8.2The Periodic Table
Group I properties — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
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Lesson summary
8.2 Group I properties — COMBINED SCIENCE (CHEMISTRY) notes: Describe the Group I alkali metals and their trends.Name — Group I metals form alkaline solutions with water.Lithium, sodium and potassium are the common examples.Outer shell — each atom has one outer electron.Soft — th…
- Appearance
- Conductors
- Low melting points
- Low density
- Reactivity
- Soft — they are soft and easy to cut, softer down the group
Section 1 of 16The alkali metals
Name
- Group I metals form alkaline solutions with water.
- Lithium, sodium and potassium are the common examples.
Outer shell
- Outer shell each atom has one outer electron.
Section 2 of 16Physical properties
Soft
- Soft they are soft and easy to cut, softer down the group.
Appearance
- Appearance shiny silvery when freshly cut.
Conductors
- Conductors they conduct heat and electricity.
Low melting points
- Low melting points lower than other metals and generally decreasing down the group.
Low density
- Low density lower than other metals.
Section 3 of 16Chemical properties
With air
- With air they react readily with oxygen and water vapour, so they are stored under oil.
With water
- 2M + 2H2O → 2MOH + H2, forming an alkaline hydroxide and hydrogen.
Reactivity
- Reactivity increases down the group.
Safety
- Safety only the first three metals are used in school demonstrations.
Section 4 of 16Reactions with water
| Metal | Equation | Observations |
|---|---|---|
| Lithium | 2Li + 2H2O → 2LiOH + H2 | Relatively slow, fizzing, moves on the surface |
| Sodium | 2Na + 2H2O → 2NaOH + H2 | More vigorous, moves rapidly, dissolves quickly |
| Potassium | 2K + 2H2O → 2KOH + H2 | Even more vigorous, lilac flame, dissolves very quickly |
Section 5 of 16Trends down the group
Trends down the group
Melting point
- Melting point decreases.
Density
- Density increases, with an exception early in the group.
Reactivity with water
- Reactivity with water increases.
Section 6 of 16Predicting rubidium, caesium and francium
Rubidium
- Rubidium very violent reaction that may explode with sparks.
Caesium
- Caesium extremely violent, can explode due to rapid production of heat and hydrogen.
Francium
- Francium extremely reactive but rare and radioactive so predictions cannot be confirmed.
Section 7 of 16More from the specification
More from the specification
Periodic
- Describing properties that repeat at regular intervals along the table
Group 1 alkali metals
- Highly reactive soft metals with one valence electron that react vigorously with water to form alkaline hydroxides and hydrogen.
Group 7 halogens trends
- Reactivity decreases down the group from chlorine to bromine (red-brown liquid) and iodine (dark grey solid/purple vapour).
- (pale yellow-green gas)
Halogen displacement
- A more reactive halogen displaces a less reactive halide ion from aqueous solution.
Group 0 noble gases
- Monatomic unreactive elements with complete outer electron shells providing electronic stability.
Transition elements
- The central block of metals between Group II and Group III.
Physical property
- A property observed or measured without changing the material.
Element
- A substance made of only one type of atom.
Halogens
- Group 17 non-metals that form diatomic molecules.
Halogen
- A Group VII non-metal with seven outer electrons.
Aqueous
- Dissolved in water.
Displacement
- A reaction in which a more reactive element takes the place of a less reactive one in a compound.
Section 8 of 16Why reactivity increases down Group I
Why reactivity increases down Group I
Outer electron
- Outer electron each atom has one outer electron.
Down the group
- Down the group atoms have more shells, so the outer electron is further from the nucleus and more shielded.
Result
- Result the outer electron is lost more easily, so reactivity increases.
Section 9 of 16Reaction with water
Equation
- 2M + 2H2O → 2MOH + H2.
- Example2Na + 2H2O → 2NaOH + H2.
Products
- Products an alkaline metal hydroxide solution and hydrogen gas.
- The solution turns universal indicator blue or purple.
- Hydrogen gives a squeaky pop with a lighted splint.
Section 10 of 16Storage and safety
Stored under oil
- Stored under oil the metals react with air and water vapour.
Demonstrations
- Demonstrations only lithium, sodium and potassium are used in schools.
Section 11 of 16Flame tests for Group I ions
| Ion | Flame colour |
|---|---|
| Li+ | Red |
| Na+ | Yellow |
| K+ | Lilac |
Section 12 of 16Trends in physical properties
Melting point
- Melting point decreases down the group.
Hardness
- Hardness the metals become softer down the group.
Density
- Density increases down the group, with an exception early in the group.
Section 13 of 16Using data to identify trends (supplement)
Using data to identify trends (supplement)
Put the metals and their data in order of position in the group.
Look for a general pattern in the values.
Use the pattern to predict the property of another group member.
- Prediction
- rubidium, caesium and francium will react more vigorously than lithium, sodium and potassium.
Section 14 of 16More from the specification
More from the specification
Trends in Group 7 Halogen Physical Properties
- Halogens exist as diatomic non-metal elements whose physical states transition down the group from pale yellow fluorine gas, green chlorine gas, red-brown liquid bromine, to dark grey-black solid iodine.
Reactivity Trends Down the Halogen Group
- Chemical reactivity of halogens decreases down Group 7 as atomic radius and shielding increase,
- reducing the nucleus's ability to attract an incoming electron into its valence shell.
Halogen Displacement Reactions
- A more reactive halogen displaces a less reactive halide ion from aqueous solution;
- for example, adding chlorine water to a potassium bromide or potassium iodide solution oxidises bromide to bromine and iodide to iodine.
Contrasting Halogens with Group 1 Metals and Noble Gases
- While Group 1 alkali metals become more reactive down the group by losing one electron, halogens gain one electron to achieve stable octets like unreactive Group 0 noble gases.
Periodic
- Describing properties that repeat at regular intervals along the table
Noble gases
- The Group 0 elements, which are unreactive monatomic gases
Transition elements
- The central block of metals between Group II and Group III.
Physical property
- A property observed or measured without changing the material.
Element
- A substance made of only one type of atom.
Halogens
- Group 17 non-metals that form diatomic molecules.
Halogen
- A Group VII non-metal with seven outer electrons.
Observation
- What is seen, heard, smelt or measured
Aqueous
- Dissolved in water.
Displacement
- A reaction in which a more reactive element takes the place of a less reactive one in a compound.
Section 15 of 16Key terms
| Term | Meaning |
|---|---|
| Alkali metal | Group I metal. |
| Alkaline | Having pH above 7. |
| Reactivity | How readily a metal reacts. |
| Hydroxide | Compound containing OH^{-}. |
| Outer shell | Highest-energy shell of electrons. |
| Trend | General pattern down a group or across a period. |
| Term | Meaning |
|---|---|
| Alkali metal | Group I metal. |
| Shielding | Inner shells reducing attraction between nucleus and outer electron. |
| Hydroxide | Compound containing OH^{-}. |
| Flame test | Test using flame colour to identify a metal ion. |
| Trend | Pattern in properties down a group. |
Section 16 of 16Exam technique
1
Saying reactivity decreases down Group I — it increases.
2
Saying Group I metals are hard — they are soft.
3
Saying Group I metals react to give acidic solutions — they give alkaline solutions.
4
Storing the metals in water — they are stored under oil.
1
Saying the outer electron is lost less easily down the group.
2
Saying Group I hydroxides are acidic — they are alkaline.
3
Saying density always increases regularly — there is an exception.
4
Using water to put out a Group I metal fire.
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