Involved with bonding and determine chemical properties. ... The Periodic Table â The order in which electrons fill is somewhat confusing. The Perio...
Electron Configuration – a representation of how electrons fill atomic orbitals in an atom. (1) Aufbau Principle – (from German aufbau meaning “building up” or “construction”) ‒ Electrons occupy the available atomic orbitals from the lowest energy. (low to high) (2) Pauli Exclusion Principle – (named after Austrian physicist Wolfgang Pauli) ‒ A maximum of two electrons can occupy any atomic orbital. (3) Hund’s Rule – (named after German physicist Friedrich Hund) ‒ If there are more than one orbital with the same energy, occupy an empty orbital before pairing up. (if possible, don’t share) We can use the orbital energy diagram to help us know how these orbitals are filled. A symbol “3p4” means there are four electrons in the 3p subshell. A neutral atom of the element N has 7 electrons. Its electron configuration, based on the rules, is: 1s2 2s2 2p3 Because the electron configuration of an element can be very cumbersome to write out, we can write it in a short form or core notation by abbreviating the electrons that are a part of the closest previous noble gas of an atom. For example, the short form electron configuration for a neutral atom of N is: [He] 2s2 2p3. Example 1: Write the long- and short-form ground state electron configurations for the following species using the orbital energy diagram: Oxygen (8 electrons) Argon (18 electrons) 3s
Core Electrons – inner electrons, abbreviated by the noble gas. Valence Electrons – electrons in the highest energy electron shell. Involved with bonding and determine chemical properties. When atoms lose electrons to form cations, they lose the electrons found in the highest shell. When atoms gain electrons to form anions, they add electrons according to Aufbau Principle to the available orbital with the lowest energy.
The Periodic Table – The order in which electrons fill is somewhat confusing. The Periodic Table can be helpful for us to predict the electron configuration of an element because it is arranged in the way electrons are filled. s block 1s
p block 2s
1s
2p
3s
d block
3p
4s
3d
4p
5s
4d
5p
6s
5d
6p
7s
6d
7p f block 4f 5f
Example 2: Use the species in Example 1. Write the long form ground state electron configuration for the species in Example 1 using the Periodic Table instead of the orbital energy diagram. In the long form electron configuration, box the electrons that are core electrons, and circle the electrons that are valence electrons. Write the short form electron configuration of the species in Example 1 using the Periodic Table. Patterns in the Periodic Table – The valence electrons of an element determine its properties. Elements in each family across the Periodic Table have the same number of valence electrons. This explains why elements in the same family have similar chemical properties. Fill in the patterns observed for number of valence electrons and the expected ion formed for each family. H He 1s1 1s2 Li Be B C N O F Ne 1 2 2 1 2 2 2 3 2 4 2 5 2s 2s 2s 2p 2s 2p 2s 2p 2s 2p 2s 2p 2p2 2p6 Na Mg Al Si P S Cl Ar 1 2 2 1 2 2 2 3 2 4 2 5 3s 3s 3s 3p 3s 3p 3s 3p 3s 3p 3s 3p 3s2 3p6 General ns1 ns2 ns2 np1 ns2 np2 ns2 np3 ns2 np4 ns2 np5 ns2 np6 Form: # of Valence Electrons:
He:
1
2
3
4
5
6
7
2 Others: 8
Ion +1 +2 +3 –3 –2 –1 0 Formed Example 3: For each of the following elements, determine the number of valence electrons and predict the likely charge of a typical ion that might form. Titanium [Ar] 4s2 3d2 2 valence electrons Forms Ti2+ Selenium [Ar] 4s2 3d10 4p4 4 valence electrons Forms Se2– Notice that the elements tend to gain or lose electrons to form ions that have the same electron configuration (or are isoelectronic) as a noble gas, so we say that they have a pseudo-noble gas configuration. Elements in the same family tend to form ions that have the same charge because they have similar valence electron configurations.
