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IGCSE Chemistry Edexcel
1.4 The Periodic Table
Contents
1.4.1 Periodic Table: Basics
1.4.2 Electronic Configurations
1.4.3 Classify Metals & Non-Metals
1.4.4 Electronic Configuration & Reactivity
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1.4.1 Periodic Table: Basics
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Arrangement of the Periodic Table
There are over 100 chemical elements which have been isolated and identified
Elements are arranged on the periodic table in order of increasing atomic number
Each element has one proton more than the element preceding it
This is done so that elements end up in columns with other elements which have similar
properties
The table is arranged in vertical columns called groups and in rows called periods
Period: These are the horiz ontal rows that show the number of shells of electrons an atom
has and are numbered from 1 - 7
E.g. elements in period 2 have two electron shells, elements in period 3 have three electron
shells
Group: These are the vertical columns that show how many outer electrons each atom has and
are numbered from 1 – 7, with a final group called group 0 (instead of group 8)
E.g. group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements
have atoms with 6 electrons in the outermost shell and so on
The Periodic Table
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The Periodic Table of the Elements
Exam Tip
The atomic number is unique to each element and could be considered as an element's
“fingerprint”.
The number of electrons changes during chemical reactions, but the atomic number does not
change.
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1.4.2 Electronic Configurations
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Deducing Electronic Configurations
We can represent the electronic structure of atoms using electron shell diagrams
Electrons orbit the nucleus in shells and each shell has a different amount of energy associated
with it
The further away from the nucleus, the more energy a shell has
Electrons first occupy the shell closest to the nucleus which can hold a maximum of 2 electrons
When a shell becomes full of electrons, additional electrons have to be added to the next shell
The second shell and third shell can hold 8 electrons each
The outermost shell of an atom is called the valence shell and an atom is much more stable if it
can manage to completely fill this shell with electrons
In most atoms, the outermost shell is not full and therefore these atoms react with other atoms in
order to achieve a full outer shell of electrons (which would make them more stable)
In some cases, atoms lose electrons to entirely empty this shell so that the next shell below
becomes a (full) outer shell
Deducing electron configuration
You should be able to write the electron configuration for the first twenty elements
Electronic Configuration of the First 20 Elements Table
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Note: Although the third shell can hold up to 18 electrons, the filling of the shells follows a more
complicated pattern after potassium and calcium. For these two elements, the third shell holds 8 and
the remaining electrons (for reasons of stability) occupy the fourth shell first before filling the third
shell
Exam Tip
You should be able to represent the first 20 elements using either electron shell diagrams or
written electronic configuration.
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Electronic Configurations & the Periodic Table
Electronic configuration: The arrangement of electrons into shells for an atom (e.g. electronic
configuration of carbon is 2 . 4)
Electronic configuration and position in periodic table
The number of notations in the electronic configuration will show the number of shells of
electrons the atom has, showing the period
The last notation shows the number of outer electrons the atom has, showing the group
Example: Electronic configuration of chlorine:
Shorthand electronic configuration
Period: The red numbers below the electronic configuration show the number of notations which
is 3, showing that a chlorine atom has 3 shells of electrons
Group: The last notation, which is 7, shows that a chlorine atom has 7 outer electrons matching
group 7 of the periodic table
The position of chlorine on the periodic table
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The position of chlorine in the periodic table
Exam Tip
All of the shells up to the outer shell will be full. Electron transfer occurs with electrons from the
outer shell only.You can use the term ‘shell’ or ‘energy level’ to describe the space that electrons
occupy.
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1.4.3 Classify Metals & Non-Metals
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Classify Metals & Non-Metals
We can use properties such as electrical conductivity and acid-base character to classify
elements as metals or non-metals
Characteristic Properties of Metals and Non-Metals
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Metals & Non-Metals in the Periodic Table
The location of the metals and non-metals shows a clear pattern when highlighted on a periodic
table
Another thing that is striking, is that you can see that the vast majority of elements are metals
A zig-zag line between the blue and purple elements in this diagram separates the metals on the left, from
the non-metals on the right. Elements which border the line are hard to classify as they have
characteristics of both sides, so the term semi-metal or metalloid is used.
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1.4.4 Electronic Configuration & Reactivity
Similar Chemical Properties
Chemical properties of elements in the same group
Elements in the same group in the periodic table will have similar chemical properties
This is because they have the same number of outer electrons so will react and bond similarly
The group number of an element which is given on the periodic table indicates the number of
electrons in the outer shell (valence electrons)
This rule holds true for all elements except helium; although is in group 0, it has only one shell,
the first and innermost shell, which holds only 2 electrons
We can use the group number to predict how elements will react as the number of valence shell
electrons in an element influences how the element reacts.
Therefore, elements in the same group react similarly
By observing the reaction of one element from a group, you can predict how the other
elements in that group will react
By reacting two or more elements from the same group and observing what happens in those
reactions you can make predictions about reactivity and establish trends in reactivity in that
group
For example, lithium, sodium and potassium are in group 1 and can all react with elements in group
7 to form an ionic compound
The group 1 metals become more reactive as you move down the group while the group 7 metals
show a decrease in reactivity moving down the group
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Why Noble Gases are Unreactive
The elements in group 0 of the periodic table are called the noble gases
They are all non-metal, monatomic (exist as single atoms), colourless, non-flammable gases at
room temperature
The group 0 elements all have full outer shells of electrons; this electronic configuration
is extremely stable
Elements participate in reactions to complete their outer shells by losing, gaining, or
sharing electrons
The Group 0 elements do not need to do this, because of their full outer shells which makes
them unreactive and inert
Other than helium which has 2 electrons in its outer shell, the noble gases have eight valence
electrons (which is why you may see this group labelled “group 8”)
Electronic configurations of the Noble gases:
He = 2
Ne = 2, 8
Ar = 2, 8, 8
Kr = 2, 8, 18, 8
Xe = 2, 8, 18, 18, 8
The periodic table highlighting the noble gases – they occupy the group furthest to the right
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