4: Inorganic Chemistry and the Periodic Table Flashcards
What is the trend of reactivity in Group 2
Reactivity increases down Group 2 elements
Why does reactivity increase down Group 2
- First and second ionisation energies decrease down Group 2
- Therefore it is easier for the elements to lose their two valance electrons down the group
- This is due to the attraction of the nucleus and valance electrons decreasing down the group due to increasing atomic radii and the increasing shielding
How do Group 2 elements behave in redox reactions
- Each metal atom is oxidised, losing its two valance electrons, forming a +2 ion
- Another species gains these electrons and is reduced
- Therefore Group 2 elements are reducing agents
How can the reactivity of Group 2 elements be tested
- Reacting with dilute HCl: bubbles of hydrogen gas are given off much faster down the group (more vigorous)
- Reacting with oxygen: more reactive with oxygen down the group
What is the general equation for the reaction between Group 2 metals and oxygen
What is the general equation for the reaction between Group 2 metals and water
Why is magnesium oxide sometimes formed when magnesium reacts with water
- Magnesium reacts extremely slowly with cold water, and the solution formed is only slightly soluble
- When magnesium is heated in steam, it reacts vigorously to make magnesium oxide
What is the general equation for the reaction of Group 2 metals and chlorine gas
Are Group 2 oxides acidic or basic
- All are basic
- Apart from BeO which is amphoteric
Define amphoteric
A substance that can act as both an acid (proton donor) and a base (proton acceptor)
What happens when Group 2 oxides react with water
- They form alkaline solutions which become more alkaline down the group
Oxide + water ➡️ hydroxide
What is the general equation of the reaction between a Group 2 oxide and dilute hydrochloric/sulphuric acid
Metal oxide + dilute acid ➡️ metal salt (chloride/sulphate) + water
What happens when Group 2 metal hydroxides react with dilute acids
- Form colourless solutions of metal salts
- Except barium sulphate which is insoluble, making a white precipitate
Metal hydroxide + dilute hydrochloric/sulphuric acid ➡️ metal salt (chloride/sulphate) + water
What is the ionic reaction that takes place when Group 2 oxides react with water
What is the trend in alkalinity in Group 2 solutions
Increases down the group
Why does alkalinity of Group 2 hydroxides increase down the group
- Solubility of Group 2 hydroxides increases down the group,
- So the concentration of OH- ions in the solution increases, increasing the pH of the solution
- Making it more alkaline
What is the general equation for Group 2 hydroxides dissolving in water
What is the trend of solubility in Group 2 sulphates
Solubility decreases down the group
What is the trend of solubility of Group 1 hydroxides and sulphates
They are all soluble in water
Are Group 1 or 2 hydroxides more soluble
Group 1 hydroxides are more soluble
What is thermal decomposition
The breakdown of a compound into two or more different substances using heat
What is the only Group 1 carbonate that decomposes
- Only lithium carbonate can be thermally decomposed at Bunsen temperatures
What is the general equation for the thermal decomposition of Group 2 carbonates
What is the only Group 1 nitrate that thermally decomposes
- Lithium nitrate
What is the general equation for the incomplete decomposition of Group 1 nitrates (not lithium)
What is the general equation for the thermal decomposition of Group 2 nitrates
What is the trend in thermal stability in Group 1 and 2 carbonates and nitrates
Thermal stability increases down both groups
Why does thermal stability increase down Group 1 and 2 carbonates and nitrates
- Ionic radius of the cations increases down the groups
- Positive ions with larger ionic radii have lower polarising power and distort the electron clouds of the anions less
- Positive ions with smaller ionic radii have higher polarising power and distort the electron clouds one the anions more
- The more polarised the anion is, the more likely it is to be thermally decomposed as the bonds in the carbonate and nitrate ions become weaker and less heat is needed to free CO2 and NO2
Describe the flame test process
- Dip an unreactive metal wire (in chrome/platinum) in concentrated HCl, then hold it in the blue flame of the Bunsen burner until there is no colour change (cleans to avoid contamination)
- Dip the wire in the solid metal sample and place it on the edge of the blue Bunsen flame
- Observe the colour
Why are are colours produced in flame tests
- Heat causes electrons in the sample to jump to a higher energy level
- The electron is unstable at this energy level, so falls back down
- As it falls energy is emitted in the form of visible light
Mg2+ flame test
Bright white flame
Ba2+ flame test
Apple green
Ca2+ flame test
Brick red