Group - a vertical column of elements, they have simular properties, elements in the same group have the same number of electrons on the outer shell.
Period - Horizontal row of elements which have trends in physical and chemical properties as move accross the row.
S - block - all elements that have their highest energy electrons in s - orbital (outer electrons)
P - block - all elements that have p - orbital electrons on outer shell
D - block - all elements have outer electrons on d - orbital
Placing hydrogen and helium
Helium - placed in noble gases - cause simular properties, but s orbital not p.
Hydrogen - sometimes placed in group 1 - cause can form +ve ion, although different properties (gas) sometimes placed with halogens
Trends in Period 3 Elements
Physical Properties Boiling and Melting Points
Na ---> Ar
Generally increase from Na --> Si then decrease to Ar
Na ---> Al (all metals - have metallic bonding)
charge increases on the metal ions Na+, Mg+2, Al+3 = stronger attraction and more delocalised e-/+ve ion so more energy needed to overcome.
Si (a metalliod) giant covalent structure, many strong covalent bonds need to be broken = lots of energy needed to overcome.
Period 3 - m/b Points
Lower melting/boiling points
Phosphorous, Sulphur, Chlorine & Argon
- (non - metals) small, seperate molecules
- held together by van der waals' forces (weaker)
- little energy needed to overcome
Phosphorous exists as P(4) molecules
Sulphur exists as S(8) molecules (so has higher b/m.point)
Chlorine exists as Cl(2) molecules (Ar exists as 1) decreases because VDWf's weakens as less e-'s (smaller molecules/atoms)
Period 3 - m/b Points - Questions
Q1.) From Na ---> P which has the highest melting point? Explain why?
Q2.) State the trend in boiling points from Na ----> Si? Explain why?
Q3.) State and explain the trend of boiling point from P ---> Ar?
Q4.) Explain why there is a large increase in boiling point from Na and Mg to Al
Q5.) Explain why Si has a much higher melting point compared to sulphur?
Q6.) State and explain the boiling points of Na ---> Al ?
Q7.) Explain why sulphur has a higher boiling point than phosphous and why phosphous has a higher boiling point than chlorine?
Q8.) From phosphous to Argon state the element that doesn't follow the decreasing pattern? explain why?
First Ionisation Energy - Period 3
The first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions, with a single +ve.
Endothermic (gaseous so energy isn't used changing it's state)
General Equation = X (g) ---> X+ (g) + e- (state symbols)
- more protons in nucleus - nuclear charge increases
- therefore more attraction between nucleus & outer e-
- negligible sheliding - e- on same energy level
- so more enery needed to remove outer e-
Mg ---> Al Al outer e- on p higher e.level = more energy. Mg outer e- on orbital s.
First Ionisation Energy - Period 3
Phosphous ---> Sulphur
P = unpaired electrons on 3P orbital more energy
S = 2 paired electrons on 3P orbital less energy
Theres some repulsion between paired electrons in the same sub level, this reduces the force of attraction to the nucleus - so less energy needed to remove a pair electron
than needed to remove unpaired electron from phosphous
therefore increase in ionisation energy of phosphous compared to drop in sulphur.
First Ionisation Energy - Questions
Q1.) Al has a higher ionisation energy compared to Na, explain why?
Q2.) Explain why sulphur has a lower ionisation energy compared to phosphous?
Q3.) Will Na or Cl have a higher ionisation energy explain why?
Q4.) Does a Na atom have a higer or lower ionisation energy than Na+ ion? Explain?
Q5.) Which has the higher ionisation energy Na atom or Na- ion? Explain?
Q6.) From Na ---> P the trend increases in ionisation energies, why does Al not follow the trend and is lower than expected?
Trend in Atomic Radius - Period 3
Na ---> Ar Decrease
- Number of protons increase
- so nuclear charge increases
- more electrons
- but negligible shielding - on same sub level
- so force of attraction between the nucleus & outer e- increases
- therefore atomic radius decreases
Q1.) State and explain the trend in atomic radius Na ---> Cl ?