Periodicity Flashcards
(22 cards)
In periodicity what are the 3 properties considered?
covalent radius
ionisation energy
electronegativities
When you are looking at the 3 properties what is it appropriate to consider?
Their trends going across the period of elements and down a group of elements.
What is the covalent radius (atomic size) of an atom?
It is the measure of the covalent radius, which is half the distance between the nuclei of two bonded atoms of an element.
What trend do we notice happen to the covalent radius as we go across a period and why?
The covalent radius decreases because of the increasing positive nucleur charge. There is a greater attraction between the increasing number of protons and electrons.
What is meant by increasing positive nucleur charge?
Meaning there is a greater attraction between the increasing number of protons and electrons.
How does the covalent radius decrease as we go across a period?
the nucleus pulls the energy levels/shells closer towards the nucleus.
What trend do we notice happen to the covalent radius as we go down a group and why?
The covalent radius of atoms increases because there are more energy levels/shells
As we go down a group why does the increasing nucleur charge have little effect on the outer electrons? What is this effect called?
the outermost electrons are shielded (‘‘screening effect’’) by the inner electrons
Why is the iconic radius of aluminium Al3+ smaller than phosphorus P3-?
electron arrangements:
Al3+ 2,8
P3- 2,8,8
Because P3- has 3 occupied energy levels it is larger of the two ions.
What is ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms
What equation do we use for the first ionisation energy?
E(g) > E+(g) + e-
What type of reaction is removing an electron and why?
endothermic because energy is ‘‘put in’’ to pull an electron away from the outer shell of an atom.
Describe and explain the trend happening to the ionisation energy as we go across a period?
Increases
As the positive nucleur charge increases across a period, the attraction the nucleus has for the electrons also increases. Electrons are closer to the nucleus and therefore are more difficult to remove. As a result more energy is required to remove an electron
Describe and explain the trend happening to the ionisation energy as we go down a group?
decreases
The outer shell is furthest from the nucleus therefore the attraction from the nucleus on the outer electrons is smaller. As a result, less energy is required to remove a outer electron.
In addition, the electrons from each new energy level going down a group will be ‘shielded’ by the inner electrons (screening effect). Therefore the outer electrons are less attracted to the nucleus and easier to remove.
What is the second ionisation energy?
energy required to remove a second electron from an ion in the gaseous state.
e.g. Why is there a sudden jump in ionisation energy between sodiums first and second ionisation?
it is removing an electron closer to the nucleus. There is a stronger attraction and as a result a great deal more energy is needed to remove this second electron in comparison to the first.
What is electronegativity?
the measure of the ability of an atom to attract electron in a covalent bond.
What will an atom with a high electronegativity tend to do?
attract bonded electrons towards it.
What do write above the bonded atoms to show the distribution of electrons?
delta (use symbol)+ for element with lower electronegativity
delta (use symbol)- for element with higher electroneativity
If taking hydrogen chloride as an example. What type of bond is it said to have and why?
Polar because chlorine is more electronegative than hydrogen it has a greater share of the bonding electrons.
Describe the trend which happens to the electronegativity as we go across a period?
Electronegativity increases across a period. There is an increase in the positive nuclear charge across a period and this causes the atom to attract bonded electrons more strongly.
Describe the trend which happens to the electronegativity as we go down a group?
Electronegativity decreases as we go down a group. An increase in the number of electron shells causes the bonding electrons to be less attracted to the positive nuclear charge. As the electrons are less strongly attracted, the electronegativity decreases.
