Physical key ideas

Why is ionisation needed?

To create an electric current and so ions are accelerated by the electric field

Electron impact

Sample is vaporised and electron gun fires electrons at sample

X (g) ➡ X+ (g) + e-

Electron spray ionisation

Sample is dissolved in volatile solvent and fine needle injected to produce fine mist

X(g) + H+ ➡ XH+ (g)

Why is electron spray used for larger molecules?

Less fragmentation

What occurs during acceleration?

Ions accelerated by electric field

What occurs in the flight tube/ion drift?

Lighter ions travel faster as they have a faster velocity

What occurs during detection?

Ions hit negative plate and gain electrons

Abundance is proportional to size of current produced

Trend of ionisation energy across a period?

Increases

More protons

Greater attraction between electrons being removed and nucleus

Shielding stays the same

Trend of ionisation energy down a group

More shielding

Weaker attraction between nucleus and outer electrons being removed

1st deviation (Mg + Al) and (Be+B)

Electrons in p shell easier to remove- IE decreases

2nd deviation (P + S) and (N + O)

Paired electrons repel each other- easier to remove- IE decreases

Atomic radius down a group

Increases

Shielding increases

Decreases nuclear charge

Increases overall size

Atomic radius across a period

Decreases

(Shielding stays the same)

Increase nuclear charge

Reduces overall size

Largest ionic radius

One with smallest number of protons

Weakest pull on its electrons

Isotopes characteristics

Chemical properties e.g reactivity is identical

Electronic structures e.g ionisation energy and atomic radius

Plum pudding model

Atom- ball of positive charge with negative electrons embedded in it

Nuclear model

Mass of atom in nucleus

Positive charge of atom in nucleus

Bohr model

Electrons in energy levels

Gold foil experiment

Deflected at point P- atom mostly empty space

Deflected at point Q- concentration of positive charge in atom

When is ionic bonding stronger and MP higher?

When ions are smaller and have higher charges

E.g. MgO has a higher melting point than NaCl as the ions involved (Mg2+& O2- are smaller and have higher charges than those in NaCl , Na+& Cl- )

When is a molecule polar?

Asymmetrical shape e.g bent or trigonal pyramidal

(polar bonds i.e high difference in electronegativity)

When does a molecule have a permanent dipole?

Asymmetrical shape e.g bent or trigonal pyramidal

(Polar bonds i.e high difference in electronegativity)

Electronegativity down a group

Decreases

Shielding increases

Electronegativity across a period

Increases

Number of protons

How VDW forces form

Random movement of electrons creates dipole in one molecule

Induces dipole in another molecule

Attraction between s+ and s- in different molecules

Oxidation state exceptions

H = normally +1, but in metal hydrides e.g NaH; -1

Cl, Br and I = normally -1 except in compounds with oxygen and fluorine

O = normally -2, but perioxides e.g H2O2 and compounds with flourine; -1