CCEA GCSE Chemistry 1.1 Atomic Structure Exam Questions

About CCEA GCSE Chemistry 1.1 Atomic Structure

Atomic Structure is the first topic of Unit 1 in CCEA GCSE Chemistry (Structures, Trends, Chemical Reactions, Quantitative Chemistry and Analysis). It explains how scientists' ideas about the atom changed over time and what atoms are made of. You need the relative mass, charge and position of protons, neutrons and electrons, how to work out their numbers from atomic and mass numbers, and how to write electronic configurations for the first 20 elements. Isotopes and relative atomic mass calculations are also included. Everything in bonding, the Periodic Table and quantitative chemistry depends on this topic. Examiners like questions on the alpha scattering evidence and relative atomic mass calculations.

What you need to know

• Atomic models Dalton described atoms as solid indivisible spheres. Thomson's plum pudding model had electrons in a sphere of positive charge. Rutherford's alpha scattering experiment showed most of the atom is empty space with a small, dense, positive nucleus. Bohr placed electrons in shells, and Chadwick discovered the neutron.
• Subatomic particles Proton: relative mass 1, charge +1, in the nucleus. Neutron: relative mass 1, charge 0, in the nucleus. Electron: relative mass 1/1840 (negligible), charge -1, in shells around the nucleus. Atoms are neutral because they have equal numbers of protons and electrons.
• Atomic and mass numbers Atomic number = number of protons. Mass number = protons + neutrons. Number of neutrons = mass number - atomic number.
• Electronic configuration Electrons fill shells in the order 2, 8, 8 for the first 20 elements, for example sodium is 2,8,1 and calcium is 2,8,8,2. The number of outer electrons matches the group number, and the number of shells matches the period.
• Isotopes Isotopes are atoms of the same element with the same atomic number but different mass numbers (different numbers of neutrons). They have the same chemical properties because they have the same electronic configuration.
• Relative atomic mass Relative atomic mass is the average mass of the atoms of an element relative to 1/12 of the mass of a carbon-12 atom, taking account of the abundance of each isotope. Ar = sum of (mass x abundance) / 100.

Common mistakes in 1.1 Atomic Structure

• Saying isotopes have different numbers of protons. They have the same number of protons but different numbers of neutrons.
• Giving the mass of an electron as 0. Its relative mass is about 1/1840, which is negligible but not zero.
• Forgetting to divide by 100 in relative atomic mass calculations, or rounding the answer when the question asks for one decimal place.
• Describing the alpha scattering results without linking each to a conclusion. Most passed through (atom is mostly empty space); a few were deflected (nucleus is positive); very few bounced back (nucleus is small and dense).
• Writing electronic configurations as 2,8,9 for potassium. The correct configuration is 2,8,8,1.

Try three 1.1 Atomic Structure exam-style questions