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Samenvatting it's all chemistry 3 vwo hoofdstuk 7 & 8
samenvatting van scheikunde hoofdstuk 7 & 8, over de ''classification of substances" en over ''organic chemistry''
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Voorbeeld 2 van de 11 pagina's
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Chemistry summary chapter 7 & 8Ch. 7: a classification of substances:
7.1 conductivity of electricity
Conductivity:
You can classify substances around you in many some different ways. For this one you consider a
property of a substance, namely electrical conductivity.
A substance will conduct electricity when two conditions are met simultaneously:
• The substance must consist of changed particles
• The charged particles must be able to move freely
Metals:
A metal will conduct electricity in both the solid and the liquid phase. In both phases must therefore
be charged particles that can move freely.
Molecular substances:
A molecular substance is a substance that only consists of atoms of non-metals (for example candle
wax C18 H36 O2). Molecular substances do not conduct electricity in either phase.
Salts:
Salts consist of metal and a non-metal atoms (for example Zinc chloride). Salts cannot conduct
electricity in the solid phase, but in the liquid phase they can. Salts therefore do consist of charged
particles, but cannot always move freely.
7.2 Metals
Characteristics of metals:
There are just over 70 elements that are metals. Metals have some characteristics
in common, they:
• Have, in there pure form, a shiny surface
• Conduct heat and electricity
• Are malleable, especially when they are hot
• Can, when molten, be mixed with other metals
The metal atoms are arranged regularly in a lattice, which for metals is called a
metallic lattice.
In figure 7.8 you can see an atomic model of Bohr for a sodium atom. The electron
in the outer shell is called the valence electron. A metal atom can release one or
two electrons from its outer shell and then adopt a positive charge. Such a
positively charged atom is called an ion.
, A metallic lattice is formed when positive metal ions are arranged in regular pattern. The delocalised
valence electrons move among these positive ions. This way an attractive force is established
between the positively and negatively charged particles. The bonding between metal ions and
delocalised electrons is called metallic bonding. In figure 7.9 you can see a model of the metallic
lattice of sodium.
In solid state, there are negatively charged electrons in the metal which can move, so the metal can
conduct electricity. In the liquid state, the positively charged metals aren’t in a lattice anymore, but
move through the liquid. There are then – charged electrons and + charged metal ions that can
move. There is also electrical conductivity.
What this looks like at micro level:
In the solid state the positive ions can (after some heating) move along each other within the lattice,
hardly changing the pattern (you bend the metal). The force of attraction between positive and
negative particles remains, so the metal can be shaped without breaking.
Difference between metals:
You can classify metals as light and heavy metals. You need to take the difference in density into
account. An important distinction between metals is their difference in nobleness. This refers to the
resistance of a metal to corrosion. Corrosion is a complex process in which metals react with
substances from the environment, such as water and oxygen. In iron this sometimes called rusting.
Based on the differences in resistance to corrosion, metals are classified as precious metals, semi-
precious metals, reactive metals and highly reactive metals.
Alloys:
The properties of a metal can be changed by melting a metal together with another metal. An alloy
(cooled down mixture of 2 metals) is then formed.
Alloy Metal components Application
Brass Copper and zinc Yellow copper: bolts, nuts,
nipples, soldering (hard)
Bronze Copper and tin Artefacts, tools
Solder Tin and lead Soldering (soft)
Silver amalgam (alloy Silver and mercury Fillings in dentistry
containing mercury)
Duralumin Aluminium and copper Aircraft construction, motor
cycles
Stainless steel Iron and chromium (or nickel) Construction, household
articles
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