4.3 Elements in Group 1

Short Answer Questions

1. What is another name for the elements in Group 1 of the periodic table?
   Answer
   Alkali metals.
2. Name the six alkali metals.
   Answer
   Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
3. How many valence electrons do alkali metals have?
   Answer
   One.
4. Are alkali metals generally reactive or unreactive?
   Answer
   Very reactive.
5. Are alkali metals found in pure form in nature?
   Answer
   No, due to their high reactivity.
6. How does the reactivity of alkali metals change as you go down the group?
   Answer
   It increases.
7. Are alkali metals hard or soft?
   Answer
   Soft.
8. Do alkali metals have high or low melting points?
   Answer
   Low melting points.
9. What is the appearance of freshly cut alkali metals?
   Answer
   Silvery.
10. What happens to alkali metals when exposed to air?
    Answer
    They tarnish rapidly.
11. How do alkali metals react with oxygen?
    Answer
    They react to form metal oxides.
12. How do alkali metals react with chlorine?
    Answer
    They react to form metal chlorides.
13. What type of reaction is an alkali metal reaction with oxygen or chlorine?
    Answer
    Exothermic.
14. How many valence electrons do alkali metals need to lose to form a stable ion?
    Answer
    One.
15. What type of ion do alkali metals typically form?
    Answer
    Positive ions (cations).
16. Is lithium more or less reactive than potassium?
    Answer
    Less reactive.
17. What is the state of alkali metals at room temperature?
    Answer
    Solid.
18. Are alkali metals good or poor conductors of electricity?
    Answer
    Good conductors.
19. How does atomic size change as you move down Group 1?
    Answer
    It increases.
20. Are alkali metals found in large or small amounts in the Earth’s crust?
    Answer
    They are relatively abundant in the Earth's crust, although always found in compounds due to their reactivity.

Explanation Questions

1. Explain why alkali metals are so reactive.
   Answer
   Alkali metals are highly reactive because they have only one valence electron, which they readily lose to achieve a stable electron configuration (duplet or octet). This electron is relatively far from the nucleus and is therefore weakly held, so it is easily removed. This makes them very reactive with other elements.
2. Why does the reactivity of alkali metals increase down the group?
   Answer
   As you go down Group 1, the atomic size increases because of the addition of extra electron shells. The valence electron is further from the nucleus and less strongly attracted to it, making it easier to remove. As the electron is more easily lost, the reactivity of the metal increases.
3. Describe the general reaction of alkali metals with water.
   Answer
   Alkali metals react with water to form a metal hydroxide and hydrogen gas. These reactions are exothermic and can be vigorous, especially with the heavier alkali metals.
4. Explain why alkali metals are stored under oil.
   Answer
   Alkali metals are stored under oil because they react readily with air (oxygen and moisture) and need to be protected from these reactants. The oil prevents any contact with air or water vapour.
5. Why do alkali metals have low melting and boiling points?
   Answer
   Alkali metals have low melting and boiling points because they have weak metallic bonding. The single valence electron is delocalised and involved in bonding but only contributes weakly to the overall bonding strength, meaning less energy is needed to break the bonds between the atoms.
6. How do alkali metals form ions?
   Answer
   Alkali metals form positive ions (cations) by losing their single valence electron. This results in a stable electron configuration and a +1 charge, with the number of electrons then being equal to the number of protons minus one.
7. Compare the reactions of lithium, sodium, and potassium with water.
   Answer
   Lithium reacts slowly and steadily with water, producing lithium hydroxide and hydrogen gas. Sodium reacts more vigorously, producing sodium hydroxide and hydrogen gas. Potassium reacts the most vigorously out of the three, often igniting the hydrogen gas produced and causing an explosion as it reacts with water to produce potassium hydroxide and hydrogen gas. The general trend is, therefore, that the reactivity with water increases down the group.
8. Explain why the atomic size of alkali metals increases down the group.
   Answer
   As you move down Group 1, each element has an additional electron shell. This increased number of electron shells results in a larger atomic radius and a larger overall atomic size, as the outermost electrons are further from the nucleus.
9. How does the reaction between an alkali metal and a halogen result in a stable compound?
   Answer
   Alkali metals have a single electron in their outer shell, and halogens are one electron short of a full outer shell. In a reaction between an alkali metal and a halogen, the alkali metal loses its valence electron and becomes a positive ion, whilst the halogen gains an electron and becomes a negative ion. The electrostatic attraction between the oppositely charged ions results in the formation of a stable ionic compound such as a metal halide with a giant ionic lattice structure.
10. Why are alkali metals considered good conductors of electricity?
    Answer
    Alkali metals are good conductors of electricity because their single valence electron is delocalised and free to move throughout the metallic structure. This is in response to an external electrical field. These free electrons act as charge carriers making them good conductors.