Periodicity of Physical Properties of the Elements in Period 3 (Cambridge (CIE) A Level Chemistry): Flashcards
Exam code: 9701
1/180Still learning
Know0
Define periodicity.
Was this flashcard helpful?
Cards in this collection (18)
Define periodicity.
Periodicity is the repeating pattern of chemical and physical properties shown by elements across the periods of the periodic table.
Why does atomic radius decrease across Period 3?
Atomic radius decreases across Period 3 because the nuclear charge increases with each additional proton, while the number of electron shells stays the same (so shielding is constant). The stronger attraction pulls the outer electrons closer to the nucleus.
True or False?
Shielding increases across Period 3, causing atomic radius to decrease.
False.
Shielding remains roughly constant across Period 3 because all elements have the same number of electron shells. It is the increasing nuclear charge that pulls electrons closer, reducing the atomic radius.
Across Period 3, cations are .......... than their parent atoms because they have .......... electrons and reduced shielding.
Across Period 3, cations are smaller than their parent atoms because they have fewer electrons and reduced shielding.
Why are Period 3 anions larger than their parent atoms?
Anions gain one or more electrons into their outer shell, increasing electron-electron repulsion. The nuclear charge stays the same, so the electron cloud spreads out, making the ion larger than the parent atom.
Define atomic radius.
An atomic radius is the distance between the nucleus and the outermost electron of an atom, measured as half the distance between the nuclei of two bonded atoms of the same element.
True or False?
Silicon has the highest melting point of all Period 3 elements.
True.
Silicon has a giant covalent structure with strong covalent bonds throughout, giving it the highest melting point in Period 3.
Electrical conductivity across Period 3 increases from Na to .......... and then .......... significantly for P, S, Cl and Ar.
Electrical conductivity across Period 3 increases from Na to Al and then decreases significantly for P, S, Cl and Ar.
Explain the trend in ionic radius from Na+ to Si4+ across Period 3.
From Na+ to Si4+, ionic radius decreases because the increasing nuclear charge attracts the electrons in the second principal quantum shell more strongly, pulling them closer to the nucleus.
Why does the melting point increase from Na to Al across Period 3?
Na, Mg and Al have giant metallic lattice structures. Going from Na to Al, each atom donates more electrons to the delocalised 'sea' (1, 2 and 3 respectively), increasing the strength of metallic bonding and raising the melting point.
Define metallic bonding.
Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a surrounding 'sea' of delocalised electrons.
True or False?
Silicon is a good electrical conductor because it has a giant covalent structure.
False.
Although silicon has a giant molecular (covalent) structure, it has no delocalised electrons, so it cannot conduct electricity easily. It is classified as a semimetal (metalloid).
P, S, Cl and Ar exist as .......... molecules with weak .......... forces between them, giving them low melting points.
P, S, Cl and Ar exist as simple molecules with weak instantaneous dipole-induced dipole forces between them, giving them low melting points.
Why does sulphur (S8) have a higher melting point than phosphorus (P4)?
Sulphur exists as larger S8 molecules compared to the smaller P4 molecules. Larger molecules have stronger instantaneous dipole-induced dipole forces between them, so more energy is needed to separate them.
True or False?
Aluminium is a better electrical conductor than sodium because it donates more electrons to the delocalised sea.
True.
Aluminium donates 3 electrons per atom to the delocalised sea compared to 1 from sodium, so there are more free electrons available to carry charge, making Al a better conductor.
In metals, the .......... electrons from the valence shell are free to move, allowing the metal to conduct .......... .
In metals, the delocalised electrons from the valence shell are free to move, allowing the metal to conduct electricity.
Why does silicon have the highest melting point in Period 3?
Silicon has a giant molecular structure in which each Si atom is covalently bonded to four neighbouring Si atoms. These strong covalent bonds require a large amount of energy to break, giving silicon the highest melting point in Period 3.
Define semimetal.
A semimetal (metalloid) is an element with properties intermediate between metals and non-metals, such as silicon, which has a giant covalent structure but only very limited electrical conductivity.
Sign up to unlock flashcards
or