Chemical Science: Atomic Structure and Mixtures

Study Notes

All substances are made of atoms that cannot be broken down by chemical reactions.
Elements are made of only one type of atom.
Compounds contain more than one type of atom.
Mixtures contain two or more elements or compounds not chemically bonded.
Chemical reactions involve the formation of one or more new substances; they usually involve an energy change.
Components of a compound cannot be separated by physical means; they can only be separated by chemical means.

A mixture consists of two or more elements or compounds not chemically combined.
The chemical properties of each substance in the mixture are unchanged.
Mixtures can be separated by physical processes, including filtration, crystallisation, simple distillation, fractional distillation and chromatography.

Dalton's atomic theory proposed atoms were tiny spheres that could not be divided.
Thomson's plum pudding model described atoms as spheres of positive charge with negative charges spread throughout.
Rutherford's experiment with alpha particles and gold foil led to the nuclear model of the atom, with a positively charged nucleus and negatively charged electrons orbiting the nucleus.
Bohr's model refined Rutherford's model, proposing electrons orbit the nucleus in specific energy levels or shells.
Later experiments revealed that the nucleus could be subdivided further, leading to the discovery of neutrons.
Atoms are very small, with a radius of about 0.1nm (1 x 10⁻¹⁰ m).
Protons and neutrons are found in the nucleus and electrons orbit the nucleus in shells.
The first shell can hold 2 electrons, the second can hold 8, and the third can hold 8.
Atoms sometimes lose or gain electrons to form ions, which have a charge different to their original state.

Atoms of the same element can have different numbers of neutrons and are called isotopes.
Isotopes have the same chemical properties but different physical properties like density.
The average relative atomic mass of an element takes into account the abundance of the isotopes.
The relative atomic mass is calculated using the following equation: ( (% of isotope 1 x mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100 )

The periodic table arranges elements in order of increasing atomic number.
The rows are called periods and the columns are called groups.
Elements within the same groups have similar chemical properties.
Elements in the same period have the same number of electron shells.
Metals are located on the left and bottom of the periodic table.
Non-metals are located on the right and top of the periodic table; they do not form positive ions.

Transition metals are located between Group 2 and Group 3.
Transition metals have high melting points, boiling points, and densities.
Transition metals are good conductors of heat and electricity.
Transition metals are strong and malleable.
Many transition metals are used as catalysts, playing a role in speeding up chemical reactions.
Copper is a transition metal used in plumbing due to its high melting point, its ability to conduct heat, its strength and malleability, and its inertness to water.