Periodicity
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- Created by: avcaseasyas123
- Created on: 02-12-15 07:11
What is periodicity?
The repeating pattern of physical + chemical properties shown by the different periods.
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Define the atomic radius.
Half the distance between the nuclei of two bonded atoms of the same element.
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Why does the atomic radius decrease across a period?
The number of protons in the nucleus increases which attracts the energy level closer to the nucleus so the atomic radius decreases across a period. Across the period the ions contain the same number of electrons (isoelectronic).
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What are cations?
Positive ions –contain fewer electrons than protons so the electrostatic attraction between nucleus & outermost electron is greater + the ion is smaller than the parent atom.
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What are anions?
Negative ions: contain more electrons than protons so are larger than the parent atom.
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Describe melting point down group 1 and Group 7.
Group 1: melting point decreases down group as atoms become larger + the strength of the metallic bond decreases. Group 7: intermolecular forces between the diatomic molecules increase down group so melting point increases.
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What is electronegativity?
A relative measure of the attraction that an atom has for a shared pair of electrons when it’s covalently bonded to another atom.
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Why does electronegativity increase across a period and decrease down the group?
Because as the size of the atom increases the electronegativity decreases down a group.
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What is electron affinity?
The energy change when an electron is added to an isolated atom in the gaseous state.
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What is the first ionisation energy of an element?
The energy required to remove one electron from an atom in its gaseous state.
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Why do ionization energy values generally increase across a period?
As the extra electrons are filling the same energy level and the extra protons in the nucleus attract this energy level closer making it harder to remove an electron.
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Why do ionization energies decrease down the group?
As the outer electron is further from the nucleus and therefore less energy is required to remove it.
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Why do group 1 metals make good reducing agents?
As they can readily lose an electron (they react by losing their outer electron to form the metal ion). Group 7 elements are good oxidizing agents.
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Describe reactivity down group 1 and 7.
Increases down group 1 as the outer electron is in successively higher energy levels + less energy is required to remove it. Decreases down group 7 as the outer shell is increasingly at higher energy levels + further from the nucleus.
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How can the presence of halide ions in solution be detected/tested?
By adding silver nitrate solution. The silver ions react with the halide ions to form a precipitate of the silver halide which react with light to form silver metal = basis for old-fashioned film photography.
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What does it mean for a metal oxide to be amphoteric?
It can either be basic or acidic depending on whether it’s reacting with an acid or a base i.e. Aluminium oxide.
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Why is silicon called a metalloid?
As it is a semiconductor and possesses some of the properties of a metal and some of a non-metal.
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What is a transition element?
An element that possesses an incomplete d sub-level in one or more of its oxidation states. They have variable oxidation states, form complex ions with ligands, have coloured compounds & display catalytic + magnetic properties.
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Why aren’t Scandium or Zinc typical transition metals?
As scandium’s common ion Sc3+ has no d electrons. Zinc isn’t a transition metal as it contains a full d sub-level in all of its oxidation states.
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Transition metals gain electrons on the 3d shell before the 4s shell.
Transition metals lose electrons from 4s shell first.
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Give examples of how transition metals are used as catalysts?
Increase rate of chemical reactions. Platinum + palladium used in catalytic converters fitted into cars.
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What is ferromagnetism?
Permanent type of magnetism where the unpaired electrons align parallel to each other in domains irrespective of whether an external magnetic/electric field is present.
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How can unpaired electrons make transition metals weakly magnetic when the field is applied?
Unlike paired electrons where the spins cancel each other out, the spinning unpaired electrons create a small magnetic field + will line up in an applied magnetic/electric field is present.
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What is coordination number?
The number of lone pairs bonded to the metal ion. Compounds with a co-ord no. of 6 are octahedral in shape, 4 = tetrahedral/square planar and 2 = linear.
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What is weak ligand splitting?
When the five d orbitals are split by the ligands according to the spectrochemical series. If the ligands are low in this series + split the d orbitals giving 4 units of paramagnetism as there will be 4 unpaired electrons.
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What causes diamagnetism in transition metal complexes?
Ligands high in the spectrochemical series will cause a larger splitting. Only the lower d orbitals will be occupied + the complex will be diamagnetic as there are no unpaired electrons. Iron (II) complex ions can be paramagnetic or diamagnetic.
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What are ligands?
Neutral molecules or anions which contain a non-bonding pair of electrons. These electron pairs can form co-ordinate covalent bonds with the metal ion to form complex ions.
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What are monodentate ligands?
Ligands that utilise just 1 non-bonding pair to form a co-ordinate covalent bond to the metal ion.
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Describe the factors affecting the colour of transition metal complexes.
The nature of the transition element. The oxidation state, the identity of the ligand + the stereochemistry of the complex.
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Why does copper sulfate appear blue?
The five d-orbitals are split so that 3 are in the lower energy + 2 are in the higher energy. The difference in energy between the two levels corresponds to diff wavelengths of light. Copper sulfate absorbs red & green + reflects blue.
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Other cards in this set
Card 2
Front
Define the atomic radius.
Back
Half the distance between the nuclei of two bonded atoms of the same element.
Card 3
Front
Why does the atomic radius decrease across a period?
Back
Card 4
Front
What are cations?
Back
Card 5
Front
What are anions?
Back
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