In this topic of IBDP Chemistry, we will be going back to the basics of chemistry. We will be discussing what elements are, the difference between compounds and mixtures, and the different states of matter.
In IBDP Chemistry, all substances are made up of elements. Elements are like the building blocks in chemistry. They cannot be broken down by any chemical process - they are already the most simple substances in chemistry.
- There are over 100 known elements - these are listed in the periodic table.
- Each element has a symbol associated with it, along with an atomic number (i.e. the number of protons) and the mass of one mole of each element.
- In your IBDP Chemistry exams, you will be given access to the periodic table in your data booklet, so you don't need to memorise it.
- The smallest part of an element is called an atom.
- The structure of the atom for each element is different - hence there are different chemical and physical properties associated with each element.
Compounds and Mixtures
Compounds are a type of substance where there are more than one element chemically combined in a fixed ratio.
- Compounds can be broken down into its component elements by chemical processes.
- The chemical and physical properties of compounds are different from their component elements.
- An example of a compound would be water (H2O).
- It is a compound because it can be broken down into its component elements (hydrogen and oxygen) by chemical processes.
- Not only that, but each molecule of water consists of a fixed ratio of hydrogen to oxygen - two atoms of hydrogen to one atom of oxygen.
Mixtures are a type of substance where elements/compounds are combined together, but are not chemically bonded.
- Since the compounds/elements in a mixture are not chemically combined, the component of the mixture retain their individual chemical and physical properties.
- There are two types of mixtures - homogenous and heterogenous mixtures.
- Homogenous mixtures are when the components of the mixture are in the same phase - it is harder for one to separate the components of the mixture.
- An example of homogenous mixture is air. The air surrounding us consist of different substances, including oxygen, nitrogen, carbon dioxide etc. However, they all exist in the same phase, and they cannot be easily separated.
- Heterogenous mixtures are when the componenets of the mixture are not in the same phase - they can easily be separated, and there is a physical boundary between the components.
- An example of heterogenous mixtures is sand and water.
- Heterogenous mixtures can also be in the same state - an example of this would be oil and water.
States of Matter
- Solids have a fixed shape and volume.
- Particles in a solid state are held together by intermolecular forces in a fixed position.
- Particles vibrate around a fixed point, but they are unable to move around freely.
- As heat is applied to a solid, at a certain temperature, the vibration of the particles will be able to overcome the intermolecular forces which hold them together - in this case, the solid melts.
- Liquids have a fixed volume, but do not have a fixed shape - instead, they take up the shape of the container which they are held in.
- Particles are held together by intermolecular forces, but they also have translational velocity (i.e. the ability to move around) - this enables diffusion to occur.
- Diffusion of liquids is when the liquids move from a region of high concentration to low concentration.
- This can be seen by placing a piece of paper into water - you can observe how the water spreads from the point of contact to the rest of the paper.
- As heat is applied to the liquid, the particles move faster. Some will move faster than others, and escape from the surface of the liquid and form a vapour (a gaseous substance).
- Once the pressure of the vapour is equal to the pressure above the liquid, the liquid boils.
- Particles of gaseous substances are widely spaced and completely fill the container.
- Particles move with rapid and random motion, allowing diffusion to occur.
- Pressure is created when the gaseous particles collide with the walls of the container.
- The intermolecular forces between particles are negligible.
- The volume of the individual gas molecules themselves are negligible compared to the total volume of gas.
This is the end of this topic.