Download THE ATOM Elements Isotopes Ions

THE ATOM
• Our modern idea of an atom is a
very small nucleus containing
protons (positively charged) and
neutrons (neutral), surrounded by
a cloud of electrons (negatively
charged).
•
•
•
Protons and neutrons are about the same size
Electrons are about 1/1846 the size of a proton. Almost all of the mass (about 99.99%) of
an atom is in the nucleus. The rest is empty space.
If an atom was the same size as the school oval, the nucleus would be the size of a green
pea on the cricket pitch and the electrons would be pinpoints moving around the
boundary at rapid speeds.
Elements
•
•
In an element, all of the atoms have the same number of protons.
There are about 112 different elements, each with its own symbol. The first letter is
always capital. If there is a second letter, it is lowercase e.g. Mg, Na.
Isotopes
•
•
•
Isotopes have the same number of protons but a different number of neutrons.
Isotopes of elements have the same chemical properties, as that only depends on the
number of protons (and electrons).
A different number of neutrons changes the mass and this only affects the physical
properties e.g. melting point and boiling point.
12 C
6
Atomic Number
Mass Number
Atomic Number = number of protons in the nucleus of the atom.
Mass Number = number of protons and neutrons in the nucleus of the atom.
Name
Hydrogen
Carbon
Carbon
Chlorine
Potassium
•
Symbol
1
1H
12
6C
14
6C
35
Cl
17
39
K
19
Atomic
No.
Mass
No.
No. of
protons
No. of
neutrons
No. of
electrons
1
1
1
0
1
6
12
6
6
6
6
14
6
8
6
17
35
17
18
17
19
39
19
20
19
In a neutral atom, the number of protons in the nucleus and the number of electrons
orbiting the nucleus is always the same.
Ions
•
Ions are charged atoms. There are a different number of electrons to protons. They are
formed when an element either loses or gains electrons.
e.g.
Na+
has 11protons but only 10 electrons.
has 16 protons but 18 electrons.
S2-
ELECTRON CONFIGURATION
The electrons of an atom are not arranged randomly, but exist in shells. They
are negatively charged but they do tend to pair up (much like girls going to the
toilet!!! ☺).
They can pair up because they spin on their axis and thus generate a magnetic
field. Two electrons spinning on their axis in the opposite direction will be
attracted towards each other due to the magnetism.
The maximum number of electrons that each shell can hold increases as you
increase the distance from the nucleus (because there is more volume), but the
force of attraction on them by the nucleus will decrease the further away they
are.
The formula used to work out the maximum number of electrons each shell can
hold is 2n2 where n is the number of the shell.
Shell Number
1
2
3
4
5
6
7
Old Naming
System
K
L
M
N
O
P
Q
Max. no. of
electrons
2
8
18
32
50
72
98
These shells
never get
filled.
It actually follows a mathematical progression:
1 pair
1 pair
1 pair
+ 3 pairs
1 pair
+ 3 pairs
+ 5 pairs
2 electrons 8 electrons 18 electrons
+ 3 pairs
+ 5 pairs
+ 7 pairs
32 electrons
ELECTRONIC CONFIGURATION
OF FIRST 36 ELEMENTS
Name
Symbol
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulphur
Chlorine
Argon
Potassium
Calcium
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Gallium
Germanium
Arsenic
Selenium
Bromine
Krypton
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Atomic
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Elec.
Config.
1
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.8.6
2.8.7
2.8.8
2.8.8.1 *
2.8.8.2 *
2.8.9.2
2.8.10.2
2.8.11.2
2.8.12.2
2.8.13.2
2.8.14.2
2.8.15.2
2.8.16.2
2.8.17.2
2.8.18.2
2.8.18.3
2.8.18.4
2.8.18.5
2.8.18.6
2.8.18.7
2.8.18.8
* Potassium and
calcium appear to
have a ‘funny’
configuration. The
third shell is not full
before electrons
appear in the fourth
shell (1 pair). At this
stage of your
chemical career,
remember the rule
“you can’t have
more than 8
electrons in the outer
shell of an element.”