Module 3: Periodic Table and Energy AS Flashcards
What is Enthalpy, H?
The heat content that is stored in a chemical system
Who arranged elements into seven Octaves?
John Newlands
What is the definition for the activation energy?
The minimum energy required to start a chemical reaction
What were the disavantages to Mendeleev’s periodic table?
Isotopes had yet to be discovered, and there was no place for them in Mendeleev’s table. It also didn’t include any noble gases which hadn’t been discovered yet.
What were the advantages to Mendeleev’s periodic table?
He left space for unknown elements. His work also indicated that some accepted atomic weights were incorrect , while his table provided for variance from atomic weight order
What is the standard enthalpy change of combustion?
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions.
eg: CH4 + 2O2 –> CO2 + 2H2O
What is the standard enthalpy change of formation of a compound?
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states.
NB: Forming 1 mole of an element in its standard state has a value of zero by definition
What is the definition of Periodicity?
The trend in properties that’s repeated across each period.
Eg, All group 7 elements are very reactive because, having 7 outer shell electrons, they only need one more electron for a full outer shell.
What is the unit for an enthalpy change?
kJmol-1
Which orbital would fill first: 3d or 4s?
4s
There are various ways to remember this; eg use your periodic table and notice that after 3p6 (Ar), the next element is an s block element (K is [Ar]4s1).
If you use this method, note the pattern that the first shell contains only 1 type of orbital (s, so 1s); the second shell contains 2 types of orbital (s and p, so 2s and 2p); the third shell contains 3 types of orbital (s, p and d, so 3s, 3p and 3d). Notice that shell number is not the same as row number in the periodic table.
What is ionisation?
When atoms lose or gain electrons
What is ionisation energy?
The energy needed to form positive ions
What is the first ionisation energy (1st I.E)?
- How easily an atom loses and electron to form a 1+ ion
- The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions
Sketch an energy level diagram for the orbitals from 1s to 4p
Define ionisation energy
The energy required to remove 1 mole of electrons from 1 mole of gaseous ions.
Note: Always endothermic
1st IE: X(g) –> X+(g) + e-
2nd IE: X+(g) –> X2+(g) + e-
Describe the shapes of s, p and d orbitals
Cr and Cu do not fill the 3d orbitals as you might expect. What is their electron configuration, and why?
Cr: [Ar]3d54s1 (Half-filled shells more stable)
Cu: [Ar]3d104s1 (filled 3d and 1 electron in 4s more stable)
How does the atomic radius affect the nuclear attraction experienced by the outer electrons?
The larger the atomic radius, the smaller the nuclear attraction experienced by the outer electrons
Describe how we fill electron orbitals.
This is the “Aufbau” (or Building up) principle. We start from the lowest energy orbital. Each sub-orbital can hold 2 electrons. We keep putting electrons into the orbitals from the bottom upwards.
s orbitals have only 1 sub orbital, so hold 2 electrons in total (and this explains why the s block is 2 elements wide)
p orbitals have 3 sub orbitals, so hold 6 electrons in total (and this explains why the p bolck is 6 elements wide)
d orbitals have 5 sub orbitals, so hold 10 electrons in total (and this explains why the d bolck is 10 elements wide)
How does nuclear charge affect the attractive force on the outer electrons?
The higher the nuclear charge, the larger the attractive force on the outer electrons
This explains, within a period, the atoms of group 8 elements being smaller than the atoms of group 1 elements
What is the sign of DELTA H for an exothermic reaction?
Negative,
Because the enthalpy of the products is smaller than the enthalpy of the reactants.
What is electron shielding/screening?
When the inner shells of electrons block charge from the nucleus being experienced by the outer-shell electrons
Do more inner shells in an atom create a larger or smaller shielding effect?
Larger
(More shells of electrons blocking nuclear charge)
How does the shielding effect change the nuclear attraction experienced by outer electrons?
The larger the shielding effect, the smaller the nuclear attraction experienced by outer electrons
Is the value for DELTA H in an endothermic reaction positive or negative.
Positive,
The enthaply of the products is greater than the enthalpy of the reactants.
What are successive ionisation energies?
They are a measure of the amount of energy requires to remove each electron in turn
(For example, the second ionisation energy is how easily a 1+ ion loses an electron to form a 2+ ion)
What factors effect nuclear attraction experienced by an electron?
Atomic radius
Nuclear charge
Electron shielding
Why is each successive ionisation energy higher than the one before?
- As one electron is removed, there is less repulsion between the remaining electrons, meaning each shell is drawn slightly closer to the nucleus
- The positive nuclear charge outweighs the negative charge every time an electron is removed
- As the distance between the electrons and the nucleus decreases, the nuclear attraction increases
- More energy is needed to remove the electrons
How do you find out the value of Kc?
Products ÷ Reactants
eg:
A + 2B ⇔ 2C
Kc = [C]2 / [A][B]2
What is Calorimetry?
the quantitative study of energy in a chemical reaction
This is typically achieved by conducting an experiment in such a way that a substance with known mass and known specific heat capacity is warmed or cooled by the reaction. The change in thermal energy can be found using
Q = mc(DELTA)T
What is the trend in ionisation energies across a period?
Increase, due to:
Increasing number of protons creating higher attraction
Electrons being added to the same shell, drawing it inwards
Same number of inner shells so shielding will hardly change
what is meant by the term ‘specific heat capacity’?
the energy required to raise the temperature of 1g of a substance by 1K
what is the biggest experimental error and how can you reduce it?
Heat loss - insulating the equipment with draught shields
what is a Bomb Calorimeter?
a sophisticated piece of equipment which minimises heat loss as much as possible, it uses pure oxygen to ensure complete combustion is acheived.
Does the first ionisation energy of an atom increase or decrease across a period?
Increases
State the trend in solubility of group 2 metal hydroxides
Solubility increases down the group:
Be(OH)2 is insoluble
Mg(OH)2 is slightly soluble
Ba(OH)2 is the most soluble
State the trend in alkalinity of Group 2 hydroxides
Alkalinity increases down the group:
Be(OH)2 is insoluble, so zero concentration of OH- ions
Mg(OH)2 is slightly soluble, very low concentration of OH- ions
Ba(OH)2 is the most soluble, so highest concentration of OH- ions
State the physical states (at STP) and colours of the halogens
Flourine: gas, (very pale green/yellow)
Chlorine: gas, pale green
Bromine: liquid, orange
Iodine: solid, dark purple
NOTE: Bromine liquid will give off brown fumes; Iodine solid sublimes, forming a purple vapour.
State the colours of chlorine, bromine and iodine:
- In water
- In cyclohexane
Chlorine: Pale green in water; pale green in cyclohexane
Bromine: Orange in water; orange in cyclohexane
Iodine: Brown/orange in water; violet in cyclohexane
Give an ionic equation for the reaction of silver ions with any halide ion (X- = halide)
Ag+(aq) + X-(aq) –> AgX(s)
Give the colours of the silver halides
Silver chloride: White
Silver bromide: Cream
Silver iodide: yellow
How is ammonia used to identify silver halides?
Silver chloride: Dissolves in DILUTE ammonia
Silver bromide: Dissolves in CONCENTRATED ammonia only
Silver iodide: INSOLUBLE in ammonia
State the test for Ammnium ions
Ammonium ions react with hydroxide (from sodium hydroxide solution) to produce ammonia and water:
NH4+(aq) + OH-(aq) –> NH3(g) + H2O(l)
Add a small amount of ammonium containing salt to sodium hydroxide solution in a test tube and warm gently. Balance a piece of moist, pink litmus on the mouth of the test tube. If ammonium ions were present, the ammonia formed turns the pink litmus blue.
To test for carbonate ions…
Add a sample of the carbonate to a soluion of dilute acid. The effervescing suggests CO2, which can be confirmed by bubbling the gas through limewater. If the limewater goes cloudy, the gas evolved was CO2, formed by the reaction below:
CO32-(s) + 2H+(aq) –> H2O(l) + CO2(g)
To test for sulfate ions…
Barium sulfate is insoluble. If you have a solution which you suspect includes sulfate, combing a few drops of this with a few drops of a solution containing barium ions will produce a white precipitate of barium sulfate:
Ba2+(aq) + SO42-(aq) –> BaSO4(s)
Give 2 uses of group 2 metal compounds
The 2 uses you need to know arise from the basicity of group 2 compounds (Remember, Group 2 is also called the “Alkaline Earth” metals)
- Calcium hydroxide is added to fields by farmers to increase the pH of acidic soils
- Magnesium hydroxide and calcium carbonate are used to neutralise excess stomach acid (Magnesium hydroxide is often used as a suspension, “milk of magnesia” and calcium carbonate is often in tablets as both compounds are very poorly soluble in water)
Give uses of chlorine
Chlorine is used to kill bacteria in drinking water
Risks from using chlorine are that
- The gas is toxic (so used at low concentrations)
- Chlorine can react with hydrocarbons formed by rotting vegetation. The compounds made might be carcinogenic. However, the risk from this to human health is lower than the risk of disease contracted through use of untreated drinking water.
Define average bond enthalpy
The energy to break one mole of a specified type of bond in a gaseous molecule:
- Energy is always required to break bonds
- Bond enthalpies are always endothermic
- Bond enthalpies always have positive values
- The actual bond enthalpy can vary depending on the chemical environment of the bond. The average is calculated using actual values but in different environments.
Define Hess’ Law
