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L1: The Periodic Table
 The periodic table is a remarkable way to show the manifold
relationships between differing kinds of elements
• The modern table was devised in 1869 by Dimitri Mendeleyev
• He arranged the elements by weight and by their chemical
properties
The periodic table arranges all the elements
in groups according to their properties.
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Mendeleev
The Periodic Table
• To make the periodic table, the elements are first laid out in
order of increasing Atomic/Proton Number
• Based on the arrangements of the electrons outside the nucleus
– Elements whose atoms have 1 outer-shell electron are picked
out of the list in order and called Group 1
– Elements whose atoms have 2 outer-shell electron are
picked out of the list in order and called Group 2.
– Next: Group 3 followed by Group 4 and so on.
• The Groups are arranged side by side to give the periodic
table
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Arrangement of Elements
Vertically into
columns called
GROUPS
Groups
Horizontally Into rows called PERIODS
Periods
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Groups
If you looked at one
atom of every element
in a group you would
see…
Each atom has the same
number of electrons in it’s
outermost shell.
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Groups
Example: The group 1 atoms all have 1 electron in
their outer shells
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Groups
Example: The group 2 atoms all have 2 electrons in
their outer shells
Be (Beryllium)
Atom
Mg (Magnesium) Atom
What is happening to the number of shells as you go down the
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group?
Groups
Fact : Elements in the same group have the same
number of electrons in the outer shell (this
correspond to their group number)
H
e
H
Li
B
e
B
C
N
O
F
N
e
N
a
M
g
Al
Si
P
S
Cl
Ar
K
C
a
Fe
Ni
C
u
Zn
A
g
E.g. all group 1 metals
have __ electron in
their outer shell
A
Br Kr
I
H
Pt
These elements
u have
g
__ electrons in their
outer shells
Xe
These elements
have __ electrons
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in their outer shell
The Periodic Table
Fact : As you move down through the groups an
extra electron shell is added:
Li
B
e
Na
M
g
K
C
a
E.g. Lithium has 3
H
electron in the
configuration 2,1
H
e
Ni
Sodium hasFe11
electrons in the
configuration 2,8,1
Potassium has 19
electrons in the
configuration __,__,__
Pt
C
u
Z
n
A
g
A
u
N
e
B
C
N
O
F
Al
Si
P
S
Cl Ar
Br Kr
I
X
e
H
g
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Periods
If you looked at an atom from each
element in a period
you would see…
Each atom has the same number of electron holding
shells.
What is happening to the number of electrons in the outermost
shell?
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Periods
Eg: The period 4 atoms each have 4 electron
containing shells
4th Shell
K (Potassium)
Kr (Krypton)
Atom
Atom
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Fe (Iron) Atom
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The groups
• The periodic Table is divided into several groups
based on the properties of different atoms.
• The table has 8 groups of elements plus a block of
transition metals.
• Some of the groups have special names:
– Group 1: alkali metals
– Group 2: alkaline earth metals
– Group 7: halogens
– Group 0 or 8: noble gases
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The groups
• Groups can be separated into metals and
non-metals
• Transition metals: atoms have more
complicated electron arrangements
• Contains many common metals such as
iron (Fe), Nickel (Ni) and copper (Cu).
 A group of elements is sometimes called a
family, because its elements resemble each
other. Sometimes they look alike and usually
behave alike.
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The Periodic Table
Fact : Most of the elements are metals:
H
Li
Be
These elements
are metals
He
Na Mg
K
Ca
Fe
Ni
Cu
Zn
Ag
Pt
Au
This line divides
metals from nonmetals
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Br Kr
I
Xe
Hg
These elements are
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non-metals
Regions of the Periodic Table
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Valence Electrons
• The number of outer or “valence” electrons in an atom affects
the way an atom bonds.
• The way an atom bonds determines many properties of the
element.
• This is why elements within a group usually have similar
properties.
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Group 1: The Alkali Metals
Alkali Metals •The first three elements of Group 1: lithium
[2,1], sodium [2,8,1], potassium [2,8,8,1]
– Soft metals that can be cut with a
knife
– So light that they float on water
– Silvery & shiny when freshly cut;
quickly tarnish
– Have low melting & boiling points
compared with other metals
 All react in a similar way
sodium
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Group 1: The Alkali Metals
• They have similar properties because:
– 1 electron in the outermost shell.
– they have one more electron than a
stable Noble Gas electron structure.
– So, they readily lose the outer
electron when they chemically react
Trends within group 1:
• Down the group:
– Reactivity increases as atoms get
larger–WHY?
– Melting and boiling points decreasesWHY?
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Group 2- the Alkaline earth metals
Alkaline Earth Metals
•Silvery metals
•Fairly reactive
–Less reactive
compared with
elements in
group I
•Many are found in
rocks in the earth’s
crust
Magnesium
Magnesium
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oxide
Group 2- the Alkaline earth metals
Trends down the group
 Less reactive compared with elements
in group 1; they have to give up two outer
electrons to obtain a full outer shell.
Reactivity increases down the group-WHY?
M.ps and B.Ps generally decrease down the
group.
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Group 7: The Halogens
Most common halogens: chlorine, bromine and iodine
chlorine
iodine
Bromine
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Group 7 –Halogens – Some uses
salt makers
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Group 7 –the Halogens
• Halogens have similar properties
because their atoms have 7 electrons
in the outer shell.
eg: fluorine [2,7], chlorine [2,8,7]
• They are reactive because their
atoms are just one electron short of a
full outer shell.
• They are diatomic because two
atoms can gain full shells by sharing
electrons with each other
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Group 7 –the Halogens
Trends within group 7:
•Down the group:
–Reactivity decreases as
atoms get larger.
–m.p and b.p increase
because the attraction
between the molecules
increase.
Gas
Liquid
solid
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Group 7: Halogens & its uses
Fluorine:
• Fluorides are added to toothpaste and sometimes
drinking water. It has been shown that fluorides
can reduce dental decay (damage to teeth)
especially in young children
• It is used to make making refrigerants and
detergents
Chlorine:
• The most common use of chlorine is in drinking
water and swimming pool as it can kill harmful
bacteria.
• To ,manufacture insecticides, solvents, bleach, food
paints, plastic, dyes, textiles, petroleum products,
paper products etc.
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Group 7: Halogens & its uses
Bromine:
• Bromine is also used to disinfect water as it can kill the
bacteria present in the water.
• The inorganic form of bromine is used in photography film,
• It is also used in, dyes and medicines.
Iodine:
• The compounds are basically used in medicine, photography
and dyes.
• Is a good antiseptic to kill bacteria
• Another very important use of iodine is as it is quite radio
opaque, it can be used as X-ray radio contrast agent, for
intravenous injection.
• Is also an important dietary mineral
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Group 8 – The noble (inert)
gases
• Non metals
• Colourless mono-atomic gases
• Very unreactive because they
have full outer shells ( V stable)
• All noble gases are not identical
• Density of the gases increase down
the group; because mass of atom
increases
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Colors Noble Gases
produce in lamp tubes:
• Ne (Neon): orange-red
• Ar (Argon): pale lavender
• He (Helium): pale peach
• Kr (Krypton): pale silver
• Xe (Xenon): pale, deep blue
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Jellyfish lamps made with noble
gases
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Transition Metals
• Most are good
Conductors of
electricity
• Malleable (easily
bent/hammered into
wires or sheets)
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Transition metals
•
•
•
•
•
•
•
Hard and dense
High m.p
Not very reactive
Form coloured compounds
Have variable valency
Many are used in making alloys
Many are used as catalysts
Iron in air gives iron(III) oxide
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Hydrogen
• Stands on its own in the
periodic table
• It has one outer electron,
like group 1 metals, but
unlike them it is a gas
• It usually reacts like a non
metal
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Trends across the periodic table
• Number of outer shell
electrons increase by one
from one group to the next
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Trends across the periodic table
• The electron arrangements of the first 20 elements:
• The number of outer shell electrons increase by 1 with each
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group.
General Periodic Trends
• Atomic and ionic size
• Metallic activity
• Nonmetallic activity
Higher effective nuclear charge
Electrons held more tightly
Larger orbitals.
Electrons held less
tightly.
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Trends…
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Atomic Size
• Size goes UP on going down a group.
• Because electrons are added further from
the nucleus, there is less attraction.
• Size goes DOWN on going across a period.
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Atomic
Radii
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Ion Sizes
+
Li,152 pm
3e and 3p
Li + , 78 pm
2e and 3 p
Forming
a cation.
• CATIONS are SMALLER than the atoms
from which they come.
• The electron/proton attraction has gone UP
and so size DECREASES.
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Ion Sizes
F, 71 pm
9e and 9p
F- , 133 pm
10 e and 9 p
Forming
an anion.
• ANIONS are LARGER than the atoms from
which they come.
• The electron/proton attraction has gone
DOWN and so size INCREASES.
• Trends in ion sizes are the same as atom
sizes.
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