Bonding & Substance Properties (AQA GCSE Combined Science: Trilogy: Chemistry): Flashcards
Exam code: 8464
1/520Still learning
Know0
- FrontStates of Matter
In a solid, particles are in a ________ arrangement and ________ about fixed positions. In a gas, particles move ________ in all directions and are ________ apart.
Was this flashcard helpful?
Cards in this collection (52)
In a solid, particles are in a ________ arrangement and ________ about fixed positions. In a gas, particles move ________ in all directions and are ________ apart.
In a solid, particles are in a regular arrangement and vibrate about fixed positions. In a gas, particles move quickly in all directions and are far apart.
What is the key difference between boiling and evaporation?
Boiling occurs at a specific temperature (the boiling point) and forms bubbles of gas inside the liquid. Evaporation occurs only at the surface of the liquid and can happen over a range of temperatures, even below the boiling point.
True or False?
The melting point and freezing point of a pure substance are different temperatures.
False.
A pure substance melts and freezes at the same temperature. For example, water both melts and freezes at 0°C.
What is sublimation and which substances undergo it?
Sublimation is when a solid changes directly into a gas without passing through the liquid state. Examples include iodine and solid carbon dioxide (dry ice).
When a solid melts, thermal energy is converted into ________ energy. This causes particles to vibrate ________ until they start to ________.
When a solid melts, thermal energy is converted into kinetic energy. This causes particles to vibrate more until they start to flow.
True or False?\n\nA substance with a melting point of −95°C would be a liquid at −100°C.
False.\n\n−100°C is below the melting point of −95°C. A substance is in the solid state at any temperature below its melting point, so this substance would be a solid at −100°C.
A substance is a ________ below its melting point, a ________ between its melting and boiling points, and a ________ above its boiling point.
A substance is a solid below its melting point, a liquid between its melting and boiling points, and a gas above its boiling point.
What does a horizontal section on a heating curve represent?
A horizontal section represents a change of state (e.g. melting or boiling). The temperature stays constant because the energy absorbed is used to overcome the intermolecular forces between particles, not to increase kinetic energy.
True or False?
The simple particle model accurately describes all types of particles because it treats them all the same way.
False.
Treating all particles the same is a limitation of the model. Real particles can be atoms, ions, or molecules with different properties. The model also ignores the intermolecular forces that exist between particles in different substances.
What are the three main limitations of the simple particle model?
It treats all particles as small, solid, and inelastic spheres, regardless of whether they are atoms, ions, or molecules.
It does not distinguish between different types of particle or mixtures.
It ignores the intermolecular forces between particles in different substances.
Sodium chloride has a melting point of 801°C and a boiling point of 1413°C. What is its state at 25°C and at 1200°C?
At 25°C (below the melting point of 801°C): solid.
At 1200°C (between the melting and boiling points): liquid (molten).
The four state symbols are:
solid = ________
liquid = ________
gas = ________
dissolved in water = ________
The four state symbols are:
solid = (s)
liquid = (l)
gas = (g)
dissolved in water = (aq)
What is the difference between the state symbols (l) and (aq)?
(l) = the substance is a pure liquid.
(aq) = the substance is dissolved in water (an aqueous solution).
For example, pure ethanol uses (l), but ethanol dissolved in water uses (aq).
True or False?
Molten magnesium chloride (liquid at high temperature) should be given the state symbol (g).
False.
Molten means melted to a liquid, so the correct state symbol is (l). The symbol (g) is only for substances in the gas state.
Complete the equation by adding state symbols:
CuCO3 (s) + 2HCl (___ ) → CuCl2 ( ___) + CO2 ( ___) + H2O ( ___)
HCl is dissolved in water (aq), both products in solution are (aq), carbon dioxide is a gas (g), and water is a liquid (l):
CuCO3 (s) + 2HCl (aq) → CuCl2 (aq) + CO2 (g) + H2O (l)
True or False?
It is acceptable to write the word "gas" or the capital letter (G) as a state symbol in a chemical equation.
False.
State symbols must be lowercase letters in brackets: (s), (l), (g), (aq). Writing "gas", "(G)", or a chemical formula instead of a state symbol will not be awarded marks.
Describe how ionic compounds behave as electrical conductors.
Ionic compounds are poor conductors in the solid state because the ions are held in fixed positions in the lattice and cannot move. They are good conductors when molten or dissolved in water, because the ions are then free to move and carry a charge.
Why do ionic compounds have high melting and boiling points?
Ionic compounds have a giant lattice structure. There are strong electrostatic forces of attraction between oppositely charged ions acting in all directions. A large amount of energy is needed to overcome these forces, giving ionic compounds high melting and boiling points.
Ionic compounds conduct electricity when ________ or when ________ in water, because the ________ are free to move and carry a charge.
Ionic compounds conduct electricity when molten or when dissolved in water, because the ions are free to move and carry a charge.
True or False?
An ionic compound conducts electricity in the molten state because electrons can move through it.
False.
In ionic compounds, it is the ions that move and carry a charge, not electrons. When molten, the ions are free to move, allowing electrical conductivity.
Why does magnesium oxide (MgO) have a higher melting point than sodium chloride (NaCl)?
MgO contains Mg2+ and O2- ions with a charge of ±2.
NaCl contains Na+ and Cl- ions with a charge of ±1.
The higher the charge on the ions, the stronger the electrostatic forces, so more energy is needed to overcome them. MgO therefore has a higher melting point than NaCl.
True or False?
Magnesium oxide has a higher melting point than sodium chloride because its ions carry a higher charge, creating stronger electrostatic forces.
True.
Mg2+ and O2- ions carry a charge of ±2, compared to Na+ and Cl- at ±1. Higher ion charges produce stronger electrostatic forces between the ions, which require more energy to overcome. This gives MgO a higher melting point than NaCl.
Explain why small covalent molecules have low melting and boiling points.
Small covalent molecules have weak intermolecular forces between the molecules. These forces require little energy to overcome, so the substances melt and boil at relatively low temperatures. The strong covalent bonds within each molecule are not broken at the melting or boiling point.
Why do small covalent molecules not conduct electricity, even when molten?
Small covalent molecules are neutral and have no overall charge. There are no free ions or free electrons to move and carry a current, even in the liquid state.
When a covalent substance melts or boils, it is the ________ between the molecules that are overcome, not the ________ within each molecule.
When a covalent substance melts or boils, it is the intermolecular forces between the molecules that are overcome, not the covalent bonds within each molecule.
True or False?
When water boils, the covalent bonds between hydrogen and oxygen atoms break.
False.
When water boils, the intermolecular forces between water molecules are overcome. The covalent O-H bonds within each water molecule remain intact throughout.
How does the size of a molecule affect its boiling point?
As molecules increase in size, the intermolecular forces between them also increase. These stronger forces require more energy to separate the molecules, so larger molecules generally have higher boiling points.
True or False?
A small covalent molecule such as hexane will conduct electricity in the molten state.
False.
Unlike ionic compounds, molten covalent substances have no free ions or free electrons. Without charged particles to move and carry a current, they cannot conduct electricity.
What is a polymer?
A polymer is a very large molecule made by joining together large numbers of smaller molecules called monomers. The atoms within each polymer chain are linked by strong covalent bonds.
What forces hold atoms together within a polymer chain and the separate polymer chains together?
The atoms within each polymer chain are held together by strong covalent bonds.
The separate polymer chains attract each other by weak intermolecular forces. These forces are larger than those between small molecules, which is why polymers are usually solid at room temperature.
Within a polymer chain, atoms are linked by ________ bonds. Between separate polymer chains, the forces of attraction are called ________ forces.
Within a polymer chain, atoms are linked by covalent bonds. Between separate polymer chains, the forces of attraction are called intermolecular forces.
How does polymer chain length affect the melting point of a polymer?
As polymer chain length increases, the intermolecular forces between the chains become stronger, so the melting point increases. At very long chain lengths, the melting point eventually levels off.
True or False?
The separate polymer chains in a polymer are held together by covalent bonds.
False.
The atoms within each polymer chain are linked by covalent bonds, but the chains are held to each other by weak intermolecular forces. It is these forces that are overcome when a polymer melts.
What three features identify a repeat unit in a polymer diagram?
A polymer repeat unit has:
Bonds that extend outside the brackets on both sides
A subscript n on the bottom right of the brackets, indicating a large number of repeating units
A repeating structural pattern inside the brackets.
Describe the structure of a giant covalent substance.
Giant covalent substances contain a huge number of non-metal atoms bonded to each other by strong covalent bonds. They form a giant lattice with a fixed ratio of atoms. Examples include diamond, graphite and silicon dioxide (SiO2).
Why do giant covalent structures have very high melting and boiling points?
Giant covalent structures have very high melting and boiling points because: (1) they have a giant lattice structure; (2) the atoms are held together by strong covalent bonds throughout the lattice; and (3) a large amount of energy is needed to break these bonds.
In the structure of silicon dioxide, each silicon atom forms ________ covalent bonds, and the ratio of silicon to oxygen atoms is ________.
In the structure of silicon dioxide, each silicon atom forms four covalent bonds, and the ratio of silicon to oxygen atoms is 1:2 (giving the formula SiO2).
True or False?
If a covalent substance is solid at room temperature, it is likely to be a giant covalent structure rather than a simple molecular substance.
True.
Giant covalent structures are solid at room temperature because of the large number of strong covalent bonds throughout the lattice. Simple covalent molecules are usually liquids or gases because they have weak intermolecular forces that are easily overcome.
State two physical properties of giant covalent structures such as diamond and silicon dioxide.
Giant covalent structures are:
Very hard
Have a very high melting point
Do not conduct electricity, as they have no free electrons or free ions to carry a charge.
True or False?
Silicon dioxide (SiO2) will conduct electricity in the molten state.
False.
Unlike ionic compounds, molten silicon dioxide produces no free ions. All bonding in SiO2 is covalent, so there are no charged particles to carry a current in any state.
Define alloy.
An alloy is a mixture of two or more metals, or a metal with a non-metal such as carbon. Alloys are usually harder and stronger than the pure metals they contain. Steel is an example: a mixture of iron and carbon.
Why are most metals malleable?
In a pure metal, the atoms are arranged in layers. When a force is applied, the layers can slide over each other, allowing the metal to be bent or hammered into shape without breaking.
Alloys are harder than pure metals because they contain atoms of ________ sizes, which causes the layers to become ________, making it difficult for the layers to ________ over each other.
Alloys are harder than pure metals because they contain atoms of different sizes, which causes the layers to become distorted, making it difficult for the layers to slide over each other.
True or False?
An alloy is harder than a pure metal because the different types of atoms form new bonds with each other.
False.
Alloying does not create new chemical bonds. The alloy is harder because the different-sized atoms distort the layers, preventing the atoms from sliding over each other easily. No new bonding is involved.
Why do metals have high melting and boiling points?
Metals contain a giant lattice of positive ions surrounded by delocalised electrons. There are strong electrostatic forces of attraction between the positive ions and the delocalised electrons. A large amount of energy is needed to overcome these forces, giving metals high melting and boiling points.
True or False?
When explaining why alloys are harder than pure metals, the word “particles” is acceptable instead of “atoms” or “ions”.
False.
Mark schemes for alloy hardness are very specific. You must use the word atoms (or ions) throughout your answer. “Particles” is not sufficient to gain credit.
Explain why metals are good conductors of electricity.
Metals contain delocalised electrons that are free to move through the structure. These electrons carry electrical charge through the metal, allowing a current to flow.
Explain why metals are good conductors of thermal energy.
The delocalised electrons in the metal are free to move through the structure. As they move, they transfer thermal energy through the metal. This makes metals good conductors of heat as well as electricity.
Metals conduct electricity because they contain ________ electrons that are free to ________ charge ________ the structure.
Metals conduct electricity because they contain delocalised electrons that are free to carry charge through the structure.
True or False?
Metals conduct electricity because the positive metal ions are free to move through the lattice.
False.
The positive metal ions remain in fixed positions in the lattice. It is the delocalised electrons that are free to move and carry charge through the metal.
What is wrong with the phrase “delocalised electrons carry charge throughout the metal”?
Mark schemes requires “through” not “throughout” or “around.” These words do not give direction to the electron movement and are explicitly rejected. The correct answer states electrons carry charge through the structure.
True or False?
When explaining how a metal conducts thermal energy, you can say “delocalised electrons carry electrical charge through the structure.”
False.
For thermal conductivity, the mark scheme requires the delocalised electrons to transfer energy through the structure. “Carry electrical charge” is the answer for electrical conductivity and is explicitly ignored for thermal conductivity questions.
Sign up to unlock flashcards
or