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





