3 Periodicity Flashcards
In what ways are the elements arranged on the periodic table?
elements arranged in order of increasing atomic number, from 1 to 118.
What does the period of an element show?
A row of elements thus arranged is called a period. The period number, n, is the outer energy level that is occupied by electrons.
What does the group show?
The group shows the number of valence (outer shell) electrons
What 2 elements don’t necessarily fit any groups?
Since the electronic configurations of H and He are unusual, they do not fit comfortably into any group. They are thus allocated a group based on similarities in physical and chemical properties with other members of the group
What blocks are there on the periodic table?
s,p,d,f blocks
What elements belong to the s-block?
The s-block elements are all those with only s electrons in the outer shell
What elements belong to the p-block?
The p-block elements are all those with at least one p-electron in the outer shell
What elements belong to the d-block?
The d-block elements are all those with at least one d-electron and at least one s-electron but no f or p electrons in the outer shell (up to 5d)
What elements belong in the f block?
The f-block elements are all those with at least one f-electron and at least one s-electron but no d or p electrons in the outer shell
What is periodicty?
the study of periodic trends in known as periodicity
How would you right the electron configuration of germaninum? (valence shell)
4s2 4p2
What is the atomic radius a measure of?
The atomic radius of an element is a measure of the size of an atom
Define atomic radius
It is the distance between the nucleus of an atom and the outermost electron shell
Is atomic radius precise?
It can be quite hard to determine exactly where the boundary of an atom lies, so a variety of approches are taken such as half the mean distance between two adjacent atoms
What factors may affect atomic radius?
This will vary depending on the type of structure and bonding, but it gives a comparative value for atoms
How does atomic radius change:
a) down a group
b) across a period
a) They generally increase down each group
b) They generally decrease across each period
What can be used to explain periodic trends?
These trends can be explained by the electron shell theory
Why do atomic radii decrease as you move across a period?
because the atomic number increases (increased positive nuclear charge) but at the same time extra electrons are added to the same principal quantum shell
The larger the nuclear charge, the greater the pull of the nuclei on the electrons which results in smaller atoms
Why do atomic radii increase moving down a group?
Atomic radii increase moving down a group as there is an increased number of shells going down the group
The electrons in the inner shells repel the electrons in the outermost shells, shielding them from the positive nuclear charge
This weakens the pull of the nuclei on the electrons resulting in larger atoms
Why does the atomic radius sharply increase at the alkali metals?
This is because the alkali metals at the beginning of the next period have one extra principal quantum shell
This increases shielding of the outermost electrons and therefore increases the atomic radius
What is the ionic radius?
The ionic radius of an element is a measure of the size of an ion
How does ionic trend change down a group?
The trend down a group is the same as atomic radius – it increases as the number of shells increases
What does the trend across a period for ionic radius depend on?
The trend across a period is not so straightforward as it depends on whether it is positive or negative ions being considered
How does the trend of ionic radius change with increasing negative charge?
Ionic radii increase with increasing negative charge
How does the trend of ionic radius change with increasing positive charge?
Ionic radii decrease with increasing positive charge
Why does ionic radius increase with increasing negative charge?
Ions with negative charges are formed by atoms accepting extra electrons while the nuclear charge remains the same
The extra electrons experience repulsion with the other valence electrons which increases the ionic radius
The greater the negative charge, the larger the ionic radius
Why does ionic radius decrease with increasing positive charge?
Positively charged ions are formed by atoms losing electrons
The nuclear charge remains the same but there are now fewer electrons which undergo a greater electrostatic force of attraction towards the nucleus
which decreases the ionic radius
The greater the positive charge, the smaller the ionic radius
What is the ionisation energy?
ionisation energy (IE) of an element is the amount of energy required to remove one mole of electrons from one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
What conditions are ionisation energies measured under?
Ionisation energies are measured under standard conditions which are 298 K and 100 kPa
What are the units of IE?
kilojoules per mole (kJ mol-1)
What is the first IE?
The first ionisation energy is the energy required to remove the one mole of electrons from one mole the gaseous atoms
How could you represent the first IE of Ca?
Ca(g) → Ca+ (g) + e–
1st ∆H I.E. = +590 kJ mol-1
Are the IEs of the group 1 metals higher or lower than the noble gases?
As could be expected from their electronic configuration, the group I metals show low IE whereas the noble gases have very high IEs
How does first IE change:
a) down a group
b) across a period
a) decreases down a group
b) increases across a period
What 4 factors influence first ionisation energy?
- size of the nuclear charge
- distance of outer electrons from the nucleus
- shielding effect of inner electrons
- spin-pair repulsion
How does the size of the nuclear charge affect the first ie?
the nuclear charge increases with increasing atomic number, which means that there are greater attractive forces between the nucleus and outer electrons, so more energy is required to overcome these attractive forces when removing an electron
How does distance of outer electrons from the nucleus affect first ie?
electrons in shells that are further away from the nucleus are less attracted to the nucleus so the further the outer electron shell is from the nucleus, the lower the ionisation energy
how does the shielding effect of inner electrons affect first ie?
the shielding effect is when the electrons in full inner shells repel electrons in outer shells preventing them to feel the full nuclear charge so the greater the shielding of outer electrons by inner electron shells, the lower the ionisation energy
How does spin-pair repulsion affect the first ie?
paired electrons in the same atomic orbital in a subshell repel each other more than electrons in different atomic orbitals; this makes it easier to remove an electron (which is why the first ionization energy is always the lowest)
What factors cause ionisation energy to increase across a period? 3
Across a period the nuclear charge increases
The distance between the nucleus and outer electron remains reasonably constant
The shielding by inner shell electrons remains the same
How does the ionisation energy change from the last element in a period and the first element of the next period?
There is a rapid decrease in ionisation energy between the last element in one period and the first element in the next period
What 3 factors cause a rapid decrease between element at end of period and next element at beginning?
The increased distance between the nucleus and the outer electrons
The increased shielding by inner electrons
These two factors outweigh the increased nuclear charge
Why is there a slight decrease in 1st I.E between beryllium and boron?
as the fifth electron in boron is in the 2p subshell which is further away from the nucleus than the 2s subshell of beryllium
Why is there a decrease in the 1st ie between nitrogen and oxygen?
between nitrogen and oxygen due to spin-pair repulsion in the 2p subshell of oxygen
What 2 exceptions are there to the increase of first ie across a period?
- beryllium and boron
- nitrogen and oxygen
How does nuclear charge change down a group?
going down a group the nuclear charge increases
What factors cause the first ie to decrease down a group?
The distance between the nucleus and outer electron increases
The shielding by inner shell electrons increases
The effective nuclear charge is decreasing as shielding increases
What trend is there in successive ionisation energies and why?
The successive ionisation energies of an element increase as removing an electron from a positive ion is more difficult than from a neutral atom
What happens in successive i.e when more electrons are removed?
As more electrons are removed the attractive forces increase due to decreasing shielding and an increase in the proton to electron ratio
What is the succesive i.e dependent on?
The increase in ionisation energy, however, is not constant and is dependent on the atom’s electronic configuration
Why does the first electron removed have a low i.e?
The first electron removed has a low ionisation energy as it is easily removed from the atom due to the spin-pair repulsion of the electrons in the x orbital
Why is the second electron harder to remove? (i.e)
The second electron is a little more difficult to remove than the first electron as you are removing an electron from a positively charged ion
Why is the 3rd electron even harder to remove? (i.e)
The third electron is much more difficult to remove than the second one corresponding to the fact that the third electron is in a principal quantum shell which is closer to the nucleus (3p)
What does a graph of the logarithms of successive i.es show?
The graph shows there is a large increase in successive ionisation energy as the electrons are being removed from an increasingly positive ion
What do the big jumps on an i.e graph show?
The big jumps on the graph show the change of shell and the small jumps are the change of subshell
What happens when atoms gain electrons?
When atoms gain electrons they become negative ions or anions
What is electron affinity?
The amount of energy released when one mole of electrons is gained by one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
What is electron affinity the opposite of?
ionisation energy
What are the units of EA?
The units of EA are kilojoules per mole (kJ mol-1)
What type of reaction is the first ea?
The first electron affinity is always exothermic
E.g. the first electron affinity of chlorine is:
Cl (g) + e– → Cl– (g) ∆H = – 349 kJ mol-1
Does the second EA have to be exothermic? Why?
no, can be endothermic
This is due to the fact that you are overcoming repulsion between the electron and a negative ion, so energy is required making the process endothermic overall
What trends does EA show and to what other trends are they similar?
The pattern is very similar to ionisation energies, except that it is inverted and the minimum points are displaced one element to the right
What does the strongest pull on electrons correlate to?
The strongest pull on electrons correlates with the greater amount of energy released when negative ions are formed
What group does not appear on an EA chart?
Noble gases do not form negative ions, so they don’t appear in this chart
Where do EA’s reach a peak?
The electron affinities reach a peak for group 2 and group 5 elements
How do EA’s change down a group?
Electron affinities generally decrease down a group
Why do electron affinities change down a group?
As the atoms become larger the attraction for an additional electron is less, since the effective nuclear charge is reduced due to increased shielding
How does the “temp” of the EA’s change down the group?
Electron affinity become less exothermic going down the group
What element is an exception?
An exception to this is fluorine whose electron affinity is smaller than expected
Why is fluorine an exception?
This is because fluorine is such a small atom and an additional electron in the 2p subshell experiences considerable repulsion with the other valence electrons
What is electronegativity?
Electronegativity is the ability of an atom to attract a pair of electrons towards itself in a covalent bond
Why does electronegativity occur?
This phenomenon arises from the positive nucleus’s ability to attract the negatively charged electrons, in the outer shells, towards itself
What scale is used to assign a value of electronegativity for each atom?
The Pauling scale is used to assign a value of electronegativity for each atom
What atom is the most electronegative?
Fluorine is the most electronegative atom on the Periodic Table, with a value of 4.0 on the Pauling Scale
Why is fluorine so high on the Pauling Scale
It is best at attracting electron density towards itself when covalently bonded to another atom
Where does attraction occur in an atom?
Attraction exists between the positively charged protons in the nucleus and negatively charged electrons found in the energy levels of an atom
How does an increase in the number of protons affect nuclear attraction?
An increase in the number of protons leads to an increase in nuclear attraction for the electrons in the outer shells
Overall, what does an increased nuclear charge cause relating to EN?
Therefore, an increased nuclear charge results in an increased electronegativity
How does atomic radius affect attraction?
Electrons closer to the nucleus are more strongly attracted towards its positive nucleus
Those electrons further away from the nucleus are less strongly attracted towards the nucleus
How does atomic radius affect EN?
Therefore, an increased atomic radius results in a decreased electronegativity
How does EN change down the group?
There is a decrease in electronegativity going down the group
How does effective nuclear charge change down a group?
We say the effective nuclear charge has decreased down the group
Why does electrongeativity decrease down a group? what factors? 3
The nuclear charge increases as more protons are being added to the nucleus
However, each element has an extra filled electron shell, which increases shielding
The addition of the extra shells increases the distance between the nucleus and the outer electrons resulting in larger atomic radii
Overall, there is decrease in attraction between the nucleus and outer bonding electrons
How does EN change across a period?
Electronegativity increases across a period
Why does electronegativity increase across a period? (3)
The nuclear charge increases with the addition of protons to the nucleus
Shielding remains the same across the period as no new shells are being added to the atoms
The nucleus has an increasingly strong attraction for the bonding pair of electrons of atoms across the period
This results in smaller atomic radii
What 6 types of chemical properties can be used to categorise metals/non-metals?
electron arrangement bonding electrical conductivity type of oxide reaction with acids physical characteristics
How do non/metals differ via electro arrangement?
M - 1-3 (more in periods 5&6) outer shell electrons
N- 4-7 outer shell electrons
How do non/metals differ via bonding?
M - metallic due to loss of outer shell electrons
n - covalent by sharing of outer shell electrons
How do non/metals differ via electrical conductivity?
M - good conductors of electricity
N - poor conductors of electricity
How do non/metals differ via type of oxide?
M - basic oxides (few amphoteric)
N - acidic oxides (some are neutral)
How do non/metals differ via reactions with acids?
M - many react with acids
N - do not react with acids
How do non/metals differ via physical characteristics?
M - malleable, high mp and bp
N - flaky, brittle, low mp and bp
How are the properties of non/metals explained?
The typically properties of metals and non-metals can be explained by reference to their trends in atomic radius, ionic radius, ionisation energy, electron affinity and electronegativity
What type of I.E’s and EN’s do metals have? What does this affect?
The low ionisation energies and low electronegativities of metals can account for the ability of their valence electrons to move away from the nucleus
This is known as ‘delocalisation‘ of the electrons
How do EN’s and I.E’S change from left to right?
These properties increase from left to right as you transition from metal to metalloid to non-metal
What do the EN’s and I.E’s of non-metals account for?
The high electronegativity and electron affinity of non-metals can be related to their tendency to share electrons and form covalent bonds, either with themselves or other non-metal elements
What explains the behaviour of metalloids?
The similarities in electronegativities of the diagonal band of metalloids which divides the metals from the non-metals explains the behaviour of metalloids
What can provide evidence of changing chemical trends?
acid-base character of oxides
How does the nature of oxides change across a period?
The broad trend is that oxides change from basic through amphoteric to acidic across a period
What type of oxide is aluminium?
Aluminium oxide is amphoteric
What does it mean if the oxide is amphoteric?
which means that it can act both as a base (and react with an acid such as HCl) and an acid (and react with a base such as NaOH)
What does it mean if the oxide is amphoteric?
which means that it can act both as a base (and react with an acid such as HCl) and an acid (and react with a base such as NaOH)
What can be used to describe the acidic or basic nature of oxides across a period?
The acidic and basic nature of the Period 3 elements can be explained by looking at their structure, bonding and the Period 3 elements’ electronegativity
Where is the difference between electronegativity the biggest?
oxygen and Na, Mg and Al is the largest
What type of bond will the metals in period 3 form?
Electrons will therefore be transferred to oxygen when forming oxides giving the oxide an ionic bond
How will Si, P and S form bonds with oxygen?
The oxides of Si, P and S will share the electrons with the oxygen to form covalently bonded oxides
Why do metals form alkaline solutions?
The oxides of Na and Mg which show purely ionic bonding produce alkaline solutions with water as their oxide ions (O2-) become hydroxide ions (OH–)
Why do non-metals form acidic solutions?
The oxides of P and S which show purely covalent bonding produce acidic solutions with water because when these oxides react with water, they form an acid that donates H+ ions to water
What do metallic oxides form when they react with water?
The metallic oxides form hydroxides when they react with water
What do non-metallic oxides form when they react with water?
The non-metallic oxides form oxoacids when they react with water
Practice equations chemical trends
ayy
What type of property of an element can be predicted by its location on the periodic table?
metallic and non-metallic behaviour
What type of structure does bonding between metal and non-metals usually have/
Metal and non-metal elements generally form ionic compounds so the elements Na to Al have giant ionic structures
How does the ionic nature of compounds change down a group?
The oxides become more ionic as you go down the group as the electronegativity decreases
How does the ionic nature of compounds change across a period?
The oxides become less ionic as you go across a period as the electronegativity increases
What do oxides of non-metals form?
The oxides of non-metals such as S, N and P form molecular covalent compounds
Why are the group 1 meta;s called alkali metals?
The group 1 metals are called the alkali metals because they form alkaline solutions with high pH values when reacted with water
What configuration do all group 1 metals end with?
They all end in the electron configuration ns1
What are 4 physical properties of group 1 metals?
Are soft and easy to cut, getting softer and denser as you move down the group
Have shiny silvery surfaces when freshly cut
Conduct heat and electricity
They all have low melting points and low densities and the melting point decreases going down the group as the atomic radius increases and the metallic bonding gets weaker
What will alkaline metals react with?
oxygen and water vapour (even in air)
What do alkaline metals for, when reacting with water?
reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas
What is the general equation (use m for the metals) between a group 1 metal and water?
2M + 2H2O –> 2MOH + H2
What is formed when an alkali metals reacts with a halogen?
alkali metal halide salt
What is the general equation for the reaction between a group 1 metal and a halogen?
2M + Cl2 –> 2MCl
How does the reactivity of the alkaline metals change down the group?
becomes increasingly vigorous going down group 1
What are the 3 reasons for the reactivity becoming more vigorous down group 1?
The atoms of each element get larger going down the group
This means that the ns1 electron gets further away from the nucleus and is shielded by more electron shells.
The further an electron is from the positive nucleus, the easier it can be lost in reactions
Are halogens poisonous?
yes
What is special about halogens?
Halogens are diatomic, meaning they form molecules of two atoms
How many valence electrons do halogens have?
All halogens have seven electrons in their outer shell
What type of ions (special name) do halogens form?
They form halide ions by gaining one more electron to complete their outer shells
How does the density and mp and bp of the halogens change as you go down the group?
The density and melting and boiling points of the halogens increase as you go down the group
How does reactivity change going down group 17?
Reactivity of group 17 non-metals decreases as you go down the group
What does the halogen e- configuration end in?
ns2np5
What must halogens do to form ions?
Each outer shell contains seven electrons and when they react, they will need to gain one outer electron to get a full outer shell of electrons
How does electron affinity change going down the group? How is atomic radius affected?
Going down the group, the electron affinity decreases and the atomic radius increases
How does shielding change while going down the group?
As you go down group 17, the number of shells of electrons increases so shielding also increases
Why does reactivity decrease going down group 17? (simple)
This means that the outer electrons are further from the nucleus so there are weaker electrostatic forces of attraction that attract the extra electron needed
The electron is attracted less readily, so the lower down the element is in Group 17 the less reactive it is
When does a halogen displacement react occur?
A halogen displacement occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
What colour does chlorine have in an aqueous solution?
very pale green, but usually appears colourless as it is very dilute
What colour does bromine have in an aqueous solution?
orange but will turn yellow when diluted
What colour does iodine have in an aqueous solution?
brown
What happens when you add chlorine solution to potassium bromide? Colour change
If you add chlorine solution to colourless potassium bromide solution, the solution becomes orange as bromine is formed
Chlorine is above bromine in group 17 so it is more reactive
Chlorine will therefore displace bromine from an aqueous solution of a metal bromide
What is the equation for the reaction between chlorine and potassium bromide?
2KBr (aq) + Cl2 (aq) → 2KCl (aq) + Br2(aq)
What is a transition element?
an element whose atom has an incomplete d sub-shell or which can give rise to cations with an incomplete d sub-shell. Ions of transition elements have characteristic properties due to their partially filled d-subshell.
Why is Zn not a transition metal?
Zn, though part of the d-block, is not a transition metal. The common oxidation state is Zn2+ which does not have a partially filled d-subshell. Instead, both Zn and Zn2+ have a completely filled d-subshell.
What causes transition metals to have their unique properties?
the characteristic properties of transition metals that
arise from their partially filled d-subshell.
What charge ion can all transition metals form and why?
Every transition metal can form ions with charge +2 owing to the fact that 4s electrons are lost before any 3d electrons. But many of the transition metals can also occur in other oxidation states: e.g. Fe
Complex ions
2+ 3+ + 2+ and Fe , Cu and Cu
.
What is a complex ion?
a number of ligands form dative covalent bonds to a positive (metal) ion
What is a ligand?
a molecule or anion that donates a non-bonding pair of electrons to form a dative covalent bond with a metal ion
What is the coordination number?
the number of ligands around the central ion
What type of complex ions do most transition metals form in water? Give an example with aluminium?
Most of the transition metal ions and some non-transition metal ions form hexahydrated complexes in water, such as [Al(H2O6] 3+
how are hexahydrated complexes formed?
Six water molecules donate one electron paireach, forming six dative covalent bonds
What type of structure do hydrated complex ions have?
complexes with a coordination number of 6 have an octahedral geometry.
What necessary criterion does the ligand need to bond with the metal ion?
so long as the ligand can donate an electron pair
What ligand would displace water and why?
ammonia readily displaces water ligands, because it can form stronger dative covalent bonds than water.
What is the spectrochemical series?
The order of ligand bond strength is called the spectrochemical series
List the spectrochemical series
I−
Describe the energy levels in a free ion (5-d orbital specifically)
In a free ion, the energy levels of each of the 5 d-orbitals are the same, they are said to be degenerate.
What causes d-orbitals splitting?
But when bonds with a particular geometry form such as described above, the d-electrons closer to the ligands will have a higher energy than those further away, which results in the d-orbitals splitting in energy.
Why is d-orbital splitting important for tm?
This splitting is what gives transition metals their characteristic properties.
Which ligand would cause the greatest d-orbital splitting and why?
the CN– ligands cause a larger splitting of the d-orbital energy level because they form stronger bonds
What happens when electrons absorb light?
electrons can absorb light, thereby moving into an excited state.
in a tm, where does an excited e- move from and to?
When light is absorbed, an electron moves from a d-orbital with lower energy to a d-orbital with higher energy.
why can we “see” the electrons moving between the split d-orbitals?
The energy difference between the split d-orbitals is typically in the range of visible light.
Why do tm have coloured compounds?
So while [Fe(H2O)6]2+ may absorb red photons, [Fe(CN)6]4– will absorb photons with more energy such as blue light, because the energy levels are split further apart.
What colour will a tm compound appear?
The colour that is observed is the complementary colour to the light that is absorbed, so a solution containing [Fe(H2O)6]2+ will appear green.
What does the light absorption of a tm compound depend on? (3)
The colour of light absorption (i.e. the amount of splitting of the d-orbitals) thus depends on the identity and oxidation state of the central ion,
the identity of the ligand and the coordination number/geometry around the central ion.
How can a SMALL magnetic field be formed? (atoms)
When orbitals are partially filled, often (some of) the electrons in the orbitals are unpaired. Each electron has a spin, which when two electrons are paired cancel each other out.
How can a bigger magnetic field be created?
When electrons are unpaired each produces a tiny magnetic field. When those spins line up in a material they can produce a substantial magnetic field.
what does it mean if a metal is ferromagnetic?
Fe,Ni,Co show ferromagnetism - permanently magnetic
When is a substance paramagnetic?
when electrons are unpaired (weak ligand splitting
What does it mean if a substance is paramagnetic?
slightly attracted by a magnet
When is a substance diamagnetic?
no unpaired electrons (strong ligand field splitting)
What does it mean if a substance is diamagnetic
slightly repelled by a magnet
