Compounds Chapter 2 1

Transcription

1 Compounds Chapter 2 1

2 Types of Matter Homogeneous matter has the same appearance, composition, and properties throughout. Heterogeneous matter has visibly different phases which can be seen, or properties that vary through the substance. 2

3 Classification of Matter 3

4 Classification of Matter A mixture is two or more pure substances that can be separated by physical changes or method. Pure substances have a distinct set of physical and chemical properties and cannot be separated by physical changes. 4

5 Pure Substance A compound is a pure substance that can be decomposed by a chemical change or method into two or more elements. Two or more elements together. An element is a pure substance with its own set of physical and chemical properties that cannot be decomposed into simpler substances. Simplest form of matter. (Chapter One) 5

6 Classify Water Aluminum foil Air Oxygen Cake 6

7 What is in your coffee? Why do we drink coffee? How does it work? The active ingredient caffeine interferes with biochemical reactions in the body. 7

8 How does coffee work? The activity releases adrenaline; which activates the release of dopamine 8

9 Why do Atoms Combine? To mimic or acquire the stability of the noble gases. Stability is due to number of valence electrons noble gases contain. Atoms of elements will accept or give away electrons to become more stable. 9

10 Reactivity of Elements What will elements do to have the same number of electrons as the noble gases? What will Sodium do? (b) (c) 11p + 11 e- Na Na + + e - 11p + 10 e- 10

11 Reactivity of Elements What will potassium do? Argon has 18 e - 19 p + 19 e- -1e - 19 p + 18 e - Potassium Atom Potassium Ion (K + ) In general: Cation M 1A M 1A e - 11

12 Formation of Ions What about Magnesium? What s the closest noble gas to magnesium? Neon has 10 e - 12 p + 12 e- -2e - 12 p + 10 e- Magnesium Atom Magnesium Ion (Mg +2 ) Cation M 2A M 2A e - 12

13 Where do the electrons go? Must find an element that might need some extra electrons. What will bromine do? Who s the closest noble gas? Krypton has 36 e - 35 p + 35 e- + 1e - 35 p + 36 e- Bromine Atom X 7A + 1e - X 7A -1 Bromide Ion (Br - ) Anion 13

14 Formation of Monatomic Ions Group 1A-3A Metals Group 5A-7A Nonmetals Na Na e - N + 3 e - N 3- Ca Ca e - S + 2 e - S 2- Al Al e - F + e - F - Cations Anions Lose or give away electrons Cation + Anion = Ionic Compound Accept electrons 14

15 Ionic Compounds Form when electrons are transferred from one element to the other. Metals give away electrons and become cations Nonmetals accept electrons from metals 15

16 To write the formula of the ionic compound first predict the charge of each element and then write the neutral formula. Positive has to cancel negative. Practice the following: a) Ions that come from elements sodium and fluorine b) Ions that come from elements calcium and bromine c) Ions that come from elements magnesium and nitrogen 16

17 Naming Ionic Compounds Write the name of the cation (metal ion). The name of a cation is the same as the metal name. Write the name of the anion (nonmetal ion) by changing the ending of the element name to ide. Ca 2+ = calcium ion S 2- = sulfide ion Name the previous exercise 17

18 Transition Metals As metals they give away electrons. They give away a variable number of electrons from: 1e - to 7e - For most transition metals the highest number of electrons corresponds to the roman numeral in the column. Most common charges are +2 and +3. Get the charge of the metal from the anion to which it s combine. 18

19 Exceptions to the Variable Charges Three exceptions: Ag gives away 1e - to form Ag + Zn gives away 2e - to form Zn +2 Cd gives away 2e - to form Cd +2 19

20 Predict the Correct Chemical Formula for: Co +3 and sulfide A) CoS b) Co 2 S c) Co 3 S 2 d) Co 2 S 3 Cadmium and iodide A) CdI b) CdI 2 c) Cd 2 I c) Cd 2 I 3 20

21 Naming Ionic Compounds of Transition Metals Add the charge of the metal as a Roman numeral in parenthesis. cobalt (II) fluoride. What is the name of FeCl 2 Mn 2 O 3 a) Magnesium (II) oxide b) manganese (II) oxide c) Manganese (III) oxide d) manganese oxide 21

22 Polyatomic Ions Group of elements that together have a charge. 22

23 A few more polyatomic ions Group of elements that together have a charge. ClO 4 - Perchlorate One more O: Charge is the same ClO 3 - Chlorate Parent polyatomic ion (looks like Nitrate) ClO 2 - Chlorite One less O: Charge is the same ClO - or OCl - ---> Hypochlorite One less O: Charge is the same 23

24 What s the Chemical Formula? Boron hydroxide Palladium (IV) hypochlorite Ammonium sulfite 24

25 From Formulas to Names Fe 2 (SO 4 ) 3 a. iron (II) sulfate b. iron (III) sulfite c) iron sulfate d. iron (III) sulfate Pb(NO 3 ) 4 25

26 Properties of Ionic Compounds Solids at Room Temperature High Melting and Boiling Point When dissolved in water the solutions are conductors of electricity. Strongest type of intermolecular force: ion-ion 26

27 Sharing of Electrons 27

28 Lewis Dot Structures Valence electrons are represented as dots around the symbol of an element. Electrons are not paired unless necessary Noble gases have eight valence electrons in their outer shell or energy level. 28

29 The Octet Rule Atoms want to have eight electrons in the outer shell, as the stable noble gases. Atoms may gain, lose or share electrons to obtain eight electrons in the outer shell. Hydrogen and helium can hold only two electrons in their outer shell. What is the Lewis structure of fluoride? 29

30 Covalent Compounds Share electrons to complete their octet. Formed by nonmetals interacting or attracted to other nonmetals. The bond forms by overlap of electron clouds. Represented as a tug-of-war or holding hands. Simplest representation is a molecule 30

31 Covalent Compounds H + H F + F O + O Reason for the existence of diatomic elements 31

32 Covalent Bonds Single Covalent Bond - Sharing of two electrons between two atoms. Double Bond Sharing of four electrons between two atoms. Triple Bond Sharing of six electrons between two atoms. 32

33 Number of Covalent Bonds Formed by Nonmetal Atoms Lewis Dot Structure Number of Bonds: Lone Pair or Nonbonding Electrons not used in bond 33

34 Naming Covalent Compounds Opposite to ionic compounds nonmetals combine to other nonmetals in different proportions. CO vs. CO 2 carbon monoxide vs. carbon dioxide We need prefixes to indicate how many. 34

35 Naming Covalent Compounds 1 mono 6 hexa 2 di 7 hepta 3 tri 8 octa 4 tetra 9 nona 5 penta 10 deca Only for covalent compounds 35

36 Let s Try It! Name each binary molecule a) BF 3 b) SCl 6 c) CoI 2 d) P 2 O 5 36

37 Lewis Structure What molecules look like in Three-Dimensions

38 Lewis Structure Drawings Calculate total number of valence electrons. Connect all atoms to the central atom with single bonds. Subtract valence electrons used (2e - /bond) Complete the octet of outside atoms using lone pairs. If left over electrons available, give to central atom. Check that central atom has a complete octet. If less than eight electrons, take two electrons from outside atom and form a double bond.

39 Lewis Structure SO 2 SO 3-2 PCl 5

40 Formal Charges For each atom F. C. = Column # - (# dots + # bonds) Expanded octet Larger atoms in period 3 or below can accommodate more than 8 e -

41 Lewis Structure SO 3-2 PCl 5

42 GRAMS AND MOLES

43 Mass of Chemical Compounds Formula or Molecular Weight is the sum of the atomic mass of the elements in the formula. Sodium chloride (NaCl) has a formula weight of 58.5 amu Na + Cl - NaCl amu amu amu amu = atomic mass unit is the mass of an atom 43

44 Avogadro s Number of Molecules 1 molecule is at microscopic level 1 mole is at macroscopic level 1 mole = 6.02 x atoms or molecules 1 mole is the most important unit of measurement for chemists because the relation exist within chemical formulas or chemical equations. 44

45 Molar Mass The mass (in grams) of one mole (6.02 x10 23 ) of substance. Molar mass can be used to convert between the number of moles of a particular compound and its mass. 6.02x10 23 Atoms or Molecules 1 mole Molar Mass in grams What is the molar mass of silver nitrate? 45

46 How many moles of silver nitrate are used if 85.7 grams are used in an experiment? A) mol b) 1.98 mol c) mol d) mol How many molecules of silver nitrate are in the above question? 46

47 Practice What is the mass of moles of sodium bicarbonate? How many moles of sodium bicarbonate are in g of it? a) 2061 mol b) mol c) mol d) 1 mol How many molecules of sodium bicarbonate are contained in 24.54g? 47

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