Topic 3: Periodicity Flashcards
Periodicity
The repeating pattern of physical and chemical properties shown by different periods in the periodic table
Atomic Radius
- Distance from the nucleus to the outermost electron
Group Trend of Atomic Radius
- Additional electrons are occupying additional energy levels
- Electron experience increases shielding and are further away from the nucleus
- As a result, there is a decrease in attractive forces of nucleus with the outer electrons
Periodic Trend of Atomic Radius
- Additional electrons are occupying the same energy level. As a result shielding is constant.
- However, additional protons are also being added to the nucleus. As a result, the outer electrons experience an increase in effective nuclear charge (ENC)
- As a result, there is an increase in attractive forces of nucleus with the outer electrons and the electrons are pulled closer to it.
Bonding Atomic Radius
Half of the distance between the centre of the nuclei of 2 covalently-bonded atoms
Why is atomic radius (RnB) > covalent radius (Rb)?
- The covalent bond is formed by the overlapping of atomic orbitals
- The overlapping region becomes common ground
Ionic Radius (IR)
Distance from the nucleus to the outermost electron in an ion
Cation vs Neutral Counterpart
- cation is smaller than the neutral counterpart due to the loss of electrons from the valence shell
- The outermost occupied energy level is one less (n-1) than in the neutral atom (n)
Anion vs Neutral Counterpart
- Anion is larger than the neutral counterpart due to the gain of electrons in the valence shell
- Increases electron repulsion in the outer energy level
Group Trend of Ionic Radius
Ionic Radius Increases
- Following the formation, valence electrons are still occupying an additional energy level relative to the one above them in the group
Period Trend of Ionic Radius
Ionic Radius Decreases
- Outer electrons occupy the same energy levels and protons are being added to the nucleus
- Therefore, shielding is constant and the nucleus increases the effective nuclear charge (ENC)
- Results in electrons more strongly attracted to the nucleus and pulled closer to it
First Ionization Energy (IE)
IS the energy required to remove the first electron from a neutral gaseous atom in its ground state.
X(g) + energy → X^-1 (g) + e^-
Group Trend of First Ionization Energy (IE)
First Ionization Energy Decreases
- Atomic radius is increasing, outer electrons are further away from the nucleus and sheilding effect increase greater than the nuclear charge, so electrons hold a stongly attracted to the nuclues
- Requires
Periodic trends of melting points
Across a period (→):
- m.pt depends on the element structure and the type of attractive forces holding atoms together
- metals: have metallic bonding, so ↑ no of e-s = ↑ m.pt
- metalloids: macromolecular covalent structures with strong bonds = ↑ m.pt
- non-metals: simple molecular structures with weak intermolecular forces = ↓ m.pt
- noble gases: monatomic molecules = ↓ m.pt
Down a group (↓):
- Gp 1: ↑ no. of shells = ↑ shielding effect = ↑ radius = ↓ m.pt
- Gp. 7: ↑ attractive forces between diatomic molecules = ↑ m.pt
First ionization energy
Energy required to remove one mole of electrons from one mole of gaseous atoms
Periodic trends of ionization energy
- across a period (→): ↑ no. of valence e-s = ↑ no. of protons = ↑ ionisation energy
- values don’t increase regularly across a period
- due to new sub-levels being filled
- and existence of paired electrons (paired e-s have greater repulsion between them so are easier to remove)
- down a group (↓): ↑ no. of shells = ↑ distance between nucleus and electron = ↓ ionisation energy
Discrepancies in periodic trends of ionization energy
Drop in value between:
- Be and B
- Mg and Al
- N and O
- P and S
- Be and B, and Mg and Al, due to existence of a new subshell in B and Al
- N and O, and P and S, due to the fact that electrons in O and S’s outer orbitals are paired
Electron affinity
Energy change when one mole of electrons is added to one mole of gaseous atoms
- ↑ tendency = ↑ Eea
Factors affecting electron affinity
- nuclear charge: ↑ nuclear charge = ↑ Eea
- size of atom: ↑ atomic radius = ↓ Eea
- e. config.: stabler configs = ↓ Eea
Periodic trends of electron affinity
- across a period (→): ↓ radius and ↑ nuclear charge = ↑ Eea
- down a group (↓): ↑ radius and ↑ nuclear charge = but effect of ↑ radius is greater = so ↓ Eea
Electronegativity
A measure of the ability of atoms to attract a shared pair of electrons toward itself in a covalent bond
Periodic trends of eleectronegativity
Polar covalent bond
Type of oxides
Group 1 trends
Reaction between alkali metals and water
Alkali metals: difference in reaction to water
Reaction between alkali metals and halogens
Group VII trends
Characteristics of halogens
Transition metals
Properties of transition metals
Blocks in which the periodic table is divided according to the last orbital of an element
a) s-block
b) p-block
c) d-block
d) f-block
s-block
Group 1, Group 2 and He
p-block
Group 13 - 18 (excluding He)
d-block
Groups 3 - 12 (including La and Ac)
f-block
Elements 58 - 71 and Elements 90 - 103