Aula #03

Dalton’s Atomic Theory

2

8 X2Y16 X 8 Y+Proportion /relation between matter

atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherford’s Model of the Atom

What made by Rutherford and his

assistants Geiger and Marsden is perhaps one of the most important experiments of nuclear physics.

1. atoms positive charge is concentrated in the nucleus

2. proton (p) has opposite (+) charge of electron (-)

3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

particle velocity ~ 1.4 x 107 m/s(~5% speed of light)

(1908 Nobel Prize in Chemistry)

Alfa -particlehelium-4 nucleus

- Neutron, n - Protons, He2+

- Electrons, e

Atomic number, Mass number and Isotopes

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

Isotopes are atoms of the same element (X) with

different numbers of neutrons in their nuclei

XA

Z

H1

1H (D)

2

1H (T)

3

1

U235

92U238

92

Mass Number

Atomic NumberElement Symbol

Isotopes are atoms of the same element (X)

with different numbers of neutrons in their nuclei

XA

Z

Mass Number

Atomic NumberElement Symbol

U235

92

92 protons, 92 electrons

143 (235 - 92) neutrons,

Atomic number, Mass number and Isotopes

Mass Relationships in Chemical Reactions

Atomic/Nano/Micro Worldatoms & molecules

Macro WorldGrams; tons

The mole (mol) is the amount of a substance that contains as many elementary entities as there

6.022140857 × 1023

are atoms in exactly 12.00 grams of 12C

Avogadro’s number (NA) 6.022 140 76 × 1023

Mass Relationships in Chemical Reactions

The mole (mol) is the amount of a substance that contains as many elementary entities as 6.022 140 76 × 1023

there are atoms in exactly 12.00 grams of 12C …IUPAC 2018

http://physics.nist.gov/cgi-bin/cuu/Value?na

Lorenzo Romano Amedeo Carlo Avogadro

On this scale

1H = 1.008 amu

16O = 16.00 amu

Atomic mass is the mass of an atom in atomic mass units (amu)

Natural abundance of lithium:

6Li (6.015 amu) 7.42%

7Li (7.016 amu) 92.58%

Average atomic mass of lithium:

7.42 x 6.015 + 92.58 x 7.016

100= 6.941 amu

Li

Average atomic mass (6.941)

= 6.941 amu

Li

Mass Relationships in Chemical Reactions

Atomic/Nano/Micro Worldatoms & molecules

Macro WorldGrams; tons

Avogadro’s number (NA) 6.022140857 × 1023 mol-1

1 mole (mol) Li MW=6.941 g/mol 6.941 gram

1 mole (mol) C MW=12.0107 g/mol 12.0107 gram

Mass Relationships in Chemical Reactions

Carbon 12.0107 gSulfur 32.065 gMercury 200.59 gCopper 63.546 gIron 55.845 g

One Mole of:

Mass Relationships in Chemical Reactions

6x (12.0107) + 12x(1.00794) + 6x(15.9994)

180.1559 gmol-1

Mass Relationships in Chemical Reactions

How many molecules are in 5.0 g of Saccharose ?

342.2965 gmol-1

Formula: C12H22O11

Molar mass: 342.2965 g/mol

5.0 g

Avogadro’s number (NA)

x 6.022140857 × 1023 mol-1

mol

= 12 x 8.8 × 1021 atoms of C

= 8.8 × 1021 molecules of Saccharose

= 22 x 8.8 × 1021 atoms of H

= 11 x 8.8 × 1021 atoms of O

Mass Relationships in Chemical Reactions

5.0 g of Saccharose ?

Formula: C12H22O11

Molar mass: 342.2965 g/mol

Avogadro’s number (NA)

6.022140857 × 1023 mol-1

20 milhões x 20 milhões x 20 milhões

= 8.8 × 1021 molecules of Saccharose

Mass Relationships in Chemical Reactions

Mass Relationships in Chemical Reactions

%C =2 x (12.01 g)

46.07 gx 100% = 52.14%

%H =6 x (1.008 g)

46.07 gx 100% = 13.13%

%O =1 x (16.00 g)

46.07 gx 100% = 34.73%

52.14% + 13.13% + 34.73% = 100.0%

C2H6O

Ethanol

Percent composition of an element in a compound =

n x molar mass of element

molar mass of compoundx 100%

Mass Relationships in Chemical Reactions

nK = 24.75 g K x = 0.6330 mol K1 mol K

39.10 g K

nMn = 34.77 g Mn x = 0.6329 mol Mn1 mol Mn

54.94 g Mn

nO = 40.51 g O x = 2.532 mol O1 mol O

16.00 g O

Empirical formula of a compound that has the following percent composition by mass:

K= 24.75% , Mn= 34.77%, O= 40.51%

Base ..100 g

K : ~~ 1.00.6330

0.6329

Mn : 0.6329

0.6329= 1.0

O : ~~ 4.02.532

0.6329

nK = 0.6330, nMn = 0.6329, nO = 2.532

KMnO4

Mass Relationships in Chemical Reactions

Combustion 11.5 g ethanol

Collect 22.0 g CO2 and 13.5 g H2O

g CO2 mol CO2 mol C g C

g H2O mol H2O mol H g H

g of O = g of sample – (g of C + g of H)

6.0 g C = 0.5 mol C

1.5 g H = 1.5 mol H

4.0 g O = 0.25 mol O

C0.5H1.5O0.25

Divide by smallest subscript (0.25)

Empirical formula C2H6O

Ethane reacts with oxygen to form carbon dioxide and water

C2H6 + O2 2 CO2 + 3 H2O

Balancing Chemical Equations

C2H6 + O2 CO2 + H2O

multiply O2 by 72

C2H6 + 7/2O2 2 CO2 + 3 H2O

2C2H6 + 7O2 4CO2 + 6H2O

Balancing, C & H

Mass Relationships in Chemical Reactions

2NO + 2O2 2NO2

NO is the limiting reagent

O2 is the excess reagent

limiting reagent

Mass Relationships in Chemical Reactions

In one process, 124 g of Al are reacted with 601 g of Fe2O3

2Al + Fe2O3 Al2O3 + 2Fe

Calculate the mass of Al2O3 formed.

g Al mol Al mol Fe2O3 needed g Fe2O3 needed

OR

g Fe2O3 mol Fe2O3 mol Al needed g Al needed

Mass Relationships in Chemical Reactions

In one process, 124 g of Al are reacted with 601 g of Fe2O3

2Al + Fe2O3 Al2O3 + 2Fe

Calculate the mass of Al2O3 formed.

g Al mol Al mol Fe2O3 needed g Fe2O3 needed

OR

g Fe2O3 mol Fe2O3 mol Al needed g Al needed

124 g /26.98 gmol-1

= 4.60 mol

601 g /159.688 gmol-1

= 3.76 mol

4.60/2 = 2.30 mol

3.76x2 = 7.52 mol

Mass Relationships in Chemical Reactions

Theoretical Yield is the amount of product that wouldresult if all the limiting reagent reacted.

Actual Yield is the amount of product actually obtainedfrom a reaction.

% Yield = Actual Yield

Theoretical Yield

x 100

Glass transition

Liquid Nitrogen

Liquid nitrogen is

nitrogen in a liquid state at an extremely low temperature.

It is a colorless liquid with a density of 0.807 g/ml at

its boiling point (−195.79 °C (77 K; −320 °F))

Liquid nitrogen

liquid nitrogen can be stored and transported,

for example in vacuum flasks.