Topic 3: Periodicity Flashcards
periodicity
the repeating pattern of physical and chemical properties shown by different periods in the periodic table
atomic radius
the distance from the centre of the nucleus to the outermost shell of electrons
periodic trend of atomic radius
- across a period (→): ↑ nuclear charge = ↓ radius
- because all elements in a period are isoelectronic, but no. of protons ↑
- down a group (↓): ↑ no. of shells = ↑ shielding effect = ↑ radius
bonding atomic radius
- aka covalent 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
the effective distance from the nucleus of the ion up to which it has an influence in the ionic bond
characteristics of ionic radius
- radius of cation < radius of parent atom
- as the no. of shells decreased by 1
- radius of anion > radius of parent atom
- as anions contain more e-s
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 ionisation energy
- the amount of energy required
- to remove 1 mol of e-s from 1 mol of atoms in gaseous state
periodic trends of ionisation 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 ionisation 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
- amount of energy released when a mole of electrons is added to a mole of gaseous atoms
- represents ability of an atom to hold additional e-s
- ↑ 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
