melting points Flashcards
What is the periodic trend in structure and melting point across periods 2 and 3? (2)
As you go across periods 2 and 3, the structure of the elements changes
Different structures will have different melting points.
What are the three main types of structures across a period? (1)
Giant metallic
Giant covalent
Simple molecular
Which elements in periods 2 and 3 have a giant metallic structure? (2)
Lithium (Li), Beryllium (Be) Sodium (Na), Magnesium (Mg), Aluminium (Al)
What is the trend in melting point of elements with giant metallic structure? (4)
The strength of metallic bonding increases across the group
Due to a greater positive charge of the ions
There are more electrons released into the lattice
So there is a greater attractive electrostatic force
Which elements in periods 2 and 3 have a giant covalent structure? (2)
Boron (B), Carbon (C), Silicon (Si)
What is the general melting point of elements with giant covalent structures? (3)
Giant covalent structures are lattices with very strong covalent bonds between atoms
Covalent bonds require a lot of energy to break
Elements with giant covalent structures generally have very high melting points
Why does sulfur (S₈) have a higher melting point than phosphorus (P₄) in period 3? (2)
S₈ has more electrons than P₄.
This results in stronger London forces
More energy is required to overcome the London forces
Therefore sulfur has a higher melting point
Which elements in periods 2 and 3 have a simple molecular structure? (1)
Nitrogen (N₂), Oxygen (O₂), Fluorine (F₂), Neon (Ne), Phosphorus (P₄), Sulfur (S₈), Chlorine (Cl₂), Argon (Ar)
What is the structure of graphene? (3)
Single layer of graphite
Hexagonally arranged (planar 120°) carbons
Has delocalised electrons which can move about the layer
What is the strength of graphene? (2)
Thinnest and strongest material in existence
Due to its giant covalent network of strong covalent bonds
What is the electrical conductivity of graphene? (3)
Highly conductive
Due to delocalised electrons
Which can move about the ring and carry a charge
What is the melting point of elements with simple molecular structures? (3)
Simple covalent molecules have weak van der Waals interactions between molecules
These interactions require little energy to break
Elements with simple molecular structure generally have low melting points
What is the general trend of melting point across the period? (4)
Melting points peak towards the middle of the period
The first elements have giant metallic structures, having melting points which increase with increasing ionic charge
The middle of the period consists of elements which form giant covalent structures, which have very high melting points
The end of the period consists of elements which form simple covalent molecules which have relatively low melting points
