Electron ArrangementsElectron Configurations

Learning Objectives• Express the arrangement of electrons in

atoms using electron configurations

Electron Arrangements

• Heisenberg uncertainty principle – the principle that states that it’s impossible to know the exact velocity and position of an electron (or any other type of particle) at the same time

• Atomic orbital – an area around the nucleus where electrons are likely to be found– Four types of orbitals each with different

shape(s)• s, p, d, f

Atomic Orbitals

• Quantum numbers – the sets of numbers used to describe the properties of atomic orbitals and the electrons in them– Describe the shape, size, and

energy level of orbitals and the direction of electrons’ spins

• Principal quantum number (n) – a number that denotes an atomic orbital’s size and principle (or main) energy level– Energy levels are also called

shells– Electrons further from the

nucleus have more energy

Atomic Orbitals

• Principal energy levels are divided into sublevels– Sublevels are also called subshells

• Sublevels are labeled by the principal energy level they belong to and their orbital type

Atomic Orbitals

• Higher principal energy levels contain more sublevels

• Each sublevel type contains a different number of orbitals– s sublevels contain one s-orbital– p sublevels contain three p-orbitals– d sublevels contain five d-orbitals– f sublevels contain seven f-orbitals

• Each orbital holds up to two electrons– s sublevels hold up to two electrons– p sublevels hold up to six electrons– d sublevels hold up to ten electrons– f sublevels hold up to 14 electrons

Atomic Orbitals

• Electron configuration – a set of numbers and letters that describe an atom’s electron arrangement

• Ground-state electron configuration – an arrangement of electrons that gives an atom the least possible energy– Most stable electron arrangement– Three rules govern ground-state electron

configurations• Aufbau principle• Pauli exclusion principle• Hund’s rule

Ground-State Electron Configurations

• Electrons achieve ground state by occupying orbital closest to nucleus since it has the lowest possible energy

• Aufbau principle – the principle that states that electrons fill available orbitals with the least energy first

Ground-State Electron Configurations

• Aufbau diagrams show the order of orbitals from least to greatest energy– All orbitals in the same sublevel have the same

energy– Within a principle energy level, each sublevel

has a different amount of energy

Ground-State Electron Configurations

• Within a principle energy level, sublevels are ranked by energy– s < p < d < f

• Orbitals of different principal energy levels can overlap

Ground-State Electron Configurations

• Periodic table can be divided into blocks denoting the highest occupied orbitals for elements

Ground-State Electron Configurations

• Highest energy electrons of a neutral atom will be found in the sublevel indicated by the period and the block of the periodic table containing the element– Use the periodic table to determine the order

orbitals are filled

Ground-State Electron Configurations

• Pauli exclusion principle – the principle that states that each orbital can hold a maximum of two electrons

• Electrons have opposite spins when in same orbital– Direction of the electron’s spin

is represented by the direction of the arrow• If two electrons are in the same

orbital, one must be represented with an arrow pointing down and the other with an arrow pointing up

Ground-State Electron Configurations

• Particles with like charges repel– Electrons are negatively charged so they will

tend to keep as far apart as possible

• Hund’s rule – the rule that states that when filling equal energy orbitals, electrons fill each orbital singly before filling orbitals with another electron already in them– Ex) There are three p orbitals of equal energy in

2p sublevel• Electrons will fill each p orbital individually before

filling an orbital with another electron in it

Ground-State Electron Configurations

• Boxes or lines are used to represent orbitals• Arrows used to represent electrons– Direction represents spin

• Drawing orbital diagrams– Determine highest energy sublevel of atom– Use the Aufbau principle to draw sublevels in

filling order– Fill orbitals with the correct number of electrons

• Atomic number is same as number of electrons in neutral atom

Orbital Diagrams

• Lists atom’s sublevels with the number of electrons in each sublevel

• Writing electron configurations– Determine the highest energy sublevel of the

atom– Write the sublevels in the order they are filled– Write the number of electrons in each sublevel

as a superscript on each sublevel• Sum of superscripts should equal the total number of

electrons

Electron Configuration Notation

• For elements with larger numbers of electrons, electron configuration notation requires a lot of writing

• Noble gas configuration – a short hand way of writing an electron configuration in which the noble gas of the previous period is written in brackets to represent the electron configuration up to that point and the remainder of the electron configuration is written afterwards– Ex) Noble gas configuration of iron begins with

argon• First part of iron’s electron configuration is identical to

argon

Noble Gas Configuration Notation

• End of the electron configuration of each element contains valence electrons

Noble Gas Configuration Notation

Learning Objectives• Express the arrangement of electrons in

atoms using electron configurations

Electron Arrangements