Shapes of Molecules and Polyatomic Ions Flashcards
How are atoms held together in chemical substances?
By chemical bonds
What are dative bonds?
Dative bonds form when one atom provides both the electrons that form the covalent bond.
What is the name of shape of an atom with 180 degree bond angles?
Linear
What is the name of the shape of molecule with three atoms attached to the central atom and the bond angle?
Trigonal Planar with 120 degree bond angle
What is the name of the shape of molecule with two atoms attached to the central atom and 1 lone pair of electrons and the bond angle?
Angular with <120 degree bond angle
What is the name of the shape of molecule with four atoms attached to the central atom and the bond angle?
Tetrahedral with 109.5 bond angle
What is the name of the shape of molecule with three atoms attached to the central atom with one lone pair of electrons?
Trigonal pyramidal with <109.5 bond angle
What is the name of the molecule with two atoms attached to the central atom with two lone pairs of electrons?
Bent/angular with «109.5 bond angle
What is the name of the molecule with five atoms attached to the central atom and the bond angle?
Trigonal Bipyramidal with bond angles of 90 and 120 degrees.
What is the name of the molecules with four atoms attached to the central atom with one pair of lone electrons?
Sawhorse/Seesaw with bond angle of <120 and <90 degrees
What is the name of the molecules with three atoms attached to the central atom with two lone pairs of electrons?
T-shape with bond angle <90 degrees
What is the name of molecules with two atoms attached to the central atom with three lone pairs of electrons?
Linear with bond angle of 180 degrees.
What is the name of the molecule with six atoms attached to the central atom?
Octahedral with 90 degree bond angle
What is the name of the molecule with 5 atoms attached to central atom with one lone pair of electrons?
Square pyramidal with <90 bond angle
What is the name of the molecule with 4 atoms attached to central atom with two lone pairs of electrons?
Square planar with 90 degree bond angles
What is the name of the molecule with 3 atoms attached to the central atom with three lone pairs of electrons?
T-shape with bond angle <90
What is the name of the molecule with two atoms attached to the central atom with four lone pairs of electrons?
Linear with bond angle of 180 degrees.
What is the name, symbol and charge of the chloride ligand?
Chloride, Cl^-1 (-1)
What is the name, symbol and charge of the oxide ligand?
Oxido, O^-2 (-2)
What is the name, symbol and charge of the cyanide ligand?
Cyanido, CN^-1 (-1)
What is the name, symbol and charge of the hydroxide ligand?
Hydroxido, OH^-1 (-1)
What is the name, symbol and charge of the oxalate ligand?
Oxalato, O4C2^-2 (-2)
What is the name, symbol and charge of the ammonia ligand?
Ammine NH3 (0)
What is the name, symbol and charge of the water ligand?
Aqua, OH2 (0)
What is the name, symbol and charge of the carbon monoxide ligand?
Carbonyl, CO (0)
When is the complex the most stable?
D
When is r on the diagram?
The distance between the two nuclei (bond length)
What is the repulsive effect?
When electron pairs are pushed as far apart as possible as possible minimising repulsion between them.
What is the trend of the repulsive effect?
bonded:bonded < bonded:lone < lone:lone
What do we call the repulsive effect?
Valence Shell Electron Pair Repulsion (VSEPR)
How do you calculate the number of electron pairs?
-taking the total number of valence (outer) electrons on the central atom and adding
one for each atom attached
- adding an electron for every negative charge
- removing an electron for every positive charge
-dividing the total number of electrons by two to give the number of electron pairs
What are transition metals?
d-block transition metals are defined as metals with an incomplete d subshell in at least on of their ions.
What are the exceptions to transition metals and why?
Zinc - completed d orbitals
Scandium - unfilled d orbitals
What are oxidation states?
Similar to valency that an element has when it is part of a compound.
What are the rules for assigning oxidation numbers?
- uncombined elements have an oxidation number of 0
- ions containing single atoms have an oxidation number that is the same as the charge
on the ion - in most of its compounds, oxygen has an oxidation number of −2
- in most of its compounds, hydrogen has an oxidation number of +1
- the sum of all the oxidation numbers of all the atoms in a neutral compound must add
up to zero - the sum of all the oxidation numbers of all the atoms in a polyatomic ion must be equal
to the charge on the ion
What can oxidation numbers be used to determine?
Whether an oxidation-reduction reaction has taken place. Increased oxidation number means oxidation has taken place where as a decrease means that reduction has taken place.
What does it usually mean if a compound has a high oxidation state?
May be an oxidising agent
What does it usually mean if a compound has a low oxidation state?
May be a reducing agent
What does it mean if there has been a distinct colour change?
Ions have changed from one oxidation state to another.
What is a complex?
Consists of a central metal ion surrounded by ligands.
What are ligands?
Ligands are negative ions or uncharged molecules with one or more non-bonding pairs of electrons. They are electron donors, giving their non-bonding electrons to unfilled metal orbitals. This forms dative covalent bonds.
What are monodentate ligands?
Monodentate ligands will donate one pair of electrons to the central transition metal forming a dative covalent bond. examples include chloride, cyanide, ammonia and water.
What are bidentate ligands?
Bidentate ligands will donate two electron pairs. These electron pairs must be on separate atoms in order to orientate around a central transition metal. examples include oxalate ion and 1,2-diaminoethane
What is the coordination number?
The total number of bonds from the central metal ion to the ligand(s).
Why are certain transition metals coloured?
They absorb light in certain parts of the visible spectrum.
What is the colour that is seen?
It is the complementary colour that to that absorbed.
What happen if white light is seen?
All the colours are absorbed
What happens to the colour of transition metals when ligands are attached?
When different ligands are attached to the transition metal, the energy absorbed will change. This results in different wavelengths of light being transmitted and accounts for a change in the colour of transition metal compounds.
Why are transition metals able to absorb light?
Due to the 5 degenerate d-orbitals splitting in terms of energy.
Where do ligands attach and what is the effect of this?
Ligands attach along the dz^2 and dx^2y^2 which will result in the electrons in the orbitals being repelled by electrons in the ligands. The orbitals will have higher energy than the three d orbitals that lie between the axes and therefore the 5 d orbitals are no longer degenerate.
How is colour produced in transition metals?
In terms of d-d transitions. Light is absorbed when electrons in a lower energy are promoted to a higher energy level.
What do different ligands produce?
different crystal field splittings complexes of the same metal ion with different ligands with different colours
Why can transition metals be considered as catalysts?
The presence of unpaired d-electrons or empty-d orbtials allow intermediate complexed to form, providing alternative reaction pathways of lower activation energy.
What is a homogenous catalyst?
They are in the same phase as the reactants. These can from intermediate complexes with the reactive molecules which results in a change in oxidation state.
What is a heterogenous catalyst?
Are in different phase to reactants e.g. liquids and solids. Adsorption of the reaction molecules onto active sites allow the reaction to be catalysed
