Periodicity and period 3 Flashcards
What is ionisation energy?
The energy required to remove one electron completely from a n atom of an element to form an ion
Define the first ionisation energy
The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form one mole of gaseous +1 ions
X ——>. X^+ + e^-
What is atomic radius?
The distance from the centre of the atom to the edge of the cloud of electrons
What is the trend in atomic radius across a period and explain why.
Decreases across a period
Number of protons increases (increased nuclear charge) so the nucleus is more positive attracting the outer electrons more pulling them in towards the nucleus
What is the trend in atomic radius down a group and explain why.
Increases down a group
Since the number of electron shells increases and therefore there is more inner shells of electrons shielding the outer shells from the attraction of the nucleus.
The affect of the nuclear charge is insufficient compared to electron shielding.
What factors affect ionisation energy?
Atomic radius
Nuclear charge
Electron shielding
(The latter two affect atomic radius)
Explain why a large atomic radius causes a decrease in ionisation energy.
The larger the atomic radius the further away the outer electrons are held from the nucleus and therefore the weaker the forces of attraction between the positive nucleus and negative outer electrons so they are lost more easily meaning less energy is required to remove the electrons from their atoms and hence ionisation energy decreases.
Explain the trend in ionisation energy across a period
Increases across a period
Number of protons increases and therefore there is a greater nuclear charged
Their causes the outer shell to be drawn towards the nucleus as there is no increase in shielding and therefore the outer electrons are attracted to the nucleus more so more energy is required to remove an electron from its atom.
Explain the trend in ionisation energy down a group
Decreases down a group
Increased shells and therefore increased shielding on the outer electrons by the inner electron shells so there is less attraction between the positively charged nucleus and the outer electrons meaning less energy is required to remove an electron form it’s atom and hence ionisation energy decreases
Why is second ionisation energy always greater than the first ionisation energy?
After the first ionisation energy, the atom now has a positive charge as an electron has already been removed.
Therefore more energy is required to remove an electron from an already positive atom hence the second ionisation energy is greater than the first.
What is the general trend in successive ionisations energies of an atom?
(Eg sodium atom)
Eg sodium
1st IE to 2nd IE- there is a large jump from the first to the second ionisation energy as the first electron is alone in its outer shell
2nd IE to 9th IE- steady increase in ionisation energy as all the electrons are removed from the same quantum shell
9th IE to 10th IE- large jump as the 10th and 11th electrons are in the inner most shell and therefore have the largest force of attraction to the positive nucleus.
What is the trend in melting points across a period?
Groups 1-4:
Steady increase in boiling and melting points as all elements have a giant lattice structure
Groups 4-5:
Sharp decrease in boiling and melting point as unlike Carbon (group 4) nitrogen exists as simple molecules and therefore has weak intermolecular forces
Groups 5-7:
Melting and boiling points remain relatively low as these elements are still simple molecular elements
What is the trend in Melting point for period 3 elements?
Metals
Silicon
Non metals
Metals:
Melting point steadily increases as the ionic charge and therefore their abundance of delocalised electrons increases
So the strength of metallic bonds increases and hence the melting point increases
Silicon:
Has a giant covalent structure and therefore has a high melting point
Non metals:
Melting point depends on the size of van der waals Forces is attraction. This is therefore dependent on the number of electrons and how closely the molecule can pack together
What is the trend in atomic radius for period 3 elements?
Atomic radius decreases
Number of protons increases ( therefore greater nuclear charge)with no extra electron shells and therefor no increase in shielding so there is a greater force of attraction between the positive nucleus and negative electrons so the outer electrons are pulled closer to the nucleus and atomic radius decreases
What is the trend in ionisation energy for period 3 elements?
Increases across the period
Proton number increases ( greater nuclear charge) with no extra electrons shells and therefore no added shielding. Therefore electrons are pulled closer to the nucleus as the forces of attraction are greater and more energy is required to remove electrons from their atoms so ionisation energy increases.
