Periodicity & Group 2/7 elements Flashcards
Why does atomic radius decrease down a group?
As the number of protons increase the positive charge of the nucleus increases meaning electrons are pulled closer to the nucleus so atomic radium is smaller.
Why do magnesium, sodium and aluminum have high boiling points?
They are metals and their melting and boiling points increase across the period because metal-metal bonds gets stronger a there’s an increase in positive charges so there is a decrease in the radius.
How do van der waals forces affect melting and boiling points?
- Phosphorus, sulfur and chlorine are molecular substances and their melting points depend on the strength of the van der waals forces between molecules. Van der waals forces are weak so the elements have low melting points
- Sulfurs the biggest molecule so stronger van der waals forces.
- Argon exists as individual atoms so have very weak van der waals forces so low melting point.
Describe group 2 elements:
- They have two electrons in their outer shell.
- They loose there outer electrons forming 2+ ions and are all.
Describe atomic radius and ionization energies in group 2:
- As you go down the group, the atomic radius gets larger because extra electron shells are added as you go down the group.
- First ionisation energy decreases down group because each element has extra electron shell making it easier to remove electrons.
Describe reactivity and melting points in group 2:
- Reactivity increases down the group as they loose electrons forming positive ions (easier it is to remove electrons the more reactive the element is).
- They have metallic structure with delocalized electrons. The larger the ionic radius is the further away the delocalized electrons are so less attraction they feel and less energy needed to break bonds.
Describe solubility trends in group 2:
Generally there is an increase in solubility down the group because group 2 elements contain single charged negative but those containing double charged negative ions decrease in solubility.
Why are group 2 elements known as the alkaline earth metals?
Because many of their common compounds are used for neutralizing acids for example:
- Calcium hydroxide Ca(OH)2 is used in agriculture to neutralize acid soils.
- Magnesium hydroxide (Mg(OH)2) is used in some indigestion tablets as an antacid (a substance which neutralizes excess stomach acid).
What is the equation for neutralization?
H+ (aq) + OH- (aq) —–> H2O (l)
What is barium sulfate used for?
It’s used in barium metals to diagnose problems with esophagus, stomach or intestines as it coat the tissues making them show up on the x rays.
How is magnesium used in the extraction of titanium?
- Titanium(IV) oxide (TiO2) is converted to titanium(IV) chloride (TiCl4) by heating it with carbon in a stream of chlorine gas. It is then purified by fractional distillation before being reduced by magnesium at 1000°C.
TiCl4 (g) + 2Mg (l) - Ti (s) + 2MgCl2 (l)
How can calcium oxide and calcium carbonate remove sulfur dioxide?
Burning fossil fuels produce sulfur dioxide which pollutes atmosphere and can be removed by using calcium oxide (lime) and calcium carbonate (limestone) by mixing them in water forming a slurry which is then sprayed onto the flue gases. The sulfur dioxide reacts with the alkaline slurry producing calcium sulfite CaSO3.
Describe the main properties of the first 4 halogens:
Fluorine- F2, Pale yellow, gas
Chlorine- Cl2, Green, gas
Bromine- Br2, red-brown, liquid
Iodine- I2, grey, solid
- Electronegativity decreases down the group.
- Boiling points increase down the group due to increase of the van der waals forces as size and mass of molecules increases.
How do halogens displace less reactive halide ions?
When halogens react they gain an electron and get less reactive down the group and halogens become less oxidizing. A halogen will displace a halide from solution if the halide is below it in the periodic table.
How does chlorine and sodium hydroxide make bleach?
If you mix chlorine gas with cold, diluted sodium hydroxide you get sodium chlorate solution NaClO
