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1
1.1
1.2
1.3
1.4
1.5
1.6
1
Atomic Structure
and Relative Masses
The Atomic Nature of Matter
The Experimental Evidence of Atomic Structure
Sub-atomic Particles
Atomic Number, Mass Number and Isotopes
Mass Spectrometer
Relative Isotopic, Atomic and Molecular Masses
New Way Chemistry for Hong Kong A-Level Book 1
1.1
The Atomic
Nature of Matter
2
New Way Chemistry for Hong Kong A-Level Book 1
1.1 The atomic nature of matter (SB p.2)
What is “atom”?
The Greek philosopher Democritus
3
New Way Chemistry for Hong Kong A-Level Book 1
1.1 The atomic nature of matter (SB p.2)
These are iron
atoms!!
Continuous
division
Iron
Continuous
division
4
New Way Chemistry for Hong Kong A-Level Book 1
1.1 The atomic nature of matter (SB p.2)
Dalton’s atomic theory
John Dalton proposed his Dalton’s atomic
theory
5
New Way Chemistry for Hong Kong A-Level Book 1
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.
Check Point 1-1
6
New Way Chemistry for Hong Kong A-Level Book 1
1.2
The Experimental
Evidence of
Atomic Structure
7
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.3)
Discovery of electrons
• A beam of rays came out from the
cathode and hit the anode
• He called the beam cathode rays
8
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.4)
The beam was composed of negatively
Deflected in
Deflected
in
charged fast-moving particles.the magnetic
the electric
field
9
field
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.4)
Measure the mass to
charge ratio (m/e) of
the particles produced
The particles
were constituents
of all atoms!!
10
Independent of the
nature of the gas inside
the discharge tube
He called the
particles ‘electrons’.
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.4)
Thomson’s atomic model
An atom is
electrically neutral
Atom
11
No. of
positively
charged
particles
New Way Chemistry for Hong Kong A-Level Book 1
=
No. of
negatively
charged
particles
1.2 The experimental evidence of atomic structure (SB p.4)
How are the particles distributed in
an atom?
+
+
+
• An atom was a
positively charged
sphere
+
+
+
Positive
charge
12
• Negatively charged
electrons embedded in
it like a ‘raisin pudding’
Electron
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.4)
Gold foil scattering experiment
• performed by Ernest
Rutherford
13
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.4)
• He bombarded a thin gold foil with a beam of
fast-moving -particles (+ve charged)
Observation:
• most -particles
passed through the
foil without
deflection
• very few -particles
were scattered or
rebounded back
14
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.5)
Interpretation of the experimental results
• The condensed core is called ‘nucleus’
• The positively charged particle is called ‘proton’
15
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.5)
Rutherford’s atomic model
Expectation:
Mass of atom
= Total mass of protons
Mass of atom
> Total mass of protons
16
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.5)
Chadwick’s atomic model
• presence of
neutrons
• proved by James
Chadwick
17
New Way Chemistry for Hong Kong A-Level Book 1
1.2 The experimental evidence of atomic structure (SB p.5)
Chadwick’s atomic model
Proton
Electron
Neutron
18
Check Point 1-2
New Way Chemistry for Hong Kong A-Level Book 1
1.3
19
Sub-atomic
Particles
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.6)
Sub-atomic particles
3 kinds of sub-atomic particles:
• Protons
• Neutrons
• Electrons
20
Inside the condensed
nucleus
Moving around the
nucleus
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.7)
A carbon-12 atom
21
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.6)
Characteristics of sub-atomic particles
Sub-atomic
particle
Symbol
Proton
p or 1H
1
Neutron
n or1 n
0
Electron
e- or 0 e
-1
Location in
atom
Nucleus
Nucleus
Surrounding the
nucleus
Actual charge
(C)
1.6  10-9
0
1.6 x 10-9
Relative charge
+1
0
-1
Actual mass (g)
1.7  10-24
1.7  10-24
9.1  10-28
1
1
0
Approximate
relative mass
(a.m.u.)
22
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.6)
Relative size of the atom and the nucleus
Check Point 1-3
23
New Way Chemistry for Hong Kong A-Level Book 1
1.4
Atomic Number,
Mass Number
and Isotopes
24
New Way Chemistry for Hong Kong A-Level Book 1
1.4 Atomic number, mass number and isotopes (SB p.7)
Atomic number
The atomic number (Z) of an element is the
number of protons contained in the nucleus
of the atom.
Atomic
number
=
Number of
protons
=
Reason: Atoms are
electrically neutral.
25
New Way Chemistry for Hong Kong A-Level Book 1
Number of
electrons
1.4 Atomic number, mass number and isotopes (SB p.8)
Mass number
The mass number (A) of an atom is the sum
of the number of protons and neutrons in the
nucleus.
Mass
number
26
=
Number of
protons
+
New Way Chemistry for Hong Kong A-Level Book 1
Number of
neutrons
1.4 Atomic number, mass number and isotopes (SB p.8)
Atomic numbers and mass numbers
of some common atoms
Atom
No. of
No. of
protons electrons
No. of
Atomic Mass
neutrons number number
Hydrogen
1
1
0
1
(1 + 0)
=1
Oxygen
8
8
8
8
(8 + 8)
= 16
Argon
18
18
22
18
(18+22)
= 40
27
New Way Chemistry for Hong Kong A-Level Book 1
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.
Representation:
Mass
number
Symbol of the
element
A
X
Atomic
number
28
Z
New Way Chemistry for Hong Kong A-Level Book 1
1.4 Atomic number, mass number and isotopes (SB p.8)
e.g. the two isotopes of chlorine are written
as:
35
Cl
17
37
Cl
17
OR labelled as Cl-35 and Cl-37.
Check Point 1-4
29
New Way Chemistry for Hong Kong A-Level Book 1
1.4 Atomic number, mass number and isotopes (SB p.9)
Isotopes of some common elements
Element
Hydrogen
Carbon
30
Isotope Atomic
No. of
No. of
Natural
number protons neutrons abundanc
e (%)
1
1H
2
1H
1
1
0
99.8
1
1
1
0.02
12
6C
13
6C
14
6C
6
6
6
98.89
6
6
7
1.11
6
6
8
trace
New Way Chemistry for Hong Kong A-Level Book 1
1.5
31
Mass
Spectrometer
New Way Chemistry for Hong Kong A-Level Book 1
1.5 Mass spectrometer (SB p.10)
Mass spectrometer
A highly accurate
instrument!
32
New Way Chemistry for Hong Kong A-Level Book 1
1.5 Mass spectrometer (SB p.10)
Mass spectrometer consists of 6 parts:
33
New Way Chemistry for Hong Kong A-Level Book 1
1.8 Mass spectrometer (SB p.21)
Mass spectrum of Cl2:
m/e ratio Corresponding
ion
35Cl+
35
34
37
37Cl+
70
35Cl─35Cl+
72
35Cl
─ 37Cl+
74
37Cl
─37Cl+
New Way Chemistry for Hong Kong A-Level Book 1
1.8 Mass spectrometer (SB p.21)
Mass spectrum of CH3Cl:
Check Point 1-5
m/e ratio Corresponding
ion
35Cl+
35
37
50
35
37Cl+
12CH
51
13CH
52
12CH
New Way Chemistry for Hong Kong A-Level Book 1
35Cl+
─
3
3
3
─ 37Cl+
─37Cl+
1.6
Relative Isotopic,
Atomic and
Molecular Masses
36
New Way Chemistry for Hong Kong A-Level Book 1
1.9 Relative isotopic, atomic and molecular masses (SB p.22)
Relative isotopic mass
The relative isotopic mass of a particular isotope
of an element is the relative mass of one atom of
that isotope on the carbon-12 scale.
e.g. relative isotopic mass of Cl-35 = 35
relative isotopic mass of Cl-37 = 37
37
New Way Chemistry for Hong Kong A-Level Book 1
1.9 Relative isotopic, atomic and molecular masses (SB p.22)
What is carbon-12 scale?
use carbon-12 as the reference standard
Mg has the
same mass as
two C-12 atoms
38
New Way Chemistry for Hong Kong A-Level Book 1
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.
39
New Way Chemistry for Hong Kong A-Level Book 1
1.9 Relative isotopic, atomic and molecular masses (SB p.23)
What is the relative atomic mass of Cl?
The relative abundances of
Cl-35 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
40
New Way Chemistry for Hong Kong A-Level Book 1
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.
41
New Way Chemistry for Hong Kong A-Level Book 1
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)
= 50.50
Example 1-6
Check Point 1-6
42
New Way Chemistry for Hong Kong A-Level Book 1
The END
43
New Way Chemistry for Hong Kong A-Level Book 1
1.1 The atomic nature of matter (SB p.3)
Back
(a) What does the word “atom” literally mean? (a) Indivisible
(b) Which point of Dalton’s atomic theory is based on the law
of conservation of mass proposed by Lavoisier in 1774
which states that matter is neither created nor destroyed
(b) Atoms can neither be
in the course of a chemical reaction?
created nor destroyed.
(c) Which point of Dalton’s atomic theory is based on the law
of constant proportion proposed by Proust in 1799 which
states that all pure samples of the same chemical
compound contain the same elements combined together
in the same proportions by mass?
(c) Atoms of different elements combine to form a
compound. The numbers of various atoms combined
bear
a simple whole
number
ratio
each
44
New
Way Chemistry
forto
Hong
Kong other.
A-Level Book 1
Answer
1.2 The Experimental evidence of atomic structure (SB p.4)
Back
(a) Atoms were found to be divisible. What names wer given
to the particles found inside the atoms? (a) Electron, proton
and neutron
(b) Give the most important point of the following
experiments:
(i) E. Goldstein’s gas discharge tube experiment;
(ii) J. J. Thomson’s cathode ray tube experiment;
(iii) E. Rutherford’s gold foil scattering experiment.
(b) (i) Discovery of cathode rays
(ii) Discovery of electrons
(iii) Discovery of nucleus in atoms
45
New Way Chemistry for Hong Kong A-Level Book 1
Answer
1.3 Sub-atomic particles (SB p.6)
The identity of an element is determined by the
number of which sub-atomic particle?
Answer
The identity of an element is determined by
the number of protons in its atomic nucleus.
Back
46
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic Particles (SB p.7)
Back
(a) Which part of the atom accounts for almost all the mass of
that atom? (a) Nucleus
(b) The mass of which sub-atomic particle is often assumed
to be zero? (b) Electron
Answer
47
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.7)
Are there any sub-atomic particles other than protons,
neutrons and electrons?
Answer
Other than the three common types of subatomic particles (proton, neutron and
electron), there are also some sub-atomic
particles called positron (anti-electron) and
quark.
Back
48
New Way Chemistry for Hong Kong A-Level Book 1
1.3 Sub-atomic particles (SB p.7)
If bromine has two isotopes, 79Br and 81Br, how many
physically distinguishable combinations of Br atoms are
there in Br2?
Answer
There are three physically distinguishable
combinations of Br atoms (79Br—79Br,
79Br—81Br and 81Br—81Br) in Br .
2
Back
49
New Way Chemistry for Hong Kong A-Level Book 1
1.4 Atomic number, mass number and isotopes (SB p.8)
Back
Write the symbol for the atom that has an atomic number of
11 and a mass number of 23. How many protons, neutrons
and electrons does this atom have?
23
11
50
Na, 11 protons, 12 neutrons, 11 electrons.
New Way Chemistry for Hong Kong A-Level Book 1
Answer
1.5 Mass spectrometer (SB p.12)
Back
Label the different parts of the mass spectrometer.
A – Vaporization chamber
B – Ionization chamber
C – Accelerating electric field
D – Deflecting magnetic field
E – Ion detector
51
New Way Chemistry for Hong Kong A-Level Book 1
Answer
1.5 Mass spectrometer (SB p.12)
Back
The mass spectrum of neon is given below. Determine the
relative atomic mass of neon.
Relative atomic mass of neon
(20  114)  (21 0.2)  (22  11.2)
=
(114  0.2  11.2)
= 20.18
Answer
52
New Way Chemistry for Hong Kong A-Level Book 1
1.6 Relative isotopic, atomic and molecular masses (SB p.14)
(a) The mass spectrum of lead is given below. Given that the
relative atomic mass of lead is 207.242, calculate the
relative abundance of the peak at m/e of 208.
Let x be the relative abundance
of the peak at m/e of 208.
(204  1.5 + 206  23.6 + 207 
22.6 + 208x)  (1.5 + 23.6 + 22.6
+ x) = 207.242
x = 52.3
The relative abundance of the
peak at m/e of 208 is 52.3.
Answer
53
New Way Chemistry for Hong Kong A-Level Book 1
1.6 Relative isotopic, atomic and molecular masses (SB p.14)
Back
(b) The mass spectrum of dichloromethane is given below.
Calculate the relative molecular mass of dichloromethane.
The relative molecular mass of
dichloromethane
= (84  94 + 85  3.0 + 86  59 +
87  2.2 + 88  13 + 89  2.5 +
90  0.8)  (94 + 3.0 + 59 + 2.2 +
13 + 2.5 + 0.8)
= 85.128
The relative molecular mass of
dichloromethane is 85.128.
Answer
54
New Way Chemistry for Hong Kong A-Level Book 1