periodicity, group 2 and group 7 Flashcards
how are elements ordered in the periodic table
in rows and columns, in order of increasing proton number
period definition
a row in the periodic table
group definition
a column in the periodic table
ionisation energy definition
the amount of energy required to remove 1 mole of electrons from 1 mole of gaseous atoms forming 1 moles of gaseous 1+ ions
are ionisation reactions endothermic or exothermic
they are all endothermic as they all require energy
- this also means they have + enthalpy change values
what is electron shielding + how does it affect ionisation energy
the amount of electron shells between nucleus and outermost electron
the more electron shells between the positive nucleus and the negative electron being removed, the smaller the effect of nuclear charge on the electron, and so the less energy is needed to remove it
remember electrons which share a p sub-shell will experience repulsive forces from secondary electron, making it easier to remove
what is atomic radius + how does it affect ionisation energy
relates to the size of the atom
the bigger the atom, the further away negative outer electrons are from positive nucleus, the smaller the effect of the nuclear charge is on the electron being removed and so less energy is required to remove it
what is nuclear charge and how does it affect ionisation energy
the strength of the positive charge in the nucleus, depending on number of protons
the more protons in the nucleus, the greater the nuclear charge and so the greater the attraction between the nucleus and outer electrons, meaning more energy is needed to remove the electron
how does IE change down a group
IE tends to decrease
although nuclear charge increases, shielding and atomic radius also decreases so the effect of nuclear charge on outermost electron decreases so less energy needed to overcome
how does IE change across a period
IE tends to increase across a period, as although shielding stays the same, nuclear charge increases and atomic radius decreases as a result, outermost electrons are closer to positive nucleus and experience stronger forces of attraction, so more energy is needed to remove the electron
why does IE decrease at group 3 when going across a period
evidence for having subshells
this is where electrons are being removed from p-subshell rather than s-subshell, further away from the nucleus as its a higher energy level so less energy needed to over come nuclear attraction
why does IE decrease at group 6 when going across a period
evidence for having electron repulsion in an orbital
first atom where the p orbital is filled with 2 electrons, these repel each other making it easier to remove so less energy required
successive ionisation definition
the removal of more than 1 electron from the same atom
how does reactivity change as you go down group 2
reactivity increases
group 2 react by losing 2 electrons, going down shielding and atomic radius increase so electrons lost more readily
how does boiling point change as you go down group 2
boiling point increases
number of electrons and atomic radius increases so more london forces, more energy to overcome
for group 2 elements, why is 2nd IE always greater than 1st IE
+1 ion is smaller than the atom due to the nuclear charge drawing outer electrons in closer, as now there is 1 more proton than electron, so more energy is needed to remove 2nd electron
how does melting point change as you go across a period
group 1 - forms giant metallic lattices, high melting point
group 2 - forms giant metallic lattices, even higher melting point as double delocalised electrons and stronger ion charges (2+)
group 3 - forms giant metallic lattices, slightly higher melting point
group 4 - forms giant covalent lattices, highest melting point
group 5 - simple molecular structures held together by london forces, low melting point (slightly lower than 1)
group 6 - forms simple molecular structure, larger than 5 so slightly higher melting point
group 7 - forms diatomic molecules held by simple covalent bonds, low melting point
group 8 - exists as individual atoms, only london forces between them so very low melting point
what are observable physical properties of group 7 elements from F to I
F = a pale yellow gas
Cl = a pale green gas
Br = brown-orange liquid
I = grey solid
how does reactivity change as you go down group 7
reactivity decreases
group 7 react by gaining 1 electron, as you go down electronegativity decreases because atomic radius and shielding increases, so nuclear attraction decreases so don’t gain electrons as readily
how does boiling point change as you go down group 7
boiling point increases
number of electrons and atomic radius increases so more london forces, more energy to overcome
what is a halogen displacement reaction and why does it occur
a redox reaction between 2 different halogens, where the more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
this occurs because halogens are oxidising agents, so the more reactive halogen acts as the oxidising agent, itself becoming reduced to gain an electron
what would you observe during a halogen displacement reaction
a colour change
the colour of the solution indicated which free halogen is present in the solution (the one that has been displaced)
what can you add to more easily observe the colour change that occurs during a halogen displacement reaction
an organic solvent such as hexane
this will form a coloured band above the aqueous solution as the halogen dissolves in it
what colours do Cl Br and I appear in aqueous and organic solvents
aqueous
Cl = pale green/colourless
Br = yellow
I = brown precipitate
organic
Cl = colourless
Br = yellow
I = purple
disproportionation definition
a reaction in which the same species is oxidised and reduced
equation for the disproportionation reaction between Cl and H20
Cl2(g) + H2O(l)»_space; HCl(aq) + HClO(aq)
uses of HClO
HClO = chloric (I) acid
- can sterilise water by killing bacteria
- dissociates to form ClO-
- ClO- can also sterilise water
- it can also act as bleach (will turn indicator red then colourless)
equation for the disproportionation reaction between Cl and NaOH
Cl2(g) + 2NaOH(aq)»_space; NaCl(aq) + NaClO(aq) + H2O(l)
uses of NaCl and NaClO
- this mixture of compounds is used as bleach
- it is also used to disinfect water/kill bacteria
advantages and disadvantages of using compounds of Cl to treat water
advantages
- used to kill bacteria which makes it safer to drink and for use in pools
disadvantages
- potential toxic effects of Cl
- risk of the formation of chlorinated hydrocarbons
benefits to treating water with Cl outweigh the potential risks
