Electron Configurations Ch. 4 Atomic Structure Electron Configurations

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

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

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

Rules for Arrangements

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

Order for Filling Sublevels

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

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

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

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

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

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

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

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

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

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

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

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

Atomic/Ionic Radii

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

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-

Ionization Energy

Ionization Energy

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

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

Electron Affinity

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

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

Electronegativity

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