Electron Arrangements Electron 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