1.6 - The Periodic Table Flashcards
- Periodic Table Trends, Group 1,2 and 7 chemistry
What is the term for rows in the periodic table?
Periods
What is the term for columns in the periodic table?
Groups
What trend is observed across a period?
Ionisation energy
What trends are observed down a group?
Physical properties
Same outer electron configuration
What is first ionisation energy?
The first ionisation energy of an element is the energy required to remove one electron from each atom in a mole of gaseous atoms.
Which group are the best reducing agents?
Trend in reducing ability in this group?
Group 1 - Group 1 elements have better reducing ability down the group
Caesium = most electropositive
What Group is the best oxidising agent?
What is the trend in oxidising ability in this group?
Group 7 - Group 7 elements are better reducing agents further up the group.
What is unique about d-Block elements?
They often exist in more than one oxidation state, so can both donate and accept electrons
Define Electronegativity
The measure of an atom’s ability to attract a bonding electron in a covalent bond.
What is the most electronegative element and what is it given on the Pauling Scale?
Fluorine - 4.0
Are elements more or less electronegative across a period - Why?
Elements are more electronegative across a period -
- There is an increase in nuclear charge across the period.
- However, bonding electrons are always shielded by the same inner electrons.
- So nuclear charge increases but shielding effect and distance from the nuclear doesn’t.
- This creates greater attraction between the nucleus and the bonding pair.
-This means the element is more able to attract a bonding electron and therefore is more electronegative.
Are elements more or less electronegative down a Group?
Elements become less electronegative down a group -
- There is an increase in shielding effect from inner electrons and distance from the nucleus.
-This outweighs the increase in nuclear charge, therefore attraction between the bonding electrons and the nucleus decreases.
- This means the element is less able to attract a bonding electron, therefore it is less electronegative.
What three factors are there when considering the electronegativity of an element?
-Nuclear charge
-Distance between the bond and nucleus
-Shielding effect caused by inner electrons
Does first ionisation energy increase or decrease across a period?
Generally it increases -
- Increase in nuclear charge
- Electrons are being added to the same shell/ energy level
-Therefore little increased shielding effect
-Therefore, a greater attraction between the nucleus and outer electrons
- Atoms become smaller
Anomalies in first ionisation energy?
Groups 2-3
Groups 5-6
Why is there anomaly in F.I.E trends between Group 2-3?
There is a decrease in I.E between Groups 2 and 3.
- In Group 3 the outer electron is in a new subshell of a slightly higher energy level.
-The inner s-subshell shields the outer electron reducing the I.E required.
Why is there an anomaly in F.I.E between Groups 5-6?
There is a decrease in F.I.E between Group 5-6.
- In Group 5 all of the outer electronsa re in their own orbitals.
In Group 6, the additional electrons shares an orbital.
-The repulsion between electrons in the same orbital makes it easier to remove, therefore a decrease in I.E
Why does ionisation energy decrease down a group?
The increase distance from the nucleus + increase shielding effect from inner electrons outweighs the increase in nuclear charge, therefore easier to remove, therefore lower I.E.
What factors does melting point depend on?
Structure and bonding present
Melting point trend in Group 1?
melting point decreases down the group -
Metallic bonding becomes weaker
-Metallic bonding depends on the attraction of the nucleus to the delocalised valence electrons.
-This becomes weaker upon descending Group 1 as the atoms become bigger and so the valence electrons become further away from the nucleus.
Bonding Trends Across Period 3?
Na, Mg, Al, Si, P, S, Cl, Ar
- Na, Mg and Al - Metallic bonding present therefore high melting point
Melting point increases in the metals as there is a stronger metallic bonds
Greater charge and more delocalised electrons per atom. - Silicon is a giant covalent structure, therefore very high melting point.
-P, S and Cl are all simple covalent structures. Weak intermolecular Van der Waals forces result in a low melting point.
-Argon is atomic therefore it is held together by very weak dipole-induced dipole-induced forces, hence the lowest emlting point.
Reactivity in Group 1 and 2 -
Reactivity increases down both groups
Atoms get bigger therefore the distance from nucleus increases.
The increase in distance + increased shielding effect from inner electrons outweighs the increase in nuclear charge.
Therefore it easier to form the cation, less energy required.
Difference in reactivity between Group 1 and 2
Group 2 is less reactive.
It takes more energy to remove two electrons
Group 2 elements are smaller, therefore increased attraction.
How do you test for cations?
Flame test
What do use to perform a flame test?
Nichrome Wire - Dipped in HCl
Mg 2+ Flame Colour
Colourless
Ca 2+ Flame Colour
Brick Red
Sr 2+ Flame Colour
Crimson
Ba 2+ Flame Colour
Apple Green
Li + Flame Colour
Scarlet
Na + Flame Colour
Orange/Yellow
K+ Flame Colour
Lilac
Thermal Stability of Group 2 Carbonates and hydroxides
Thermal stability increases down the group
Products of Group 2 thermal decomposition
A metal oxide and a gas
Why does thermal stability increase down Group 2?
Mg2+ ion is smaller and so has a high charge density. The high charge density polarises the carbonate ion, destabilising it.
This allows it to break down easily
Ba2+ ion has the same charge but is a much larger ion, for this reason it has a low charge density.
The low charge density means it isn’t capable of polarising and by extension destabilising the carbonate ion.
Therefore more heat energy is required for decomposition.
Testing rate of thermal decomposition with Group 2 carbonates?
CO2 is produced, so limewater can be used to test for the presence of the product CO2.
Group 2 reacting with HCl
Group 1 with HCl
Sr + 2HCl —-> SrCl2 + H2
Chloride and hydrogen gas
Group 1 is too reactive to be added to acids
Group 1 solubility in water?
All Group 1 compounds are soluble in water
Which Group 2 compounds are always soluble?
Nitrates (NO3 -)
Which Group 2 compounds are always insoluble?
Carbonates (CO3 2-)
Trend in Group 2 Sulphates solubility in water
Magnesium Sulphate is completely soluble
Ca and Sr are partially soluble - Slight PPT
Barium Sulphate produces a heavy white PPT
What type of precipitate can be associated with barium sulphate
Heavy/dense white precipitate
Trend of Group 2 hydroxide’s solubility in water
Less soluble down the Group
MgSO4 is insoluble - White PPT
Calcium and Strontium are partially soluble - Slight white PPT
Barium Hydroxide is soluble
How does each Group 1 metal react in water?
Li - Fizzes and floats
Na - Forms a ball that fizzes and floats rigorously
K - Ignites and floats
Equation for Group 1 metals reacting with water
Metal Hydroxide and hydrogen
2Na (s) + 2H20 (l) —-> 2NaOH (aq) + H2 (g)
How do Group 2 metals react with water
Less vigorously than Group 1
Mg - Requires steam to react
Ca - Bubbles and clouds as a PPT forms
Ba - Greater reaction and clearer solution
Equation for Group 2 reacting with water
Hydroxide and hydrogen
Ca + 2H2O —-> Ca(OH)2 + H2
How do Group 2 metals react with oxygen?
Form metal oxides
Are metal oxides and hydroxides basic or acidic?
Basic
Wh
How do the halogens exist?
As diatomic molecules
Group 1 and 2 pH in solution
Group 1 oxides dissolve to soluble hydroxides as the only product - High pH solution
Group 2 oxides are similar but are less soluble further up the group
So the resulting solution may not have a high pH as the basic hydroxide is solid (PPTed)
Mg(OH)2 solution = Not high pH
Melting and boiling point trend in Group 7?
Melting point increases down the Group 7 -
- Down the Group the number of electrons increases, this increases the strength of intermolecular Van der Waals forces
Therefore melting point increase
Group 7 elements as oxidising agents?
- Down the group atomic radius increases
- Distance from the nucleus and increase shielding effect.
- This reduces the effect nuclear charge, therefore more difficult to gain and electrons
- Therefore, decreased oxidising power.
Reaction between Sodium and chlorine?
Sodium is burnt in a jar of chlorine gas to form NaCl - It’s a very exothermic reaction
Define Volatility
How readily a substance vaporises
What colour is aqueous Chlorine?
Green
What colour is aqueous Bromine?
Orange
What colour is aqueous Iodine?
Brown
What colour are aqueous halide ions?
Colourless
Trend of displacement in the Halogens?
A halogen can displace halide ions lower down the group.
Chlorine displaces Bromide and iodide
Bromine displaces Iodide
What can transition metals be used to show about the halogens and how?
Their relative oxidising power
Fluorine reacts with iron and oxidises it from 0 to 3+
In the same reaction iodine oxidises iron from 0 to 2+
Fluorine is therefore the greater oxidising agent
How do you test for halides?
Silver Nitrate Test
What colour precipitates form from silver halides?
AgCl - White PPT
AgBr - Cream PPT
AgI - Yellow PPT
How do you further test the silver halide precipitate?
Add aqueous ammonia
How do silver halides react with ammonia?
AgCl dissolves in dilute NH3
AgBr dissolves in concentrated NH3
AgI does not dissolve in either concentrated nor dilute NH3
Aqueous Cl2 reacts with aqueous Bromide - What colour can be expected at the end of the reaction and why?
Orange - The chlorine displaces the Bromide and becomes colourless
Bromide becomes bromine and is orange in colour
Pros and cons of using Chlorine to treat water
PROS -
- ClO- ion kills bacteria
- Kills bacteria and waterborne diseases (Cholera and Typhoid)
CONS -
- Chlorine can react to form halogenoalkanes which are toxic and carcinogenic.
- Mass medication
Pros and cons of using Fluorine to treat water
PROS -
- Reduces tooth decay
CONS -
- Can cause fluorosis which damages the enamel
- Mass Medication
