IB DP Chemistry: SL复习笔记3.2.2 Periodic Trends: Group 1 - The Alkali Metals

The group 1 metals

• The group 1 metals are called the alkali metals because they form alkaline solutions with high pH values when reacted with water
• Group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium
• They all end in the electron configuration ns¹

Physical properties of the group 1 metals

• The group 1 metals:
  • Are soft and easy to cut, getting softer and denser as you move down the group
  • Have shiny silvery surfaces when freshly cut
  • Conduct heat and electricity
  • They all have low melting points and low densities and the melting point decreases going down the group as the atomic radius increases and the metallic bonding gets weaker

The alkali metals are located on the left of the periodic table in the first column of the s block

Chemical properties of the Group 1 metals

• They react readily with oxygen and water vapour in air so they are usually kept under oil to stop them from reacting
• Group 1 metals will react similarly with water, reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas

The Reactions of Group 1 Metals and Water

• Test yourself on this example question:

Answer:

The correct option is D.

• • Bubbles of hydrogen gas are given off. The sodium melts, so that tells you it is an exothermic reaction and the product, sodium hydroxide, is very soluble so a clear, colourless solution would be formed.

Alkali metals with halogens

• All the alkali metals react vigorously with the halogens in group 17
• The reaction results in an alkali metal halide salt

2Na (s) + Cl₂ (g) → 2NaCl (s)

• The reaction becomes increasingly vigorous going down group 1 because
  • The atoms of each element get larger going down the group
  • This means that the ns¹ electron gets further away from the nucleus and is shielded by more electron shells.
  • The further an electron is from the positive nucleus, the easier it can be lost in reactions

Can you apply what you have just learned? Check out the following example question:

Answer:

The correct option is C.

• • You need to choose the lowest element in group 1 and the highest element in group 17 to predict the most vigorous reaction as reactivity increases going down group 1, but decreases going down group 17