Matter and Mass💥
- Atoms are the smallest building blocks of elements. They are made from three types of subatomic particle: protons, neutrons and electrons.
- Protons and neutrons are held together tightly in a tiny space in the centre of the atom called the nucleus. Electrons move around in a large area surrounding the nucleus.
- Protons have a positive charge. Electrons have a negative charge. Neutrons are neutral (they have no charge). This makes it easier to remember. NEUtrons are NEUtral.
- There is the same amount of positive protons as negative electrons. This means that an atom has no overall charge.
- Elements are made from only one type of atom. Different elements have different numbers of protons in the nucleus.
- The mass of a proton is 1 atomic mass unit.The mass of the other particles are compared to this.
The Periodic Table🧐
- In 1869, Dmitri Mendeleev arranged the elements known at that time into a table in order of increasing atomic mass. He put elements with similar properties underneath each other.
- Mendeleev left gaps in the table to make the elements fit the pattern. He correctly predicted that new elements would be discovered to fill the gaps. He was able to predict the properties of these elements by looking at the properties of the elements around them.
- The modern periodic table shows each element like this:
- Elements appear in order of their atomic number. Elements in the same group (columns) have similar properties.
- Non-metal elements are at the top right. All the other elements are metals.
- All atoms of the same element have the same number of protons in their nucleus.
- Isotopes are atoms of the same element with different numbers of neutrons in their nucleus. This is a common question in I/GCSE Chemistry. They have the same amount of protons and electrons, and the same chemical properties, but a different mass.
- Hydrogen has three isotopes: 3H, 2H, 1H.
- Relative Atomic Mass is the average mass of an atom of the element, taking into account the number and abundance (percentage) of all the different isotopes.
- Because of the existance of isotopes, not all relative atomic masses are whole numbers.
Drafted by Catrina (Chemistry)