Topic 3: The periodic table
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Which way are groups and which was are periods?
Groups are the vertical columns Periods are the horizontal rows
Roughly where are metals, non metals and metalloids on the periodic table? (imagine)
Yellow: Metals Pink: Non metals Green: Metaloids
What are the elements called when they have both properties of both metals and non metals?
Metalloids shaded green are metalloids
What are metalloids?
Elements when they have both properties of both metals and non metals
Which is the most abundant element in the Universe: about 90% of the atoms?
Hydrogen
What are noble gases also known as?
Inert gases
What are the elements that have been omitted called?
Lanthanoid elements and actinoid elements
What does a metallic structure consist of?
consists of a regular lattice of positive ions in a sea of delocalised electrons
What can the metallic and non-metallic properties of elements be related to? What energy?
Ionisation energies
What must the element do to form a metallic structure?
They must be able to lose electrons fairly readily to form positive ions
How does the ionisation energy change across a period and down a group?
Across: ionisation energy increases → so elements lose electrons less easily • so metallic structures are formed by elements on the left hand side of the periodic table, which have lower ionisation energies Down: Ionisation energy decrease → therefore elements are much more likely to exhibit metallic behaviour lower down a group
What are the properties a metallic element would generally have?
• Large atomic radii • Low ionisation energies • Less exothermic electron affinity values • Low electronegativity
How are valence electrons presented on the periodic table?
As groups
For groups 13-18, how are valence electrons shown?
group number - 10 ex. elements in group 13 have 3 valence electrons
What does the period number indicate?
The number of shells (main energy levels) in the atoms - or which is the outer shell (main energy level)
What is the periodic table divided into blocks according to?
According to the highest energy sub-shell (sub-level) occupied by electrons. → in the s block, all elements have atoms in which the outer shell electron config. is ns1 or ns2 (n is the shell number) and in the p block it is the p subshell that is being filled
What are the physical properties that can be deduced from the periodic table?
• Atomic radius • Ionic radius • First ionisation energy • Electron affinity • Electronegativity
What does the atomic radius describe?
The size of an atom The larger the atomic radius, the larger the atom
How does atomic radius change across and down a period?
Across: Decreases across a period, because nuclear charge increases across the period with no significant change in shielding → Meaning that the outer electrons are pulled in more strongly and the radius is smaller Down: Increase because atoms have increasingly more shells
What does the ionic radius measure?
The size of an ion
In general, are positive/negative ions bigger or smaller than their atomic radii?
In general, the ionic radii of positive ions are smaller than their atomic radii, and the ionic radii of negative ions are grater than their atomic radii
Why does Na have a bigger ionic radius than Na+?
Because Na has one extra shell whereas Na+ lost one. There is also a greater amount of electron-electron repulsion in Na because there are 11 electrons compared to 10. The electron cloud is therefore larger in Na than in Na+ because there are more electrons repelling for the same nuclear charge pulling the electrons in.
How does ionic radius change across a period?
It is not a clear-cut trend because the type of ion changes going from one side to the other Positive ions are formed on the left hand side and the negative ion on the right hand side. Even though on the same period (have same shells), there are just more valence electrons on the right hand side (negative) for there to be a stronger election-electron repulsion
How does the ionic radius change for negative and positive ions?
For positive ions, there is a decrease in ionic radius as the charge on the ion increases For negative ions, the size increases as the charge increases