This question is about elements in the periodic table - AQA - GCSE Chemistry Combined Science - Question 4 - 2019 - Paper 1

Mendeleev left gaps in his periodic table to accommodate undiscovered elements, allowing for a more accurate reflection of the periodic trends.

The boiling points of the elements in Table 2 are low due to the weak intermolecular forces acting between their molecules. These weak forces require little energy to overcome, resulting in low boiling points.

In Table 2, as one moves down the group from fluorine to bromine, the boiling points increase. This increase is primarily due to the larger molecular size and the increase in the strength of intermolecular forces, requiring more energy to overcome them.

Neon is unreactive because it has a full outer shell of electrons, which makes it stable and unlikely to form bonds with other elements. Its electronic structure is 1s² 2s² 2p⁶.

To determine the number of atoms in 1 g of argon, we use the formula:

Number of moles = mass (g) / molar mass (g/mol)

Since the relative atomic mass of argon (Ar) is 40 g/mol, the number of moles in 1 g of argon is:

Number of moles = 1 g / 40 g/mol = 0.025 moles.

Using Avogadro's constant:

Number of atoms = number of moles × Avogadro's constant

Number of atoms = 0.025 moles × 6.02 × 10²³/mol ≈ 1.51 × 10²² atoms.