Chem 1 - Periodicity

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

Physical Properties                                    Boiling and Melting Points

Na ---> Ar

Generally increase from Na --> Si then decrease to Ar

Explain

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.

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)

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?

Generally Increases

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.

Phosphous ---> Sulphur

P = unpaired electrons on 3P orbital         more energy

S = 2 paired electrons on 3P orbital          less energy

Explain

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.

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?

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 ?