ELECTRON CONFIGURATIONS

Early Models of the Atom Rutherford Small, massive, positively charged nucleus nucleus surrounded by electrons Niels Bohr Showed electrons occupy orbitals Orbitals have certain energy levels

Electrons Orbit the nucleus At ground state they occupy lowest energy state Electrons excited by heating When cooled electron returns to original orbital releasing energy (light)

Energy Levels and Sub-levels Electron configuration uses numbers and letters to describe position and energy level of electrons present. Energy level identified by a number that relates to rows in the periodic table. 1, 2, 3 etc. A letter represents a sub-level. s,p,d or f. First level has 1 sublevel (1s), second has 2 (2s, 2p) , third has three (3s, 3p, 3d). Each sublevel has a number of orbitals which can hold two electrons. A superscript number identifies specific orbital. S has 1, P has 3, d has 5 and f has 7

Orbitals and the Periodic Table

Filling Orbitals Electrons always fill orbitals with the lowest energy first. 1s<2s <2p<3s<3p<4s<3d Copy Fig 5.2 From the Study guide

Orbital filling Diagram Orbitals are filled so that as many electrons remain unpaired as possible. High energy level ___ ___ ___ ___ ___ Example: Nitrogen 7 electrons 3d ___ 4s ___ ___ ___ 3p ___ 1s2 2s2 2p3 ↑ ↑ ↑ 3s ___ ___ ___ ↑ ↓ 2p ___ 2s ↑ ↓ Low energy level ___ 1s

Energy levels and sub-levels Main energy level Sub-levels Max. no. of electron pairs in sub-level Max. no. of electrons in sub-level Max. no. of electrons in main level 1 s 2 8 p 3 6 18 d 5 10 4 f 7

Example Lithium with 3 electrons 1s2 2s1 Potassium with 19 electrons Iron with 26 electrons 1s2 2s2 2p6 3s2 3p6 4s1 1s2 2s2 2p6 3s2 3p6 3d6 4s2

Affect of Stability Full and half filled orbitals have the most stable states. This can result in a higher level orbital e.g. 3d being filled before a lower level orbital e.g. 4s E.g. Copper 1s2 2s2 2p2 3s2 3p6 3d10 4s1

Ions When ions are formed electrons are gained (anion) or lost (cation) to form a stable arrangement. E.g. P3-, S2-, Cl- & Ar are all 1s2 2s2 2p2 3s2 3p6 They are Isoelectronic

Ion Formation Electrons are lost from highest energy levels first. That means 4s electrons are lost BEFORE 3d electrons

Write electron configuration for each of the following atoms: Practice Write electron configuration for each of the following atoms: C 6. Ca S 7. Ni Ti 8. Zn V 9. Cr Br 10. Cu

Give the electron configuration of each of the following ions Cu2+ Br- Mn2+ Ca2+ Ga3+ Complete the following table Element or ion Atomic number No of protons Mass number No of neutrons Charge Electron configuration 11 23 Fe3+ 30 3+ 16 34 1S2 2S2 2P6 3S2 3P6 28 [Ar] 3d3