Periodicity
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what is the trend in atomic radius across period 3
• decreases • outer electrons are all in the same energy level so the outer electron has the same shielding • nuclear charge inreases (more protons)
define elecronegativity
the ability of an atom to attract a pair of electrons in a covalent bond
what is the trend in electronegativity across period 3
• it increases • nuclear charge increases • atomic radius decreases therefore bonding pair is closer to the nucleus • electron pair in covalent bond is more attracted to atoms nucleus
define ionisation energy
energy required to remove one mole of electrons from a mole of gaseous atoms
what is sodiums first ionisation energy equation
Na (g) → Na⁺ (g) + e⁻
what is the trend in ionisation energy across period 3
• it increases across the period (in general) • outer electron is closer to the nucleus • nuclear charge increases therefore a greater attraction between nucleus and outer shell electron
what is the trend in ionisation energy down a group
• it decreases down a group • atomic radius increases therefore electron is further from the nucleus • weaker attraction between nucleus and outer electron therefore elctron is easier to remove
why is Al ionisation energy less than that of Mg
it’s outmost electron is in the 3P orbital which is further away from the nucleus thanthe 3S orbital and therefore less energy is needed to remove it
why does Sulfur have a lower ionisation energy than Phosphorous
in phosphorous each of the 3p electrons occupie a different 3p orbital whilst in sulfur one of the 3p orbitals must contain 2 electrons. the repulsion between the pair of electrons makes it easier to remove one of them despite the increase in nuclear charge
what is the order of melting point for period 3
Si>Al>Mg>Na>S>P>Cl>Ag
what is the order of boiling point across period 3
Al>Si>Mg>Na>S>P>Cl>Ag
why does Na,Mg,Al have relatively high melting points
• as they have metallic bonding • electrostatic attraction between metal ions and delocalised electrons
stronger metallic bonding if:
• size of charge is larger • ionic radius decreases • more delocalised electrons
what is Silicon and why is it’s melting point so high
• as it’s a giant covalent (macromolecular) • 4 stong covalent bonds per silicn atom • huge amount of energy to break • mpt is very very high
why are the simple moleculars ordered as S>P>Cl
• as they all have vdw forces between the molecules • vdw forces increase with size and number of electrons • S8 - has 128e- P4 - has 60e- Cl2 - has 34e-
why does Argon have the lowest melting point
as they only have weak vdw forces between atoms
define periodicity
the repeating pattern of physical or chemical properties going across the periods