Periodic trends
In chemistry, the periodic table has periodic trends. These are patterns in the periodic table that show how some elements change across the periods (rows) and groups (columns). They were discovered by Dmitri Mendeleev in 1863. There are many different periodic trends. These trends can be atomic radius, ionization energy, electron affinity, electronegativity, nucleophilicity, electrophilicity, valency, nuclear charge, and metallic character.[1]
Mendeleev made the periodic table according to atomic weight.[2] He put empty spaces where newer elements would be, once they were discovered.[3] His periodic table let him predict how 3 unknown elements would act. These elements would later be discovered to be gallium, scandium, and germanium.[4] Mendeleev organized the table by atomic weight. However, Henry Moseley discovered that organizing the table by atomic number would better show the properties of the periodic table.[3]
Summary of trends
[change | change source]| Periodic property | Across the period | Down the group |
|---|---|---|
| Atomic radius | Decreases | Increases |
| Nucleophilicity | ||
| Metallic character | ||
| Nuclear charge | Increases | |
| Effective nuclear charge | Decreases | |
| Ionization energy | ||
| Electron affinity | ||
| Electronegativity | ||
| Nonmetallic character | ||
| Valence electrons | Constant | |
| Valency | First increases then decreases |
Atomic radius
[change | change source]
The atomic radius is the distance from the atomic nucleus to the farest electron orbital. However, electron orbitals don't have a set size because of quantum mechanics. Therefore, atomic radius is found by putting two of the same atom next to each other. Then, half the distance between the two atomic nuclei is found. This is the atomic radius.
In general, the atomic radius becomes bigger when one goes down a group (column). As one moves down the group, there are more electron shells. This new shell makes the electron bigger.
In general, the atomic radius becomes smaller as one goes from left to right in a period (row). As one goes from left to right, the atomic number becomes bigger. As one goes from left to right, there are also more valence electrons in the furthest shell. More valence electrons creates a bigger effective nuclear charge. A bigger effective nuclear charge makes the atomic radius of an element smaller.[5][6][7]
Related pages
[change | change source]References
[change | change source]- ↑ Schrobilgen, Gary J. (2019). "Chemistry at the Edge of the Periodic Table: The Importance of Periodic Trends on the Discovery of the Noble Gases and the Development of Noble-Gas Chemistry". In Mingos, D. Michael P. (ed.). The Periodic Table I. Structure and Bonding. Vol. 181. pp. 157–196. doi:10.1007/430_2019_49. ISBN 978-3-030-40024-8.
- ↑ Edwards, Peter P.; Egdell, Russell G.; Fenske, Dieter; Yao, Benzhen (18 September 2020). "The periodic law of the chemical elements: 'The new system of atomic weights which renders evident the analogies which exist between bodies'". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 378 (2180): 20190537. Bibcode:2020RSPTA.37890537E. doi:10.1098/rsta.2019.0537. PMC 7435142. PMID 32811357.
- ↑ 3.0 3.1 Egdell, Russell G.; Bruton, Elizabeth (2020-09-18). "Henry Moseley, X-ray spectroscopy and the periodic table". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 378 (2180): 20190302. Bibcode:2020RSPTA.37890302E. doi:10.1098/rsta.2019.0302. PMID 32811359.
- ↑ Sztejnberg, Aleksander (2018). "Dmitri Ivanovich Mendeleev (1834 – 1907), Prominent Russian Scientist. References to His Great Scientific Achievements in the Literature between 1871 and 1917". Revista CENIC. Ciencias Químicas. 49 (1): 1–13.
- ↑ "atomic and ionic radius". www.chemguide.co.uk. Retrieved 2022-06-30.
- ↑ Huggins, Maurice L. (April 1922). "Atomic Radii. I". Physical Review. 19 (4): 346–353. Bibcode:1922PhRv...19..346H. doi:10.1103/PhysRev.19.346.
- ↑ Rahm, Martin; Hoffmann, Roald; Ashcroft, N. W. (17 March 2017). "Corrigendum: Atomic and Ionic Radii of Elements 1–96". Chemistry – A European Journal. 23 (16): 4017. doi:10.1002/chem.201700610. PMID 28318129.
Further reading
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