C24 Transition Elements Flashcards
Define a transition element
A d block element that forms at least one stable ion with partially filled d subshell
Where are the transition metals located in the periodic table
In the middle block from Ti to Cu
What are the 2 elements in the d block that are not considered as transition metals
Scandium and zinc
Why’s scandium and zinc not considered as transition metals
Scandium only forms Sc^3+, where the d orbitals are empty
Zinc only forms Zn^2+ where the d orbitals are full
What is the noble gas configuration of chromium
[Ar]4s^1 3d^5
What’s the noble gas configuration of copper
[Ar]4s^1 3d^10
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 conductors of heat and 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 in potassium manganate (VII), what’s the oxidation number of Mn
Mn = +7
What are the 2 main ways in which transition metals act as an effective catalyst
They provide a surface on which reaction can take place
They change oxidation states to form intermediates required for pathways with lower activation energy
Give some examples of transition metal located and the processes/reactions they catalyse
Iron - haber process
Vanadium (V) oxide - contact process
Nickel - hydrogenation of alkenes
Manganese (IV) oxide decomposition of hydrogen peroxide
Copper sulfate - hydrogen production
What is a complex ion
Transition metal ion bonded to one or more ligands by coordinate bonds
Define a ligand
Molecule or an ion that can donate a pair of electrons to the metal to form a coordinate bond
What’s a coordinate bond
A bond in which one of atom of the atom provides both the electrons required for bonding, also known as dative bonding
What’s does the coordination number indicate
The number of coordinate bonds formed between the metal ion and its ligands
What’s a mono/unidentate ligand
a ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
What’s a bidentate ligand
A ligand that forms 2 coordinate bonds to the central metal ion (2 lone pairs to donate)
What’s 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
How many coordinate bonds does EDTA^4- form
Six
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 a transition metals act compound is dissolved in water? What shape is it?
Aqua ion
6H2O ligands around the central metal ion
Octahedral complex ion is formed
If a transition metals act compound ion has 2 ligands, what shape is it usually?
Linear
If a transition metals act compound ion has 4 ligands, what shape is it usually?
Tetrahedral
Name an exception to the general rule that ions with 4 ligands is generally tetrahedral. What shape is it?
Platinum is square planar —> forms cisplatin
What shape is a complex ion if it has 6 ligands
Octahedral
How can complex ions display E/Z or Cis-trans isomerism? What shapes of ions does this apply to
Ligands differ in the way in which they’re arranges in space 2 ligands of the same type can be on the same side of the metal ion(next to each other), which forms the E or Cis-isomer 2 ligands of the same type can be opposite sides of the metal ion(not next to each other), which forms the Z or trans-isomer. Applies to square planar and octahedral complex ions.
What conditions are needed for a complex ion to display optical isomerism
Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
What’s cis-platin used for? Describe its mechanism of action?
Its used as anti-cancer drug
It binds to DNA of fast growing cancer cells and prevent cell division, hence reducing the growth of cancer
Which metal ion is present in haem group
Fe^2+
What’s the coordination number of a haem group
6
What are the ligands in haem group
4 nitrogen forming the porphyrin
1 oxygen
1 globin
Why is CO toxic
CO also coordinately bonds to the Fe^2+, and bonds more strongly to Fe^2+ than O2.
Stops O2 from bonding haemoglobin, so O2 cannot be transported around the body
What colour is [Cu(H2O)6]^2+ solution
Pale blue
What colour is [Cu(NH3)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’s precipitation reaction?
A reaction where soluble ions in separate solutions are mixed to form an insoluble compound
What colour is Fe^2+’s aqua ion
Green
What colour is Fe^3+’s aqua ion
Pale brown
What colour is Cr^3+’s aqua ion
Violet
What colour is Mn^2+’s aqua ion
Pink
When Cu^2+ reacts with NH3 or OH^-, what colour is precipitate
Blue
When Fe^2+ reacts with NH3 or OH^-, what colour is the precipitate
Green
When Mn^2+ reacts with NH3 or OH^-, what colour is the precipitate
Brown
When Cr^3+ reacts with NH3 or OH^-, what colour is the precipitate
Green
When Fe^3+ reacts with NH3 or OH^-, what colour is the precipitate
Brown
What colour is MnO4-
Purple
Write a half equation for the reduction of MnO4^- to Mn^2+
MnO4^- + 8H^+ + 5e- ———> Mn^2+ + 4H2O
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
What colour is CrO7^2-
Orange
What colour is Cr^3+
Green
Write a half equation for the reduction of Cr2O7^2- to Cr^3+
Cr2O7^2- + 14H^+ + 6e^- ———> 2Cr^3+ + 7H2O
Describe how to test for metal ions
Fill half of the test tube with sample
Add aq ammonia/NaOH drop by drop
Colour of precipitate indicates the ion present
Write the method used to test for ammonium ions
Fill half the test tube with sample
Add NaOH and warm gently
Smelly gas is produced; damp red litmus paper turns blue
Why does lime water turn milky in the presence of CO2
When CO2 is bubbled in calcium hydroxide (lime water), calcium carbonate precipitate is formed
Carbonate test
Add dilute nitric acid
Effervescence (bubbles) = carbonate present
Test for CO2
Bubble through lime water [saturated aq of Ca(OH)2]
Lime water turn cloudy —> white precipitate of calcium carbonate forms
Sulfate test
Add barium chloride or barium nitrate
BaSO4 forms as a white precipitate as it is very insoluble
Ionic equation:
Ba^2+(aq) + SO4^2-(aq) —> BaSO4(s)
What’s the ionic equation of the sulfate test
Ba^2+(aq) + SO4^2-(aq) —> BaSO4(s)
Halide test
Silver halides are insoluble in water
- Add aq silver nitrate to aq of halide
- silver halide precipitate forms
Cl^- = white
Br^- = cream
I^- = yellow - add aq ammonia to test solubility
Cl^- = soluble in dilute NH3(aq)
Br^- = soluble in conc NH3(aq)
I^- = insoluble in conc NH3(aq)
Ammonium ion test
What’s the electron configuration of chromium
24 electrons
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5
What’s the electron configuration of copper
29 electrons
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3s^10
Why do the electron configurations of chromium and copper not follow the expected trend
Because of stability
It’s believed that a half-filled d^5 sub-shell and a fully filled d^10 sub-shell give additional stability. To atoms of chromium and copper.
What happens when forming a d-block atom
When forming an atom, 4s orbital fills before the 3d orbitals
What happens when forming a d-block ion
When forming an ion, 4s orbital empties before the 3d orbitals
Why are Sc and Zn not classified as transition elements
They don’t form an ion with a partially filled d-orbital.
Sc only forms Sc^3+by loss of 2 4s electrons and 1 3d electron
Sc^3+ : 1s^2 2s^2 2p^6 3s^2 3p^6
Zn only forms Zn^2+ by loss of its 2 4s electrons
Zn^2+ ; 1s^2 2s^2 3s^2 3p^6 3d^10
Sc^3+ have empty d-orbitals and Zn^2+ have full d-orbitals
Sp Sc and Zn do not form ions with partially filled d-orbitals and aren’t therefore classified as elements
They don’t form an ion with a partially filled d-orbital.
Sc only forms Sc^3+by loss of 2 4s electrons and 1 3d electron
Sc^3+ : 1s^2 2s^2 2p^6 3s^2 3p^6
Zn only forms Zn^2+ by loss of its 2 4s electrons
Zn^2+ ; 1s^2 2s^2 3s^2 3p^6 3d^10
Sc^3+ have empty d-orbitals and Zn^2+ have full d-orbitals
Sp Sc and Zn do not form ions with partially filled d-orbitals and aren’t therefore classified as elements
