Learn

10

Physical Properties

Beginner
2
m

Physical properties of a substance are a way of measuring different features of that element or compound and classifying them.

All elements have differing physical properties. Some of these physical properties are appearance, melting point, boiling point, density, solubility and texture.


Melting Point


The melting point of a substance is the point at which it will change from a solid to a liquid in state. It is also defined as the freezing point because at exactly this point a liquid will turn into a solid. Melting points are often measured in degrees C but can also be given in Fahrenheit. The universally measured unit used is Kelvin, with 0 Kelvin being what we define as absolute zero.


When a solid melts thermal energy is applied and the solid state which is ordered and regularly arranged breaks down as the bonds and forces between the atoms are overpowered. Melting points are often used to determine the purity of a substance. For example the melting point of ice is 0 degrees however when salt is added it will decrease the melting point due to the impurity added.


Metals for example are very strong because of their bonds and have high melting and boiling points. This is compared to non metals which have low melting and boiling points and tend to exist as gases and liquids. If we look at a metal such as titanium this has a melting point of 1668c compared to bromine which has a melting point of -7.2c. So at room temperature which is 25c titanium will be a solid and bromine will be a brown liquid as it requires less energy to turn it into a liquid and gas than metals like titanium do.


Boiling point


The boiling point of a substance is the point on a temperature scale when a liquid will turn into a gas. Boiling point and evaporation are two processes that occur. However evaporation can occur at the surface of a liquid at most temperatures as particles overcome the forces between the atoms in the liquid. When heat is applied the liquid particles which are already free moving begin to move more due to their kinetic energy. The gas particles eventually have enough energy to overcome the forces holding them in the liquid and they are released. When they are released they will form a gas spreading out and moving freely. For example when water is boiled its boiling point of pure water is 100c, but before this temperature some particles will leave the surface as the particles have energy to overcome the forces holding them in the liquid.


Whilst most substances will turn from a liquid to a gas some solids may also instantly turn into a gas, this is known as sublimation. Iodine and solid carbon dioxide are good examples where the solid particles at room temperature will begin to evaporate and create a gas.

Terms in section
Melting point

Melting point is the temperature at which a solid turns into a liquid. The temperature when atoms have enough energy to over come their bonds and turn into a liquid.

Degrees

Degrees celsius is a scale for measuring temperature devised by Swedish scientist Anders Celsius. He based 0c on the freezing point of water and 100c as the boiling point of water.

Fahrenheit

Fahrenheit is a scale for measuring temperature devised in 1724 by German scientist Daniel Fahrenheit which placed 0F as the temperature at which a brine solution ( a solution of water, ice and salt) freezes

Kelvin

Kelvin is a scale for measuring temperature commonly used in chemistry due to its use all around the world. It was devised by William Kelvin, a Scottish engineer. The scale uses absolute zero as its starting point.

Absolute Zero

Absolute zero is the temperature measured in kelvin, a temperature where in theory atoms will have no kinetic energy

Room temperature

Room temperature is the temperature recorded when a thermometer is left in a room usually around 22-25 degrees

Sublimation

Sublimation is when a solid turns directly into a gas

Evaporation

Evaporation is when a liquid turns into a gas

Previous

State Changes of Elements

2
m
Next

Chemical Properties

1
m