalent, and covalent.

51 Electronegativity is the measure of the ability of an atom in a bond to attract electrons. Increases UP and to the RIGHT

52 the farther the atoms are from each other on the periodic table, the greater their electro-negativity difference

53 purely ionic bond = complete transfer of electrons from one atom to another. o the electronegativity difference in a bond is 2.0 or greater purely covalent bond = electrons are shared equally. o difference in electronegativities is zero. polar covalent = (most compounds) somewhere in between the two extremes; have both ionic and covalent properties o Electronegativity difference is between 0.5 and 2.0

54 The greater the difference between the electronegativities of the bonding atoms, the more ionic the bond It is calculated by subtracting the smaller electronegativity from the larger, so EN is always positive For example, EN for cesium and fluorine is = 3.3.

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56 In a polar covalent bond, there is a partial transfer of the shared electrons to the more electronegative atom.

57 Because there was not a complete transfer of an electron, the charges on the poles are NOT 1+ and 1, BUT δ + and δ.

58 Which of the following covalent bonds is the most polar? a.) H F b.) H H c.) H C d.) H N

59 Metallic Bonds The valence electrons of metal atoms are loosely held by the positively charged nucleus In metallic bonding, metal atoms don't lose their valence electrons

60 Metal atoms release their valence electrons into a sea of electrons shared by all of the metal atoms. This is a metallic bond

61 Properties of Metallic Bonding Malleable - can be pounded or rolled into thin sheets Ductile - can be drawn into wires because electrons can move around so easily inside metals they can conduct electricity

62 Bonding in metals is not rigid. As a metal is struck by a hammer, the atoms slide through the electron sea to new positions while continuing to maintain their connections to each other.

63 INTERmolecular Forces The state of a substance (solid, liquid, gas) depends on it s intermolecular forces = attractions BETWEEN molecules (weaker than ionic or covalent bonds)

64 INTERmolecular Forces 1.Hydrogen bonds ***strongest 2.Van der Waals forces a.) dipole interactions b.) dispersion forces ***weakest

65 Hydrogen Bonding why does water form drops? a hydrogen atom of one molecule is attracted to the strongly electronegative atom (such as N, O, F) in a neighboring molecule

66 Van der Waals forces dipole interactions electrical attraction between oppositely charged regions of polar molecules

67 Van der Walls dispersion forces electron motion in one molecule affects the electron motion on another molecule strength increases as the # of electrons increases

68 VESPR Theory VESPR Theory the repulsion between electron pairs causes molecular shapes to adjust so that valence electron pairs stay as far apart as possible

69 What s so special about carbon? organic chemistry study of compounds that contain carbon it has four electrons in its outermost energy level it can form single, double, or triple bonds with other atoms. it readily bonds with other carbon atoms

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71 The end