Chapter 7: Periodic Table, Ionisation Energies, and Bonding + Structure

where are the spdf blocks??

first ionisation energy definition:

the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous +1 ions

what 3 factors affect an ionisation energy?

1. atomic radius

2. nuclear charge

3. electron shielding

the first electron to be removed from an atom will be in the…

highest energy level → experiencing the least attraction from the nucleus

how does atomic radius affect ionisation energy?

the larger the atomic radius, the weaker the attraction between the nucleus + outer electrons. This means it is easier to lose an outer electron

how does nuclear charge affect ionisation energy?

• more protons → greater attraction between nucleus + outer electrons

how does electron shielding affect ionisation energy?

• electrons = negatively charged

• inner shells repel outer shells

• this repulsion = ‘shielding effect’

• easier for an outer electron to be lost

write the first 2 ionisation energies for helium:

why do successive ionisation energies increase? (in general!)

• after the first electron is lost, the remaining electron/s are pulled closer to the nucleus

• this remaining nuclear attraction increases

• more ionisation energy = required to remove this second electron

def. of second ionisation energy:

energy required to remove one electron from each ion in one mole of gaseous +1 ions of an element to form one mole of gaseous +2 ions.

what charged ion does a 2nd ionisation energy produce?

+2 ion

what does a big jump upwards between successive ionisation energies tell us?

that the higher numbered electron is removed from a different electron shell, closer to the nucleus + with less shielding

what does this table tell us?

how do 1st ionisation energies changes going across the period (→) GENERALLY SPEAKING !!

• general increase across each period 📈📈

• sharp decrease in first ionisation energy between the end of one period + the start of the next

trend in first ionisation energy down a group:

• decrease down a group

• look at He, Ne, Ar

• look at Li, Na, K

why do 1st ionisation energies decrease down a group?

what is the most important factor as to why first ionisation energies increase across a period?

increase nuclear charge

in periods 2 + 3, why is there not a complete increase in 1st ionisation energies across the period (Beryllium → Boro)

• Beryllium + Boron

  • marks the start of the filling of the 2p subshell

  • 2p subshell has a higher energy subshell

  • therefore, easier to remove than one of the 2s electrons in beryllium

  • first ionisation energy of boron is less than the first i.e. of beryllium

in periods 2 + 3, why is there a decrease in successive ionisation energies between N → O

• marks the first electron pair to be in an orbital (2p orbital)

• the paired electrons repel, making it easier to remove and electron from an oxygen atom than a nitrogen atom

• first ionisation energy of oxygen is less than the first ionisation energy of nitrogen

metallic bonding:

cations fixed in positions, and delocalised electrons are free to move + charry a charge

for metals containing +2 cations, how many electrons are needed?

twice as many as the cations, to balance the charge

what kind of structure does a metal have?

giant metallic lattice

3 properties of metals:

• strong metallic bonds

• high electrical conductivity

• high melting + boiling points

why do metals have a high boiling point?

large amounts of energy are required to overcome the strong electrostatic attraction between the cations + electrons

why are most metals insoluble?

you might expect polar solvents to interact with charges in metallic lattice

this doesn’t happen → reactions occur instead!!

simple molecular lattices are held together by…

weak intermolecular forces

carbon + silicon form…

giant covalent lattices:

• tetrahedral

• high melting + boiling points → strong covalent bond

• insoluble → strong covalent bonds cannot be broken by interactions with solvents

• non-conductors of electricity (mostly!) → no electrons free to move and carry a charge

which two allotropes of carbon can conduct electricity?

graphene + graphite

• only 3/4 of the outer electrons are used in covalent bonds

• remaining electron is in a pool of delocalised electrons + are free to move

graphite is…

a stack of graphene layers (with weak forces between the layers)

do giant structures have high mp? do simple structures?

giant = yes → have strong forces to overcome

simple = no → have weak forces to overcome

melting points across a period

1. increases between groups 1 → 4

2. sharp decrease between group 4 → 5

3. melting points are comparatively low from groups 5 → 8

which 3 elements form giant covalent structures?

Boron, Carbon, and Silicon

what do Phosphorus and Sulphur exist as?

P₄ + S₈