atoms, molecules,and ions

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ATOMS, MOLECULES,AND IONS ABOUT A CENTURY LATER, AN ENGLISH PHYSICIST, J.J.THOMSON 1856 – 1940) PROVIDED THE CLUE FROM HIS EXPERIMENTS USING CATHODE X-RAY TUBES. DALTON’S ATOMIC THEORY. (1766 – 1844) - ELEMENTS ARE MADE OF TINY PARTICLES CALLED ATOMS. - EACH ELEMENT IS CHARACTERIZED BY THE MASS OF ITS ATOM. ATOM OF THE SAME ELEMENT HAVE THE SAME MASS, BUT ATOM OF DIFFERENT ELEMENTS HAVE DIFFERENT MASS. - CHEMICAL COMBINATION OF ELEMENTS TO MAKE DIFFERENT SUBSTANCES OCCURS WHEN ATOMS JOIN TOGETHER IN SMALL, WHOLE- NUMBER RATIO. - CHEMICAL REACTIONS ONLY REARRANGE THE WAY THAT ATOMS ARE COMBINED; THE ATOM ITS SELT ARE NOT CHANGED HOWEVER, THE DALTON’S THEORY COULD NOT EXPLAIN THE QUESTION : WHAT IS THE ATOM MADE OF?

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Page 1: Atoms, Molecules,And Ions

ATOMS, MOLECULES,AND IONS

ABOUT A CENTURY LATER, AN ENGLISH PHYSICIST, J.J.THOMSON 1856 – 1940) PROVIDED THE CLUE FROM HIS EXPERIMENTS USING CATHODE X-RAY TUBES.

DALTON’S ATOMIC THEORY. (1766 – 1844)- ELEMENTS ARE MADE OF TINY PARTICLES CALLED ATOMS.- EACH ELEMENT IS CHARACTERIZED BY THE MASS OF ITS ATOM. ATOM OF THE SAME ELEMENT HAVE THE SAME MASS, BUT ATOM OF DIFFERENT ELEMENTS HAVE DIFFERENT MASS.- CHEMICAL COMBINATION OF ELEMENTS TO MAKE DIFFERENT SUBSTANCES OCCURS WHEN ATOMS JOIN TOGETHER IN SMALL, WHOLE- NUMBER RATIO.- CHEMICAL REACTIONS ONLY REARRANGE THE WAY THAT ATOMS ARE COMBINED; THE ATOM ITS SELT ARE NOT CHANGED

HOWEVER, THE DALTON’S THEORY COULD NOT EXPLAIN THE QUESTION : WHAT IS THE ATOM MADE OF?

Page 2: Atoms, Molecules,And Ions

THOMSON’S CATHODE X-RAY TUBE

WHEN A SUFFICIENT HIGH VOLTAGE IS APPLIED ACROSS THE ELECTRODES, AN ELECTRIC CURRENT FLOWS THROUGH THE TUBE FROM CATHODE TO ANODE, AND A GLOW IS VISIBLE (CATHODE RAY)THIS CATHODE RAY CAN BE DEFLECTED BY EITHER MAGNETIC FIELD OR ELECTRIC FIELDTHOMSON PROPOSED THAT THE CATHODE RAYS MUST CONSIST OF TINY NEGATIVELY CHARGED PARTICLES, WHICH IS NOW KNOWN AS ELECTRON. THOMSON WAS ABLE TO CALCULATE THE CHARGE TO MASS RATIO OF THE ELECTRON.

Page 3: Atoms, Molecules,And Ions

THE CHARGE OF ELECTRON WAS MEASURED BY MILLIKAN BY OIL DROP EXPERIMENT : 1.602 176 X 1019 C. (C = COULOMB).

THE MASS OF ELECTRON IS 9.109 382 X 10-28 g

SINCE A MOLECULE MUST BE NEUTRAL ELECTRICALLY, THERE MUST ALSO BE POSITIVELY CHARGED PARTICLES IN THE SAME ATOM.

RUTHERFORD EXPLAINED HIS EXPERIMENT RESULTS THAT A METAL ATOM MUST BE ALMOST ENTIRELY EMPTY SPACE, AND HAVE ITS MASS CONCENTRARED IN A TINY CENTRAL CORE THAT WAS CALLED NUCLEUS.

FURTHER EXPERIMENTS HE SHOWED THAT A NUCLEUS IS COMPOSED OF TWO KINDS OF PARTICLES CALLED PROTONS AND NEUTRONS

Page 4: Atoms, Molecules,And Ions
Page 5: Atoms, Molecules,And Ions

+PROTONS ELECTRONS

-

NEUTRONNUCLEUS

A COMPARISON OF SUBATOMIC PARTICLES

mass chargeParticles grams amu coulombs e

Electron 9.109 382 x 10-28 5.485 799 x 10-4 - 1.602 176 x 10-19 -1Proton 1.672 622 x 10-24 1.007 276 + 1.602 176 x 1019 +1Neutron 1.674 927 x 10-24 1.008 665 0 0

ATOMIC NUMBER.ELEMENTS DIFFER FROM ONE ANOTHER ACCORDING TO THE NUMBER OF PROTONS IN THEIR ATOMS ( CALLED ATOMIC NUMBER, Z).

ATOM :CONSIST OF ELECTRONS, PROTONS AND NEUTRONS

MASS NUMBER (A) = NUMBER OF PROTON (Z) + NUMBER OF NEUTRONS (N)

Page 6: Atoms, Molecules,And Ions

ISOTOPES

INFACT, THAT IN DIFFERENT ATOM OF THE SAME ELEMENT CAN HAVE DIFFERENT MASS NUMBERS. IT DEPEND ON HOW MANY NEUTRON THEY HAVE.

ATOM WITH IDENTICAL ATOMIC NUMBER, BUT DIFFERENT MASS NUMBER ARE CALLED ISOTOPES.

HIDROGEN FOR EXAMPLE HAS 3 ISOTOPES. ( H, D, T).

+ + +

PROTIUM (H)1 PROTONNO NEUTRONMASS NUMBER = 1

DEUTERIUM (D)1 PROTON1 NEUTRONMASS NUMBER =2

TRITIUM (T)1 PROTON2 NEUTRONMASS NUMBER = 3

- --

Page 7: Atoms, Molecules,And Ions

FOR A GIVEN ISOTOPE, IT IS REPRESENTED BY SHOWING ITS ELEMENT SYMBOL WITH ITS MASS AS A LEFT SUPERSCRIPT AND A MASS NUMBER AS LEFT SUBSCRIPT.

H = H1

1 H = D2

1H = T3

1

C12

6

SYMBOL OF ELEMENT

MASS NUMBER

ATOMIC NUMBER

C13

6CARBON HAS AN ISOTOPE

IT HAS 6 PROTONS AND 7 NEUTRONS IN ITS NUCLEUS

Page 8: Atoms, Molecules,And Ions

ATOMS ARE SO TINY THAT IT IS NOT CONVINIENT TO USE gram AS A UNIT MASS. CHEMIST USE A UNIT FOR AN ATOM IS ATOMIS MASS UNIT (amu), OR dalton (Da).

ATOMIC MASS

1 amu IS EXACTLY 1/12 OF THE MASS OF A CARBON 12 AND EQUAL TO 1.660 539 X 10-24 g.

THE MASS OF NEUTRON IS ALMOST EXACTLY THE SAME AS PROTON.

WHAT IS THE MASS OF CARBON?CARBON ACCURS NATURALLY AS A MIXTURE OF CARBON 12 (NATURAL ABUNDANCE 98.89%) AND CARBON 13 (1,11%).

ATOMIC MASS OF C = (FRACTION OF 12C) (MASS OF 12C) + (FRACTION OF 13C) (MASS OF 13C)

= 0.889 X 12 amu + 0.0111 X 13.0034 amu = 11.867 amu + 0.144 amu = 12.011 amu.

THIS NUMBER IS THE AVERAGE MASS OF THE CARBON.THERE IS ANOTHER ISOTOPE OF C, ei. 14C, BUT ITS ABUNDANCE IS TOO SMALL THAT CAN BE IGNORED IN CALCULATING MASS NUMBER.

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COMPOUNDS AND MIXTURES

ALL THE MANY KINDS OF MATTER CAN BE CLASSIFIED AS EITHER PURE SUBSTANCES OR MIXTURES. PURE SUBSTANCES CAN BE ELEMENTS OR CHEMICAL COMPOUNDS, WHILE MIXTURES CAN BE HETEROGENEOUS OR HOMOGENEOUS.

MATTER

MIXTURE PURE SUBSTANCES

HETEROGENEOUS HOMOGENEOUS ELEMENTS CHEMICAL COMPOUNDS

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CHEMICAL COMPOUNDS : A PURE SUBSTENCE FORMED BY A COMBINATION OF TWO OR MORE DIFFERENT ELEMENTS, BY A CHEMICAL REACTION. THE PROPERTIES OF THE COMPOUNDS ARE DIFFERENT FROM THE PROPERTIES THEIR CONSTITUENT ELEMENTS.

A COMPOUND IS WRITTEN BY ITS CHEMICAL FORMULA, AND THE CHEMICAL REACTION IS WRITTEN WITH A STANDARD FORMAT CALLED A CHEMICAL REACTION.

O2 + 2 H2 2 H2O

Page 11: Atoms, Molecules,And Ions

MIXTURES ARE FORMED IF TWO OR MORE SUBSTANCES ARE ADDED TOGETHER IN RANDOM PROPORTION WITHOUT CHEMICALLY CHANGING THE INDIVIDUAL SUBSTANCE IN THE MIXTURES.

HETEROGENEOUS MIXTURES : WHEN THE MIXING OF TWO OR MORE MATTERS IS NOT UNIFORM, AND HAVE REGION OF DIFFERENT COMPOSITION.FOR EXAMPLE: SAND AND SUGAR, WATER AND GASOLINE ETC.

HOMOGENEOUS MIXTURE : WHEN THE MIXING IS UNIFORM, AND HAVE A CONSTANT COMPOSITION THROUGH OUT.FOR EXAMPLE : AIR IS A GASEOUS MIXTURE OF O2 AND N2; SEA WATER IS A LIQUID MIXTURE OF NaCl, BRASS IS A SOLID MIXTURE OF Cu AND Zn.

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MOLECULES, IONS AND CHEMICAL BONDS

THE CHEMICAL REACTION OCCURS WHEN ATOMS OR MOLECULES COLLIDE ONE TO ANOTHER TO FORM A COMPOUND.IN A COMPOUND, ATOMS ARE JOINED TOGETHER BY A CHEMICAL BOND

THERE ARE THREE KINDS OF CHEMICAL BONDS : COVALENT BONDS, IONIC BONDS AND METALLIC BONDS.

COVALENT BOND : FORMED AS A RESULT OF SHARING TWO ELECTRONS BETWEEN TWO ATOMS. THE UNIT OF MATTER THAT RESULTS WHEN TWO OR MORE ATOMS ARE JOINED TOGETHER BY COVALENT BOND IS CALLED A MOLECULE.

FOR EXAMPLES: H2O ; NH3 ; HCl ETC.SOME MOLECULES EXIS AS A COMBINATION OF TWO ELEMENTS OF THE SAME KIND SUCH AS H2, Cl2, Br2, I2. (DIATOMIC MOLECULES)

IONIC BOND : FORM AS A RESULTS OF A TRANSFER OF ONE OR MORE ELECTRONS FROM ONE ATOM TO ANOTHER

Na + Cl Na+ + Cl-

Page 13: Atoms, Molecules,And Ions

ACIDS AND BASES

AMONG THE MANY IONS, TWO OF THE MOST IMPORTANT ARE THE HYDROGEN CATION (H+) AND THE HYDROXIDE ANION (OH-). THESE IONS ARE FUNDAMENTAL TO THE CONCEPT OF ACID AND BASE.

ACID IS A SUBSTANCE THAT PROVIDE H+ ION IN WATER (HCl, HNO3, H2SO4, H3PO4.

BASE IS A SUBSTANCE THAT PROVIDE OH- ION IN WATER (NaOH, KOH, Ba(OH)2.

WHEN ANY OF THE ACIDS OR BASES DISSOLVED IN WATER, THE ACID WILL PROVIDE H+, AND BASES PROVIDE OH-.

HCl(g) H+(aq) + Cl- (aq)HNO3 (l) H+ (aq) + NO3

-(aq)H2SO4(l) H+(aq) + SO4

=2-(aq)H3PO4(aq) H+(aq) + PO4

3-(aq)

DISSOLVE IN H2O

DISSOLVE IN H2O

DISSOLVE IN H2O

NaOH(s) Na+(aq) + OH-

KOH(s) K+ (aq) + OH-

Ba(OH)2(s) Ba2+(aq) + OH-

DISSOLVE IN H2O

DISSOLVE IN H2O

DISSOLVE IN H2O

Page 14: Atoms, Molecules,And Ions

NAMING CHEMICAL COMPOUNDS

BINARY IONIC COMPOUNDS.ARE NAMED BY IDENTIFYING FIRST THE POSITIVE ION AND THEN THE NEGATIVE ION. THE POSITIVE ION TAKE THE SAME NAME AS THE ELEMENT AND THE NEGATIVE ION TAKE THE FIRST PART OF ITS ELEMENT’S NAME AND THEN ADDS THE ENDING –IDE.Eg. KBr = POTASSIUM BROMIDE LiF = LITHIUM FLUORIDE CaBr2 = CALCIUM BROMIDE AlCl3 = ALUMINIUM CHLORIDE

METALS TEND TO FORM POSITIVE IONS (CATIONS) AND NON-METALS TEND TO FORM NEGATIVE IONS (ANIONS.

ELEMENTS WITHIN A GIVEN GROUP OF THE PERIODIC TABLE FORM SIMILAR KINDS OF IONS, AND THE CHARGE OF THE IONS DEPEND OF THE GROUP NUMBER.

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MAIN GROUP CATIONS AND ANIONS.

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COMMON TRANSITION METAL IONS. ONLY IONS THAT EXIST IN AQUEOUS SOLUTION ARE SHOWN

Iron can form two different cations, the doubly charged Fe2+ ion and the triply charged Fe3+ion. To distinguish them, use the Roman numeral in parentheses to indicate the number of charge.For example:

Fe2+ Fe3+ Sn2+ Sn4+

Iron(II) ion Iron(III) ion Tin(II) ion Tin(IV) ionFerrous ion Ferric ion Stannous ion Stannic ion

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NAMING BINARY MOLECULAR COMPOUNDS

THEY ARE NAMED BY ASSUMING THAT ONE OF THE TWO ELEMENTS IN THE MOLECULE IS MORE CATIONLIKE AND THE OTHER IS MORE ANIONLIKE. THE CATIONLIKE ELEMENT TAKES THE NAME OF THE ELEMENT IT SELF AND THE ANIONLIKE ELEMENT TAKE THE -IDE ENDING.

HF = HYDROGEN FLUORIDE ; NaCl = SODIUM CHLORIDE

NON-METALS OFTEN COMBINE IN DIFFERENT PROPORTION TO FORM DIFFERENT COMPOUNDS. IN THIS CASE, NUMERICAL PERFIXES ARE USUALLY INCLUDED IN THE NAMES OF BINARY MOLECULAR COMPOUNDS.

CO : CARBON MONOXIDE (NOT CARBON MONOOXIDE) (NOTE: AVOID HAVING TWO VOWEL AT ONE TIME TOGETHER)

CO2 : CARBON DIOXIDESF4 : SULFUR TETRAFLUORIDEN2O4 : DINITROGEN TETROXIDE

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NAMING COMPOUNDS WITH POLYATOMIC IONS

POLYATOMIC IONS ARE NAMED IN THE SAME WAY AS BINARY IONIC COMPOUNDS :1ST IDENTIFY THE CATION, THEN THE ANION.

Eg. Ba(NO3)2. THE CATION IS BARIUM (Ba2+) AND THE ANION IS A POLYATOMIC ANION, NITRATE (NO3

-). THEN Ba(NO3)2 IS NAMED BARIUM NITRATE.

BUT THERE IS NO SYSTEMATIC WAY OF NAMING THE POLYATOMIC ANION, SO IT IS NECESSARY TO MEMORIZE THE NAMES, FORMULA, AND CHARGE OF MOST COMMON IONS AS LISTED BELOW.

Page 20: Atoms, Molecules,And Ions

SOME COMMON POLYATOMIC IONS

When there are more than two oxoanions in the series, the prefixe hypo is used for the anion with less oxygen, and prefix per for the anion with more oxygen.ClO- Hypochlorite : less oxygen then chlorideClO2

- ChloriteClO3

- ChlotareClO4

- Perchlorate : more oxygen then chlorate

Page 21: Atoms, Molecules,And Ions

Some pair of ions are related by the presence or the absence of a hydrogen. The ion that has additional H sometimes reffered to using the prefix bi-

HCO3- Hydrogen carbonate (bicarbonate) ion. CO3

2- Carbonate ion.HSO4

- Hydrogen sulfate (bisulfate) ion. SO42- Sulfate ion

NAMING ACIDS.Most acids are oxoacids, that is, contain oxygen in addition to hydrogen and another element.

The names of oxoacids are related to the names of the corresponding oxoanions as described previously, with –ite or -ate ending of the anion name replace by –ous or -ic acid.

For example. HNO2 Nitrous acids

HNO3 Nitric acid

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ASSIGNMENT 2.

1. What is the different between an atom atomic number and its mass number?2. Based on the law of multiple proportion, how many g of hydrogen would you expect 2.34 g of nitrogen to combine with to yield ammonia, NH3? To yield hidrazine, N2H4?3. Identify these elements. how many p, n and e in each atom?

4. Naturally accurring boron consist of two isotopes: 10B (19.9%) with an isotopic mass of 10.0129 amu and 11B (80.1%) with an isotopic mass of 11.00931 amu. What is the atomic mass of boron?5 write the formulas of the following compounds. a. aluminium hydride b. Tin(II) bromide c. calcium acetate d. barium chloride e. Mercury(II) perchlorate

6. Tellurium, a group 6A element, forms the oxoanions TeO42- and

TeO32-. What are the likely names of these ions? To what other group

6A oxoanions are they analogous?

X12

X28

24 58 X80

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