Unit 1: Periodicity; Group 2 and 7 Flashcards
What makes atoms of elements in a group have similar properties?
They have similar outer shell electron configurations.
What is periodicity?
A repeating pattern across different periods
What varies first ionisation energies?
- Nuclear charge (increases across period)
- FIE decreases down a group because: atomic radius increases, however electron shielding increases as well and outweighs atomic radius.
Definition of first ionisation energy
The energy required to remove one electron from each atom in a mole of gaseous atoms to form one mole of gaseous 1+ ions.
Describe the reactivity of Group 2 elements
- Each atom loses 2 electrons from its outer shell to form a 2+ ion
- Reactivity increases down the group
- Easier to lose electrons down the group
- Ionisation energies decreases down the group
What is the group 2 elements reaction with oxygen like?
- They react vigorously with oxygen
- It’s a redox reaction
- The product is an ionic oxide
What is the group 2 elements reaction with water like?
- They react with water to form hydroxides
- Hydrogen gas is formed
- magnesium reacts slowly with water, rate increases down the group
Does it become easier or more difficult to decompose the group 2 carbonates down the group?
The carbonates become more difficult to decompose with heat as you move down the group
What is a use of calcium hydroxide?
Used by farmers/gardeners as “lime” to neutralise acidic soils.
What is a use of magnesium hydroxide?
Is used to relieve indigestion. It neutralises excess acid in the stomach.
What is a disproportionation reaction?
A reaction in which the same element is both reduced and oxidised.
What are the physical properties of Group 7 elements?
- They have low melting and boiling points
- They exist as diatomic molecules.
Van Der Waals’ forces and the group 7 elements
-down the group, number of electrons increase leading to an increase in van der Waals’ forces between molecules.
How do you test for halide ions?
- dissolve unknown halide in water
- add aqueous silver nitrate solution
If unsure of results of halide ion test, what other test can you do and what are the results?
Add aqueous ammonia solution
- chloride is soluble in dilute NH3 solution
- bromide is soluble in conc NH3 solution
- iodide is soluble in neither
