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1
Atomic
Structure
2
THE NATURE OF ATOMS
3
THE NATURE OF ATOMS
An Atom is the smallest amount
of an Element that can exist
THE NATURE OF ATOMS
4
Atoms have a Nucleus, which
contains Neutrons (no Charge)
and Protons (+ve Charge)
+
+
+ +
The Nucleus of a
Beryllium atom
has four protons
and five neutrons
5
THE NATURE OF ATOMS
Atoms of Beryllium also have four
even smaller Electrons (-ve Charge)
which orbit around the nucleus
6
THE NATURE OF ATOMS
Electrons move in a series of layers
and take up most of the space in an
atom, but have virtually no Mass
7
THE NATURE OF ATOMS
Of the three Particles, only Protons
and Electrons have a charge, while
only Protons and Neutrons have any
mass (1 u = 1 Atomic Mass Unit)
P
N
E
+ve
1u
neutral
1u
-ve
negligible
8
ISOTOPES
9
ISOTOPES
The “vital statistics” for an
atom are the Mass Number
and the Atomic Number
Here “Carbon-12”
has 6 protons, and
so it must have 6
neutrons (6 + 6 = 12)
and also 6 electrons
(charges balance)
Mass Number
= Protons + Neutrons
12
6
C
Atomic Number
= Protons
10
ISOTOPES
An element usually has certain
numbers of neutrons, protons
and electrons in each atom
All atoms of an
element have
the same number
of protons and
electrons, but the
neutrons can vary
ISOTOPES
11
Atoms of an element may exist
with different numbers of neutrons
and these are called Isotopes
e-
+
e-
+
e-
+
E.g. Hydrogen always has 1 proton,
but may have 0, 1 or 2 neutrons
ISOTOPES
12
Isotopes of an element have the same
Chemical properties but have slightly
different Physical properties, e.g. mass
Chlorine-37 has 17
protons, so it has 20
neutrons and 17
electrons, but there
is also Chlorine-35
with 18 neutrons
Mass Number
= Protons + Neutrons
37
17
Cl
Atomic Number
= Protons
ISOTOPES
13
75% Cl-35
25% Cl-37
Chlorine-37 has 17
protons, so it has 20
neutrons and 17
electrons, but there
is also Chlorine-35
with 18 neutrons
As Chlorine
usually contains
3/ Cl-35 and
4
1/ Cl-37, the
4
atomic mass is
35.5 approx
14
ARRANGEMENT OF ELECTRONS
Ernest Rutherford
15
ARRANGEMENT OF ELECTRONS
Electrons orbit
rapidly around the
nucleus in distinct
Shells, each of
which can only hold
limited numbers
16
ARRANGEMENT OF ELECTRONS
1st Energy
Level
2nd Energy
Level
3rd Energy
Level
17
ARRANGEMENT OF ELECTRONS
Max 2
Electrons
Max 8
Electrons
Max 18
Electrons
(inner 8,
outer 10)
18
ARRANGEMENT OF ELECTRONS
Sodium
O
8P, 8N
Na
11P, 12N
Oxygen
19
ARRANGEMENT OF ELECTRONS
ELEMENT ELECTRONS ARRANGEMENT
Hydrogen
1
1
Helium
2
2
Lithium
3
2,1
Beryllium
4
2,2
Boron
5
2,3
Carbon
6
2,4
Nitrogen
7
2,5
Oxygen
8
2,6
Fluorine
9
2,7
Neon
10
2,8
Sodium
11
2,8,1
Magnesium
12
2,8,2
Aluminium
13
2,8,3
Silicon
14
2,8,4
20
ARRANGEMENT OF ELECTRONS
If the outer shell is full, this
is a stable arrangement and
the element is unreactive
Neon
1/--страниц
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