Transcript Atomic structure - Browser Express

Chapter 1
Atomic Structure
1.1
The Atomic Nature of Matter
1.2
The Experimental Evidence of
Atomic Structure
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1.1 The atomic nature of matter (SB p.2)
Dalton’s atomic theory (1808)
John Dalton proposed
his Dalton’s atomic
theory.
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1.1 The atomic nature of matter (SB p.2)
Main points of Dalton’s atomic theory
1.
All elements are made up of atoms.
2.
Atoms can neither be created nor destroyed.
3.
Atoms of the same element are identical. They have the same
mass and chemical properties.
4.
Atoms of different elements are different. They have different
masses and chemical properties.
5. Atoms of different elements combine to form a compound. The
numbers of various atoms combined bear a simple whole
number ratio to each other.
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1.2 The experimental evidence of atomic structure (SB p.3)
Discovery of electrons
Cathode Ray Discharge Tube
- A beam of rays came out from the cathode (-)
and hit the anode (+).
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1.2 The experimental evidence of atomic structure (SB p.4)
The beam was composed of negatively charged fastDeflected in the
Deflected
in
the
moving particles called ‘electrons’.
magnetic field
electric field
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1.2 The experimental evidence of atomic structure (SB p.4)
Location of protons?
Gold foil scattering
experiment
- performed by Ernest
Rutherford
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1.2 The experimental evidence of atomic structure (SB p.4)
He bombarded a thin gold foil with a beam of fastmoving -particles (+ve charged)
Observation:
-most -particles passed
through the foil without
deflection
-very few -particles
were scattered or
rebounded back
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Interpretation of the experimental results
- Most of the atom is empty space.
- The mass concentrated at the center of an atom called
‘nucleus’.
- The nucleus is positively charged.
- The positively charged particle is called ‘proton’.
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1.2 The experimental evidence of atomic structure (SB p.5)
Mass of atom
Total mass of protons
>
Chadwick’s atomic model
- the presence of neutrons
- proved by James
Chadwick
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1.2 The experimental evidence of atomic structure (SB p.5)
Chadwick’s atomic model
Proton
Electron
Neutron
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1.3 Sub-atomic particles (SB p.6)
Characteristics of sub-atomic particles
Sub-atomic
particle
Symbol
Proton
p or 1H
1
Neutron
n or 1 n
0
Electron
e- or 0 e
-1
Location in atom
Nucleus
Nucleus
Surrounding the
nucleus
Actual charge (C)
1.6 x 10-9
0
1.6 x 10-9
Relative charge
+1
0
-1
Actual mass (g)
1.7 x 10-24
1.7 x 10-24
9.1 x 10-28
1
1
0
Approximate
relative mass
(a.m.u.)
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1.4 Atomic number, mass number and isotopes (SB p.8)
Isotopes
Isotopes are atoms of the same element with the same
number of protons but different numbers of neutrons.
Cl has 2 isotopes: Cl-35 and Cl-37
Isotopes
12
Cl-35
Relative
abundance
75%
Cl-37
25%
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1.8 Mass spectrometer (SB p.20)
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1.8 Mass spectrometer (SB p.20)
Mass spectrometer
A highly accurate
instrument!
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1.8 Mass spectrometer (SB p.20)
Mass spectrometer consists of 6 parts:
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1.8 Mass spectrometer (SB p.21)
Mass spectrum of Cl2:
m/e ratio
16
35
Corresponding
ion
35Cl+
37
37Cl+
70
35Cl─35Cl+
72
35Cl
─ 37Cl+
74
37Cl
─37Cl+
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1.8 Mass spectrometer (SB p.21)
Mass spectrum of CH3Cl:
m/e ratio
35
Corresponding
ion
35Cl+
37
37Cl+
50
17
12CH
35Cl+
─
3
51
13CH
52
12CH
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35Cl+
─
3
3
─37Cl+
1.9 Relative isotopic, atomic and molecular masses (SB p.23)
Relative atomic mass
The relative atomic mass of an element is the weighted
average of the relative isotopic masses of its natural
isotopes on the carbon-12 scale.
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1.9 Relative isotopic, atomic and molecular masses (SB p.23)
What is the relative atomic mass of Cl?
The relative abundances of Cl35 and Cl-37 are 75.77 and
24.23 respectively
Relative atomic mass of Cl
(35  75.77)  (37  24.23)
=
(75.55  24.23)
= 35.48
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1.9 Relative isotopic, atomic and molecular masses (SB p.23)
Relative molecular mass
The relative molecular mass is the relative mass of a
molecule on the carbon-12 scale.
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1.9 Relative isotopic, atomic and molecular masses (SB p.23)
What is the relative molecular mass of CH3Cl?
Relative molecular mass of
CH3Cl
(50 123)  (51  2)  (52  40)
=
(123  2  40)
= 50.5
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1.9 Relative isotopic, atomic and molecular masses (SB p.24)
Check Point 1-6
(a) The mass spectrum of
lead is given on the
right.
the abundance of the peak
Let xGiven
be thethat
relative
relative
atomic mass
at m/e 208.
of lead is 207.242,
(204  1.5
206  23.6 + 207  22.6 +
calculate
the+relative
208x)  (1.5
+ 23.6 + 22.6 + x) = 207.242
abundance
of the
peak
 at m/e 208.
x = 52.3
 The relative abundance of the peak at
m/e 208 is 52.3.
Answer
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1.9 Relative isotopic, atomic and molecular masses (SB p.24)
Check Point 1-2 (cont’d)
(b)The mass spectrum of
dichloromethane
is given
on
Let y be the relative
molecular
mass of
thedichloromethane.
right. Calculate the
relative molecular mass of
y = (84  94 + 85  3.0 + 86  59 + 87  2.2 + 88
dichloromethane.
 13 + 89  2.5 + 90  0.8 )  (90 + 3.0 + 59
+ 2.2 + 13 + 2.5 + 0.8)
= 85.128
 The relative molecular mass of
dichloromethane is 85.128.
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Answer
The END
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The END
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