transition elements Flashcards
define a transition element
a d-block element that forms at least 1 stable ion with a partially filled d-subshell
where are the transition metals located in the periodic table
in the d-block from Ti to Cu
what are the 2 elements in the d-block that are not considered as transition metals?
- scandium
- zinc
why are scandium and zinc not considered transition metals?
- scandium only forms Sc3+, where the d-orbitals are empty
- zinc only forms Zn2+, where the d-orbitals are full
which electrons do transition metals lose first when forming ions?
4s
what are some characteristic physical properties of transition metals?
- metallic
- high density
- high melting and boiling point
- shiny
- good conductor of heat + electricity
what are the characteristic chemical properties of transition metals?
- variable oxidation states → take part in many redox reactions
- coloured compounds/ions in solution
- good catalysts
- form complex ions
in potassium manganate (VII), what is the oxidation number of Mn?
7+
what are the 2 main ways in which a transition metal acts as an effective catalyst
- they provide a surface which absorb substances on which reaction can take place
- they change oxidation states by losing or gaining electrons within their d-orbitals to form intermediates required for pathways with lower activation energies
why are catalysts good for industries + environments
allow reactions to happen faster at lower temperatures and pressures, reducing energy usage
what are the disadvantages of using transition metals as catalysts in industries
- pose health risks as many of the metals and their compounds are toxic
- long term exposure to copper can damage the liver and kidneys
- exposure to manganese can cause psychiatric problems
give some examples of transition metal catalysts and the processes/reactions they catalyse
- iron - haber process
N2+3H2 ⇌ 2NH3
what is a complex ion
transition metal ion bonded to 1 or more ligands by coordinate bonds
define a ligand
molecule/ion that can donate a pair of electrons to the metal to form a coordinate bond
what is a coordinate bond?
a bond in which one of the atom provides both the electrons required for bonding
what does the coordination number indicate
the number of coordinate bonds formed between metal ion and its ligands
what is a mono/unidentate ligand
a ligand that forms 1 co-ordinate bond to the central metal ion (1 lone pair to donate)
what is a bidentate ligand
a ligand that forms 2 coordinate bonds to the central metal ion (2 lone pairs to donate)
what is a multidentate ligand
a ligand that forms 3 or more coordinate bonds to the central metal ion
give some examples of common monodentate ligands
- Cl-
- H2O
- NH3
- CN-
name the most common bidentate ligand
ethane-1,2-diamine
ethanedioate; how many coordinate bonds can it form to a transition metal ion?
2 co-ordinate bonds
benzene-1,2-diol; how many coordinate bonds can it form to a transition metal ion?
2 co-ordinate bonds
how many co-ordinate bonds does EDTA4- form?
6
EDTA is a chelating agent, what does that mean?
EDTA decreases the concentration of metal ions in the solution by binding to them and forming complex ions
what ion is usually formed when transition metal compound is dissolved in water? what shape is it?
- aqua ion
- 6 H2O ligands around the central metal ion
- octahedral complex ion is formed
if a transition metal ion has 2 ligands, what shape is it usually?
linear (180)
if a transition metal ion has 4 ligands, what shape is it usually?
tetrahedral (109.5)
if a transition metal ion has 6 ligands, what shape is it usually?
octahedral (90)
name an exception to the general rule that ions with 4 ligands is generally tetrahedral, what shape is it?
platin is square planar, forming cisplatin
how can complex ions display E-Z or cis/trans iosmerism? what shapes of ions does this apply to?
- ligands differ in the way which they are arranged in space
- 2 ligands of the same typ ecan be on the same side of metal ion - forms E or cis isomer
- 2 ligands on the same type can be on opposite side of ion - forms Z or trans iosomer
- applies to square planar and octahedral complex ions
what conditions are needed for a complex ion to display optical isomerism
- octahedral molecules with 2 or more bidentate ligands
- so mirror images are non-superimposable
what is cis-platin used for? describe its mechanism of action
- used as anti-cancer drug
- binds to DNA of fast growing cancer cells and prevents cell division
- reduces growth of cancer
which metal ion is presented in a haem group?
Fe2+
what is the coordination number of a haem group?
6
what are the ligands in a haem group?
- 4 nitrogen
- 1 oxygen
- 1 globin
why is CO toxic
- CO also coordinately bonds to the Fe2+
- CO bonds more strongly to Fe2+ than O2
- stops O2 from bonding to haemoglobin
- so O2 cannot be transported around the body
what colour is [Cu(H2O)6]2+ solution
pale blue
what colour is [Cu(NH2)4(H2O)2]2- solution
deep blue
what colour is [CuCl4]2- solution
yellow
what colour is [Cr(H2O)6]3+ solution
dark green
what is a precipitation reaction
a reaction where soluble ions in separate solutions are mixed to form an insoluble compound
why are redox titrations with transition metal compounds said to be self-indicating
- they usually involve a colour change as the metal is changing oxidation state
- sometimes an indicator is still needed/useful
describe how to test for metal ions
- fill half of the test tube with the sample
- add aqueous ammonia or sodium hydroxide drop wise
- colour of precipitate indicates ion present
when Cu2+ reacts with NH3 or OH-, what colour is the precipitate?
blue
when Fe2+ reacts with NH3 or OH-, what colour is the precipitate?
green
when Mn2+ reacts with NH3 or OH-, what colour is the precipitate?
brown
when Cr3+ reacts with NH3 or OH-, what colour is the precipitate?
green
when Fe3+ reacts with NH3 or OH-, what colour is the precipitate?
brown
describe the method used to test for ammonium ions
- fill half test tube with sample
- add sodium hydroxide and warm gently
- smelly gas is produced, damp red litmus paper turns blue
why does lime water turn milky in presence of CO2
- when CO2 is bubbled in calcium hydroxide (lime water)
- calcium carbonate precipitate is formed
why does lime water turn milky in presence of CO2
- when CO2 is bubbled in calcium hydroxide (lime water)
- calcium carbonate precipitate is formed
