1.18 - 1.21 The periodic table
1.18 Organising the Elements
1.19 Deducing electron configurations
A carbon atom has 6 protons and therefore 6 electrons. The electrons are arranged in two shells; 2 electrons in the first shell and 4 electrons in the second shell. The electron configuration of a carbon atom can be therefore represented as: 2, 4
1.19 Activity 1. Looking for patterns
Filling up nicely.
Starting with the innermost shell .
2 electrons ( maximum for shell 1)
8 electrons ( maximum for shell 2)
7 electrons left over = (17 - (8 + 2))
1.20 - 1.22 Activity 2. Periodic variations
Study the presentation to investigate and answer the following questions:
- What can you say about the connection between the number of electrons in the outer shell of the atoms and the group number shown?
- What can you say about the number of occupied electron shells and the period number.
- What can you say about the electron configuration of the noble gases?
- Where on the periodic table are the metals found?
- What can you say about the electrical conductivity of the metals compared with that of the non- metals?
The metals can be found to the left and bottom of the periodic table.
Acid or base?
This video animation shows how the acid/base properties of the oxides varies across the periodic table. The pattern is not perfect partly because many non-metals can form more than one oxide and also because their solubility varies. However a general trend can be seen.
Stop the video after 21 seconds and try to predict what the trend will be. Test your prediction by watching the rest of the video.
The oxides of the semi-metal elements (e.g Si, Ge) tend to be "neutral" and not very soluble in water. These oxides will however dissolve in both acids and in alkalis. Such oxides are known as amphoteric oxides.
1.19 Activity 3. Configurations and positions
1.23 Family resemblances
Looking at the electron arrangements of the atoms in groups 1, 2 and 3 you can see that the atoms of group 1 elements have 1 electron in their outermost shell, group 2 elements all have 2 electrons and group 3 elements 3. This carries on in groups 4,5,6,7.
For example: lithium Li , sodium Na, and potassium K :
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1.24. Activity 4. A Noble family
Hence, the noble gases are chemically unreactive or inert.
noble, inert, 8 or 0?
In the shortened periodic table, the group number is the same as the number of outer shell electrons in the atoms of that group. This is not true for the noble gases. Helium only has 2 electrons in its outer shell, while the others all have 8 . Because of this, the group number was changed to 0 .
Originally the group was known as the inert gases as it was thought that they would not react with anything. However in 1962 a chemist called Bartlett made a compound from Xenon. The preferred name for the group is now the noble gases.
Noble Gases quiz
Why is argon used to fill light bulbs ? Open or Close
Argon gas is used to surround the filament in incandescent light bulbs. Argon is inert and therefore does not react with the white hot filament. If air was used the filament would quickly react with the oxygen in it and the lamp would blow.
Why is helium rather than hydrogen preferred for use in airships? Open or Close
Helium and hydrogen are both less dense than air and so can both be used to provide the uplift for a airship. However, hydrogen is very flammable and was the cause of the Hindenburg disaster in 1937.
Helium is inert and is therefore quite safe to use in gas balloons and airships.
What does the word inert mean ? Open or Close
Inert is used to refer to a substance that does not react with others. The noble gases are all fairly inert due to the full outer shell of electrons.
Nitrogen gas is quite inert due to its triple bond. The precious metals such as gold, platinum, and silver can also be describes as inert. The noble gases are thought to have been named after these noble metals.
Why is the preferred name for this group the "noble gases" Open or Close
For a long time, many people believed the noble gases to be completely nonreactive and unable to form chemical compounds. Although these elements don't form compounds readily, examples of molecules containing xenon, krypton, and radon have been found. At high pressure, even helium, neon, and argon participate in chemical reactions. The name "noble" is preferable to inert since strictly speaking they are not completely inert.
Did you know? Open or Close
- The first noble gas to be discovered was argon.
- Argon glows violet in a gas discharge tube. It is the gas found in plasma balls.
- Argon gas is prepared by fractionating liquid air.
- The Earth's atmosphere contains 0.94% argon.
- Mars' atmosphere contains 1.6% Argon
- The thin atmosphere of the planet Mercury is about 70% argon.