Elements, Atoms & The Periodic Table Flashcards
What are electrons in orbitals characterised by?
4 quantum numbers
What are the four quantum numbers?
n, l, ml, ms
What is n in respect to electron quantum numbers?
The principal quantum number
What does the principle quantum number tell you?
It tells you how far the electron is from the nucleus (i.e the energy level/shell of an electron in an atom)
How does the period in the periodic table relate to the principal quantum number?
In the S and P-blocks, the principle number is the same as the period number.
In the D-block it is the period number subtract 1
What is l in respect to electron quantum numbers?
l is the angular momentum quantum number
What does the angular momentum quantum number tell you?
It defines the radial spatial distribution of the wavefunction, i.e what type/shape of subshell the electron is in
What are the possible values of l?
The value of l is limited by n. It must be at least n-1. When n is 3, l can be 2, 1 or 0
Which subshell does each value represent in l quantum numbers?
0 = s
1 = p
2 = d
3 = f
What is ml in respect to electron quantum numbers?
ml is the magnetic quantum number
What does the magnetic quantum number tell you?
It defines the orientation of the wave function, i.e which orbital within a subshell the electron is found
What are the possible values of ml?
The value of ml is limited by l.
It can be anywhere between + and - l
For example, if l = 1, ml can be -1, 0 or +1
How many orbitals are there in s-orbitals?
1, so there is only one value for ml (0)
How many orbitals are there in p-orbitals?
3, so there are three values for ml (-1, 0, 1)
How many orbitals are there in d-orbitals?
5, so there are five values for ml (-2, -1, 0, 1, 2)
How many orbitals are there in f-orbitals?
7, so there are seven values for ml (-3, -2, -1, 0, 1, 2, 3)
What does ms represent?
The spin quantum number
What does the spin quantum number tell you?
The direction of spin on the electron
What is the Pauli exclusion principle?
Electrons fundamentally cannot occupy the same space. Only electrons can occupy any one orbital, and one must spin up and one spin down.
Therefore, no two electrons in the same atom can share the same set of quantum numbers
What are the possible value of ms?
+1/2 (spin up) or -1/2 (spin down)
What is the Aufbau principle?
Electrons are found in the lowest available energy orbital
What is Hund’s rule?
With degenerate orbitals, the lowest energy configuration is achieved by putting electrons in different orbitals, with parallel spins
Why is the lowest energy configuration achieved by putting electrons in different orbitals, with parallel spins?
- Electrons in different orbitals are spatially separated
- Electrons with the same spin (up, up) do a better job of avoiding each other than electrons with opposite spin (up, down)
What are core electrons?
Inner electrons that are not valence electrons, and are not involved in chemical bonding
What are valence electrons?
Electrons that are involved in chemical bonding
What does degenerate mean in chemistry?
Of equal energy
What general principles can be used to explain apparent anomalies in electron configuration (e.g. 4s filling before 3d)?
- Completely filled, and half-filled subshells are slightly more stable than partially filled subshells
If the value of electron affinity is positive, what does this tell you about how favourable the reaction is?
If the value is positive (endothermic), the reaction is very unfavourable
If the value of electron affinity is negative, what does this tell you about how favourable the reaction is?
If the value is negative (exothermic), then the reaction is favourable
The more negative the value, the more stable the anion formed.
What are some subtle factors that affect bond geometry?
- Lone pair repulsion is more significant than bond pair repulsion
- Repulsions between pairs at 90 degrees are the most significant
- Double and triple bonds occupy more space than a single bond
What does VSEPR stand for?
Valence Shell Electron Pair Repulsion
What is VSEPR?
The optimal geometry around the central atom depends on the number of lone and bond pairs surrounding it. The bonded atoms will organise themselves in such a way to minimise repulsion
Method to count electrons for VSEPR predictions
- Identify the central and peripheral atoms
- Count the number of valence electrons of the central atom
- Count the number of electrons donated to the central atom
- Determine the total number of electron pairs
- Determine which are bonding and which are lone pairs
What does isoelectronic mean?
Having the same number of electrons or the same electronic structure
What is enthalpy of formation?
The energy required to form a compound from its constituent elements in their natural state (under standard conditions)
How is enthalpy of formation often measured?
Directly (experimentally)
What does it mean if the enthalpy of formation is positive?
The reaction is endothermic
What does it mean if the enthalpy of formation is negative?
The reaction is exothermic
What is lattice enthalpy?
The change in enthalpy when an ionic solid is broken apart into isolated ions in the gaseous state
How do you measure lattice enthalpy?
It is very difficult to measure lattice enthalpy directly/experimentally, so instead Born-Haber cycles are used
What is Coulomb’s law?
Like charges repel and opposite charges attract, with a force proportional to the product of the chargers, and inversely proportional to the distance between them
What does Coulomb’s law mean with respect to lattice enthalpy?
Lattice energy is related to the charge on the ions and the ionic radii (i.e the distance between the ions), as this controls the strength of the electrostatic interactions between the ions.
What is the relationship between ionic radii and charge, and the lattice enthalpy?
The smaller the ion (the shorter the distance between) and the larger the charge, the larger the lattice enthalpy
What 2 things does the solubility of a salt depend on?
The balance between:
- Lattice enthalpy
- Enthalpy of hydration
What is enthalpy of hydration?
The amount of energy released when one mole of gaseous ions are hydrated (for a salt that means dissolved in water)
What value determines the solubility of a salt?
Enthalpy of solution
What 2 values can you use in a Born Haber cycle to determine enthalpy of solution?
The values for lattice energy and energy of hydration added together will give you the value or enthalpy of solution
What value of enthalpy of solution tells you the salt is soluble?
If the value for enthalpy of solution is negative, the salt is soluble
Why do metals often dissociate to form a sea of delocalised electrons?
Due to their low ionisation energies
Why do metals tend to have low ionisation energies?
Due to their low electronegativities and large radii
What is the trend in metallic character as you go down a group?
Metallic character increases down a group
What is the reactivity of group 2 elements compared to group 1 elements?
Group 2 elements are generally less reactive than their group 1 counterparts
What does amphoteric mean?
Reacts both as a base and acid
What is diagonal relationship in the periodic table?
Elements diagonal to one another in the periodic table are chemically similar
Where do you mostly find double/triple bonds?
Multiple bonds (double/triple) are more stable/common for lighter elements
What is bond enthapy?
The energy required to break a bond
What is the relationship between bond energy and halide size in hydrogen halide bonds?
As halide size increases, bond energy decreases (the bond becomes easier to break)
What is the relationship between bond energy and halide size in halide-halide bonds?
As halide size decreases, bond energy increases (bond becomes stronger)
The exception to this is F2, in which the fluorine atoms are so close together that the electrons repel; this causes the F-F bond to be weaker than Cl-Cl
What is the trend in metallic character across a period?
Metallic character decreases across a period
