Electronic structure + periodic table Flashcards
Quantum shells?
- according to the quantum theory: electrons can only exist in certain well-defined energy levels AKA quantum shells
- All electrons in a given quantum shell have similar but not identical energies
- Shells contain different types of sub shell These sub shells have different number of orbitals which can each hold up to two electrons
Electrons in the first four quantum shells?
- Electrons in 1st quantum shell have lowest energy for that element
- 1st shell located in region closest to nucleus, 2nd outside the first etc.
- Each quantum shell apart from 1st is further divided into sub shells of slightly different energy levels
Sub-shell definition?
A group of electrons in the same type of orbital within a shell (s, p, d or f)
Sub shells in first four quantum shells?
- Only 1 sub shell in first quantum shell - 1s subshell
- 2 subshells - 2s and 2p - electrons in 2p have slightly higher energy level than those in 2s
- 3 sub shells - 3s, 3p and 3d electrons in 3d have slightly higher energy level than those in 3p (3s < 3p < 3d)
- 4 subshells - 4s, 4p, 4d, 4f electron energies increase in the order
Orbital definition?
A region in an atom that can hold up to two electrons with opposite spins - electrons can move anywhere within the shape
- If u map a single electron’s position at regular intervals - possible to build up 3D map of places where electron is likely to be found - most of the time it’s located within a fairly easily defined region of space close to the nucleus
- sizes and shapes are such that: there’s a 90% probability of finding electron within boundaries
s orbitals?
- Each subshell contains orbitals
- Spherical - 2s orbital is larger but same shape as 1s
- On diagram: x, y and z are 3D Cartesian Axes AKA axis at mutual right angles
p orbitals?
- dumbbell shapes
- 3 p-orbitals right angles to e/o
- px - 90° along X axis (horizontal)
- py - 90° along y axis (vertical)
- oz - 90°along Z axis (looks diagonal)
- r 5 d orbitals in the d sub shell
- r 7 f orbitals in the f subshell
How many electrons can each sub shell hold?
- s - 1 orbital - hold 1 x 2 = 2 electrons
- p - 3 orbitals - hold 3 x 2 = 6 electrons
- d - 5 orbitals - hold 5 x 2 = 10 electrons
- f - 7 orbitals - hold 7 x 2 = 14 electrons
Shell number, sub shells, number of electrons
- 1st quantum shell = 1s = 2 electrons
- 2nd quantum shell = 2s, 2p = (2+(3x2) ) = 8
- 3rd quantum shell = 3s, 3p, 3d = (2+(3x2)+(5x2) = 18
- 4th quantum shell = 32
Spin-pairing definition?
When two electrons occupy one orbital they “spin” in opposite directions
- Within an orbital: electrons pair up with opposite spin so atom is as stable as poss
- arrows
- If electron spins are unpaired therefore unbalanced - it produces a natural repulsion between electrons - making atom very unstable so diff arrangement of electrons
Electrical configuration - how to write?
e.g. 1s² :
Big number = shell number
Letter = sub shell
Small number = number of electrons in shell
1. Fill up lowest energy subshells 1st
*exception: 4s sub shell has lower energy level than 3d, even though principle quantum number is bigger so 4s fills up 1s
2. Electrons fill orbitals singly b4 they start pairing up - due to electron repulsion
Using the periodic table to work out electron configuration?
- blocks named according to which subshell the last electron occupies
- It can be split into an s-block, d-block and p-block
- s-block elements: Group 1 + 2
- p-block elements: Group 3 - 8
- d-block elements: Sc - Zn (period 4) + Y - Cd (period 5)
Groups?
all elements in main group (Group 1-8) contain same outer electron configuration so - hv similar chemical properties
*n = quantum shell no.
Periods?
- elements in period hv same no. quantum shells (containing electrons)
- show repeating trends in physical & chemical properties
Configuration of an ion?
- For ions up to calcium: write configuration of atom -> add/remove electrons to or from highest -energy level
- Transition metal ions: Lose from 4S first then 3D
exception of Cr and Cu?
An electron from 4s orbital moves into 3d orbital to create: a more stable hall full/full 3d subshell respectively (take 1 electron away from 4s and add to 3d)
Periodicity definition?
A regularly repeating pattern of atomic, physical & chemical properties with increasing atomic number
Measuring atomic radii?
- the dis from centre of nucleus to boundary of electron cloud
- since atom doesn’t hv a well-defined boundary…
- distance between 2 nuclei (from centres)/2
Different radii?
- covalent radius: 2 bonded atoms
- van der Waals radius: for noble gases
- metallic radius: metals
Why does the atomic radius decrease across each period?
- as the no. protons in nucleus increases - nuclear charge increases so
- increase in electrostatic force of attraction between nucleus + outer electrons so
(-attraction - so atomic radius decreases
Melting + boiling points?
- elements w giant lattice structures have high mp + bps
- simple molecular structures low
Why is the first IE of the Group 3 element less than that of Group 2 element (in the same period)? e.g. Be + B & Mg + Al
- although nuclear charge of B greater - outer electron has more energy (in 2p orbital rather than 2s like Be)
- so energy required to remove this electron less than Be’s
- also: 2p electron in B experiences greater electron-electron repulsion/shielding as - 2 inner sub-shell rather than only 1
- same as Mg + Al - just 3s & 3p
Why is the first IE of the Group 6 element less than that of Group 5 element (in the same period)? e.g. N + O
N: 1s2 2s2 2p3(2px1 2py1 2pz1) (all unpaired electrons)
O: 1s2 2s2 2p4(2px2 2py1 2pz1)
- 1st electron removed from O atom is 1 of the 2, paired electrons in 2px orbital…
- presence of 2 electrons in single orbital increases electron-electron repulsion in orbital so…
- less energy required to remove 1 of these electrons than to remove 1 from a N atom - despite larger nuclear charge of O
