Elements, Compounds, Mixtures

Element

An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.

Nitrogen

Nitrogen is an element.

Water

Water is a compound composed of hydrogen and oxygen atoms chemically combined.

Compound

A compound consists of atoms of different elements chemically bonded together in a fixed ratio.

Separation of Compounds

Compounds cannot be separated into their elements by physical means.

Mixture

A mixture contains more than one element or compound in no fixed ratio, which are not chemically bonded.

Difference between Compound and Mixture

A compound consists of two or more elements that are chemically combined, while a mixture consists of two or more substances that are not chemically combined.

Classification of Substances

All substances can be classified into one of these three types: elements, compounds, or mixtures.

Air

Air = mixture

Ammonia, NH3

Ammonia, NH3 = compound

Chlorine, Cl2

Chlorine, Cl2 = element

Copper sulfate, CuSO4

Copper sulfate, CuSO4 = compound

Difference between Element and Compound

An element consists of only one element, while a compound consists of two or more elements that are chemically combined.

Copper Wire

Copper wire is an element.

Copper Sulfate and Periodic Table

Copper sulfate is not in the Periodic Table because it is a compound / not an element.

Homogeneous Mixture

A homogeneous mixture is a mixture with a uniform composition and properties throughout.

Air as Mixture

Air is an example of a homogeneous mixture.

Heterogeneous Mixture

A mixture that has a non-uniform composition and different properties throughout is called a heterogeneous mixture.

Concrete

Concrete is an example of a heterogeneous mixture.

Simple Distillation

Simple distillation is a technique used to separate a liquid from a solution (e.g., water from a salt solution) by boiling the solution and condensing the vapour.

Simple Distillation Uses

Simple distillation is used to separate: a liquid and soluble solid from a solution (e.g., water from a solution of salt water), a pure liquid from a mixture of liquids.

Fractional distillation

A technique used to separate two or more liquids that have different boiling points from a mixture.

Chromatography

The technique that separates solutions with more than one type of dissolved solid (solute).

Filtration

A method that separates an undissolved solid from a mixture of solid and liquid.

Crystallisation

A technique used to separate a dissolved solid from a solution.

Recrystallisation

A process used to purify impure solids.

Solubility in recrystallisation

It is important that the solid (solute) is more soluble in hot solvent than in cold.

Paper chromatography

A technique used to separate substances that have different solubilities in a given solvent, such as identifying the components of a mixture.

Filtrate

The liquid that passes through the filter in filtration.

Residue

The solid left behind on the filter paper in filtration.

Distillation

A method used to separate liquids because they have different boiling points.

Principle of recrystallisation

Using a hot solvent to dissolve both the organic solid and impurities, then as the solution cools, the solid crystallises out and leaves behind the impurities in the solution.

Freezing

The interconversion that takes place when a liquid becomes a solid.

Boiling

When a liquid changes into a gas at a constant temperature.

Kinetic energy

The type of energy that allows particles to move in the liquid state.

Melting

When a solid changes into a liquid.

Melting point and freezing point

There is no difference between the melting point and freezing point of a substance.

Condensation

When a gas changes into a liquid, usually on cooling.

Evaporation

When a liquid changes into a gas.

Melting point of pure water

0 oC.

Boiling point of pure water

100 oC.

Energy change in gas to liquid

Energy is released when a gas changes into a liquid.

Forces of attraction in phase change

When a solid turns to a liquid, the forces of attraction are overcome or broken.

True or False: Melting point and freezing point

True.

Evaporation

Evaporation occurs over a range of temperatures below the boiling point of a liquid.

Melting and Energy

During melting, particles absorb thermal energy which is converted into kinetic energy, allowing them to move more freely.

Surface Area and Evaporation Rate

The larger the surface area, the more quickly a liquid can evaporate.

Particle Movement in Solids

In solids, particles vibrate in position but cannot change location.

Particle Movement in Liquids

In liquids, particles move and slide past each other.

State of Matter with Highest Energy

The state of matter which has particles with the highest energy is gas.

(s) in Chemical Equation

(s) represents the solid state of a substance.

(g) in Chemical Equation

(g) represents the gaseous state of a substance.

(aq) in Chemical Equation

(aq) represents a substance being aqueous (dissolved in water).

Changes of State

Changes of state are physical changes that are reversible and do not change the chemical properties or makeup of the substances involved.

Deposition

Deposition is the change of a substance from a gas to a solid.

Sublimation

Sublimation is the change of a substance from a solid directly into a gas.

Absolute Zero

Absolute zero is the lowest possible temperature, equal to 0 K or -273.15 °C, at which atoms and molecules have zero kinetic and potential energy.

Particles at Same Temperature

Particles of different substances at the same temperature have the same average kinetic energy, but may have different velocities due to different masses.

Temperature and Kinetic Energy during Melting

During melting, temperature remains constant while energy is used to break bonds between particles, with no increase in kinetic energy.

Particle Movement and Temperature Increase

As temperature increases, particle movement increases, resulting in higher average kinetic energy.

300 K in Degrees Celsius

300 K in degrees Celsius is: 300 K - 273 = 27 °C.

Change in Temperature of K and °C

A change in temperature of 1 K is equal to a change of 1 °C.

50 °C in Kelvin

50 °C in Kelvin is 323 K.

Heating Curve Labels

From left to right, the labels should be solid, solid/liquid, liquid, liquid/gas and gas.

Change in Temperature during Change of State

There is no change in temperature during a change of state.