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