CHAPTER 3. Chemical Foundations

Transcription

1 CHAPTER 3 Chemical Foundations

2 3.1 THE ELEMENTS 118 elements in 92 occur naturally, the rest are synthesized All matter in the universe can be chemically broken down into elements Compounds are made by combining atoms of elements like words are formed from letters of the alphabet. Words Compounds

3 ABUNDANCE OF ELEMENTS 9 elements make up about 98% of Earth

4 Elements of the human body: CHNOPS

5 THE WORD ELEMENT CAN HAVE SEVERAL MEANINGS Element Microscopic form Single atom of that element Element Macroscopic form Sample of that element large enough to weigh on a balance Element Generic form When we say the human body contains the element sodium or lithium, we do not mean that free elemental sodium or lithium is present. Rather we mean that atoms of these elements are present in some form.

6 NAME AND SYMBOLS FOR THE ELEMENTS Each element has a unique name and symbol Symbol usually consists of first one or two letters of elements name Oxygen = O Krypton = Kr Sometimes the symbol is taken from the original Latin or Greek name

7 FORMULAS OF COMPOUNDS The types of atoms and the number of each type is shown using chemical symbols and subscripts.

8 Write the formula for each of the following, listing the - elements in the order given One atom of sulfur and three atoms of oxygen Two atoms of nitrogen and five atoms of oxygen : 05

9 give the number of each atom in the following: Ca(NO 3 ) 2 Ca= I e N=2 0=6 AlPO 4 Ali I P=1 0=4 Al 2 (SO 4 ) 3 to 2H 2 O +1=4 0=2

10 3.2 EARLY IDEAS ABOUT MATTER Greek philosophers formed explanations based on life experiences Proposed four elements

11 DEMOCRITUS 400 BC Believed matter was made of tiny particles called atomos Cannot be created, destroyed, or divided Aristotle disagreed

12 ALCHEMY Origin of the word Chemistry Tried to make gold out of abundant elements Invented many of the techniques still used today like filtration and distillation

13 ANTOINE LAVOISIER French scientist known as the Father of Chemistry Made Chemistry quantitative by taking accurate measurements Wrote 1 st chemistry textbook Beheaded in 1794 for being funded by taxes

14 PROUST ( ) Proposed the Law of Constant Composition (1794): A given compound always contains the same proportion by mass of the elements of which it is composed.

15 JOHN DALTON (1803) Revived and Revised Democritus idea Came up with his own Atomic Theory All elements are composed of tiny particles called atoms which cannot be broken into smaller parts. # is False Cish ) All atoms of the same element are identical, atoms of different elements are different 2 -

16 3 Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms law of constant Comp. 4 Chemical reactions take place when atoms rearrange. Atoms are not created or destroyed during chemical reactions. Dalton 's Model of atom Solid sphere of matter

17 3.3 DEFINING THE ATOM The smallest particle of an element that retains the properties of the element Atoms are very small = One Cu atom = 1.28 x m Solid copper penny = 2.9 x atoms the earth! If 1 atom = size of an orange, an orange would be as big as m

18 x Scanning tunneling microscope (STM) allows individual atoms to be seen Scans across the surface of atoms silicon

19 J.J. THOMSON 1897 Worked with a cathode ray tube

20 Discovered cathode ray was attracted to positively charged plate

21 What 2 things did Thomson learn from this experiment?

22 By measuring the effects of both magnetic and electric fields on a cathode ray, Thomson determined the mass of the charged particle is less than the hydrogen atom (the lightest atom known). Why is this significant?

23 What subatomic particle did Thomson discover?

24 Thomson s model Matter is neutral so some positive charge needs to balance out the negative electrons Plum pudding model

25 ERNEST RUTHERFORD

26 In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil. Based on Thomson s model of the atom he expected the alpha particles to pass through the foil but not all did! ' # ±

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28 What conclusion can Rutherford draw from this result?

29 Rutherford concluded: Atom consists of mostly empty space If an atom had a diameter of 2 football fields the nucleus would be the size of a nickel Almost all + charge & mass are found in nucleus -

30 Rutherford Model of the atom

31 ATOMIC STRUCTURE Ernest Rutherford showed that atoms have internal structure. The nucleus, which is at the center of the atom, contains protons (positively charged) and neutrons (uncharged). Electrons move around the nucleus.

32 . JAMES CHADWICK What we knew 1. Electrons & Protons have opposite charges 2. Neutral atom has same number of electrons as protons 3. Mass of atom was too much to just be made of protons & electrons I

33 Showed nucleus contained a particle with the same mass as a proton but no charge neutron orbits = Bohr

34 Particle Symbol Location Charge Mass Electron Proton Neutron

35 The number of protons in an atom identifies it as a particular element Number of protons = atomic number Periodic table is organized in order of increasing atomic number

36 All atoms are electrically neutral therefore # of protons =

37 Determine the number of protons and electrons in an atom of Molybdenum

38 MASS NUMBER Mass number = protons + neutrons Neutrons = Mass numbers are given in atomic mass units (amu) 1 amu = 1/12 mass of Carbon-12 atom

39 ATOMIC SHORTHAND Beryllium- - -atomic number 4 mass number 9 The atomic number is written as a subscript. The mass number is written as a superscript. : Be I

40 Element Atomic Number Protons Electrons Neutrons Mass number

41 ISOTOPES Atoms with the same number of protons but different number of neutrons, and mass #

42 Most naturally occurring elements have two or more stable isotopes One is usually more common than the others Oxygen 16, oxygen 17, oxygen - 18 :%s#

43 mass number vs. atomic mass Mass number = protons + neutrons 1 whole # ) Atomic mass (on periodic table) = weighted average of all the isotopes of an element 1 decimal )

44 CALCULATING ATOMIC MASS

45 Unknown element X has two isotopes. 6 X has an atomic mass of amu and a 7.59 % abundance. 7 X has an atomic mass of amu and a 92.41% abundance. What is the atomic mass of the unknown element? What is the identity of the unknown element? oboi = ) any h. amlwthya$

46 IONS Atoms can form ions by gaining or losing electrons. Metals tend to lose one or more electrons to form positive ions called cations. My atom Mg ion Cations are generally named by using the name of the parent atom.

47 IONS Nonmetals tend to gain one or more electrons to form negative ions called anions. Chlorine atom Chloride ion Anions are named by using the root of the atom name followed by the suffix ide.

48 Element O 2- YO Atomic # 8 8 Protons Electrons Neutrons Mass number : Al B M - P Ptn Yakt C Potassium

49 Ion charges can be predicted from the periodic table

50 . WHAT CAN CHANGE IN AN ATOM? Protons NEVER!!! Neutrons if changed an isotope is formed Electrons if changed an ion is formed

51 PROTON CHANGED Whole new atom!!! Oxygen loses a proton it becomes Nitrogen Oxygen gains a proton it becomes Fluorine

52 NEUTRON CHANGED Different version of the same atom is formed (isotope) Oxygen 16 has 8 Neutrons Oxygen 17 has 9 Neutrons Oxygen 18 has 10 Neutrons

53 ELECTRONS CHANGED Charged version of the same atom is formed (ion) Oxygen gains 2 electrons 10 electrons & 8 protons Anion Oxygen loses 2 electrons 6 electrons & 8 protons Cation

54 COMPOUNDS THAT CONTAIN IONS Ions combine to form ionic compounds. Properties of ionic compounds High melting points Conduct electricity If melted au t# If dissolved in water

55 Ionic compounds are electrically neutral Total positive charge must cancel out total negative charge Nat Cl - = Nau

56 FORMULAS FOR IONIC COMPOUNDS Write cation symbol followed by anion symbol The number of cations and ions must be correct so their charge sums to zero

57 ' Write the formula for compounds containing the following ions: Potassium and oxygen kt 02 - = K2O Calcium and sulfur cast 5 : Ca Magnesium and nitrogen Mg2t N3 : 6 = My } - 6=0 Nd

58 3.4 INTRODUCTION TO THE PERIODIC TABLE In 1913 our current periodic table was developed by Henry Moseley who arranged the atoms by atomic number Periodic law when elements are arranged according to increasing atomic number, there is a periodic repetition of chemical and physical properties

59 THE MODERN PERIODIC TABLE / Columns = groups families Numbered 1 18 Correspond to the number of outermost electrons Have similar properties Some have special names Rows = periods Numbered 1 7 Correspond to outermost energy level 1 valence electrons )

60 PHYSICAL STATES AND CLASSES OF ELEMENTS Most elements are solid at room temperature Br & Hg are liquid N, O, F, Cl, and Noble gases are gas t.it

61 METALS Shiny Solid at room temperature Good conductors of heat & electricity Malleable } bent Ductile Found to the left of the staircase 1 exception = H 's, shaped

62 . Alkali metals group 1 elements Except for H Very reactive # of valence electrons = I ( +1 ion )

63 Alkaline earth metals group 2 elements Also highly reactive # of valence electrons = 2 ltd ion )

64 Transition metals group 3 12 (d block) to Number of valence electrons varies

65 Inner transition metals f block Number of valence electrons varies Lanthanide E& actinide series

66 NONMETALS Gasses or dull looking solids 1 exception = Br is liquid Poor conductors of heat and electricity Found to the right of the staircase

67 Halogens group 17 Highly reactive # of valence electrons = 7 1- lion )

68 Nobel gases group 18 Extremely unreactive # of valence electrons = 8 ( no ion )

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70 METALLOIDS Border the staircase Have properties of both metals and nonmetals Semi-conductors = conduct electricity only under certain conditions exception = Al is a metal

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72 NATURAL STATES OF THE ELEMENTS Most elements are very reactive. Elements are not generally found in uncombined form. Exceptions are: Noble metals gold, platinum and silver Noble gases Group 8 µ 18

73 NATURAL STATES OF THE ELEMENTS Diatomic Molecules Nitrogen gas contains N 2 molecules. Oxygen gas contains O 2 molecules.

74 NATURAL STATES OF THE ELEMENTS Diatomic Molecules

75 NATURAL STATES OF THE ELEMENTS Elemental Solids Carbon atoms Diamond Graphite Buckminsterfullerene