UNIT 6:TRENDS IN CHEMICAL PROPERTIES OF GROUP 1 ELEMENTS AND THEIR COMPOUNDS
UNIT 6: TRENDS IN CHEMICAL PROPERTIES OF GROUP
1 ELEMENTS AND THEIR COMPOUNDS
Key unit competence: Compare and contrast the chemical properties of the Group 1
elements and their compounds in relation to their position in the Periodic Table.
Learning objectives
By the end of this unit, students should be able to:
• Describe and explain the physical properties of Group 1 elements in terms
of metallic character and strength of metallic bond
• Describe and explain the reactivity of Group 1 elements with oxygen, water
and halogens
• State and explain the properties of Group 1 oxides and hydroxides
• Explain the trends in the solubility of Group 1 compounds
• State the uses of Group 1 elements and their compounds
• Compare the reactivity of Group 1 elements
• Interpret the trends in the thermal decomposition of Group 1 carbonates
and nitrates
• Perform experiments to test the alkalinity of Group 1 hydroxides• Carry out flame test for the presence of Group 1 metal cations in solution.
2. Identify elements of this group in question 1 above which are the most
and least reactive.
3. Give examples of compounds of some of the elements in the group in
question 1 above and suggest their uses.
6.1. Occurrence and physical properties of group 1 elements,
physical state, metallic character, physical appearance
and melting point
Activity 6.1.a
1. Study the following table of data and answer the questions that followData
metals. For this reason, the study of hydrogen is presented separately from the other
members of group 1 elements.
Francium is exceptionally rare. It is formed by the radioactive decay of heavier
elements.
Because Francium is both rare and highly radioactive, few of its properties have been
determined and we are not going to talk much about it in this Unit.
Physical Properties of Alkali Metals
Activity 6.1.b
In groups, learners make research in libraries / internet and discuss the physical
properties of group 1 elements and or explain the following statements
a) Group 1 elements show weak metallic bonding
b) Atomic radius of Na is smaller than the corresponding ionic radius of Na+
c) The shining appearance of metals disappears after a certain period of time.
Group 1 elements are grey metals, soft, and can be easily cut with a knife to expose
a shiny surface which turns dull on reaction with oxygen in air.
1. They have low melting and boiling points. They show relatively weak metallic bonding as only one valence electron is attracted by the nucleus. Also
they have a big atomic radius and the attraction of nucleus toward the valence electron is weak.
2. They are good conductors of heat and electricity
3. They have a low ionisation energies that decreases down the group
4. They have low density compared to other metals and Li, Na and K are less
dense than water
Group 1 metals color flames: When alkali metals are put in a flame they produce
Checking up 6.1
1. Discuss how the ionization energies vary in function of atomic radius for
group 1 elements.
2. Is there any relationship between the atomic radius and the melting
point in group 1 elements? Yes or No. Justify your answer
3. Why group 1 elements are said to be good conductors of electricity?
Illustrate your answer
4. The following table shows 3 unknown group 1 metals X, Y, Z and some of
their physical properties. Predict among the alkalis metal (Cs, Li, K), whichone should correspond to X,Y,Z. Justify your answer
6.2. Reactivity of group 1 elements with oxygen, water and
halogens
Activity 6.2 (a)
Analyse the case study below and answer the related question:
1. In groups learners discuss the following scenario and compare their
findings to the reactivity of a chemical element in terms of the variation
of atomic radius
Suppose that a hen is walking in the garden with its chicks. Some of the chicks
are feeding themselves just near the hen (mother). Other chicks are feeding
themselves far away from the mother. Which ones of the two groups of chicks willbe an easy prey of a predator? Explain.
Now extend your reasoning to the behavior of group 1 element and explain the
following statement
Group 1 elements react by losing their single electron in outermost shell. Arrange
them in order to show which one loses easily the single electron and which one
loses electron with difficult.
2. Consider a case of people who are warming around a fire; some are
near, others are a little bit far; who will feel the heat of the fire more thanthe others?
These activities show how the distance between two objects affects interactions
between them. The hen cannot protect the chicks that are far from her. In the other
case, people who are far from the fire feel less the heat of the fire.
This resembles the interactions between the nucleus and the valence electrons. The
attraction between the nucleus and the valence electron decreases with increasing
distance between the nucleus and the valence electrons.
When the atomic radius and volume increase, the distance between the nucleus and
the valence electrons increases, the attraction between the nucleus and the valence
electrons decreases, and it becomes easier to remove the valence electrons.
This explains the origin of properties of group 1 metals: they have low ionization
energy; lose easily the only one valence electron to form a mono-positive cation
(M+) with a rare gas electronic structure, and consequently are very active metals.
Activity6.2 (b)
a) Given the following elements of group 1(Na (Z=11), Li(Z=3), Cs(Z=55), K(Z=19) ,
Rb (Z=37). Arrange them according to their increasing reactivity and justify why.
b)Establish the electronic structure for the following species and explain how you
get it Na+,Na2+,Na-.Which one is stable and why?
6.2.1. Reactions with Oxygen
Activity 6.2.1
Experiment: burning an alkali metal in air/oxygen
Apparatuses: deflagrating spoon, Bunsen burner, glass beaker, filter paper,
Chemicals: lithium, sodium, potassium, water, and red litmus paper
Other requirements: knife, match box and petroleum gas
Procedure:
1. Cut a small piece of lithium and wrap it in piece of filter paper to remove the oil.
2. Place it on to a deflagrating spoon and heat it in a non luminous flame.
3. Observe what happens
4. When combustion is complete, dip the deflagrating spoon into a beaker of 100
ml filled up to 50 ml of water.
5. Stir the water with the spoon and then drop a piece of litmus papers into the
solution in the beaker. Observe
6. Repeat the experiment with sodium and potassium
Task on the experiment:
a) Write the equations of reactions that take place when each metal is burnt in air
b) Name the product that was formed in each case.
c) What are the color changes when the aqueous solutions above are tested with
litmus paper? Explain why?
d) Write the equations of reaction between each product in (b) with water
6.2.2. Reaction with water
Activity 6.2.2 Experiment to investigate the reaction of alkali metals with
water
Procedure:
Cut a small piece of sodium metal and put it in water in wide beaker and observe.
Test the obtained solution with red and blue litmus papers and observe.
Questions
1. Why is sodium so easy to cut?
2. What are the observations when sodium is placed in water in the beaker
3. Explain the observation when tests with red and blue litmus papers are
performed on the resulting solution and write the equation of the reaction that
takes place to explain you answer
6.2.3. Reaction with halogens
Activity 6.2.3
a) In terms of s, p, d, f orbitals write the electronic configuration of chlorine (Z=17),
bromine (Z=35) and iodine (Z=53)
b) Deduce the valency of each element.
c) Write molecular equations, complete and balance them, when
Sodium reacts with bromine Potassium reacts with iodineLithium reacts with chlorine
Checking up 6.2
1. An element J has 19 as atomic number while the element A has 35 as atomic
number.
a) Write their electronic structures in term of s, p, d, f orbitals and deduce their
respective valencies.
b) The element J is able to react with oxygen gas by forming two types of oxides
i) Write the formula of the 2 oxides that can be formed between the element J and oxygen
ii) Write the formula of the compound formed between J and A
iii) What type of bond does exist between J and A. Justify your answer.
c) Show how you would write the equation of reaction between J and water
supposing that J stands for the real symbol of the element.
d) When the reaction stated in (c) takes place a colorless solution and a colorless
gas are formed.
i) Which test would you use to identify each product of the reaction, by stating the
reagent and related observations?
Oxides of Group 1 metals dissolve in water to give strong alkaline solutions; that is
why they are said to form basic oxides.
6.3.2. Hydroxides
As said earlier hydroxides are formed when the metals or metals oxides are dissolved
in water. In solid state, these hydroxides dissolve very easily in water and in alcohol.
They dissociate completely in water to form alkaline solution; hence they are strong
bases. The basic character of the hydroxides increases as we move down the group.
Checking up 6.3
1. Complete and balance the reactions when water is reacted with the following:
a) Potassium metal b) Potassium oxide
2. Lithium hydroxide decomposes on heating. White powder X and a colorless gas
Y is released and condenses in a colorless liquid.
i) Write the chemical formula of X. ii) Propose a chemical test to identify Y3. Explain why Group 1 metals form ionic compounds?
6.4. The effect of heat on Group 1 carbonates and nitrates
6.4.1. Heating the nitrates
Activity 6.4.1
Experiment: effect of heat on nitrates.
In groups learners perform the following experiment, discuss and make
conclusions by explaining the observed phenomena, and write involved chemical
reactions.
Apparatus: glass test tubes, pair of tongs, wooden splint/match stick, Bunsen
burner/heat source and spatula.
Chemicals: Lithium nitrate, potassium nitrateOther requirements: match box
Procedure:
I.1.Take two spatula end full of lithium nitrate into a test tube and heat it strongly
until there is no further change.
2. Test the gases evolved with a damp blue litmus paper and a glowing splint.
3.Observe and make conclusions on your observations.
II .Repeat the procedure but using potassium nitrate/sodium nitrateLaboratory apparatus setting for thermal decomposition of a salt
6.4.2. Heating the carbonates
Activity 6.4.2
Experiment: effect of heat on carbonates of group 1 elements
In groups learners perform the following experiment, discuss and make conclusions
by explaining the observed phenomena, and write chemical reactions.
Apparatus: glass test tubes, pair of tongs, Bunsen burner/heat source and spatula.
Chemicals: lithium carbonate, calcium carbonate, potassium carbonate and
sodium carbonate, lime water
Other requirements: match box.
Procedure
I.1 Take a spatula end full of lithium carbonate into a test tube and heat it strongly
until there is no further change.2. Test the gases evolved with a damp blue litmus paper and lime water into another glass test tube as shown in the figure
3. Observe and make conclusions on your observations.
II .Repeat the procedure but using calcium carbonate, potassium carbonate /
sodium carbonate
6.5. Solubility of group 1 compounds
Activity 6.5
a) Group 1 elements form ionic compounds.
(i) Explain why.
(ii)State the properties of ionic compounds
b) Explain why lithium forms compounds with a covalent character contrarily to
other elements of the same group. State the properties of covalent compounds
c) Both hydroxides and carbonates of lithium are less soluble than other hydroxides and carbonates of group 1.Why?
Activity 6.6:
Experiment: Flame test of alkalis metals
Materials: Mortar and pestle, beakers, Lithium carbonate, potassium sulphate,
sodium sulphate
Procedure: Flame test wire /magnesia rod
NB: Wear your safety glasses.
Dip the flame test wire/magnesia rod in the salt to be tested. Some of the salt
should stick to flame test wire/magnesia.
Gently wave the flame test wire/magnesia rod in the flame of the Bunsenburner and note the color given of
• NaOCl is used as bleaching agent and disinfectant
• NaCl is used in seasoning food, preparing hydrogen chloride gas, in soap
production, manufacture of sodium, chlorine, sodium hydroxide and
sodium carbonate.
• Molten sodium is used as a coolant in nuclear reactor. Its high thermal
conductivity and low melting temperature and the fact that its boiling
temperature is much higher than that of water make sodium suitable for
this purpose.
• Sodium wire is used in electrical circuits for special applications. It is very
flexible and has a high electrical conductivity. The wire is coated with
plastics to exclude moisture.
• Sodium vapor lamps are used for street lighting; the yellow light ischaracteristic of sodium emission.
a. The first member of the group often shows anomalous properties. Give two
properties in which the behavior of Lithium is abnormal and explain why.
b. How does each of the following properties of the elements in Group 1 change
with the increasing atomic number? Explain why.
i. Atomic radius
ii. Ionization energy
iii. Reducing properties
iv. Reactivity with water
v. Electronegativity
c. How will successive ionization energies of Na vary?
d. Why is the Na+ ion formed in normal chemical reaction rather than Na2+?e. How are ionization energies related to the reactivity of these elements?