1:14 know what is meant by the terms atom and molecule
Atom: An atom is the smallest part of an element.
Molecule: A molecule is made of a fixed number of atoms covalently bonded together.
1:15 know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles
An atom consists of a central nucleus, composed of protons and neutrons.
This is surrounded by electrons, orbiting in shells (energy levels).
Atoms are neutral because the numbers of electrons and protons are equal.
| Mass | Charge | |
|---|---|---|
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | negligible (1/1836) | -1 |
1:16 know what is meant by the terms atomic number, mass number, isotopes and relative atomic mass (Aᵣ)
Atomic number: The number of protons in an atom.
Mass number: The number of protons and neutrons in an atom.
Isotopes: Atoms of the same element (same number of protons) but with a different number of neutrons.
Relative atomic mass (Ar): The average mass of an atom compared to 1/12th the mass of carbon-12.
1:17 be able to calculate the relative atomic mass of an element (Aᵣ) from isotopic abundances
75% of chlorine atoms are the type 35Cl (have a mass number of 35)
25% of chlorine atoms are of the type 37Cl (have a mass number of 37)
In order to calculate the relative atomic mass (Ar) of chlorine, the following steps are used:
- Multiply the mass of each isotope by its relative abundance
- Add those together
- Divide by the sum of the relative abundances (normally 100)
![\[ A_r = \frac{( (35 \times 75) + (37 \times 25) )}{100} \]](https://www.tutormyself.com/wp-content/ql-cache/quicklatex.com-0113f8af79de4c65c49213ff5f0f1314_l3.png "Rendered by QuickLaTeX.com")
![\[ A_r = 35.5 \]](https://www.tutormyself.com/wp-content/ql-cache/quicklatex.com-01950bf9b03b8605a6a2508f3e0a27ea_l3.png "Rendered by QuickLaTeX.com")
Example question:
A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%.
Calculate the relative atomic mass (Ar) of bromine.
![\[ A_r = \frac{( (79 \times 50.7) + (81 \times 49.3) )}{100} \]](https://www.tutormyself.com/wp-content/ql-cache/quicklatex.com-070b5d40d7a43c6544b0e3bdc25ecfcd_l3.png "Rendered by QuickLaTeX.com")
![\[ A_r = 79.99 \]](https://www.tutormyself.com/wp-content/ql-cache/quicklatex.com-9d467cc4bda5e7b370a0c2f489469759_l3.png "Rendered by QuickLaTeX.com")