1. Electron Configurations
Ch Atomic Structure
Electron Configurations

2. Electron Configurations
the arrangement of electrons in an atom
each type of atom has a unique electron configuration
electrons tend to assume positions that create the lowest possible energy for atom
ground state electron configuration- lowest energy arrangement of electrons

3. Rules for Arrangements
Aufbau Principle- an electron occupies the lowest-energy orbital that can receive it
Beginning in the 3rd energy level, the energies of the sublevels in different energy levels begin to overlap

4. Rules for Arrangements
Pauli Exclusion Principle- no two electrons in the same atom can have the same set of 4 quantum numbers
Hund’s Rule- orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second
all unpaired electrons must have the same spin

5. Rules for Arrangements

6. Writing Configurations
Orbital Notation:
an orbital is written as a line
each orbital has a name written below it
electrons are drawn as arrows (up and down)
Electron Configuration Notation
number of electrons in sublevel is added as a superscript

7. Order for Filling Sublevels

8. Writing Configurations
Start by finding the number of electrons in the atom
Identify the sublevel that the last electron added is in by looking at the location in periodic table
Draw out lines for each orbital beginning with 1s and ending with the sublevel identified
Add arrows individually to the orbitals until all electrons have been drawn

9. Silicon number of electrons: 14 last electron is in sublevel: 3p
1s 2s p s p
Valence Electrons- the electrons in the outermost energy level

10. Chlorine number of electrons: 17 last electron is in sublevel: 3p
1s 2s
2p s p

11. Sodium number of electrons: 11 last electron is in sublevel: 3s
1s2 2s2 2p6 3s1
1s s p 3s

12. Calcium number of electrons: 20 last electron is in sublevel: 4s
1s2 2s2 2p6 3s2 3p6 4s2
1s s p 3s
3p 4s

13. Bromine number of electrons: 35 last electron is in sublevel: 4p
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
1s s p 3s 3p
1s s p 3s 3p
4s 3d p
4s 3d p

14. Argon number of electrons: 18 last electron is in sublevel: 3p
1s2 2s2 2p6 3s2 3p6
1s s p 3s 3p

15. Noble Gas Notation short hand for larger atoms
configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets

16. Periodic Table and Periodic Trends
Ch. 5: Atomic Structure
Periodic Table and
Periodic Trends

17. Periodic Table Russian, Dmitri Mendeleev
when he arranged them by atomic mass, he found similar properties at certain intervals
published the first periodic table in 1869
left empty spaces where he predicted undiscovered elements should be
confirmed his predictions and persuaded other chemists

18. Periodic Table
In 1911, Henry Moseley (English) found that the pattern worked best if arranged by number of protons
Our current periodic tables use this method or arrangement

19. Atomic Radii
Defined by the edge of its orbital but since the edges are fuzzy, difficult to determine
Atomic Radii – half the distance between the nuclei of identical atoms that are bonded together

21. Atomic/Ionic Radii

22. Which is bigger?
Na or Rb?
Na or S?
S or Te?

23. Ionization Energy
An electron can be removed from an atom if enough energy is used
Ionization energy – the energy required to remove one electron from a gaseous neutral atom
A + energy  A+ + e-

24. Ionization Energy

25. Ionization Energy

26. Which has higher IE?
Li or F?
Ca or P?
Ba or Li?

27. Electron Affinity
Electron Affinity – the energy change when an electron is added to a gaseous neutral atom
exothermic (-)
A + e-  A- + energy

29. Electron Affinity

30. Which has higher EA?
Ge or C?
In or I?
Mg or F?

31. Electronegativity applies when an atom is in a compound NOT alone
Electronegativity – measure of how strongly an atom attracts electrons when it is in a compound
Fluorine (the most electronegative element) is assigned a 4.0 and then all the others were determined by comparison

34. Electronegativity

35. Which has higher electronegativity?
Sr or Be?
P or O?
Si or Cl?