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Flashcards in Bonding and Structure Deck (84)
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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


What is one use of fullerenes?

Carbon nanotubes