S1.4 Counting particles by mass: The mole

• The mole (mol) is the SI unit of amount of substance. One mole contains exactly the number of elementary entities given by the Avogadro constant.

• Masses of atoms are compared on a scale relative to 12C and are expressed as relative atomic mass Ar and relative formula mass Mr .

• Molar mass M has the units g mol–1

• The empirical formula of a compound gives the simplest ratio of atoms of each element in the compound. The molecular formula gives the actual number of atoms of each element present in a molecule

• The molar concentration is determined by the amount of solute and the volume of solution.

• Avogadro’s law states that equal volumes of all gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

Inquiry 2—In the study of emission spectra from gaseous elements and of light, what qualitative and quantitative data can be collected from instruments such as gas discharge tubes and prisms?

Nature of science, Structure 1.2—How do emission spectra provide evidence for the existence of different elements?

Structure 3.1—How does an element’s highest main energy level relate to its period number in the periodic table?

Structure 3.1—What is the relationship between energy sublevels and the block nature of the periodic table?

(AHL) Structure 3.1—How does the trend in IE values across a period and down a group explain the trends in properties of metals and non-metals?

(AHL) Nature of science, Tool 3, Reactivity 3.1—Why are log scales useful when discussing [H+] and IEs?

(AHL) Structure 3.1—How do patterns of successive IEs of transition elements help to explain the variable oxidation states of these elements?