Download PROTONS MASS NUMBER AND ATOMIC NUMBER Atomic Number

1.1.2 Atomic Structure
• Describe protons, neutrons and electrons.
• Describe the distribution of mass and charge in an atom.
• Describe the contribution of protons and neutrons to the
nucleus in terms of atomic number and mass number.
• Explain the term isotopes.
• Deduce the atomic structure in atoms and ions.
THE STRUCTURE OF ATOMS
Atoms consist of a number of fundamental particles,
the most important are ...
Mass / kg
PROTON
NEUTRON
ELECTRON
Charge / C
Relative
mass
Relative
charge
THE STRUCTURE OF ATOMS
Atoms consist of a number of fundamental particles,
the most important are ...
Mass / kg
Charge / C
Relative
mass
Relative
charge
PROTON
1.672 x 10-27
1.602 x 10-19
1
+1
NEUTRON
1.675 x 10-27
1
0
ELECTRON
9.109 x 10-31
1
1836
-1
0
1.602 x 10-19
THE STRUCTURE OF ATOMS
Atoms consist of a number of fundamental particles,
the most important are ...
Mass / kg
Charge / C
Relative
mass
Relative
charge
PROTON
1.672 x 10-27
1.602 x 10-19
1
+1
NEUTRON
1.675 x 10-27
1
0
ELECTRON
9.109 x 10-31
1
1836
-1
0
1.602 x 10-19
Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons
THE STRUCTURE OF ATOMS
Atoms consist of a number of fundamental particles,
the most important are ...
Mass / kg
Charge / C
Relative
mass
Relative
charge
PROTON
1.672 x 10-27
1.602 x 10-19
1
+1
NEUTRON
1.675 x 10-27
1
0
ELECTRON
9.109 x 10-31
1
1836
-1
0
1.602 x 10-19
Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons
6 x 1.672 x 10-27 + 6 x 1.675 x 10-27 + 6 x 9.109 x 10-31 =
THE STRUCTURE OF ATOMS
Atoms consist of a number of fundamental particles,
the most important are ...
Mass / kg
Charge / C
Relative
mass
Relative
charge
PROTON
1.672 x 10-27
1.602 x 10-19
1
+1
NEUTRON
1.675 x 10-27
1
0
ELECTRON
9.109 x 10-31
1
1836
-1
0
1.602 x 10-19
Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons
6 x 1.672 x 10-27 + 6 x 1.675 x 10-27 + 6 x 9.109 x 10-31 =
2.0089 x 10-26 kg
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
Mass Number (A)
PROTONS + NEUTRONS
23
Na
11
Atomic Number (Z)
PROTONS
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
Mass Number (A)
PROTONS + NEUTRONS
23
Na
11
Atomic Number (Z)
PROTONS
THESE ALWAYS GO
TOGETHER – ANYTHING
WITH 11 PROTONS MUST
BE SODIUM
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
Mass Number (A)
PROTONS + NEUTRONS
23
Na
11
Atomic Number (Z)
PROTONS
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
THERE WILL BE 12 NEUTRONS
IN THE NUCLEUS
Mass Number (A)
PROTONS + NEUTRONS
23
Na
11
Atomic Number (Z)
PROTONS
23 – 11 = 12
MASS NUMBER AND ATOMIC NUMBER
Atomic Number (Z)
Number of protons in the nucleus of an atom
Mass Number (A)
Sum of the protons and neutrons in the nucleus
Mass Number (A)
PROTONS + NEUTRONS
23
Na
11
Atomic Number (Z)
PROTONS
MASS NUMBER AND ATOMIC NUMBER
Protons
Neutrons
Electrons
A
19
21
19
B
20
Charge
Atomic
Number
0
C
+
11
23
6
E
92
0
235
F
6
0
13
H
16
Symbol
40
D
G
6
Mass
Number
0
2-
16
27Al3+
MASS NUMBER AND ATOMIC NUMBER
Protons
Neutrons
Electrons
Charge
Atomic
Number
Mass
Number
Symbol
A
19
21
19
0
19
40
40K
B
20
20
20
0
20
40
40Ca
C
11
12
10
+
11
23
23Na+
D
6
6
6
0
6
12
12C
E
92
143
92
0
92
235
235U
F
6
7
6
0
6
13
13C
G
16
16
18
2-
16
32
32S2-
H
13
14
10
3+
13
27
27Al3+
Subatomic particles in ions
In reduction and oxidation reactions, electrons are transferred.
When elements react to form ions, electrons are either lost or gained.
This results in a stable electron arrangement.
•
•
What changes to electrons occur during the formation of positive ions?
What changes to electrons occur during the formation of negative ions?
Name
Hydrogen - 1
Hydrogen - 2
Symbol
1
1
2
1
H
H
Hydrogen - 3
Lithium - 6
Lithium - 7
Chlorine - 35
Chlorine - 37
Copper – 63
Copper – 65
Zirconium – 90
Zirconium - 94
Worksheet – isotope table
Protons
neutrons
electrons
atom - ion
symbol
protons
neutrons
electrons
charge
hydrogen
H
0
hydrogen ion
H
+1
sodium
Na
0
sodium ion
Na
+1
magnesium
0
magnesium ion
+2
aluminum
0
aluminum ion
+3
nitrogen
0
nitride ion
-3
oxygen
0
oxide
-2
fluorine
0
fluoride
-1
Worksheet – Atoms & ions
The arrangement of the electrons
The electrons are found at considerable distances from the nucleus
in a series of levels called energy levels.
Each energy level can only hold a certain number of electrons.
The first level (nearest the nucleus) will only hold 2 electrons,
the second holds 8,
and the third also seems to be full when it has 8 electrons.
These levels can be thought of as getting progressively further from
the nucleus.
Electrons will always go into the lowest possible energy level (nearest
the nucleus) - provided there is space.
What is the electronic arrangement in chlorine ?
The Periodic Table gives you the atomic number of 17.
Therefore there are 17 protons and 17 electrons.
The arrangement of the electrons will be 2, 8, 7
(i.e. 2 in the first level, 8 in the second, and 7 in the third).
The electronic arrangements of the first 20 elements
Two important generalisations
If you look at the patterns in this table:
The number of electrons in the outer level is the same as the
group number. (Except with helium which has only 2 electrons.
T he noble gases are also usually called group 0 - not group 8.) This
pattern extends throughout the Periodic Table for the main
groups (i.e. not including the transition elements).
So if you know that barium is in group 2, it has 2 electrons in its
outer level; iodine (group 7) has 7 electrons in its outer level; lead
(group 4) has 4 electrons in its outer level.
Noble gases have full outer levels.
Name
Symbol
Number of protons
Number of
neutrons
Number of
electrons
Electron
configuration
23Na+
19F35Cl37Cl40Ca2+
39K+
16O214N324Mg2+
7Li+
27Al3+
Worksheet - Atomic Structure of ions
32S2-
E
x
e
r
c
i
s
e
Tasks
Write out these Key definitions
• Isotopes . .
• Atomic ( proton ) number . .
• Mass ( nucleon ) number . . .
• An ion . . .
• Questions 1, 2
• Examiners tips are . .
1.1.3 Atomic Masses
•
Explain why 12C is used as the standard measurement of relative mass.
•
Define the terms relative isotopic mass and relative atomic mass.
•
Calculate relative atomic masses.
•
Work out relative molecular masses and relative formula masses.
RELATIVE MASSES
Relative Atomic Mass (Ar)
The mass of an atom relative to the 12C isotope having a value of 12.000
Ar
= average mass per atom of an element x 12
mass of one atom of carbon-12
Relative Isotopic Mass
Similar, but uses the mass of an isotope
238U
Relative Molecular Mass (Mr)
Similar, but uses the mass of a molecule
CO2, N2
Relative Formula Mass
Used for any formula of a species or ion
NaCl, OH¯
ISOTOPES
Definition
Atoms with…
the same atomic number but different mass number
or
the same number of protons but different numbers of neutrons.
ISOTOPES
Definition
Atoms with…
the same atomic number but different mass number
or
the same number of protons but different numbers of neutrons.
Properties
Chemical properties of isotopes are identical
Physical properties (such as density) can differ
ISOTOPES
Definition
Atoms with…
the same atomic number but different mass number
or
the same number of protons but different numbers of neutrons.
Properties
Chemical properties of isotopes are identical
Physical properties (such as density) can differ
Theory
Relative atomic masses measured
by chemical methods rarely produce
whole numbers but they should do
(allowing for the low relative mass of
the electron). This was explained
when the mass spectrograph revealed
that atoms of the same element could
have different masses due to the
variation in the number of neutrons in
the nucleus. The observed mass was
a consequence of the abundance of
each type of isotope.
ISOTOPES OF
HYDROGEN
Protons Neutrons
1
H
1
1
0
2
H
1
1
1
3
H
1
1
2
ISOTOPES - CALCULATIONS
There are two common isotopes of chlorine. Calculate the average relative atomic
mass of chlorine atoms
35
Cl
17
Protons
Neutrons
%
17
18
75
17
20
25
37
Cl
17
ISOTOPES - CALCULATIONS
There are two common isotopes of chlorine. Calculate the average relative atomic
mass of chlorine atoms
35
Cl
17
Protons
Neutrons
%
17
18
75
17
20
25
37
Cl
17
Method 1 Three out of every four atoms will be chlorine-35
Average =
35 + 35 + 35 + 37
4
= 35.5
ISOTOPES - CALCULATIONS
There are two common isotopes of chlorine. Calculate the average relative atomic
mass of chlorine atoms
35
Cl
17
Protons
Neutrons
%
17
18
75
17
20
25
37
Cl
17
Method 1 Three out of every four atoms will be chlorine-35
Average =
Method 2
35 + 35 + 35 + 37
4
Out of every 100 atoms 75 are
Average =
35Cl
(75 x 35) + (25 x 37)
100
= 35.5
and 25 are
= 35.5
37Cl
MASS SPECTRA
An early application was the demonstration by Aston, (Nobel Prize, 1922),
that naturally occurring neon consisted of 3 isotopes... 20Ne 21Ne 22Ne.
• positions of peaks gives atomic mass
• peak intensity gives relative abundance
• highest abundance is scaled up to 100%
- other values are adjusted accordingly.
Abundance / %
90.92
8.82
0.26
19
20
21
22
23
m/z
Calculate the average relative atomic mass of neon using the above information.
Out of every 100 atoms
90.92 are
Average =
20Ne
, 0.26 are
21Ne
and 8.82 are
22Ne
(90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179
100
Relative atomic mass = 20.18
Can we calculate the % composition if we know the isotopes ?
Naturally occurring potassium consists of potassium-39 and potassium-41.
Calculate the percentage of each isotope present if the average is 39.1.
Assume there are x nuclei of
39K
in every 100; so there will be (100-x) of 41K
so
39x + 41 (100-x)
100
= 39.1
therefore
39 x + 4100 - 41x
= 3910
thus
- 2x = - 190
and
ANSWER
x = 95
There will be
95%
5%
39K
41K
and
Tasks
Write out these Key definitions
• Relative isotopic mass
• Relative atomic mass
• Relative molecular mass
• Relative formula mass
Calculate the relative atomic mass of the following
– give your answers to 3 significant figures
Bromine :
79 Br 50% , 81 Br 50%
Copper :
63 Cu 69% , 65 Cu 31%
Zirconium :
90 Zr 51.5% , 91 Zr 11.2%,
94 Zr 17.4%,
Lead :
204 Pb 1.5% ,
96
63.6
92
Zr 2.8%
206 Pb 23.6%,
Zr 17.1%,
91.3
207 Pb 22.6%,
208 Pb 52.3%
207.
Neon :
20 Ne 90.9% ,
21 Ne 0.2%,
22 Ne 8.9%
20.2
Tasks
Worksheet Exercise 1.1.3 Atomic Masses
Questions : 1, 2, 3