Periodic trends and bonding Flashcards
What is the trend of atomic radius across a period and down a group?
Decreases across a period, increases down a group.
Helium is among the smallest; cesium and francium are among the largest.
What is ionization energy?
Energy required to remove an electron.
It increases across a period and decreases down a group. Fluorine (or helium/neon) has one of the highest first ionization energies in its period.
What is the relationship between electron affinity and energy change?
Electron affinity = energy change on gaining an electron.
What does electronegativity measure?
How strongly an atom attracts shared electrons.
Fluorine is the highest on the Pauling scale.
What characterizes ionic bonds?
Usually metal + nonmetal, large difference in electronegativity, electron transfer.
Examples include MgO, CaO, BaCl₂.
What characterizes covalent bonds?
Nonmetals share electron pairs.
Examples include CO₂, H₂O, CH₄.
What determines the polarity of covalent bonds?
Difference in electronegativity and molecular geometry.
CO₂ is linear and symmetrical → net dipole = 0 (nonpolar); H₂O is bent → net dipole ≠ 0 (polar).
What is the Lewis Octet Rule?
Most main-group elements want 8 valence electrons.
What are exceptions to the Lewis Octet Rule?
BF₃ (incomplete octet), PCl₅, SF₆ (expanded octet).
What is lattice energy?
Energy associated with the formation of an ionic crystalline solid from gaseous ions.
What is the Born–Haber Cycle?
A stepwise thermochemical cycle to form an ionic crystalline solid from elements in their standard states.
It sums sublimation, ionization, electron affinity, bond dissociation, etc.
