EL - Inorganic chemistry and the periodic table *01 Flashcards
how does the periodic table arrange elements?
by atomic number
what does the periodic table tell us?
can be used to make predictions concerning the properties of an element in a group
arranged into period and columns
- all the elements in the same period have the same number of electron shells
- all the elements in the same group have the same number of electrons in their outer shell
- elements in the same group have similar chemical and physical properties
periodic trends in the melting points - periods one and two, (group 1-2)
show similar trends
1. for the metal melting point increases across the period - metal-metal bonds get stronger - metal ions have increasing number of delocalised electrons and decreasing ionic radius (electrons are pulled in closer as the number of protons in the nucleus increases) = HIGHER CHARGE DENSITY.
periodic trends in the melting points - periods one and two (group 3+4)
elements with giant covalent structures have strong covalent bonds.
a lot of energy is needed to break these bonds
periodic trends in the melting points - periods one and two (group 5-7)
simple molecular substances
melting point depends on strength of intermolecular forces between molecule
intermolecular forces are weak and easily broken so have low melting points
periodic trends in the melting points - periods one and two, (group 8)
noble gases
have the lowest melting points because they exist as individual atoms so have very weak intermolecular forces
what is ionisation enthalpy?
the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of 1+ gaseous atoms
X (g) –> X+ (g) + e-
what effects the size of ionisation enthalpies?
atomic radius
nuclear charge
electron shielding
how does atomic radius affect ionisation enthalpies?
the further the outer shell electrons are from the +ve nucleus the less they’ll be attracted towards the nucleus. So, the ionisation enthalpy will be LOWER
how does nuclear charge affect ionisation enthalpy?
nuclear charge = the +ve charge on the nucleus caused by the presence of protons
the more protons there are in the nucleus the more it’ll attract the outer electrons
- it will be harder to remove electron so ionisation enthalpy HIGHER
how does electron shielding affect ionisation enthalpy?
the inner electrons shield the outer electrons from the attractive force of the nucleus.
more electrons mean more shielding which means LOWER ionisation enthalpy
trend of 1st ionisation enthalpy down a group
decreases
less attraction between nucleus and outer electrons as you go down a group
- outer shells further from nucleus
- shielding increases
- although number of protons increase this doesn’t lead to an increase because it is a less important factor
trend of 1st ionisation enthalpies across a period
increases, it gets harder to remove electrons
- number of protons increasing so outer electrons attracted more strongly to the nucleus
- and since all outer shell electrons are roughly at the same energy level, generally little extra shielding or extra distance to lessen attraction
what block of the periodic table has lower 1st ionisation enthalpies?
s-block metals
- have relatively low nuclear charges, so lose outer electrons more easily a less attraction between nucleus and the outer electrons
this makes s-block metals reactive
what block of the periodic table has higher 1st ionisation enthalpies?
p-block
have higher nuclear charges than s-block metals of the same period
- increased number of protons
- so harder to remove outer electron as outer electrons more attracted to nucleus
Less likely to lose an electron
thermal stability trend in group 2 carbonates?
increases down the group
factors that affect thermal stability in group 2 carbonates
carbonate ions are large anions and can be made unstable by the presence of a cation
- the cations polarises the anion by drawing the electrons towards it
- this distorts the carbonate ion, the greater the distortion the less stable the carbonate ion
larger anions cause LESS distortion - have a LOWER CHARGE DENSITY (the charge relative to vol.)
so further down the group the larger the cations so the less distortion caused and the more stable the carbonate ion.
how do group 2 elements react?
form ions with a charge of 2+
because group 2 atoms contain 2 electrons in their outer shell and lose both electrons when they react
reactions of group 2: with water
react with water to produce a metal hydroxide and H2
eg. M (s) + 2H2O (l) –> M(OH)2 (aq) + H2 (g)
reactivity down group 2
increases down group 2
reactions of group 2: with oxygen
to produce a metal oxide
eg. 2M (s) + O2 (g) –> 2MO (s)
reactions of group 2: in water
form metal hydroxides M(OH)2
acid + base —->
salt + water
