Periodicity and Group 2 Flashcards
-What do groups and periods tell us in the periodic table?
Groups = number of outer electrons
Period = the number of electron shells an element has
Draw a periodic table in terms of S, P, D and F blocks
Draw the trend in melting/boiling points in period 3 elements.
Explain the trend in melting point for sodium to aluminium
From sodium to aluminium it increases:
- They are metallic structures, so they consist of cations surrounded by delocalised electrons.
- More protons in the nucleus and more electrons per cation = cation are smaller and increased attraction of cation for the delocalised electrons due to the “sea” being more negatively charged (as you go across there are more outer shell electrons, so therefore more delocalised electrons) and the electrons being closer to the nuclei due to reduced atomic radius= metallic bond gets stronger = melting point increases.
Explain the melting point for Silicon (trend in period 3 elements)
the highest melting point out of period 3 elements:
- macromolecular with a tetrahedral structure
- strong covalent bonds links each of the silicon atoms together = lots of energy needed to break these bonds.
Explain the melting point for phosphorus, sulfur, chlorine and Argon (trend in period 3 elements)
A general dramatic decrease in melting point due to being simple molecular substances with only Van der Waals attractions between the molecules = little energy needed to overcome this
Phosphorus contains P4 molecules. To melt phosphorus you don’t have to break any covalent bonds - just the much weaker van der Waals forces between the molecules.
Sulphur consists of S8 rings of atoms. The molecules are bigger than phosphorus molecules, and so the van der Waals attractions will be stronger, leading to a higher melting and boiling point.
Chlorine, Cl2, is a much smaller molecule with comparatively weak van der Waals attractions, and so chlorine will have a lower melting and boiling point than sulphur or phosphorus.
Argon molecules are just single argon atoms, with electrons closer to nucleus Electrons are not easily polarised since argon is very unreactive
Why does atomic radius decrease across a period?
more protons in the nucleus = no additional shielding because electrons are added to the same shell= attraction for the electrons is greater so the atoms shrink
What is the first ionisation energy trend across a period? Explain
more protons in the nucleus as you go across = no additional shielding, as the electrons are added into the same shell = atoms are slightly smaller = attraction for the outer electron is stronger = outer electron is harder to lose.
Why is there a drop in ionisation energy from one period to the next?
the next period has a new main energy level = increase in atomic radius = outer electron is further from the nucleus= less strongly attracted and easier to remove
What are group 2 metals sometimes called?
the alkaline earth metals
What are the physical properties and trends as you go down group 2 elements (magnesium to barium) in terms of atomic arrangement? Explain them
- all have two electrons in an outer s-orbital and lose them when they react to become 2+ ions
- lower charge density as you go down the group (strong nuclear force from protons not as powerful)
- increases in atomic radius as you go down the group due to an increase in atomic number = more electron shells due to more electrons
- Decreasing first ionisation energy = more shielding so shielded from attraction to nucleus by the repulsive forces of inner-shell electrons. This means less effective nuclear charge do outer electrons are lost more easily.
- Melting point decreases from Ca to Ba (magnesium is an anomaly with no explanation)= bigger ionic radius for positive ions = increased distance between positive ions and delocalised electrons= weaker electrostatic attraction between delocalised electrons and positive ions, therefore the metallic bonds are weaker
- reactivity increases due to increased atomic radius = easier to lose outer electrons
Describe the reactions of group 2 metals with water. Write the general equation
X(s) + H2O → X(OH)2 (s) + H2 g)
metal + water = metal hydroxide + hydrogen
Mg = reacts very slowly with cold water
Ca = react with cold water more readily than Mg , effervescence and a white precipitate forms, GRANULES SINK AND RISE
Ba = vigorous reaction with effervescence
- As you go down the group: fizzing becomes more vigorous, the metal dissolves faster, the solution heats up more, less precipitate forms
Describe the reaction of Magnesium with steam
- reacts rapidly to produce MgO and H2(g)
- burns with a bright white light
- MgO in the form of a white powder
Describe the solubility of group 2 metal hydroxides
Mg(OH)2 = sparingly soluble
Ca(OH)2 = soluble (forms limewater)
Sr(OH)2 = soluble
Ba(OH)2 = soluble
Why is magnesium hydroxide solution the least alkaline? Which group 2 metal hydroxide solution is the most alkaline?
It has the least amount of hydroxide ions dissolved.
Barium hydroxide
Describe the solubility of group 2 metal sulfates
MgSO4 = soluble
CaSO4 = sparingly soluble
SrSO4 = insoluble
BaSO4 = insoluble
What does solubility of group 2 metal hydroxides/sulfates tell us about the strength of the base?
the higher the solubility the stronger the base as there are more OH- ions in the solution
Write the chemical equation for the solubility of magnesium hydroxides and the solubility of barium hydroxides
What is the test for sulfate ions?
adding barium chloride acidified with hydrochloric acid/ nitric acid to a solution containing sulfate ions, then a white precipitate of barium sulfate is formed
Write the ionic equation for the test for sulfate ions
What is the full equation and the ionic equation for the formation of a precipitate when group 2 metals react with, for example, sodium sulfate
Why does barium chloride need to be acidified by hydrochloric acid/ nitric acid (HCL added before barium chloride) for the test for sulfate ions?
HCl is needed to rewact with carbonate impurities that are often found in salts, which would form a white barium carbonate precipitate = false result.
the effervescence of co2 once HCl is added would indicate carbonate was present
Write the ionic equation for when there are carbonates present during a test for sulfates
2H+ +CO32- → H2O +CO2
How are magnesium hydroxide and calcium hydroxide used in real life to neutralise acidity?
Magnesium: milk of magnesia as a laxative or used as an antacid to neutralise excess stomach acid
Calcium - used to agriculture to neturalise acid soils and provide calcium ions which are essential for plant growth
What is the ionic equation for neutralisation?
H+(aq) + OH- (aq) → H2O
How is Barium sulfate used in medicine?
known as a barium meal, barium sulfate is taken orally, and since it is insoluble in water or body fluids, it blocks x-rays. It coats the lining of soft tissue (e.g. stomach) Since it is insoluble it is not absorbed in the blood. It also has low toxicity so it’s safe.
Describe the extraction of titanium using magnesium
Titanium ore (TiO2) is converted to titanium (IV) chloride by heating it with carbon in a steam of chlorine.
Then titanium (IV) chloride is then purified by fractional distillation before being reduced by magnesium in small batches, in a furnace at almost 1000 degrees celsius
Magnesium chloride is then removed from the mixture by vacuum distillation
What is the equation for the extraction of titanium using magnesium (including the chlorine and carbon bit)
Why is titanium expensive?
- expensive cost of magnesium
- bath process = process is slower and requires more labour and the energy is lost when the reactor is cooled down after stopping
- high temperatures are required
What are the chemical equations for when calcium oxide or calcium carbonate neutralises sulfur dioxide
Describe the process used to remove sulfur dioxide using calcium oxide or calcium carbonate
wet scrubbing: A slurry is made by mixing the calcium oxide or calcium carbonate with water. It is then sprayed onto the flue gases. The sulfur dioxide reacts with the alkaline slurry and produces calcium sulfite.
You are given a sample of saturated calcium hydroxide solution. Outline the practical steps that you would take to determine the solubility of calcium hydroxide solution in this solution
Take a known volume of the saturated solution
Evaporate the filtrate to dryness
Weigh the residue of known concentration
Use your knowledge of the reactions of Group 2 metals with eater to explain why water should not be used to put out a fire in which magnesium metal is burning
- hydrogen is formed
- risk of explosion
