Zusammenfassung der Ressource
Atomic Weights
- Number of Protons = Number of Electrons
- Atomic Number = Number of Protons
- All atoms of a particular element have the same number of protons
- The atoms of different elements have different numbers of protons
- For example, all oxygen atoms have 8 protons and all sodium atoms have 11 protons
- Mass Number = Number of Atoms + Number of Neutrons
- The mass number of an atom is never smaller than the atomic number
- It can be the same but is usually bigger
- The full chemical symbol for an element shows its mass number at the top and its atomic number at the bottom
- This symbol tells us that the chlorine atom has 17 protons
- It will also have 17 electrons as this is as the number of electrons
- The total number of protons and neutrons is 35, so we can work out that there are 18 neutrons
- The electrons in an atom occupy energy levels, also known as shells.
- Each electron in an atom is found in a particular energy level. The lowest energy level (innermost shell) fills with electrons first.
- Each energy level can only hold a certain number of electrons before it becomes full.
- The first energy level can hold a maximum of two electrons, the second energy level a maximum of eight, and so on.
- The electronic structure of an atom is written using numbers to represent the electrons in each energy level.
- For example, for sodium this is 2,8,1 – showing that there are:
2 electrons in the first energy level
8 electrons in the second energy level
1 electron in the third energy level.