2 Chapter 6 • organising elements Organising elements

Fig 6.3 Xxxx.
All the things we buy or use are made of different materials, which are made up of different elements, which, in turn, are
made up of atoms. The choice of which material to use to make things is based first on the properties needed—which
material is best suited for its intended purpose. Additional factors may include availability, cost or the impact on health
or the environment.
Scientists use their knowledge of the elements to understand and explain why different materials behave in different
ways. To ensure they’re all speaking the same language and to assist in their investigations, scientists use universal
methods to name and organise elements. The periodic table is the most fundamental way in which to organise elements
because it is based on both the known properties of the elements and the very structure of the atoms themselves.
6.2 How are the elements organised?
Our modern lives depend on a number of unfamiliar materials, the
properties of some of which may have been discovered only recently.
When was the last time you stopped to think how your MP3 player
or mobile phone worked? Have you ever given any thought to where
the materials that make these gadgets come from?
The touch screen technologies you have encountered rely on
indium, which is number 49 on the periodic table. In its alloy form,
combined with tin and oxygen, indium has the amazing ability to
be both transparent and capable of conducting electricity. Hafnium,
element number 72, is so resistant to heat that it is used to coat
rocket thrusters for trips to the moon.
These types of properties have been used to classify elements for
centuries. As more properties became known, with new technologies
and a deeper understanding of matter, some rearrangement of the
elements in the periodic table was necessary. The periodic table you
know today may well change again in the future ...
6.3
Many substances give off coloured light when small samples
are placed in a flame. When this light is seen through a
spectroscope—an instrument that breaks the light up into its
colours—a pattern of coloured lines is observed. This pattern is
known as an emission spectrum and is unique for each element.
Such a simple experiment could be conducted well
before any understanding of atomic structure was proposed.
Consequently, the emission spectra of different substances were
one of several observations that contributed to early ideas about
the connection between properties and the structure of atoms.
Fig 6.2 Xxxx.
1 Think of three
gadgets you
use every day.
For each gadget,
identify the properties
of the materials used
that make them particularly
suited to the purpose of the gadget.
2 Does it matter to you why certain materials
have certain properties? Explain.
3 Consider an item of clothing. What is the
purpose of the item? To keep you warm?
To feel comfortable on your skin? Or to look
good? Are there other properties of the
materials used to make that item of clothing
that make it particularly suited to your
needs?
How are properties linked to atomic structure?
1 We now know that emission spectra are unique for
each element. How do you think this would help
scientists to analyse the composition of substances?
2 Would you consider observations of emission
spectra to be classified as direct or indirect
experimental evidence? Explain.
3 Without an explanation, observations can be
misleading and/or misunderstood. In the absence of
a clear explanation, how can scientists make sure
that their observations are as reliable as possible?
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