electron structure

what is electron configuration?

the arrangement of electrons in an atom

what are principle quantum numbers (n)?

the shell or energy level number

what is the fixed number of electrons each principle quantum number can hold?

n = 1 up to 2
n = 2 up to 8
n = 3 up to 18
n = 4 up to 32

what is the formula for the maximum number of electrons in a shell?

2n²

what are shells made up of?

atomic orbitals

what are atomic orbitals?

a region around the nucleus that can hold up to two electrons, with opposite spins
there are s, p, d, and f orbitals

what are features of the s-orbital?

the electron cloud is within the shape of a sphere
each shell from n = 1 contains one s-orbital (total of 2 electrons)
the greater the shell number, the greater the radius of its s-orbital

what are features of the p-orbital?

the electron cloud is within the shape of a dumb-bell
there are three separate p-orbitals perpendicular to each other (p_x, p_y, p_z) (total of 6 electrons)
each shell from n = 2 contains three p-orbitals
the greater the shell number, the further the p-orbital is from the nucleus

what are features of the d-orbital?

each shell from n = 3 contains five d-orbitals (total of 10 electrons)

what are features of the f-orbital?

each shell from n = 4 contains seven -forbitals (total of 14 electrons)

how do orbitals fill?

they fill in order of increasing energy
(3d is higher energy level that 4s, so filling is 3p, 4s, 3d)

how do electrons occupy orbitals?

electrons are negatively charged and those with the same spin (up or down) repel each other (spin-pair repulsion)
therefore, electrons will occupy separate orbitals in the same subshell first to minimise this repulsion, where two electrons in an orbital have opposite spins (Hund’s Rule)

what are two ways of writing out electron configuration?

full electron configuration - describes arrangement of all electrons from 1s subshell up
short hand - uses the symbol of the nearest preceding noble gas + rest of electron configuration

how are ions formed?

cations are formed when atoms lose electrons
anions are formed when atoms gain electrons
(4s subshell fills and empties before 3d subshell)

how is the periodic table split up depending on electronic configuration?

split into four main blocks which corresponds to their highest energy subshell
s block - left block of two groups
p-block - right block of six groups
d block - centre block of 10 groups

what are exceptions to the aufbau principle?

chromium is [Ar] 3d⁵ 4s¹
copper is [Ar] 3d¹⁰ 4s¹
this is because these configurations are energetically favourable