Unit 1- Principles of Chemistry
1. States of matter
Three states of matter: solids, liquids and gases
Arrangement of the particles in solids, liquids and gases:
Solid:
- arranged regularly and packed closely together.
- Only able to vibrate about fixed positions.
- Have strong forces of attraction between them which keep them together.
Liquid:
- Arranged randomly; Mostly touching but some gaps have appeared.
- Forces of attraction are less effective, the particles can move around each other
Gas:
- Particles are much further apart
- Moving randomly at high speed in all directions
- Almost no forces of attraction between
Interconversions between the three states of matter
Melting and cooling – changing states between solids and liquids
• The energy provided by the heat source makes the particles in the solid vibrate faster.
• Forces of attraction between the particles are no longer strong enough to hold them
together.
• Solid melts to form a liquid
*Melting point: the temperature at which the solid melts
*Particles in the liquid have more kinetic energy than that of in the solid.
- If the liquid is cooled again, the particles will move around more slowly.
- Forces of attraction between them will hold them in a fixed position.
- Liquid freezes to form a solid
*Freezing point: the temperature at which the liquid freezes.
*The temperature of the melting point = that of the freezing point
Boiling and evaporation – changing states between liquids and gases
Boiling
- occurs when a liquid is heated so strongly → particles moving fast enough to overcome
all the forces of attraction
- Stronger the forces of attraction, higher the boiling point of the liquid.
- Because more energy is needed to overcome the forces of attraction.
- If gas is cooled, particles move slower
- Forces of attraction start to form and hold them together as a liquid.
- Gas condenses
,Evaporation
- Occurs at any temperature
- In any liquid or gas, the average speed of the particles varies with the temperature.
- But at each temperature, some particles will be moving faster than the average and others more slowly
- Some very fast particles at the surface of the liquid gain enough energy to overcome the force of
attraction
- Break away to form a gas.
- IN A CLOSED CONTAINER!! EVAPORATION AND CONDENSATION WILL BE BOTH OCCURING AT THE SAME
TIME!
- Particles in the gas will also be colliding with particles at the surface of the liquid.
- If they are moving slowly enough, they will be held by the forces of attraction and become part of the
liquid.
Sublimation – changing states between solid and gas
- A small number of substances able to undergo sublimation and deposition.
- E.G. carbon dioxide. Gas → solid directly. (solid: dry ice)
Diffusion
: is the spreading out of particles from where they are at a high concentration to where they are at
a low concentration
Diffusion of Bromine
gas
- If the lid is removed, the brown colour diffuses upwards until both gas jars are uniformly brown.
Showing that particles of different gases travel at different speeds
Ammonia NH3 + hydrogen chloride HCl →white solid ammonium chloride NH4Cl
- Ammonia particles and hydrogen chloride particles diffuse along the tube
- The white ring of solid ammonium chloride forms closer to the hydrochloric acid end.
- Ammonia particles are lighter than hydrogen chloride particles and therefore move faster.
Diffusion in liquids
- Diffusion through a liquid is very slow if the liquid is completely still.
- It can take days for the colour to diffuse throughout all the water.
- Because the particles in a liquid move more slowly than that of in a gas
- The particles in a liquid are also much closer together than those in a gas so there is less space for particles to
move into without colliding with another one.
The solubility of solids – solutes, solvents and solutions
Solutes: substance that dissolves
Solvent: liquid it dissolves in
Solution: the liquid formed
** When you make a solution, the attractive forces between the particles in the solute are being broken. At the
same time, new attractive forces are being formed between the solvent particles and the solute particles.
** Whether a particular solid is soluble in any solvent depends on whether the new attractive forces are strong enough to overcome the old ones.
,Measuring solubility
A saturated solution: a solution which contains as much dissolved solid as possible at a particular temperature.
** solubility varies with temperature the solubility increases with temperature. The increase in kinetic energy that comes with
higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.
, 2. Elements, compounds and mixtures
Elements: substances that can’t be split into anything simpler by chemical means. *only contains one type of atom
Compounds: formed when two or more elements chemically
combine. *always combine in fixed proportions
Mixtures: various substances mixed together, and no chemical
reaction occurs. *can be made from elements and/or compounds; can be in any proportion
Simple differences between mixtures and compounds
Mixtures Compounds
Proportions In a mixture of hydrogen and oxygen gases → two could be In Water, 1 H2O has 2 hydrogen atoms + 1 oxygen atom.
mixed in any proportion → never varies
Properties In a mixture of elements, each element keeps its own In a compound, the properties change.
properties.
E.g. in a mixture of iron and sulphur, the iron is grey and the The compound iron sulphide reacts quite differently with acids to
sulphur is yellow. produce poisonous hydrogen sulphide gas
The iron reacts with dilute acids to produce hydrogen
The sulphur doesn’t react with the acid
Ease of separation Mixtures can be separated by physical means. Needs to undergo chemical reactions to separate compounds.
E.g. Filtration, Crystallisation, evaporation… E.g. electrolysis
Melting point and boiling point
Pure substances → melt and boil at fixed temperatures.
- The presence of impurities lowers the melting point of a substance and raises the boiling point.
- The melting point can be very useful in determining whether or not a substance is pure.
1. States of matter
Three states of matter: solids, liquids and gases
Arrangement of the particles in solids, liquids and gases:
Solid:
- arranged regularly and packed closely together.
- Only able to vibrate about fixed positions.
- Have strong forces of attraction between them which keep them together.
Liquid:
- Arranged randomly; Mostly touching but some gaps have appeared.
- Forces of attraction are less effective, the particles can move around each other
Gas:
- Particles are much further apart
- Moving randomly at high speed in all directions
- Almost no forces of attraction between
Interconversions between the three states of matter
Melting and cooling – changing states between solids and liquids
• The energy provided by the heat source makes the particles in the solid vibrate faster.
• Forces of attraction between the particles are no longer strong enough to hold them
together.
• Solid melts to form a liquid
*Melting point: the temperature at which the solid melts
*Particles in the liquid have more kinetic energy than that of in the solid.
- If the liquid is cooled again, the particles will move around more slowly.
- Forces of attraction between them will hold them in a fixed position.
- Liquid freezes to form a solid
*Freezing point: the temperature at which the liquid freezes.
*The temperature of the melting point = that of the freezing point
Boiling and evaporation – changing states between liquids and gases
Boiling
- occurs when a liquid is heated so strongly → particles moving fast enough to overcome
all the forces of attraction
- Stronger the forces of attraction, higher the boiling point of the liquid.
- Because more energy is needed to overcome the forces of attraction.
- If gas is cooled, particles move slower
- Forces of attraction start to form and hold them together as a liquid.
- Gas condenses
,Evaporation
- Occurs at any temperature
- In any liquid or gas, the average speed of the particles varies with the temperature.
- But at each temperature, some particles will be moving faster than the average and others more slowly
- Some very fast particles at the surface of the liquid gain enough energy to overcome the force of
attraction
- Break away to form a gas.
- IN A CLOSED CONTAINER!! EVAPORATION AND CONDENSATION WILL BE BOTH OCCURING AT THE SAME
TIME!
- Particles in the gas will also be colliding with particles at the surface of the liquid.
- If they are moving slowly enough, they will be held by the forces of attraction and become part of the
liquid.
Sublimation – changing states between solid and gas
- A small number of substances able to undergo sublimation and deposition.
- E.G. carbon dioxide. Gas → solid directly. (solid: dry ice)
Diffusion
: is the spreading out of particles from where they are at a high concentration to where they are at
a low concentration
Diffusion of Bromine
gas
- If the lid is removed, the brown colour diffuses upwards until both gas jars are uniformly brown.
Showing that particles of different gases travel at different speeds
Ammonia NH3 + hydrogen chloride HCl →white solid ammonium chloride NH4Cl
- Ammonia particles and hydrogen chloride particles diffuse along the tube
- The white ring of solid ammonium chloride forms closer to the hydrochloric acid end.
- Ammonia particles are lighter than hydrogen chloride particles and therefore move faster.
Diffusion in liquids
- Diffusion through a liquid is very slow if the liquid is completely still.
- It can take days for the colour to diffuse throughout all the water.
- Because the particles in a liquid move more slowly than that of in a gas
- The particles in a liquid are also much closer together than those in a gas so there is less space for particles to
move into without colliding with another one.
The solubility of solids – solutes, solvents and solutions
Solutes: substance that dissolves
Solvent: liquid it dissolves in
Solution: the liquid formed
** When you make a solution, the attractive forces between the particles in the solute are being broken. At the
same time, new attractive forces are being formed between the solvent particles and the solute particles.
** Whether a particular solid is soluble in any solvent depends on whether the new attractive forces are strong enough to overcome the old ones.
,Measuring solubility
A saturated solution: a solution which contains as much dissolved solid as possible at a particular temperature.
** solubility varies with temperature the solubility increases with temperature. The increase in kinetic energy that comes with
higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.
, 2. Elements, compounds and mixtures
Elements: substances that can’t be split into anything simpler by chemical means. *only contains one type of atom
Compounds: formed when two or more elements chemically
combine. *always combine in fixed proportions
Mixtures: various substances mixed together, and no chemical
reaction occurs. *can be made from elements and/or compounds; can be in any proportion
Simple differences between mixtures and compounds
Mixtures Compounds
Proportions In a mixture of hydrogen and oxygen gases → two could be In Water, 1 H2O has 2 hydrogen atoms + 1 oxygen atom.
mixed in any proportion → never varies
Properties In a mixture of elements, each element keeps its own In a compound, the properties change.
properties.
E.g. in a mixture of iron and sulphur, the iron is grey and the The compound iron sulphide reacts quite differently with acids to
sulphur is yellow. produce poisonous hydrogen sulphide gas
The iron reacts with dilute acids to produce hydrogen
The sulphur doesn’t react with the acid
Ease of separation Mixtures can be separated by physical means. Needs to undergo chemical reactions to separate compounds.
E.g. Filtration, Crystallisation, evaporation… E.g. electrolysis
Melting point and boiling point
Pure substances → melt and boil at fixed temperatures.
- The presence of impurities lowers the melting point of a substance and raises the boiling point.
- The melting point can be very useful in determining whether or not a substance is pure.
