Periodicity
Elements arranged in order of increasing atomic number.
What is the basis of the periodic table?
A bond formed when atoms share pairs of electrons.
What is a covalent bond?
Weak forces caused by temporary and induced dipoles.
What are London dispersion forces?
A molecule with an uneven distribution of charge due to permanent dipoles.
What is a polar molecule?
Elements such as Li, Be, Na, Mg, Al, K and Ca.
What are metallic elements?
Vertical columns containing elements with similar chemical properties.
What are groups?
The attraction between positive and negative ions.
What is an ionic bond?
The strength of London dispersion forces increases with the number of electrons.
What determines the strength of London dispersion forces?
The spatial arrangement of polar bonds determines whether a molecule is overall polar.
What determines molecular polarity?
Substances like H₂, N₂, O₂, F₂, Cl₂, P₄, S₈ and fullerenes.
What are covalent molecular elements?
Across a period, covalent radius decreases because nuclear charge increases while the number of occupied shells stays the same.
Why does covalent radius decrease across a period?
The simplest ratio of ions in an ionic compound.
What is an ionic formula?
Additional electrostatic attractions between polar molecules.
What are permanent dipole–permanent dipole interactions?
Polar substances dissolve in polar solvents; non‑polar substances dissolve in non‑polar solvents
What is “like dissolves like”?
Diamond, graphite and silicon.
What are covalent network structures?
The energy required to remove one mole of electrons from one mole of gaseous atoms.
What is first ionisation energy?
The bonding continuum runs from pure covalent → polar covalent → ionic.
What does the bonding continuum describe?
A strong type of intermolecular force found when H is bonded to N, O, or F.
What is hydrogen bonding?
Presence of O–H or N–H bonds suggests hydrogen bonding and therefore solubility in water.
What structural feature indicates solubility in water?
Noble gases exist as single atoms.
What are monatomic elements?
Electronegativity increases across a period due to increasing nuclear charge and decreasing atomic size.
Why does electronegativity increase across a period?
Physical properties such as melting point, boiling point, solubility and conductivity can be used to deduce bonding and structure.
How can physical properties be used to identify bonding and structure?
Hydrogen bonding in ice creates an expanded structure, making ice less dense than water.
Why is ice less dense than liquid water?
Boiling points of NH₃, H₂O and HF are anomalously high due to hydrogen bonding.
Why do ammonia, water and hydrogen fluoride have unusually high boiling points?
Melting and boiling points can be rationalised by considering intermolecular forces and number of electrons.
How can melting and boiling points be explained?