Chemistry 3 - The Periodic Table and Energy Flashcards
How are the elements arranged in a periodic table?
They are arranged in the order of increasing atomic numbers.
What is a period on a periodic table?
The horizontal rows in the periodic table.
What is a group on a periodic table?
The vertical columns.
What is meant by periodicity?
The repeating trends in chemical and physical properties.
What change happens across each period?
Elements change from metals to non metals.
How can the electron configuration be written in short?
The noble gas before the element is used to abbreviate.
For example, Li→ 1s²2s¹; Li→ [He]2s¹
Define first ionisation energy.
The energy required to remove one electron from each atom of one mole of the gaseous element to form one mole of gaseous 1+ ions.
Write an equation for the first ionisation energy of magnesium.
Mg(g)→Mg⁺(g)+e⁻
What are the factors that affect ionisation energy?
Atomic radius, nuclear charge and electron shielding or screening
Why does first ionisation energy decrease between group 2 and 3?
The decrease between groups 2 and 3 is because in group 3 the outermost electrons are in p-orbitals, whereas in group 2 they are in an s-orbital, so the electrons are easier to be removed.
Why does first ionisation energy decrease between groups 5 and 6?
The decrease between groups 5 and 6 is due to the group 5 electrons in p-orbitals are single electrons, whereas in group 6 the outermost electrons are spin paired, with some repulsion. Therefore the electrons are slightly easier to remove.
Describe and explain the trend of first ionisation energy across period 3.
First ionisation energy increases across period three because of increasing nuclear charge, decreasing atomic radius and constant electron shielding.
Which means more energy is needed to remove the first electron across the period.
It dips at aluminium because the outer electron is in a 3p orbital, which is a higher energy than the 3s orbital, so less energy is needed to remove an electron.
It dips at S because one 3p orbital contains two electrons, the repulsion between the spin paired electrons means that less energy is needed to remove an electron.
Does first ionisation increase or decrease between the end of one period and the start of the next? Why?
It decreases, this is because there is an increase in atomic radius and an increase in electron shielding.
Does first ionisation increase or decrease down a group? Why?
It decreases, this is because there is an increase in shielding and atomic radius, which decreases attraction between the outermost electron and the nucleus, which outweighs the increase in nuclear charge.
What effect does an increasing atomic radius have on the first ionisation energy?
It decreases the first ionisation energy, because the increased distance decreases the electromagnetic force of attraction between the nucleus and outermost electron.
What effect does increasing electron shielding have on the first ionisation energy?
It decreased the first ionisation energy, because the increased repulsion from the lower electrons decreases the force holding the outermost electron in its orbital.
What effect does increased nuclear charge have on the first ionisation energy?
It increases the first ionisation energy, because the increased positive charge more strongly attracts the outermost electron meaning more energy is required to remove it.
What are the properties of giant metallic lattices?
High melting and boiling point.
Good electrical conductors.
Malleability.
Ductility.
What does it mean if something is ductile?
It can be stretched out, such as being made into a wire.
What does it mean if something is malleable?
It can be shaped into different forms.
Describe the structure, forces and bonding in every element across period 2.
Li and Be form giant metallic structures; there are strong forces of attraction between the positive ions and the sea of delocalised electrons (metallic bonding).
B and C form giant covalent lattice structures; there are strong covalent bonds between atoms.
N₂, O₂, F₂ and Ne form simple molecular; there are weak intermolecular forces between molecules, with covalent bonding within the molecules.
Describe the structure, forces and bonding in every element across period 3.
Na, Mg and Al form giant metallic structures; there are strong forces of attraction between the positive ions and the sea of delocalised electrons (metallic bonding).
Si forms a giant covalent structure; there are strong covalent bonds between atoms.
P₄, S₈, Cl₂ and Ar form simple molecular structures; There are weak intermolecular forces between molecules and strong covalent bonding within the molecules.
What is a common name given to group 2 metals?
Alkaline earth metals.
What is the most reactive metal of group 2?
Barium.
List 3 physical properties of group 2 metals.
High melting and boiling points.
They are low density metals
They form colourless (white) compounds.
The highest energy electrons of group 2 metals are in which subshell?
The s-subshell.
Does reactivity increase or decrease down group 2? Why?
It increases, electrons are lost more easily because larger atomic radius and more shielding.
What happens to the first ionisation energy as you go down group 2? Why?
It decreases because:
The number of filled electron shells increases down the group, which leads to increased shielding.
The increased atomic radius leads to a weaker force between the outer electron and nucleus, which means less energy is needed to remove the outermost electron.
What type of reaction is the reaction between group 2 elements and oxygen?
A redox reaction.
Write an equation for the reaction of calcium and oxygen.
2Ca(s)+O₂(g)→2CaO(s)
What are the products when group 2 elements react with water?
Hydroxide and hydrogen gas.
Which group 2 element doesn’t react with water?
Beryllium.
Which group 2 element reacts very slowly with water?
Magnesium.
What type of reaction is the reaction between group 2 metals and water?
A redox reaction
Write an equation for the reaction of barium and water.
Ba(s)+2H₂O(l)→Ba(OH)₂(aq)+H₂(g)
What is oxidised and what is reduced in a reaction between group 2 metal and water?
The metal is oxidised
One hydrogen atom from each water molecule is reduced.
What are the products when a group 2 element reacts with a dilute acid?
Salt and hydrogen gas.
Write an equation for the reaction of calcium and hydrochloric acid.
Ca(s)+2HCl(aq)→CaCl₂(s)+H₂(g)
What is formed when group 2 oxides react with water?
Metal hydroxide.
Write an equation for the reaction between a group 2 oxide and water.
MO(s)+H₂O(l)→M(OH)₂(aq)
Which group 2 metal oxide is insoluble in water?
Beryllium oxide.
What is the trend in hydroxide solubility down group 2?
It increases down the group;
Mg(OH)₂ is slightly soluble
Ba(OH)₂ creates a strong alkaline solution
What is Ca(OH)₂ used for? Write an equation related to one of its uses.
It is used to neutralise soil.
Ca(OH)₂(aq)+2HCl(aq)→2H₂O(l)+CaCl₂(aq)
What is Mg(OH)₂ used for?
Milk of magnesia, an antacid to treat indigestion, heart burn, etc.
What is calcium carbonate used for?
It is used in building construction and is present in limestone and marble.
What is the drawback of using calcium carbonate in construction? Write a related equation.
Group 2 carbonates react with acids, so structures built using materials containing calcium carbonate are more susceptible to erosion.
CaCo₃(s)+H₂O(l)→CaCl₂(aq)+H₂O(l)+CO₂(g)
What group of elements are referred to as halogens?
Group 7.
List 2 properties of halogens.
Low melting and boiling points.
They exist as diatomic molecules.
What is the trend in boiling point down group 7? Why?
It increase down the group because;
The size of the atom increases and there are more occupied electron shells. This produces stronger London forces of attraction between molecules and take more energy to break.
What is the trend in reactivity down group 7? Why?
Reactivity decreases down the group because;
The atomic radius increases and the electron shielding increases, which lessens the force of attraction between the nucleus and outer electrons, this reduces the atom’s ability to gain an electron and form 1- ions.
What is the trend in oxidising ability down group 7? Why?
It decreases down the group, this is because the further down the group; the lesser the force of attraction between outer electrons and the nucleus and thus it is harder to gain electrons and be reduced.
What is the trend in reducing down group 7? Why?
It increases down the group, this is because the further down the group, the more occupied electron shells there and the weaker the force of attraction between the outermost electrons and the nucleus, thus it is easier to oxidise and remove electrons from it.
When a more reactive halogen takes the place of a less reactive halide, what is the reaction called?
Displacement reaction.
What is the colour of chlorine in water?
Pale green.
What is the colour of bromine in water?
Orange.
What is the colour of iodine in water?
Brown.
What is the colour of chlorine in cyclohexane?
Pale green.
What is the colour of bromine in cyclohexane?
Orange.
What is the colour of iodine in cyclohexane?
Violet.
Out of the following 3 halides; Cl⁻, Br⁻ and I⁻, which of these can be oxidised by chlorine?
Br⁻ and I⁻ ions.
Write the equation for chlorine oxidising bromide ions.
Cl₂(aq)+2Br⁻(aq)→2Cl⁻(aq)+Br₂(aq)
Write the equation for Cl₂ oxidising iodide ions.
Cl₂(aq)+2I⁻(aq)→2Cl⁻(aq)+I₂(aq)
Out of the following 3 halides; Cl⁻, Br⁻ and I⁻, which one of these can be oxidised by bromine?
I⁻ ions.
Write the equation for bromine oxidising iodide ions.
Br₂(aq)+2I⁻(aq)→2Br⁻(aq))+I₂(aq)
Out of the following 3 halides; Cl⁻, Br⁻ and I⁻, which one of these can be oxidised by iodine?
None, since it cannot displace Cl⁻, Br⁻ or its own ions.
Define disproportionation.
The simultaneous oxidation and reduction of the same element in a redox reaction.
What is the equation for the reaction of Cl₂ with water?
Cl₂(g)+H₂O(l)→HClO(aq)+HCl(aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation; chlorine is both oxidised and reduced.
Why is chlorine added to drinking water?
It kills the bacteria in the water and makes it safer to drink.
What are the two forms of the chlorate ion?
Chlorate (I)- ClO
Chlorate (V) - ClO₃
What is the equation for forming bleach?
Cl₂(aq)+2NaOH(aq)→NaCl(aq)+NaClO(aq)+H₂O(l)
NaClO is bleach.
What are anions also known as?
Negative ions.
How can you test for carbonate ion?
Add a strong acid to the sample and collect the produced gas.
Pass the gas through limewater, if the limewater turns cloudy the gas is CO₂, so CO₃²⁻ was present in the sample.
What are the observations for a positive test of carbonate ions.
Fizzing
Limewater turns cloudy
Write an equation for the carbonate ion test.
CO₃²⁻(aq)+2H⁺(aq)→CO₂(g)+H₂O(aq)
How can you test for sulfate ions?
Add dilute hydrochloric acid and add barium chloride to the sample.
What are the observations for a positive test of sulfate ions?
White precipitate of barium sulfate is produced.
Write an equation for the sulfate ion test.
Ba²⁺(aq)+SO₄²⁻(aq)→BaSO₄(s)
What do you use to test for halide ions?
Acidified AgNO₃
Why do you add HNO₃ to test for halide ions and why not HCl?
To remove CO₃²⁻, adding HCl would add Cl⁻ ions, giving a false positive result.
How can you test for a halide ion?
Dissolve the sample in water. Add aqueous silver nitrate Record the colour change If difficult to distinguish the colour, add aqueous ammonia, first dilute ammonia then concentrated ammonia Note the solubility of precipitate
Write the result and equation for a Cl⁻ test.
A white precipitate forms, which is soluble in dilute and concentrated aqueous ammonia.
Ag⁺(aq)+Cl⁻(aq)→AgCl(s)
Write the result and equation for a Br⁻ test.
A cream precipitate forms, which is soluble in concentrated aqueous ammonia only.
Ag⁺(aq)+Br⁻(aq)→AgBr(s)
Write the result and equation for a I⁻ test.
A yellow precipitate forms, which is insoluble in concentrated and dilute aqueous ammonia.
Ag⁺(aq)+I⁻(aq)→AgI(s)
When testing for carbonate, sulfate and halide ions, in which order should the tests be carried out and why?
1) Carbonate test
2) Sulfate test
3) Halide test
Because barium ions forms an insoluble precipitate of BaCO₃ and silver ions form an insoluble precipitate of Ag₂SO₄.
What are cations also known as?
Positive ions.
How can you test for ammonium ions, NH₄⁺?
Add sodium hydroxide to the sample and warm it.
Test the gas produced with litmus paper.
What are the observations for positive ammonium ions test?
Red litmus paper turns blue, ammonia also has a pungent smell.
Write the equation for ammonium ions test.
NH₄⁺(aq)+OH⁻(aq)→NH₃(aq)+H₂O(aq)
What does system mean in a chemical reaction?
The atoms are bonds involved in the chemical reaction.
Explain the law of conservation.
The amount of energy in an isolated system remains the same. Energy can neither be created nor destroyed, it can only be transferred from one form to another.
What energy change is breaking bonds associated with?
Energy is taken in to break bonds, so it is an endothermic reaction.
What energy change is making bonds associated with?
Energy is released to make bonds, so it is an exothermic reaction.
What is an endothermic reaction?
A reaction with an overall positive enthalpy change (+ΔH) so the enthalpy of products is greater than the enthalpy of reactants.
What is an exothermic reaction?
A reaction with an overall negative enthalpy change (-ΔH) so the enthalpy of products is less than the enthalpy of reactants.
What does activation energy meant?
The minimum energy required for a reaction to take place.
Which wat does the arrow for activation energy point on an enthalpy profile diagram?
It always points upwards.
What are the standard conditions?
100kPa
298K
What does “in standard state” mean?
The state an element/compound exists at at standard conditions.
Define enthalpy change of formation.
The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions.
Give an example of an equation which represents the standard enthalpy of formation.
There are many, one example is; H₂(g)+½O₂(g)→H₂O(l)
Define enthalpy change of compustion.
The energy change that takes place when 1 mole of a substance is completely combusted.
Give an example of an equation which represents standard enthalpy of combustion.
There are many, one example is; C(s)+O₂(g)→CO₂(g)
Define enthalpy of neutralisation.
The energy change that takes place when 1 mole of water is formed from a neutralisation reaction.
What does enthalpy change of reaction mean?
The energy change association with a given reaction.
How can you calculate enthalpy change from experimental data?
Use the equation Q=mcΔT Where; Q=Thermal energy m=Mass of substance being heated (usually water) c=Specific heat capacity of substance ΔT=Temperature change
Describe a simple calorimeter.
A spirit burner containing the substance being tested is set up under a tripod with a gauze and a beaker of known mass of water on top of it, with a thermometer in the water to measure the change in temperature. All of this is set up on a heatproof mat.
What are the advantages of using a bomb calorimeter?
It minimises heat loss.
Pure oxygen is used, which ensures complete combustion.
Why might experimental methods for enthalpy determination be accurate?
Heat is lost to the surroundings.
it isn’t in standard conditions.
The reaction may not go to completion.
What does average bond enthalpy mean?
The mean energy required to break one mole of bonds in gaseous molecules.
Why will using bond enthalpies not be as accurate as using standard enthalpy of combustion/formation?
Bond enthalpies are a mean for the same bond across different molecules whereas standard enthalpy of combustion and formation apply to that molecule, therefore they are more accurate.
How can you calculate the enthalpy change of reaction using average bond enthalpies?
ΔH=Σ(bond enthalpies of reaction)-Σ(bond enthalpies of products)
What is the equation used to calculate rate?
Rate= change in concentration/time
What is the unit for rate of reaction?
Moldm⁻³s⁻¹
What must particles do in order to react?
Collide with sufficient energy (activation energy) and the correct orientation.
Do most collisions result in a reaction?
No.
What are the factors that affect rate of reaction?
Temperature Pressure Concentration Surface area Catalyst
What is the effect of increasing temperature on rate of reaction? Why?
Increasing temperature leads to an increased rate of reaction. This is because a much higher proportion of particles have energy greater than the activation energy which leads to many more successful collisions per second which increases the rate of reaction.
What is the effect of increasing concentration/pressure on the rate of reaction? Why?
Increased concentration/pressure leads to an increased rate of reaction. This is because there are more particles in a given volume which leads to more frequent and successful collisions which leads to an increased rate.
What are the variables in an experiment that can be monitored to calculate the rate of reaction?
Concentration of a reactant or product
Gas volume of products
Mass of substances formed
How do you calculate rate of reaction from a concentration against time graph?
Draw a tangent and work out the gradient of the tangent using the equation.
The gradient=Δy/Δx
What is a catalyst?
A substance which increases the rate of reaction but is not used up in the reaction.
How do catalysts work and how do they increase the rate of reaction?
They provide an alternate reaction pathway (with a lower activation energy)
Due to lower activation energy, more particles have energy greater than the activation energy, so there are more frequent successful collisions, so there is an increased reaction rate.
What is a homogeneous catalyst?
A catalyst that is in the same phase as the reactants, such as a liquid catalyst mixed with liquid reactants.
What is a heterogeneous catalyst?
A catalyst that is in a different phase to the reactants.
What are catalytic converters?
They are present in vehicles to reduce toxic emissions and prevent photochemical smog.
Define activation energy.
The minimum energy that particles must collide with for a reaction to occur.
Name some important features of a Boltzmann distribution.
The area under the curve is equal to the total number of molecules.
The area under the curve doesn’t change when conditions alter.
The curve starts at the origin.
The curve doesn’t touch or cross the energy axis.
Only the molecules with energy greater than activation energy can react.
What are the axes in a Boltzmann distribution?
x-axis; energy
y-axis; number of molecules with a given energy
What does dynamic equilibrium mean?
Dynamic equilibrium us when the rate of forwards reaction equals the rate of reverse reaction and the concentration of reactants and products remain constant in a closed system.
What factors can alter the position of equilibrium?
The concentrations of reactants products
Pressure
Temperature
Explain Le Chatelier’s prinicple.
If a system at equilibrium is disturbed, the equilibrium position moves in the direction that tends to reduce the disturbance.
In the equation:
CH₄(g)+H₂O(g)⇌CO(g)+3H₂(g) ΔH°=+210kJmol⁻¹
What effect would increasing the temperature have on the position of equilibrium?
The equilibrium position would shift to the right, because the forward reaction is endothermic, and would take in energy. As such, the yield of hydrogen increases.
In the equation:
CH₄(g)+H₂O(g)⇌CO(g)+3H₂(g) ΔH°=+210kJmol⁻¹
What effect would increasing the pressure have on the position of equilibrium?
The equilibrium position shifts to the left, because the forward reaction produces more moles of gas than the reverse reaction. As such the yield of hydrogen decreases.
In the equation:
CH₄(g)+H₂O(g)⇌CO(g)+3H₂(g) ΔH°=+210kJmol⁻¹
Suggest and explain why an industrial chemist may use a high pressure for this product of hydrogen from the above reaction?
The high pressure increases the collision frequency, thus increasing the rate of reaction.
This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen.
What does a catalyst have on the position of equilibrium?
No effect. This is because a catalyst effects the rate of the forwards and reverse reaction equally, as such there is no change in equilibrium position.
What conditions affect the value of K꜀?
Temperature exclusively.
For the reaction below, deduce an expression for K꜀.
2[A]+3[B]+[C]⇌[D]+4[E]
Deduce the units for K꜀.
K꜀=([D][E]⁴)/([A]²[B]³[C])
mol⁻¹dm⁻³
What type of system is K꜀ relevant for?
Homogeneous systems in equilibrium.
What does K꜀ being greater or less than 1 suggest for the position of equilibrium?
Greater than 1=over to the right
Less than 1=over to the left
What does decreasing the temperature of an endothermic reaction have on K꜀?
K꜀ decreases.
What effect does increasing the temperature of an endothermic reaction have on K꜀?
K꜀ increases.
What effect does decreasing the temperature of an exothermic reaction have on K꜀?
K꜀ increases.
What effect does increasing the temperature of an exothermic reaction have on K꜀?
K꜀ decreases.
