Periodicity
(a) Explain why [Fe(H2O)6]3+ and [Cr(H2O)6]3+ have different colours. (b) Explain why [Fe(H2O)6]3+ and [Fe(H2O)6]2+ have different colours.
(a) [Fe(H2O)6]3+ is yellow and [Cr(H2O)6]3+ is green; the colours they show are complementary to the colours of light they absorb; colour is caused by transitions between the two sets of d orbitals in the complex; the different metals in the two complexes cause the d orbitals to split differently as they have different nuclear charges and this results in different wavelengths (colours) of light being absorbed. (b) The oxidation state of the central ion is different in the two complexes and this affects the size of the d orbital splitting due to the different number of electrons present in d orbitals. Fe2+ has the electron configuration [Ar]3d6 and Fe3+ has the electron configuration [Ar]3d5.
What is EDTA 4-?
(old name ethylenediaminetetraacetic acid) is an example of a polydentate ligand as it has six atoms (two nitrogen atoms and four oxygen atoms) with lone pairs available to form coordinate bonds. EDTA 4- is thus equivalent to six monodentate ligands and is described as a hexadentate (six-toothed) ligand. It can occupy all the octahedral sites and grip the central ion in a six-pronged claw and form a chelate.
What are properties of the halogens?
- they exist as diatomic molecules Physical properties • They are coloured. • They show a gradual change from gases (F2 and Cl2), to liquid (Br2), and solids (I2 and At2). Chemical properties • They are very reactive non-metals. Reactivity decreases down the group. • They form ionic compounds with metals and covalent compounds with other non-metals.
What are the properties of alkali metals?
-They are usually stored in oil to prevent contact with air and water. Physical properties: • They are good conductors of electricity and heat. • They have low densities. • They have grey shiny surfaces when freshly cut with a knife. Chemical properties: • They are very reactive metals. • They form ionic compounds with nonmetals
What are trends for melting points in the periodic table?
1. Melting points decrease down Group 1. The elements have metallic structures which are held together by attractive forces between delocalized outer electrons and the positively charged ions. This attraction decreases with distance. 2. Melting points increase down Group 17. The elements have molecular structures which are held together by London (dispersion) forces. These increase with the number of electrons in the molecule. This is explained more fully in Chapter 4. 3. Melting points generally rise across a period and reach a maximum at Group 14. They then fall to reach a minimum at Group 18. In Period 3, for example, the bonding changes from metallic (Na, Mg, and Al) to giant covalent (Si) to weak van der Waals' attraction between simple molecules (P4, S8, Cl2) and single atoms (Ar) . All the Period 3 elements are solids at room temperature except chlorine and argon.
1. What are oxides of Period 3? 2. What does it mean that oxide is amphoteric?
1. Oxides of metals are ionic and basic. Oxides of the non-metals are covalent and acidic. Aluminium oxide is amphoteric. 2. Amphoteric oxides show both acidic and basic properties.
Show an example of a displacement reaction of iodine and chlorine.
2I-(aq) + Cl2(aq) → 2Cl-(aq) + I2(aq) The colour changes from colourless to dark orange/brown owing to the formation of iodine. 2I-(aq) + Br2(aq) → 2Br-(aq) + I2(aq) The colour darkens owing to the formation of iodine. To distinguish between bromine and iodine more effectively, the fi nal solution can be shaken with a hydrocarbon solvent. Iodine forms a violet solution and bromine a dark orange solution.
Why are there different oxidation states of transition elements?
3d and 4s orbitals are close in energy so its easier to remove electrons from those two sublevels
What is chelate?
A chelate is a complex containing at least one polydentate ligand bonded to a central metal atom at two or more points.
What is a coordinate bond?
A coordinate bond is a covalent bond in which both the shared electrons are provided by one of the atoms. An arrow on the head of the bond is sometimes used to show a coordinate bond, with the direction indicating the origin of the electrons.
What is a coordinate bond?
A coordinate bond uses a lone pair of electrons to form a covalent bond.
What is a ligand?
A ligand is a species that uses a lone pair of electrons to form a coordinate bond with a metal ion.
What are alkalis?
Alkalis (zasady) are bases which are soluble in water. They form hydroxide ions in aqueous solution.
What is the character of aluminum oxides?
Aluminium oxide does not affect the pH when it is added to water as it is essentially insoluble. It has amphoteric properties, however, as it shows both acid and base behaviour. For example, it behaves as a base as it reacts with sulfuric acid: and behaves as an acid when it reacts with alkalis such as sodium hydroxide:
Is first electron affinity exothermic or endothermic?
As the added electron is attracted to the positively charged nucleus the process is generally exothermic
What are complex ions?
Complex is formed when a metal central ion is surrounded by molecules or ions which possess a lone pair of electrons. These surrounding species (ligands), are attached via a coordinate bond. All ligands have at least one atom with a lone pair of electrons which is used to form a coordinate bond with the central metal ion.
Where is EDTA 4- used?
EDTA4- forms chelates with many metal ions and is widely used as a food additive as it removes transition ions from solution and so inhibits enzyme-catalysed oxidation reactions.
What are properties of electron affinities across the period and the group?
Electron affinities can be thought of as the negative of fi rst ionization energy of the anion. • The Group 17 elements have incomplete outer energy levels and a high effective nuclear charge of approximately +7 and so attract electrons the most. • The Group 1 metals have the lowest effective nuclear charge of approximately +1 and so attract the extra electron the least. • The electron affinities reach a maximum for Group 2 and Group 5 elements. Group 2 elements have an electron configuration ns2, so the added electron must be placed into a 2p orbital which is further from the nucleus and so experiences reduced electrostatic attraction due to shielding from electrons in the ns orbital. The value for beryllium is actually endothermic as there is electrostatic repulsion between the electrons of the Be atom and the added electron. The electrons in the 1s and 2s orbitals of Be also shield the added electron from the positively charged nucleus. Group 15 elements have the configuration ns2npx1py1pz1 so the added electron must occupy a p orbital that is already singly occupied: the attraction between the electron and atom is less than expected as there is increased inter-electron repulsion. The value is only just exothermic for nitrogen.
What is electronegativity?
Electronegativity is the ability of an atom to attract electrons in a covalent bond.
When electron affinity is endothermic and when it is exothermic?
Energy is needed to bring two particles of the same charge closer together as they repel reach other: this is an endothermic process. Particles of the opposite charge attract each other. They will spontaneously move closer together: it is an exothermic process.
Why do transition elements show magnetic properties?
Every spinning electron in an atom or molecule can behave as a tiny magnet. Electrons with opposite spins behave like minute bar magnets with opposing orientation and so have no net magnetic effect. Most substances have paired electrons that pair up and so are non-magnetic. Some transition metals and their compounds are unusual in having some electrons that remain unpaired, which when aligned lead to magnetic properties.
Explain why Fe2+(aq) is coloured and can behave as a reducing agent, whereas Zn2+(aq) is not coloured and does not behave as a reducing agent.
Fe2+ has configuration [Ar]3d6 and Zn2+ is [Ar]3d10. Colour in transition metal complexes is due to the splitting of the d subshell into two sets of d orbitals with different energy levels; the absorption of visible light results in electrons being excited from the lower energy set to the higher energy set and the colour observed is complementary to the colour (wavelength) of light absorbed. Light can only be absorbed if the d orbitals are partially filled and the higher energy set has an empty or partially filled orbital that can accept an electron from the lower energy set. Fe2+ has partially filled d orbitals and so electronic transitions can occur from the lower energy set to the higher energy set with the absorption of visible light and it appears coloured in solution. In Zn2+ all of the d orbitals are fully occupied so an electronic transition cannot occur from the lower energy set to the higher energy set so it is unable to absorb visible light and Zn2+ is not coloured in solution. Fe2+ not in its highest oxidation state and so can be oxidized by removal of d electron; Zn2+ in its highest oxidation state and so can't be oxidized (and so can't act as reducing agent). <reducing agent loses electron>
Why are heterogeneous catalyst important in the industry?
Heterogeneous catalysis is generally preferred in industrial processes as the catalyst can be easily removed by fi ltration from the reaction mixture after use.
What are high and low melting points assocciated with?
High melting points are associated with ionic or covalent giant structures, low melting points with molecular covalent structures.
What are homogeneous catalyst and where are they particularly important?
Homogeneous catalysts are in the same state of matter as the reactants. The ability of transition metals to show variable oxidation states allows them to be particularly effective homogeneous catalysts in redox reactions. As many of the enzyme-catalysed cell reactions in the body involve transition metals as homogeneous catalysis, they are of fundamental biological importance
What is a hetergeneous catalyst? Why transition metals are great heterogeneous catalysts?
In heterogeneous catalysis, the catalyst is in a different state from the reactants. The ability of transition metals to use their 3d and 4s electrons to form weak bonds to reactant molecules makes them effective heterogeneous catalysts as they provide a surface for the reactant molecules to come together with the correct orientation.
What of the metals are ferromagnetic? What properties do they show?
Iron, nickel, and cobalt are ferromagnetic; the unpaired d electrons in large numbers of atoms line up with parallel spins in regions called domains. Although these domains are generally randomly oriented with respect to each another, they can become more ordered if exposed to an external magnetic field. The magnetism remains after the external magnetic field is removed, as the domains remain aligned due to the long range interaction between the unpaired electrons in the different atoms.
What is diamagnetism, paramagnetism and ferromagnetism?
Materials are classified as diamagnetic, paramagnetic, or ferromagnetic based on their behaviour when placed in an external magnetic field. • Diamagnetism is a property of all materials and produces a very weak opposition to an applied magnetic fi eld. • Paramagnetism, which only occurs with substances which have unpaired electrons, is stronger than diamagnetism. It produces magnetization proportional to the applied fi eld and in the same direction. • Ferromagnetism is the largest effect, producing magnetizations sometimes orders of magnitude greater than the applied fi eld. Most materials are diamagnetic as the orbital motion of their electrons produces magnetic fi elds which oppose any external fi eld. Paramagnetism is a property of single atoms or ions with unpaired spinning electrons, whereas ferromagnetism only occurs if there is long range ordering of the unpaired electrons.
Are second or next electron affinities exothermic or endothermic?
O-(g) + e- → O2-(g) This process is endothermic as the added electron is repelled by the negatively charged oxide (O-) ion, and energy needs to be available for this to occur.
Explain briefly the properties of constituent elements of the periodic table.
One of the key features of the Periodic Table is that the metals, metalloids, and nonmetals occupy different regions. The non-metals are found on the upper righthand side of the p block. The halogens, for example, are a reactive group of nonmetals in Group 17 and the noble gases are a very unreactive family of nonmetals found at the extreme right-hand side in Group 18. Metallic elements are found on the left-hand side of the table in the s block, in the central d block, and the island of the f block. The alkali metals, for example, are a reactive group of metals in Group 1 of the s block. The lanthanoides and actinoides are metals which make up the fi rst and second row of the f block.
You are given two white solids and told that only one of them is an ionic compound. Describe three tests you could carry out to determine which it is.
Test the melting point: ionic solids have high melting points. Test the solubility: ionic compounds usually dissolve in water but not in hexane. Test the conductivity: ionic compounds in aqueous solution are good conductors.
Explain why metals have lower ionization energies and electronegativities than non-metals
The ability of metals to conduct electricity is due to the availability of their valence electrons to move away from the atomic nucleus. This can be related to their low ionization energies and electronegativities. There is a transition from metal to metalloid and non-metal from left to right as these properties increase. The diagonal band of metalloids which divides the metals from the non-metals can also be related to the similar electronegativities of these elements.
Why metals have lower ionization energies and electronegativities than non-metals ?
The ability of metals to conduct electricity is due to the availability of their valence electrons to move away from the atomic nucleus. This can be related to their low ionization energies and electronegativities. There is a transition from metal to metalloid and non-metal from left to right as these properties increase. The diagonal band of metalloids which divides the metals from the non-metals can also be related to the similar electronegativities of these elements.
Why Zn is not a transition metal?
The absence of zinc (Zn) from the collection of coloured ions in the photo above is signifi cant. Zinc compounds do not generally form coloured solutions. Zinc is a d-block element but not a transition metal as it does not display the characteristic properties listed earlier; it shows only the +2 oxidation state in its compounds. The reason for its exceptional behaviour can be traced to the electronic confi guration of its atom and the Zn2+ ion - the d sub-level is complete in both species . The electron confi guration of the transition metal ions Ti2+ and Cu2+ are included for comparison. Sc3+(aq) is also colourless in aqueous solution as it has no d electrons, but it is a transition metal as its atom has an incomplete d sub-shell, and the Sc2+ ion, although not common, does exist with a single d electron.
What is the acid-base character of the period 3 oxides?
The acid-base properties of the oxides are closely linked to their bonding and structure. Metallic elements, which form ionic oxides, are basic; non-metal oxides, which are covalent, are acidic. Aluminium oxide, which can be considered as an ionic oxide with some covalent character, shows amphoteric properties - reacting with both acids and bases
How the geometry of the complex affect its splitting?
The change of the colour in the cobalt complex in the photo on the right is also in part due to the change in coordination number and geometry of the complex ion. The splitting in energy of the d orbitals depends on the relative orientation of the ligand and the d orbitals.
How are chemical properties changing depending on the place on the periodic table?
The chemical properties of an element are determined by the electron confi guration of its atoms. Elements of the same group have similar chemical properties as they have the same number of valence electrons in their outer energy level. The alkali metals in Group 1, for example, all have one electron in their outer shell and the halogens in Group 17 have seven outer electrons.
What are chemical properties of transition metals?
The chemical properties of the transition metals are very different from those of the s-block metals. Transition metals: • form compounds with more than one oxidation number • form a variety of complex ions • form coloured compounds • act as catalysts when either elements or compounds.
How do we find colours of the substance?
The colour of a substance is determined by which colour(s) of light it absorbs and which colour(s) it transmits or reflects (the complementary colour(s)). Copper sulfate, for example, appears turquoise because it absorbs orange light. Orange and turquoise are complementary colours; they are opposite each other in the colour wheel
How do we distinguish the colourful complexes and why do they have certain colours?
The colour of transition metal ions can be related to the presence of partially filled d orbitals. The ion Sc3+ is colourless because the 3d sub-level is empty; Zn2+ is colourless because the 3d sub-level is full.
How are columns orf the group called and how are rows?
The columns of the table are called groups and the rows periods
How does effective nuclear charge changes across the period and across the group?
The effective nuclear charge experienced by an atom's outer electrons increases with the group number of the element. It increases across a period but remains approximately the same down a group.
What determines the colour of the transition metal complex?
The energy separation between the orbitals is ∆E and hence the colour of the complex depends on the following factors: • the nuclear charge and the identity of the central metal ion; • the charge density of the ligand; • the geometry of the complex ion (the electric field created by the ligand's lone pair of electrons depends on the geometry of the complex ion); • the number of d electrons present and hence the oxidation number of the central ion.
What is first electron affinity?
The first electron affinity of an element is the energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions: X(g) + e- → X-(g)
How are halides formed?
The halogens react with the Group 1 metals to form ionic halides. The halogen atom gains one electron from the Group 1 element to form a halide ion X-. The resulting ions both have the stable octet of the noble gases.
What does ionic character of the compound depend on?
The ionic character of a compound depends on the difference in electronegativity between its elements. Oxygen has an electronegativity of 3.4, so the ionic character of the oxides decreases from left to right, as the electronegativity values of the Period 3 elements approach this value
Where are lanthanoides and actinoides?
The lanthanoides and actinoides both make up the f block of the Periodic Table.
What are the properties of metalloids?
The metalloid elements have the characteristics of both metals and non-metals. Their physical properties and appearance most resemble the metals, although chemically they have more in common with the non-metals. In the Periodic Table the metalloid elements silicon, germanium, arsenic, antimony, tellurium, and polonium form a diagonal staircase between the metals and non-metals.
Why metals from the first group are called alkali metals?
The metals are called alkali metals because the resulting solution is alkaline owing to the presence of the hydroxide ion formed.
What are displacement reactions of halogens?
The more reactive halogen displaces the ions of the less reactive halogen from its compounds.
How do we find the nuclear charge of an atom? Why do electrons do not experience full nuclear charge?
The nuclear charge of the atom is given by the atomic number and so increases by one between successive elements in the table, as a proton is added to the nucleus. The outer electrons which determine many of the physical and chemical properties of the atom do not, however, experience the full attraction of this charge as they are shielded from the nucleus and repelled by the inner electrons. The presence of the inner electrons reduces the attraction of the nucleus for the outer electrons.The effective charge 'experienced' by the outer electrons is less than the full nuclear charge.
What is the coordination number?
The number of coordinate bonds from the ligands to the central ion is called the coordination number.
What does conductivity of the oxides show us, when oxides are able to conduct electricity?
The oxides become more ionic down a group as the electronegativity decreases. The conductivity of the molten oxides gives an experimental measure of their ionic character, as is shown in the table below. They only conduct electricity in the liquid state, when the ions are free to move.
What alkali metals forms reactions most readily?
The reaction becomes more vigorous as the group is descended. The most reactive element, caesium, has the lowest ionization energy and so forms positive ions most readily.
How can we explain small decrease in atomic radii for transition elements?
The similarity in the properties of fi rst row d-block elements is illustrated by the relatively small range in atomic radii . To understand the trend in atomic radii it is instructive to consider the electron configuration of the elements. The unusual electron confi gurations of chromium (Cr) and copper (Cu) are due to the stability of the half-fi lled and fi lled 3d sub-level respectively. The relatively small decrease in atomic radii across the d block is due to the correspondingly small increase in effective nuclear charge experienced by the outer 4s electrons. The increase in nuclear charge due to the added proton is largely offset by the addition of an electron in an inner 3d sub-level. This similarity in atomic radii explains the ability of the transition metals to form alloys: the atoms of one d-block metal can be replaced by atoms of another without too much disruption of the solid structure. The small increase in effective nuclear charge also accounts for the small range in fi rst ionization energies across the fi rst transition series. As discussed in Chapter 2, it is the 4s electrons which are removed fi rst when the atom is ionized.
What is spectrochemical series?
The spectrochemical series arranges the ligands according to the energy separation, ∆E, between the two sets of d orbitals. The wavelength at which maximum absorbance occurs, λ max, decreases with the charge density of the ligand, as shown in the table below. The large iodide ion, which has the lowest charge density, repels the d electrons the least and so produces a small splitting. The smaller chloride ion, with a relatively high charge density, has a larger splitting. The large splitting of the CN- ion and carbon monoxide is more complex and is partly due to the presence of π bonding in the ligand; electrons in the p orbitals on the carbon atoms can interact with the d orbitals of the transition metal.
How does charge density of the ligand affects how the ligand will behave, show an example on changing ligands of water and ammonia.
The spectrum of the copper complex formed when four of the water molecule ligands are replaced by four ammonia molecules . The [Cu(NH3)4(H2O)2]2+ complex absorbs the shorter wavelength yellow light, therefore the complex has a deep blue colour. Ammonia has a greater charge density than water and so produces a larger split in the d orbitals. The higher charge density of the ammonia compared to water also explains their relative base strengths.
How does nuclear charge determine the colour of the ligand?
The strength of the coordinate bond between the ligand and the central metal ion depends on the electrostatic attraction between the lone pair of electrons and the nuclear charge of the central ion. Ligands interact more effectively with the d orbitals of ions with a higher nuclear charge. For example, [Mn(H2O)6]2+and [Fe(H2O)6]3+ both have the same electron confi guration but the iron nucleus has a higher nuclear charge and so has a stronger interaction with the water ligands. Manganese(II) compounds are pale pink in aqueous solution as the ions absorb in the green region of the visible spectrum of light, whereas iron(III) compounds are yellow/brown as they absorb higher energy light in the blue region of the spectrum.
How number of d electrons and oxidation state of the central metal ion affect colour of the complex ion (and therefore of the transition metal?
The strength of the interaction between the ligand and the central metal ion and the amount of electron repulsion between the ligand and the d electrons depends on the number of d electrons and hence the oxidation state of the metal. For example, [Fe(H2O)6]2+ absorbs violet light and so appears green/yellow, whereas [Fe(H2O)6]3+ absorbs blue light and appears orange/brown.
What are the character of bonds of oxides of period 3 elements?
The transition from metallic to non-metallic character is illustrated by the bonding of the Period 3 oxides. Ionic compounds are generally formed between metal and nonmetal elements and so the oxides of elements Na to Al have giant ionic structures. Covalent compounds are formed between non-metals, so the oxides of phosphorus, sulfur, and chlorine are molecular covalent. The oxide of silicon, which is a metalloid, has a giant covalent structure.
How alkali metals react?
They form single charged ions, M+, with the stable octet of the noble gases when they react. Their low ionization energies give an indication of the ease with which the outer electron is lost. Reactivity increases down the group as the elements with higher atomic number have the lowest ionization energies. Their ability to conduct electricity and heat is also due to the mobility of their outer electron.
What is the experiment to show magnetic properties and distinguish para-, diamagnetic?
Transition metal complexes with unpaired electrons show paramagnetic properties as they are pulled into a magnetic fi eld. Paramagnetic and diamagnetic complexes can be distinguished using the experimental arrangement. The sample to be tested, shown in green, is placed in an electromagnet. When the fi eld is turned on paramagnetic materials are attracted into the magnetic field of the electromagnet and so will move downwards causing the blue counterweight to move up; the sample appears to have increased in mass. Diamagnetic materials will move out of the fi eld in the opposite direction and so will appear to have reduced in mass.
How do transition metals appear in colours?
Transition metal compounds appear coloured because their ions absorb some of these colours. [Fe(H2O)6]3+, for example, appears yellow because it absorbs light in the blue region of the spectrum
How do transition elements form complex ions?
Transition metal ions in solution have a high charge density and attract water molecules which form coordinate bonds with the positive ions to form a complex ion.
What are transition metals?
Transition metals are element whose atoms have an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell.
What is the VSEPR theory?
Valence Shell Electron Pair Repulsion (VSEPR) theory. As its name suggests, this theory is based on the simple notion that because electron pairs in the same valence shell carry the same charge, they repel each other and so spread themselves as far apart as possible.
How do we calculate effective nuclear charge?
We do it by subtracting the closest previous number of noble electrons as they are determining the electrons within the previous energy levels.
What happens when chlorine is reacted with potassium (for example in potassium bromide)? Use the displacement reaction.
When chlorine is bubbled through a solution of potassium bromide the solution changes from colourless to orange owing to the production of bromine: 2KBr(aq) + Cl2(aq) → 2KCl(aq) + Br2(aq) 2Br-(aq) + Cl2(aq) → 2Cl-(aq) + Br2(aq) A chlorine nucleus has a stronger attraction for an electron than a bromine nucleus because of its smaller atomic radius and so takes the electron from the bromide ion. The chlorine has gained an electron and so forms the chloride ion, Cl-. The bromide ion loses an electron to form bromine.
What happens when light passes through transition element?
When light passes through a solution of [Ti(H2O)6]3+, one 3d electron is excited from the lower to the higher energy sub-level. A photon of green light is absorbed and light of the complementary colour (purple) is transmitted, which accounts for the purple colour of a solution of [Ti(H2O)6]3+.
What are the properties and rules in transition metals?
• All the transition metals show both the +2 and +3 oxidation states. (Zn is not a transition metal) The M3+ ion is the stable state for the elements from scandium to chromium, but the M2+ state is more common for the later elements. The increased nuclear charge of the later elements makes it more diffi cult to remove a third electron. • The maximum oxidation state of the elements increases in steps of +1 and reaches a maximum at manganese. These states correspond to the use of both the 4s and 3d electrons in bonding. Thereafter, the maximum oxidation state decreases in steps of -1. (therefore less oxidation states after manganese) • Oxidation states above +3 generally show covalent character. Ions of higher charge have such a large charge density that they polarize negative ions and increase the covalent character of the compound • Compounds with higher oxidation states tend to be oxidizing agents. The use of potassium dichromate(VI) (K2Cr2O7), for example, in the oxidation of alcohols.
Show the presence of homogeneous catalysts in real life examples.
• Fe2+ in heme: oxygen is transported through the bloodstream by forming a weak bond with the heme group of hemoglobin. This group contains a central Fe2+ ion surrounded by four nitrogen atoms. The O2-Fe2+ bond is easily broken when the oxygen needs to be released. • Co3+ in vitamin B12. Part of the vitamin B12 molecule consists of an octahedral Co3+ complex. Five of the sites are occupied by nitrogen atoms leaving the sixth site available for biological activity. Vitamin B12 is needed for the production of red blood cells and for a healthy nervous system.
What happens when alkali react with water?
• Lithium fl oats and reacts slowly. It releases hydrogen but keeps its shape. • Sodium reacts with a vigorous release of hydrogen. The heat produced is suffi cient to melt the unreacted metal, which forms a small ball that moves around on the water surface. • Potassium reacts even more vigorously to produce suffi cient heat to ignite the hydrogen produced. It produces a lilac coloured fl ame and moves excitedly on the water surface.
State the properties/rules of VSEPR theory.
• The repulsion applies to electron domains, which can be single, double, or triple bonding electron pairs, or non-bonding pairs of electrons. • The total number of electron domains around the central atom determines the geometrical arrangement of the electron domains. • The shape of the molecule is determined by the angles between the bonded atoms. • Non-bonding pairs (lone pairs) have a higher concentration of charge than a bonding pair because they are not shared between two atoms, and so cause slightly more repulsion than bonding pairs. The repulsion decreases in the following order: lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair
What are chemical properties of noble gases and why are they like that?
• They are colourless gases. • They are monatomic: they exist as single atoms. • They are very unreactive. Their lack of reactivity can be explained by the inability of their atoms to lose or gain electrons. They do not generally form positive ions as they have the highest ionization energies. They do not form negative ions as extra electrons would have to be added to an empty outer energy level shell where they would experience a negligible effective nuclear force, with the protons shielded by an equal number of inner electrons. With the exception of helium, they have complete valence energy levels with eight electrons; a stable octet. Helium has a complete principal first energy level with two electrons.
What are physical properties of transition metals?
• high electrical and thermal conductivity • high melting point • malleable - they are easily beaten into shape • high tensile strength - they can hold large loads without breaking • ductile - they can be easily drawn into wires • iron, cobalt, and nickel are ferromagnetic. These properties can be explained in terms of the strong metallic bonding found in the elements. As the 3d electrons and 4s electrons are close in energy, they are all involved in bonding, and form part of the delocalized sea of electrons which holds the metal lattice together. This large number of delocalized electrons accounts for the strength of the metallic bond and the high electrical conductivity. The smaller atomic radii of the d-block metals compared to their s-block neighbours also account, in part, for their higher densities.
