Chapter 1 Flashcards
(19 cards)
Define first ionisation energy.
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Why does first ionisation energy generally increase across Period 3?
Nuclear charge increases while shielding stays nearly constant, so electrons are held more tightly, increasing ionisation energy.
Explain why there is a drop in ionisation energy between Mg and Al.
Al’s outer electron is in a higher-energy 3p orbital, more shielded and easier to remove than Mg’s 3s electron.
Why is oxygen’s first ionisation energy lower than nitrogen’s?
Oxygen has paired electrons in 2p orbital causing electron-electron repulsion, making ionisation easier than in nitrogen where electrons are unpaired.
Define isotopes.
Atoms of the same element with the same number of protons but different numbers of neutrons, thus different mass numbers.
What is the relative atomic mass (Ar)?
The weighted average mass of the isotopes of an element relative to one twelfth of the mass of an atom of carbon-12.
Explain why mass spectrometry is useful for determining isotopic abundance.
It separates ions based on mass-to-charge ratio, allowing identification of different isotopes by their masses and relative intensities.
What does the mass-to-charge ratio (m/z) represent?
The ratio of the mass number of an ion to its charge number; often charge is +1, so m/z ≈ mass number.
Why are electrons arranged in shells?
To minimize energy; electrons fill the lowest energy levels first due to electrostatic attraction to nucleus.
Explain the shape of an s-orbital.
Spherical shape with electron density equally distributed around the nucleus.
Explain the shape of a p-orbital.
Dumbbell-shaped with two lobes on opposite sides of the nucleus and a nodal plane at the nucleus.
How many electrons can each s and p orbital hold?
S orbital holds 2 electrons, each p orbital holds 2 electrons; there are 3 p orbitals per shell, so 6 electrons total in p orbitals.
Explain Hund’s rule of maximum multiplicity.
Within a subshell, electrons fill orbitals singly with parallel spins before pairing up.
What is meant by electron spin?
Electron spin is a quantum property causing a magnetic moment; electrons in the same orbital have opposite spins (+½ or -½).
Describe the Aufbau principle.
Electrons fill atomic orbitals in order of increasing energy, from lowest to highest.
Why does chromium have an electron configuration ending in 4s1 3d5 rather than 4s2 3d4?
Half-filled d subshell (3d5) is more stable due to exchange energy and symmetry, so one 4s electron is promoted to 3d.
What is the effect of nuclear charge on atomic radius?
Greater nuclear charge pulls electrons closer, decreasing atomic radius.
Explain why successive ionisation energies increase.
Removing each electron reduces electron-electron repulsion and increases effective nuclear charge on remaining electrons, making removal harder.
Why is the second ionisation energy of sodium much higher than the first?
The second electron is removed from a full inner shell, which is much closer and more strongly held by the nucleus.
