Electronic Structure Flashcards
What happens in the currently accepted model of the atom?
- electrons have fixed energies
What do electrons do?
- they move around the nucleus in certain regions of the atom called shells or energy levels
What is each shell given?
- a principle quantum number
The further the shell is from the nucleus………
- the higher its energy and the larger its principle quantum number
What’s the principle quantum number for the 1st electron shell and describe its energy?
1
- this shell has the lowest energy
What is the principle quantum number of the 2nd electron shell?
2
What is the principle quantum number of the 3rd electron shell and describe its energy?
3
- this shell has the highest energy
What do experiments show?
- that not all the electrons in a shell have exactly the same energy
What does the atomic model explain?
- shells are divided into subshells
- different shells have different numbers of subshells, which each have a different energy
What can the sub shells be?
- s subshells
- p subshells
- d subshells
- f subshells
What does the first shell contain?
- one subshell 1s
What does the second shell contain?
Two subshells 2s and 2p
What does the third shell contain?
- 3 subshells 3s 3p 3d
What does the fourth shell contain?
- 4 subshells 4s 4p 4d 4f
What do the subshells have?
- different numbers of orbitals which can each hold upto 2 electrons
How many orbitals are there in the s subshell?
1
How many orbitals are there in the p subshell?
3
How many orbitals are there in the d subshell?
5
How many orbitals are there in the f subshell?
7
What is the maximum number of electrons in the s subshell?
2
What is the maximum number of electrons in the p subshell?
6
What is the maximum number of electrons in the d subshell?
10
What is the maximum number of electrons in the f subshell?
14
What is the total number of electrons in the 1st shell?
2
What is the maximum number of electrons in the 2nd shell?
8
What is the maximum number of electrons in the 3rd shell?
18
What is the maximum number of electrons in the 4th shell?
32
What is electron configuration?
- the number of electrons that an ion or atom has, and how they are arranged
What are the different ways that electron configuration can be shown?
- subshell notation
- arrows in boxes
- energy level diagrams
Describe the arrows in boxes method of electronic structure
- each of the boxes represents one orbital
- each of the arrows represents one electron
- the up and down arrows represent the electrons spinning in opposite directions
- two electrons can only occupy the same orbital if they have opposite spin
Describe the energy level diagrams for electronic configuration
- these show the energy of the electrons in different orbitals as well as the number of electrons and their arrangement
What are the steps in showing the electron configuration?
- start with the principle quantum number
- then the subshell letter (lower case)
- then the number of electrons occupying the subshell (superscript)
Name the three rules for working out the electron configurations
- Aufbau principle
- Hund’s rule
- ions rule
Describe the aufbau principle
- as part of his work on electron configuration, Niels Bohr developed the aufbau principle, which states how electrons occupy sublevels
- the aufbau principle states that the lowest energy sublevels are occupied first
- this means the 1s sub level is filled first, followed by 2s 2p 3s 3p
- however the 4s sublevel is lower in energy than the 3d, so it will fill first
Describe Hund’s rule
- electrons prefer to occupy orbitals on their own, and only pair up when no orbitals of the same energy are available
Describe the ions rule
- for the configuration of ions from the s and p blocks of the periodic table, just add or remove the electrons to or from the highest energy occupied subshell
- for negative ions add electrons, for positive ions remove electrons
- count the number of electrons
- add or remove the electrons due to charge
- fill sublevels as for uncharged atoms
What is used as shorthand in electron configurations?
- noble gas symbols in square brackets
Describe the electron configuration of transition metals
- although the 3d sublevel is in a lower principle energy level than the 4s sub level, it is actually higher in energy
- this means that the 4s sublevel is filled before the 3d sub level
- when transition metals form ions, it is the 4s electrons that are removed before the 3d electrons
- count number of electrons in atom
- fill sublevels, remembering 4s is filled before 3d
- count number of electrons to be removed
- remove electrons starting with 4s
What decides the chemical properties of an element?
- the number of outer shell electrons
Describe the electronic structure of the s block elements
- groups 1 or 2 have 1 or 2 outer shell electrons, these are easily lost to form positive ions with an inert gas configuration
Describe the electron configuration of the p block elements
- group 5, 6 and 7 can gain 1,2 or 3 electrons to form negative ions with an inert gas configuration
- groups 4 to 7 can also share electrons when they form covalent bonds
Describe the electronic structure of group 0 elements
- have completely filled s and p subshells and don’t need to gain, lose or share electrons, their full subshells make them inert
Describe the pauli exclusion principle and spin
- the pauli exclusion principle states that each orbital may contain no more than two electrons
- it also introduces a property of electrons called spin, which has two states, up and down, the spins of electrons in the same orbital must be opposite
- a spin diagram shows how the orbitals are filled, orbitals are represented by squares and electrons by arrows pointing up and down
- when two electrons occupy a sublevel, they could either completely fill the same orbital or half fill two different orbitals
- if two electrons enter the same orbital, there is repulsion between them due to their negative charges
- the most stable configuration is with single electrons in different orbitals
