Atomic Structure Flashcards
Protons
Charge: +1
Mass: 1
Neutrons
Charge: 0
Mass: 1
Electrons
Charge: -1
Mass: 1/1840, negligible
Deflection of sub-atomic particles in an electric field
Angle of deflection = k(charge/mass)
Atomic Symbols AZX
Mass noAtomic no.X
Nucleons
Protons and neutrons
Atomic number (Z)
- The number of protons in the nucleus
- Equal to no. of electrons present in an
electrically neutral atom - Unique to each element
Mass number (A)
Total number of nucleons
Isotopes
- Atoms of the same element with the same
number of protons but different number of
neutrons - Same chemical properties
-
Different physical properties due to different
masses
Orbitals
- Regions of space where there is a high
probability of locating the electrons - Each holds only 2 electrons
- Orbitals from different subshells are the same shape but different size
S-orbital
- Spherical in shape
- Labelled ns
P-orbital
- Dumbbell in shape
- Labelled npx, npy, npz
D-orbitals
- Shape is just diabolical
- Labelled nsz2, nsx2-y2, nsxy, nsxz, nszy
Relative energies of orbitals
- Orbitals closer to the nucleus are lower in
energy - Orbitals of the same subshell have equal
energy (degenerate orbitals)
Subshells
- Labelled s, p, d or f with a principal quantum number
- The lower the principal quantum number,
the closer to the shell is to the nucleus - Electrons in the same subshell have the
same energy level (degenerate)
Aufbal Principle
Electrons always fill orbitals of lower energy first before proceeding to fill orbitals of higher energy
Paui Exclusion Princple
- Each orbital can hold only 2 electrons and
they must have opposite spins - 2 electrons in the same orbital will
experience repulsion
Hund’s Rule
When a number of degenerate orbitals are available, electrons occupy them singly first before any pairing occurs
Period
Horizontal row of element with the same number of core electrons
Group
Vertical column of element with the same number of valence electrons and hence chemical properties
First ionisation energy
The amount of energy required to remove one mole of electrons from one mole of gaseous atoms, producing one mole of gaseous ions with a single positive charge
X(g) → X+(g) + e-
Successive energies become more endothermic
Nuclear charge effect
- Total positive charge of protons in nucleus
- Arieses from the attraction between
electrons and the positive nucleus - Increase with increasing no. of protons
Shielding/Screening effect
- Shielding electrons are the inner shell
electrons found in between the nucleus and
the valence electrons - Reduces the strength of nuclear attraction
experience by the valence electrons - Increases with increasing number of inner
shell electrons
Effective Nuclear Charge
The effective nuclear attraction felt by the valence electrons after taking into account both the nuclear charge effect and the shielding effect
First Ionisation energy trend across a period
- No. of protons increase, nuclear charge
increases - No. of inner shell electrons constant,
shielding effect remains constant - Hence effective nuclear charge increases
- Stronger attraction between nuclear and
valence of electrons - Hence atomic radius decreases and first
ionisation energy increases
First ionisation energy trend down the group
- No. of protons increase, nuclear charge
increases - No. of inner shell electrons increases,
distance between the nucleus and the
valence shell electrons increases - Shielding effect increases
- Hence effective nuclear charge decreases
- Weaker attraction between nuclear and
valence of electrons - Hence atomic radius increases and first
ionisation energy decreases
Successive ionisation energy for same element
- Progressively more endothermic
- Extra energy needed to overcome the
EFOA between leaving electrons and ions
of increasing positive charge -
Large jumps in IE indicate removal of
electrons from different electronic shells -
Small jumps in IE indicate removal of
electrons from an inner subshell
