Flashcards in Bonding and Structure Deck (84)
Types of bonding
Ionic (or electrovalent), colvalent, intermolecular forces, hydrogen, metallic
How are ionic compounds arranged?
In a lattice structure, and the ions are arranged in such a way that maximises the attractive forces between the oppositely charged ions and minimises repulsive forces between similarly charged ions.
In what direction do forces act in ionic compounds?
In all directions
In what direction do forces act in covalent compounds?
One direction only
What is the definition of ionic bonding?
Ionic bonding is the electrostatic force of attraction between oppositely charged ions
What experiment gives evidence for ions?
Electrolysis of copper (II) chromate
CuCrO4 is green, but when electrolysed it produces copper (II) ions which are blue (at the cathode) and chromate ions which are yellow (at the anode)
What are the physical properties of ionic compounds?
Solid at room temperature, high melting and boiling points.
Why do ionic compounds have high melting and boiling points?
The electrostatic attractions between the oppositely charged ions are strong and require a lot of energy to break down
What is the solubility of ionic compounds?
Many ionic solids are soluble in water, but insoluble in non-polar solvents
What is the conductivity of ionic substances?
They do not conduct electricity when solid, but do when melted or dissolved in water. This is because they are split up, and the cations travel to the cathode, and the anions travel to the anode, and are discharged at the electrodes
In a solid, the ions are trapped in the lattice and are not free to move
What is a covalent bond?
A covalent bond is the electrostatic force of attraction between 2 nuclei and a shared pair of electrons between them
Facts about covalent giant structures
There are no molecules and no intermolecular forces
Melting and boiling points of covalent simple molecular substances
Low mp and bp, because the only forces that have to be overcome are the weak intermolecular forces which require very little energy to overcome, as none of the strong covalent bonds between the atoms need to be broken
Melting and boiling points of covalent giant lattice structures
Strong covalent bonds have to be broken, which require lots of energy to overcome, and so covalent giant lattice structures often have extremely high melting and boiling points
Mechanical strength of covalent simple molecular structures
Force of attraction between neutral molecules is usually very weak, and so when temperature is low enough for a molecular lattice to form then it will be weak and brittle
Mechanical strength of covalent giant lattice structures
Very hard if the covalent bonds extend in 3 dimensions (e.g diamond, silica etc), but if it only extends in 2 dimensions (e.g graphite, talc, slate) they are soft and flaky
Solubility of covalent simple molecular substances
Generally, molecular substances dissolve better in non-polar solvents (e.g petrol, paraffin) than in water
Solubility of covalent giant lattice structures
Insoluble in all solvents
Conductivity of covalent simple molecular substances
Cannot conduct electricity, as there are no ions that are free to move, and all electrons are held tightly in covalent bonds and cannot travel through the substance
Conductivity of covalent giant lattice structures
Electrons in these substances are localised within covalent bonds and so cannot move through the lattice so do not conduct electricity, however, graphite can conduct electricity because of its delocalised electrons
Bonding in diamond
Each carbon atom is covalently bonded to 4 other carbon atoms in a tetrahedral structure (bond angle is 109.4°)
Density of diamond vs graphite
Diamond is more dense than graphite
Bonding of graphite
Each carbon atom is covalently bonded to 3 other atoms - interlocking hexagons in layers
Layers are held together by weak intermolecular forces
Hardness of diamond
Very hard - often used for drillbits
Hardness of graphite
Soft - layers can slide over each other
Electrical conductivity of diamond
Electrical conductivity of graphite
Good - the delocalised electrons between the layers are mobile and can move through the structure
What are allotropes?
Different forms of the same element that exist in the same physical state
What are carbon's allotropes?
Diamond, graphite and buckminsterfullerene/fullerenes