Topic 3 & 13 - Periodicity Flashcards
What are the rows in the periodic table called?
Periods
What are the columns in the periodic table called?
Groups
What do the period and group numbers give information about?
The period number gives the number of occupied electron shells
The group number gives the number of electrons in the outer shell
What happens to the nuclear charge experienced by an atom’s outer electrons in the periods and groups of the periodic table?
- Increases with the group number of the element
- Increases across a period
- Stays the same down a group
How is the atomic radius defined?
Measured as half the distance between neighbouring nuclei
Where are transition elements located in the periodic table?
Between groups 2 and 3
What is the trend in atomic radii?
- Increases down a group as the no. of occupied electron shells increases
- Decreases across a period because the attraction between the nucleus and other electrons increases as the nuclear charge increases
Where do we get the nuclear charge from?
The atomic number of each element
What are can be said about the sizes of ions?
- Positive ions are smaller than their parent atoms
- Negative ions are larger than their parent atoms
What are the trends ionic radii?
- Decrease from groups 1 to 4 for positive ions
- Decrease from groups 4 to 7 for negative ions
- Increase down a group as the no. of electron shells increases
What are the trends of ionisation energies?
- Increase across a period
- Decrease down a group
- Is the reverse of atomic radii
What is electronegativity?
The ability of an atom to attract electrons in a covalent bond
What are the trends in electronegativity?
- Increases from left to right across a period
- Decreases down a group
What are the trends in melting points?
- Decrease down group 1 (metallic structures, weaken with distance)
- Increase down group 7 (molecular structures, increase with no. of electrons)
- Generally rise across a period and reach a maximum at group 4 and fall to a minimum at group 0
Summarise the trends in the periodic table
Direction of the arrow indicates increase
cyan = atomic radius
pink = first ionisation energy
purple = electronegativity
grey = ionic radius
gold = melting point
What determines the chemical properties of an element?
Mostly the number of electrons in the outer shell
What are the chemical properties of group 0 elements? (noble gases)
- Colourless gases
- Monoatomic: exist as single atoms
- Very unreactive
- Have a stable octet
What are the chemical properties of group 1 elements? (alkali metals)
- Highly reactive (usually stored in oil to prevent reaction with ail)
- Form ionic compounds with non-metals
- Form single charged ions
- Reactivity increases down a group (lower ionisation energies
How do group 1 elements react with water?
- Produce hydrogen and a metal hydroxide
- Resulting solution is alkaline
- Reaction becomes more vigorous down a group
Lithium:
- floats and reacts slowly
- releases oxygen and keeps its shape
Sodium:
- reacts vigorously and the heat produced melts the metal into a bubble that moves around the surface of the water
Potassium:
- reacts more vigorously
- sets the hydrogen produced in fire
- produces a lilac flame and moves excitedly
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What are the physical properties of group 1 elements?
- Good conductors of electricity
- Have low densities
- Have grey shiny surfaces when freshly cut with a knife
What are the physical properties of group 7 elements?
- Coloured
- Show a gradual change from gases, to lidquid, to solids
What are the chemical properties of group 7 elements? (halogens)
- Very reactive non-metals
- Form ionic compounds with metals or covalent compounds with other non-metals
- Reactivity decreases down the group
- Exist as diatomic molecules
- Attraction for electrons is greatest in the smallest atom, F
Describe the reations between alkalis and halogens
- Form ionic halides
What happens in the displacement reaction of KBr with chlorine?
2 KBr(aq) + Cl2(aq) → 2 KCl(aq) + Br2(aq)
- the solution turns orange because Br is orange
What is the displacement reaction between iodine and bromine?
2 I–(aq) + Br2(aq) → 2 Br–(aq) + I2(aq)
- The solution darkens due to formation of iodine
What happens in a reaction between a more reactive and less reactive halogen?
The more reactive halogen displaces the ions of the less reactive halogen
How can a displacement solution be distinguished between bromine and iodine?
The solution can be shaken with a hydrocarbon solvent. Iodine forms a violet solution and bromine a dark orange one
What are halides?
Insoluble salts formed in the reactino between halogens and silver
Ag+(aq) + X–(aq) → AgX(s)
Describe the bonding of period 3 oxides
- Oxides of elements Na to Al have giant ionic structures
- Oxides of phosphorus, sulfur, and chlorine are molecular covalent
- Oxide of silicon has a giant covalent structure
- The oxides become more ionic down a group as the electronegativity decreases
What kind are oxides of metals?
Ionic and basic
What kind are oxides of non-metals?
Covalent and acidic
Which oxides of period 3 are amphoteric?
Al2O3 and SiO2
How does Na2O react with water?
Na2O(s) + H2O(l) → 2 NaOH(aq)
- alkaline solution
How does MgO react with water?
MgO(s) + H2O(l) → Mg(OH)2(aq)
- alkaline
How does a basic oxide react with water?
Forms a salt and water. The oxide ion combines with two protons to form water
How does P4O10 react with water?
Phosphorus(V) oxide reacts to produce phosphoric(V) acid:
P4O10(s) + 6 H2O(l) → 4 H3PO4(aq)
Phosphorus(III) oxide reacts to produce phosphoric(III) acid:
P4O6(s) + 6 H2O(l) → 4 H3PO3(aq)
How does SO3 react with water?
- forms sulfuric(VI) acid:
SO3(l) + H2O(l) → H2SO4(aq)
Does aluminium oxide affect the pH when added to water?
No
What kind of structures are high melting points associated with?
Ionic or covalent giant structures
What kind of structures are low melting points associated with?
Molecular covalent structures
Summarise the structure, conductivity, and oxidation number of period 3 chlorides
What is a disproportionation reaction?
A reaction in which the same element both increases and decreases its oxidation number
How does chlorine react with water?
- In a reversible reaction to produce a mixture of hydrochloric acid and chloric acids:
Cl2(aq) + H2O(l) → HCl(aq) + HOCl(aq)
- Chlorine is simultaneously oxidised and reduced
Where does a dative covalent bond get its extra electorns?
It uses a lone pair of electrons to form a covalent bond
What happens to metallic ionic chlorides in water?
They break up their lattice structure when they dissolve and give neutral solutions:
NaCl(s) → Na+(aq) + Cl–(aq)
MgCl2(s) → Mg2+(aq) + 2 Cl–(aq)
- The resulting solution can conduct electricity
What happens to covalent chlorides in water?
They are broken up (hydrolysed) when added to water to form acidic solutions
What is hydrolysis?
A reaction in which water splits a compound apart. Can lead to acidic or alkaline solutions
What are characteristic properties of transition elements?
- Variable oxidation number
- Complex ion formation
- Existence of coloured compounds
- Catalytic properties
How is the similarity of transition element properties explained?
Relatively small range in atomic radii
Why are scandium and zinc not considered transition elements?
- They do not generally form coloured solutions
- Do not display the characteristic properties
- Lack of a partially filled d orbital
Which elements from the first row of d block are not considered transition elements?
Scandium and zinc
What are the physical properties of transition elements?
- High electrical and thermal conductivity
- High melting point
- Malleable
- High tensile strength
- Ductile
What is said about the d-orbital of all transition elements?
It is partially filled
What are facts about the oxidation numbers of transition elements?
- All of them show both the +2 and +3 oxidaiton states. +3 is stable for elements from scandium to chromium, but +2 is more common for the later elements
- The maximum oxidation state of th elements increases in steps of +1 and reaches a maximum at manganese (+7)
- Oxidation states above +3 generally show covalent character
- Compounds with higher oxidation states tend to be oxidising agents
What is a ligand?
A species that uses a lone pair of electrons to form a dative covalent bond with a metal ion
What is the coordination number?
The number of dative covalent bonds from the ligands to the central ion
Why do transition elements from complex ions?
- High charge and small size attracts lone pairs
What is the ligand, coordination number, oxidation number, and shape of the complex [Fe(H2O)6]3+?
Ligand: H2O
Coordination number: 6
Oxidation number: +3
Shape: octahedral
What is the ligand, coordination number, oxidation number, and shape of the complex [CuCl4]2–?
Ligand: Cl–
Coordination number: 4
Oxidation number: +2
Shape: tehtrahedral
What is the ligand, coordination number, oxidation number, and shape of the complex [Fe(CN)6]3–?
Ligand: CN–
Coordination number: 6
Oxidation numbre: +3
Shape: octahedral
What is the ligand, coordination number, oxidation number, and shape of the complex [Ag(NH3)2]+?
Ligand: NH3
Coordination number: 2
Oxidation number: +1
Shape: Linear
Why are some complexes of transition metals coloured?
- Related to the presence of partially filled d orbitals
- d-orbital splits into two sets of orbitals of different energy
- Electronic transitions between the sets cause colouration
What are examples of the catalytic action of transition elements and their compounds?
- MnO2 in the decomposition of H2O2
- V2O5 in the Contact process
- Fe in the HAber process and in heme
- Ni in the conversion of alkenes to alkanes
- Co in vitamin B12
- Pd and Pt in catalytic converters
What is a heterogenous catalysis?
A reaction in which the catalyst is in a different state from the reactants
What is a homogenous catalysis?
A reaction in which catalysts are in the same state of matter as the reactants
