Download 03. Periodic UK Edition PM6.5

Group 6 elements
GROUP 6 ELEMENTS
The most important elements in this group are oxygen
and sulphur, both of which are non-metals. The other
elements in this group, selenium, tellurium and
polonium (radioactive) are metalloids. Each element is
characterised by having six electrons in its outer shell.
Oxygen, sulphur, selenium and tellurium are also
known as the CHALCOGENS, a word that comes from
the Greek meaning ‘brass maker’, because all these
elements are found in copper ores, and copper is the
most important metal in making brass.
The most common member of this group is oxygen,
itself the most abundant element in the Earth’s crust
and which also makes a quarter of the mass and just
over a fifth of the volume of the Earth’s atmosphere.
Oxygen is essential for most living things, and its most
important compound is water (H2O, see page 13).
Oxygen and sulphur combine to form sulphur
dioxide SO2 – an acidic gas, illustrating the non-metal
chemistry of sulphur.
Relative size of
a hydrogen atom
Group 6 elements
have six electrons
in the outer shell
6
2
Oxygen, from the Greek for acid forming,
‘oxys genes’; chemical symbol O; Group 6,
period 2; non-metal; colourless as oxygen gas
and dark blue as ozone gas; atomic number 8;
approximate relative atomic mass 16.
6
8
2
Sulphur, from the Sanskrit ‘sulvere’;
chemical symbol S; Group 6, period 3;
non-metal; yellow solid; atomic number
16; approximate relative atomic mass 32.
Selenium, from the Greek for the
moon, ‘selene’; chemical symbol Se;
Group 6, period 4; metalloid; grey
solid; atomic number 34;
approximate relative atomic mass 79.
6
18
18
8
2
6
18
8
2
Tellurium, from the Latin for earth, ‘tellus’;
chemical symbol Te; Group 6, period 5;
metalloid; silvery-white solid; atomic number
52; approximate relative atomic mass 128.
6
18
32
18
8
2
(Right) Oxygen makes up
21% of the atmosphere
by volume and 23% by
mass. It is produced by
plants during
photosynthesis and used
by living things during
respiration.
Polonium, named after Poland;
chemical symbol Po; Group 6,
period 6; metalloid, radioactive;
grey solid; atomic number 84;
approximate relative atomic
mass (209).
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Demonstration 1: oxygen dissolves in water
and so can oxidise some dissolved substances
Concentrated ammonia solution is added from a
pipette to a test tube containing white copper(I)
chloride (햲). This produces a colourless solution of
copper(I) ammine. However, the copper(I) ammine
is not stable in air and rapidly oxidises to copper(II)
ammine which is a deep indigo-blue colour (햳).
햳
햲
The way to see that this effect is produced by
oxidation is to leave the tube to stand. Within a few
moments, a very deep blue layer begins to form on
the surface of the solution that can be reached by the
air. The first signs occur in the shape of the meniscus
where the liquid meets the air. Over some minutes,
air dissolves in the solution to about one and a half
centimetres, and thus the blue colour gradually
extends into the solution.
If the blue part of the
liquid is taken off by using a
햴
pipette, the surface part of
the solution rapidly returns
to being blue as oxidation
occurs at the meniscus again.
Remarks
Deep blue
copper(II)
ammine
Ammonia
solution
The penetration of oxygen
into water, and the very
reactive nature of oxygen,
are also the reasons that
nails rust when left to stand
in water (햴).
Colourless
copper(I)
ammine
EQUATION: The rusting of iron
Copper(I)
chloride
Iron + water + oxygen ➪ iron(III) hydroxide ➪ iron(III) oxide + water
4Fe(s) + 6H2O(l) + 3O2(g) ➪ 4Fe(OH)3(s) ➪ 2Fe2O3(s) + 6H2O(l)
Rust
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