Atomic Structure Flashcards
Relative charges of proton neutrons and electrons:
+1, 0, -1
Relative masses of protons, neutrons and electrons:
1, 1, negligible
Behaviour of protons, neutrons and electrons in an electric field (direction and angle of deflection):
Protons: towards the negatively charged plate, y˚ where y˚y˚
What is direction of deflection dependent on?
Charge of the particle.
What is the angle of deflection proportional to?
charge/mass ratio of the particle.The larger the charge q, the stronger the attraction towards the oppositely charged plate. The larger the mass m, the more difficult it is to cause the particle to deviate towards the oppositely charged plate.
What is the distribution of mass in an atom?
Bulk of the mass is in the nucleus.
What is the distribution of charge in an atom?
Positive charges are located in the nucleus, negative charges are located in the electron cloud around the nucleus.
What is nucleon number?
Total number of protons and neutrons.
What is an isotope?
Atoms with the same number of protons but different number of neutrons.
How are electrons contained in an atom?
Around the nucleus are electronic shells, each shell contains subshells, each subshell contains orbitals, each orbital contains electrons.
What happens when the principal quantum value of a shell, n, increases?
The further the shell is from the nucleus, the higher the energy level of the shell, the weaker the electrostatic attraction between the nucleus and electrons, the more diffused the orbital.
What is an orbital?
A region in space where there is a high probability of finding an electron. Each can accommodate 2 electrons, has a distinctive geometrical shape, and its energy is the energy of the electron occupying it.
Traits of the s orbital:
- Spherical shape
- Non-directional
- As n increases, s orbital becomes more diffuse
Traits of the p orbitals:
- Dumbbell shape
- Three p orbitals (Px, Py, Pz)
- Directional as electron density is concentrated in certain directions along the x, y and z axes
- The three orbitals are degenerate
- As n increases, p orbital becomes more diffuse
Traits of the d orbitals:
For Dxz, Dxy, Dyz: - 4 lobed shape - Lobes pointing between the axes For Dx^2-y^2: - 4 lobed shape - Lobes aligned along the x and y axes For Dz^2: - Dumbbell surrounded by a small ring at its waist - Aligned along the z axis
Why is the 4s orbital filled before the 3d orbital?
Due to its proximity to the nucleus, s orbitals are affected to a greater degree than p and d orbitals and hence their energies decrease more rapidly than the other orbitals. As atomic number increases, there is increased nuclear charge, and the energies of orbitals decrease.
What is the Aufbau Principle?
Electrons fill orbitals from the lowest energy orbitals upwards (4s before 3d). This is because lowest energy states are most stable.
What is Hund’s Rule?
Orbitals of a subshell must be occupied singly before pairing to minimise inter-electronic repulsion.
What is the Pauli Exclusion Principle?
Each orbital can hold up to a maximum of 2 electrons and they must be of opposite spins. This ensures the magnetic attraction can counterbalance the electronic repulsion from their identical charges, allowing them to be stable.
Anomalous electronic configuration of Cr:
Instead of [Ar] 3d^4 4s^2, electronic configuration is [Ar] 3d^5 4s^1. 3d and 4s orbitals are similar in energy levels for Cr, and this minimises inter-electronic repulsion.
Anomalous electronic configuration of Cu:
Instead of [Ar] 3d^9 4s^2, electronic configuration is [Ar] 3d^10 4s^1. This is because a fully filled 3d subshell is unusually stable due to symmetrical charge distribution around the nucleus.
What is ground state?
Electrons are in the orbitals of the lowest available energy level.
What is excited state?
Electrons absorb energy and are promoted to a higher energy level.
What is an isoelectronic species?
Species with the same total number of electrons.
What affects electrostatic attraction?
Number of electronic shells, nuclear charge, shielding effect.
How does number of shells affect electrostatic attraction?
As number of shells increases, n increases, distance between nucleus and valence electrons increases, electrostatic attraction decreases.
How does nuclear charge affect electrostatic attraction?
As number of protons increases, nuclear charge increases, electrostatic attraction increases.
How does shielding effect affect electrostatic attraction?
As number of inner electrons increases, shielding effect experienced by valence electrons increases, electrostatic attraction decreases.
What is shielding?
Repulsion of negatively charged electrons in inner shells on those in outer shells to prevent them from experiencing the full effect of the actual nuclear charge.
Why does shielding ability of electrons decrease from s>p>d>f?
d and f orbitals are more diffuse.
What is effective nuclear charge?
Resultant positive charge experienced by valence electrons taking into account shielding effect (nuclear charge - shielding effect).
How does atomic radii change across a period?
It decreases across a period. Across a period, number of shells remain the same, number of protons and hence nuclear charge increases, number of electrons increases as well but are added to the valence shell, hence shielding effect is constant. Effective nuclear charge increases, electrostatic attraction between nucleus and valence electrons increases, thus electron cloud size decreases.
How does atomic radii change down a group?
Down a group, number of electronic shells increases, distance between nucleus and valence electrons increases, shielding effect experienced by valence electrons increases. Despite increasing nuclear charge, electrostatic attraction decreases, resulting in increase in electron cloud size.
How does cationic radius compare to atomic radius?
Cationic radius is smaller. Both have the same number of protons and hence same nuclear charge, however cation has one less electronic shell. Electrostatic attraction increases, decreasing electron cloud size of cation.
How does anionic radius compare to atomic radius?
Anionic radius is larger. Both have the same number of protons and hence same nuclear charge. However, anions have more electrons, thus electron-electron repulsion increases, so electrostatic attraction decreases, increasing electron cloud size of anion.
How does ionic radii of isoelectronic species change across a period?
It decreases. Ions have the same shielding effect, however number of protons and hence nuclear charge increases, thus effective nuclear charge increases. Electrostatic attraction also increases, decreasing electron cloud size.
What is first ionisation energy?
Energy required to remove 1 mol of electrons from 1 mole of M to form 1 mole of M+.
What is n ionisation energy?
Energy required to remove 1 mol of electrons from 1 mole of M(n-1)+ to form 1 mole of M(n)+.
How does first ionisation energies change across a period?
It generally increases, Number of shells remains the same, number of protons and hence nuclear charge increases, number of electrons increase but electrons are added to valence shell, so shielding effect is the same. Effective nuclear charge increases, electrostatic attraction increases and hence more energy is required to remove the electron.
Why does first ionisation energy decrease from Group 2 to Group 13?
The np electron to be removed from the Group 13 atom is at a higher energy level than the ns electron to be removed from the Group 2 atom. less energy is required to remove the former than the latter.
Why does first ionisation energy decrease from Group 15 to Group 16?
The np electron to be removed from the Group 16 atom is paired while that from the Group 15 electron is not. Due to inter-electronic repulsion, less energy is required to remove the former.
How does first ionisation energies change down a group?
It decreases. Down a group, number of shells increases, distance between nucleus and valence electrons increases, shielding experienced by valence electrons increases. Despite increasing nuclear charge, electrostatic attraction decreases, hence energy required to remove electrons decreases as well.
How do successive ionisation energies change?
They increase, as with each electron removed, the atom/ion becomes increasingly positive, which attracts electrons more strongly.
What is electronegativity?
A relative measure of its ability to attract bonding electrons.
How does electronegativity change across a period?
It increases. Across a period, number of shells remains the same, number of protons and hence nuclear charge increases. Number of electrons increases but electrons are added to the valence shell and hence shielding effect remains constant. Effective nuclear charge increases, electrostatic attraction between nucleus and bonding electrons increases.
How does electronegativity change down a group?
It decreases. Down a group, number of shells increases, distance between bonding electrons and nucleus increases, shielding effect also increases. Despite increasing nuclear charge, electrostatic attraction between nucleus and bonding electrons increases.
