3. Periodicity Flashcards
What are the factors that affect atomic radius? [2]
Nuclear charge
Shielding effect by inner electrons
What is the effective nuclear charge?
The difference between nuclear charge and shielding effect
What is the periodic trends in atomic radius?
Increase down the group
Decrease across a period
What is the general trend for ionic radius?
Radii of cations are smaller than parent atom
Radii of anions are bigger than parent atom
What is the periodic trend for ionic radius?
Cation:
Decrease down a period, increase down a group
Anion:
Decrease down a period, increase down a group
What is the defi of 1st ionisation energy?
The minimum energy required in removing one mole of valence electrons from one mole of gaseous atoms to form 1 mole of singly positively-charged gaseous ion
Periodic trends for 1st ionisation energy
Increases across a period
Decreases down a group
What are the factors affecting ionisation energy across a period and down a group?
Period: Effective nuclear charge
Group: Atomic radii
What are the 2 exceptions in 1st ionisation energy trend? Explain.
Between group 2&13 (extra sub-level)
Between group 15&16 (how the electrons are arranged in the orbital)
What are the top 4 electronegative elements?
NOF Cl
Oxygen, nitrogen, fluorine, chlorine
Defi of electronegativity
The relative attraction that an atom has for the shared pair of electrons in a covalent bond
What is the periodic trend of electronegativity? Explain.
Increase across a period
Decrease down a group
As electrostatic attraction between bonding electrons and nuclei increases, electronegativity will increase
What is the first electron affinity?
The enthalpy change when one mole of gaseous atoms acquires one mole of electrons to form one mole of singly negatively charged gaseous ions
S(g) + e- –> S- (g)
Is first electron affinity exo or endothermic?
Exothermic for most elements
Energy released when nucleus attracts electron in outer shell (like bond forming)
What is the periodic trend for first electron affinity?
Increases across a period
Decreases down a group
What is the exception for first electron affinity? Why?
Nitrogen
Addition of an extra electron –> Energy needed to overcome the inter-electronic repulsion between the paired electrons –> Less exothermic
How to explain fluorine and oxygen for electron affinity?
Energy released when nucleus attracts an electron is far greater than energy needed to overcome inter-electronic repulsion
Defi of second electron affinity?
The enthalpy change when one mole of singly negatively-charged gaseous ions acquires one mole of electrons to form one mole of doubly negatively-charged gaseous ions
What is the enthalpy change for second electron affinity? Why?
Endothermic
Always positive enthalpy, meaning we need energy
To overcome repulsion between 2 negatively-charged species (electron & anion)
Between period 2 & 3, what are the giant covalent structures (elements)
Boron, Silicon, Carbon (can also form C60)
What are the simple molecules between periods 2 & 3 (elements only)?
C60, N2, O2, F2, P4, S8, Cl2
What is the periodic trend for melting point for metals?
What is one exception to take note of for period 3?
Increases across a period
Silicon is higher than Al due to its giant covalent structure
Why does metallic bond strength increase across the period?
- Decrease in metallic radius
- Increase in no. of electrons donated per atom to the mobile sea of electrons
==> Increase in charge density
What is the periodic trend for non-metals?
Decreases across a period
Increases down a group
Due to LDF increasing down a group due to larger electron clouds
