29/03/2004
By: Ibrahim al Saieg
Contents page
. Introduction.
2. Apparatus list.
3. Implementation.
4. Analysing evidence and drawing conclusions.
5. Evaluating evidence and procedures.
Introduction
With this experiment we can determine the relative atomic mass of Lithium.
I am going to calculate the relative atomic mass of lithium by using two methods. These methods will be explained further in this coursework.
Lithium is an Alkali earth metal.
Now I am going to introduce Lithium and the group 1 elements:
The elements of Group 1, the Alkali metals, are:
symbol
electron configuration
lithium
Li
[He]2s1
sodium
Na
[Ne]3s1
potassium
K
[Ar]4s1
rubidium
Rb
[Kr]5s1
caesium
Cs
[Xe]6s1
francium
Fr
[Rn]7s1
In each element the valence electron configuration is ns1, where n is the period number. The last element, francium, is radioactive and will not be in this coursework.
Physical Properties
The alkali metals differ from other metals in several ways. They are soft, with low melting and boiling temperatures. They have low densities - Li, Na and K are less dense than water. They have low standard enthalpies of melting and vaporization. They show relatively weak metallic bonding as only one electron is available from each atom.
Alkali metals colour flames. When the element is placed in a flame the heat provides sufficient energy to promote the outermost electron to a higher energy level. On returning to ground level, energy is emitted and this energy has a wavelength in the visible region:
Li
red
Na
yellow
K
lilac
Rb
red
Cs
blue
The ionic radii of the alkali metals are all much smaller than the corresponding atomic radii.
This is because the atom contains one electron in an s level relatively far from the nucleus in a new quantum shell, and when it is removed to form the ion the remaining electrons are in levels closer to the nucleus. In addition, the increased effective nuclear charge attracts the electrons towards the nucleus and decreases the size of the ion.
Chemical Properties
The alkali metals are strong reducing agents. The standard electrode potentials all lie between -2.7V and -3.0V, indicating a strong tendency to form cations in solution. They can reduce oxygen, chlorine, ammonia and hydrogen. The reaction with oxygen tarnishes the metals in air, so they are stored under oil. They cannot be stored under water because they react with it to produce hydrogen and alkali hydroxides:
2M(s) + 2H2O(l) 2M+(aq) + 2OH-(aq) + H2(g)
eg. 2Na(s) + 2H2O(I) 2NaOH(aq) + H2(g)
This reaction illustrates the increasing reactivity on descending the Group. Li reacts steadily with water, with effervescence; sodium reacts more violently and can burn with an orange flame; K ignites on contact with water and burns with a lilac flame; Cs sinks in water, and the rapid generation of hydrogen gas under water produces a shock wave that can shatter a glass container. Na dissolves in liquid ammonia to give a deep blue solution of sodium cations and solvated electrons. This solution is used as a reducing agent. At higher concentrations the colour of the solution changes to bronze and it conducts electricity like a metal.
By: Ibrahim al Saieg
Contents page
. Introduction.
2. Apparatus list.
3. Implementation.
4. Analysing evidence and drawing conclusions.
5. Evaluating evidence and procedures.
Introduction
With this experiment we can determine the relative atomic mass of Lithium.
I am going to calculate the relative atomic mass of lithium by using two methods. These methods will be explained further in this coursework.
Lithium is an Alkali earth metal.
Now I am going to introduce Lithium and the group 1 elements:
The elements of Group 1, the Alkali metals, are:
symbol
electron configuration
lithium
Li
[He]2s1
sodium
Na
[Ne]3s1
potassium
K
[Ar]4s1
rubidium
Rb
[Kr]5s1
caesium
Cs
[Xe]6s1
francium
Fr
[Rn]7s1
In each element the valence electron configuration is ns1, where n is the period number. The last element, francium, is radioactive and will not be in this coursework.
Physical Properties
The alkali metals differ from other metals in several ways. They are soft, with low melting and boiling temperatures. They have low densities - Li, Na and K are less dense than water. They have low standard enthalpies of melting and vaporization. They show relatively weak metallic bonding as only one electron is available from each atom.
Alkali metals colour flames. When the element is placed in a flame the heat provides sufficient energy to promote the outermost electron to a higher energy level. On returning to ground level, energy is emitted and this energy has a wavelength in the visible region:
Li
red
Na
yellow
K
lilac
Rb
red
Cs
blue
The ionic radii of the alkali metals are all much smaller than the corresponding atomic radii.
This is because the atom contains one electron in an s level relatively far from the nucleus in a new quantum shell, and when it is removed to form the ion the remaining electrons are in levels closer to the nucleus. In addition, the increased effective nuclear charge attracts the electrons towards the nucleus and decreases the size of the ion.
Chemical Properties
The alkali metals are strong reducing agents. The standard electrode potentials all lie between -2.7V and -3.0V, indicating a strong tendency to form cations in solution. They can reduce oxygen, chlorine, ammonia and hydrogen. The reaction with oxygen tarnishes the metals in air, so they are stored under oil. They cannot be stored under water because they react with it to produce hydrogen and alkali hydroxides:
2M(s) + 2H2O(l) 2M+(aq) + 2OH-(aq) + H2(g)
eg. 2Na(s) + 2H2O(I) 2NaOH(aq) + H2(g)
This reaction illustrates the increasing reactivity on descending the Group. Li reacts steadily with water, with effervescence; sodium reacts more violently and can burn with an orange flame; K ignites on contact with water and burns with a lilac flame; Cs sinks in water, and the rapid generation of hydrogen gas under water produces a shock wave that can shatter a glass container. Na dissolves in liquid ammonia to give a deep blue solution of sodium cations and solvated electrons. This solution is used as a reducing agent. At higher concentrations the colour of the solution changes to bronze and it conducts electricity like a metal.
