Types of Substance Flashcards
All 32 cards in this deck
What are the four types of substance that elements and compounds can be classified as?
Ionic, simple molecular (covalent), giant covalent and metallic.
Which types of substance have high melting and boiling points?
Ionic, giant covalent and metallic substances.
True or false? A substance with a low boiling point and low solubility in water is most likely simple molecular (covalent).
True. Simple molecular substances have low boiling points and are usually not very soluble in water.
Why do ionic compounds have high melting and boiling points?
There are strong electrostatic forces between the oppositely charged ions, so a lot of energy is needed to separate them.
When does an ionic compound conduct electricity, and why?
When molten or dissolved in water (aqueous solution), because the ions are then free to move.
Why do simple molecular substances have low melting and boiling points?
The intermolecular forces between the molecules are weak, so little energy is needed to separate the molecules.
True or false? Glucose solution conducts electricity, so the lamp in a conductivity test lights up.
False. Glucose is simple molecular with no charged particles free to move, so the lamp does not light up.
Diamond and graphite are two different forms of which element?
Carbon — both are giant covalent substances.
Describe the structure of diamond.
A giant covalent (3D) lattice in which each carbon atom is joined to four other carbon atoms by covalent bonds.
Describe the structure of graphite.
Layers of carbon atoms in hexagonal rings, each carbon bonded to three others; the layers are held together by weak forces and each atom has one delocalised electron.
Why is graphite used to make electrodes?
It conducts electricity because it has delocalised electrons that can move through the graphite.
Why is graphite used as a lubricant?
The forces between its layers are weak, so the layers can slide over each other.
Why is diamond used in cutting tools?
It is very hard, because every carbon atom is held by four covalent bonds in a giant covalent structure.
What is graphene?
A single layer of graphite — one atom thick, with carbon atoms in hexagonal rings.
Why does graphene conduct electricity?
It has delocalised electrons that are free to move through the layer.
Describe the structure of a C₆₀ fullerene molecule.
A hollow ball (cage) of 60 carbon atoms, each covalently bonded to three others, arranged in rings.
True or false? C₆₀ fullerene has a very high melting point like diamond.
False. C₆₀ is simple molecular, with weak intermolecular forces between its molecules, so its melting point is low.
Describe the molecules in poly(ethene).
Very large molecules made of long chains of carbon atoms.
What type of bonds join the atoms within a poly(ethene) molecule?
Covalent bonds.
State four characteristic properties of metals.
Shiny solids, high melting points, high density and good conductors of electricity.
State two typical properties of non-metals.
Low boiling points and poor conductors of electricity.
Why do metals conduct electricity?
They contain delocalised (free) electrons that can move through the metal — not moving ions.
Why are metals malleable?
The layers of metal ions can slide over each other without breaking the structure.
Give one limitation of a dot and cross diagram.
It does not show the shape of the substance or the relative sizes of the atoms and ions.
Give one limitation of a ball and stick model.
It shows gaps and sticks between atoms, so the spacing is wrong and atoms are not really solid balls.
Give one limitation of a two-dimensional representation of a structure.
It cannot show the true three-dimensional shape and arrangement of the particles.
True or false? In a dot and cross diagram, the dots and crosses show that electrons from different atoms are actually different.
False. All electrons are identical; the dots and crosses only show which atom each electron came from.
Why do giant covalent substances, such as diamond, have very high melting and boiling points?
Melting means breaking a huge number of strong covalent bonds between the atoms, which takes a lot of energy.
Why does diamond not conduct electricity?
Each carbon atom uses all four of its outer electrons in covalent bonds, so there are no delocalised electrons (or ions) free to move.
Describe the structure and bonding in a metal.
A giant structure of positive metal ions surrounded by delocalised electrons; strong electrostatic attraction between the ions and the electrons holds it together (metallic bonding).
Why do most metals have high melting points?
The electrostatic attraction between the positive metal ions and the delocalised electrons is strong, so a lot of energy is needed to overcome it.
Which are usually soluble in water: ionic compounds or giant covalent substances?
Many ionic compounds dissolve in water; giant covalent substances such as diamond and graphite are insoluble.