atom atomos a tomos un + cut · 2010-07-02 · 1 ©prof. zvi c. koren 21.10.07 2 אשונ...

1 ©Prof. Zvi C. Koren 21.10.07

2נושא

ומולים, איזוטופים, אטומים

Atom Atomos A + tomos

un + cut


amu = atomic mass unit

Atomic Composition

e–

H+

Relative Atomic Mass Scale:

Mass of 1 atom of 12C 12 (exactly) amu


Atomic Symbols & Isotopes (איזוטופים)

XA

ZElement symbol

Atomic Number# of protons =

Mass Number# of protons + # of neutrons =

Examples of Isotopes:

C14

6 C

13

6 C

12

6 :carbonelement theof isotopes Three

for a neutral atom: # of electrons = # of protons

protium deuterium (D) tritium (T)

Isotopes = different atoms of the same elementRadioactive

Consider ions (charged species – “to go”):13C4-: #p = __, #n = __, #e = __. 3H+: #p = __, #n = __, #e = __.

carbon-12 carbon-13 carbon-14#p =

#n =

#e =

#p =

#n =

#e =

1H 2H 3HThree isotopes of the element hydrogen:


Atomic Mass or Atomic Weight (A.W.)

the weighted average of all the stable isotopes of that element

Atomic Mass or

Atomic Weight (amu)

Percent (%)

AbundanceMass (amu)

Mass

NumberSymbolElement

1.0079799.98551.0078251

HHydrogen0.01452.0141022

10.81119.9110.01293910

BBoron80.0911.00930511

15.9994

99.75915.99491416

OOxygen 0.037416.99913417

0.203917.99916018

12.011

12

(exactly)12

CCarbon

13

Table of Exact Masses of the Stable Isotopes of Some Elements

For example:

A.W. of O = 0.99759(15.994914) + 0.000374(16.999134) + 0.002039(17.999160)

= 15.9994 amu [This is the mass that appears in the Periodic Table.]

?


Notes about Atomic Weights

• All atomic masses (except for 12C) are NOT integers

• Mass number is always an integer!

• A.W. the sum of all the particles.

For example for deuterium, 2H (or D):

1 proton = 1.007276 amu

1 neutron = 1.008665

1 electron = 0.0005485799

Total mass of particles = 2.0164895799 amu

Atomic Weight = 2.014102 amu

Difference in mass = 0.002387 amu = 3.9638x10-30 kg

Why?

Mass defect: E = mc2 = (3.9638x10-30 kg)(2.997925x108 m/s)2 = 3.5625x10-13 J/atom

1 atom = 2.014102 amu = 3.3445x10-24 g

energy/gram = 1.0652x1011 J/g = 1.0652x108 kJ/g

energy/mole = 2.1454x108 kJ/mole

For exothermic chemical reactions: energy/mole 102 kJ/mole


1A

H

Li

Na

K

Rb

Cs

Fr

Chemical Periodicity

Li

Na

K

M(s) + H2O(l) MOH(aq) + ½H2(g) + Heat

Reaction Names:

Hydrolysis

Single Replacement

“Redox”

Exothermic

Gas-Forming

aqueous

Elements of the same group have similar – but not identical – properties.


mole

Mole Day is celebrated on Oct. 23 from 6:02 am to 6:02 pm


Lorenzo Romano Amadeo CarloAvogadro1776 – 1856

The word “mole”:

Coined by Wilhelm Ostwald (1896), Latin “moles” meaning “heap” or “pile”.

Avogadro’s Number:

1 mole of things = 6.022x1023 things


The mole is a number!

For example:

1 dozen = 12

1 dozen eggs = 12 eggs

1 dozen chairs = 12 chairs

1 dozen molecules = 12 molecules

1 dozen atoms = 12 atoms

1 mole = 6.022x1023

1 mole of eggs = 6.022x1023 eggs

1 mole of chairs = 6.022x1023 chairs

1 mole of molecules = 6.022x1023 molecules

1 mole of atoms = 6.022x1023 atoms

The Mole … once agin … The Bridge to the Human Scale


What’s so great about the mole or Avogadro’s Number???

Converts masses in amu to the same number in grams

Molar Mass

(g/mol)MassesAtoms/Molecules

12 g/mol

12 amu

12 g

1 12C atom

1 mol of 12C atoms

10.0129 g/mol

10.0129 amu

10.0129 g

1 10B atom

1 mol of 10B atoms

32.00 g/mol

32.00 amu

32.00 g

1 O2 molecule

1 mol of O2 molecules

2.00 g/mol

2.00 amu

2.00 g

1 H2 molecule

1 mol of H2 molecules

Molecular Weight (MW)

Formula Weight (FW)

1 g = 6.022x1023 amu

g ? amu

Avogadro’s Number is a Magic Number!!!

Atomic Weight (AW)


1 g = 6.022x1023 amu

g amu

5.0 g amu = ?

5.0 g gamu

1= 3.0 x 1024 amu

“Unit Factor”

Mass Conversions

6.022 x 1023

Example for g amu:

2.0 amu g = ?

2.0 amug

amu1 = 3.3 x 10-24 g

“Unit Factor”

6.022 x 1023

Example for amu g:


Grams Moles31.8 g Cu Moles of Cu atoms = ?

31.8 g Cug Cu

mol Cu1

63.55= 0.500 mol Cu

Moles Grams

“Unit Factor”

(A.W.)

0.300 mol Cu atoms g Cu = ?

g Cu

mol Cu1

63.55= 19.1 g Cu

“Unit Factor”

(A.W.)

0.300 mol Cu

Moles and Molar Masses of the Elements


How many moles are there in 1.00 lb of silicon?

Weight

1.00 lb Sig

lb1

453.6 molg28.0855

1= 16.2 mol Si

Moles

Grams MolesWeight


Grams Moles1.6 g CH4 Moles of CH4 molecules = ?

1.6 g CH4g CH4

mol CH41

16.0= 0.10 mol CH4

Moles Grams

“Unit Factor” (M.W.)

0.10 mol CH4 molecules g CH4 = ?

g CH4

mol CH41

16.0= 1.6 g CH4

“Unit Factor” (M.W.)

0.10 mol CH4

Molar Mass or Molecular Weight (M.W.)For Example, for CH4: MW = 12.0 + 4(1.0) = 16.0 g/mol

Also:

M

mn


Moles Number

Number of Items

0.20 mol tables # of tables = ?

0.20 mol tablesmol tables

tables6.02x1023

1= 1.2x1023 tables

Number Moles

“Unit Factor”

1.2x1023 Cu atoms mol Cu = ?

mol Cu atoms

Cu atoms6.02x1023

1= 0.20 mol Cu atoms

“Unit Factor”

1.2x1023 Cu atoms

Avogadro’s Number:

1 mole of things = 6.022x1023 things


Summary

MoleAvogadro’s

NumberMass

constantvariable

atom atomos a tomos un + cut · 2010-07-02 · 1 ©prof. zvi c. koren 21.10.07 2 אשונ...

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