Summary Chemistry Edexcel IGCSE: Topic 2; Periodic table and bonding
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Course
Science
Institution
GCSE
Chemistry Edexcel IGCSE
All content in Topic 2
Everything you need to know about the Periodic Table and boding with adequate detail.
Notes taken from the CGP Chemistry guide for this exam board.
Includes extra detail and visual guides.
Section 2- Periodic table & Bonding
The Periodic Table
In 1869, Dmitri Mendeleev arranged 50 known elements in order of atomic mass to make a
Table of Elements. It placed elements with similar chemical properties in the same vertical
groups, but he found that he must leave gaps in the table for it to work. The gaps predicted the
properties of undiscovered elements. Since, elements have been found to fit the gaps left in
Mendeleev’s table.
⤷ There are 100ish elements that all materials are made of, with more still being ‘discovered’.
⤷ The modern periodic table shows the elements in order of increasing atomic number.
⤷ It is laid out so that elements with similar properties form vertical columns called groups.
⤷ The group to which an element belongs corresponds to the number of electrons in its outer shell.
(Group 1 elements have 1 outer shell electron etc.)
⤷ Named groups: Group 1- The alkali metals, Group 7- the halogens, Group 0- the noble gases.
⤷ The rows are called periods. The properties of elements change as you move along the period.
The elements in a group all have the same number of electrons in their outer shell, hence why
they share similar properties. Hence they are arranged this way.
When only a small number of elements were known, the periodic table was made by looking at
the features of elements and arranging them in groups.
The properties of elements depend on the number of electrons they have. Atomic number is
therefore significant as it’s equal to the number of electrons each atom has. However the
number of electrons in the outer shell is more important.
The periodic table is split into metals (left) and nonmetals(right), by a zig-zag line going from
boron to astatine.
Metals conduct electricity because they allow electrons to pass through them easily. Metal oxide
is basic. This means they will neutralise acids. Metal oxides that dissolve will form solutions with
a pH of more than 7.
Non-Metals are poor conductors of electricity. Non metal oxides are acidic, This means they will
neutralise bases. They dissolve in water to form solutions with a pH of less than 7.
, Group 0 elements (noble gases)are colourless and include helium, neon and argon. They are
inert (unreactive) because it takes a lot of energy to add/remove electrons from a noble gas
atom, having a complete outer shell. Because they are inert, noble gases exist as single atoms.
Electron shells
Electrons always occupy shells/ energy levels. The lowest
energy levels are always filled first.
The first shell can have 2 electrons, and the second & third
shell can have 8.
Electron configuration can be shown as a diagram(→)
or as numbers (2.8.3)
The number of shells in an electron is the same as the period
of the element.
The group number tells you how many electrons occupy the outer shell.
Ions
⤷ charged particles. They can be single atoms or groups of atoms. Simple ions form when atoms
lose/gain electrons.
⤷ Anions (negative ions) form when atoms gain electrons (more electrons than protons)
⤷ Cations (positive ions) form when atoms lose electrons (more protons than electrons)
⤷ The number of electrons lost/ gained is the same as the charge of the ion.
⤷ Group 1,2 and 3 elements are metals which lose electrons to form positive ions.
⤷ Group 5, 6 and 7 are non-metals which gain electrons to form negative ions
⤷ Elements in the same group form ions with the same charge. (Group 1 elements form 1+ ions,
Group 2 elements form 2+, Group 7 elements form 1- ions)
⤷ MUST LEARN THESE IONS!:
Ag+, Fe²+, Pb²+, Cu²+, Fe³+, Zn²+, Hydrogen: H+, Ammonium: NH₄+, Nitrate: NO₃-, Hydroxide:
OH-, Carbonate: CO₃²-, Sulphate SO₄²-.
(Electrostatic attraction- when 2+ oppositely charged particles are attracted to each other.)
Ionic bonding
Usually, when a metal reacts with a non metal, the metal atom loses electrons to form a cation,
and the nonmetal gains an electron to form an anion. These oppositely charged ions are
strongly attracted to one another by electrostatic attractions called ionic bonds. This can be
represented by ‘dot and cross’ diagrams. E.g.
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