NJC Atomic Structure stud 2023

National Junior College SH1 H2 Chemistry 1 ATOMIC STRUCTURE Content: • The nucleus of the atom: neutrons and protons, isotopes, proton and nucleon numbers • Electrons: electronic energy levels, ionisation energies, atomic orbitals, extranuclear structure (empty space around the nucleus where electrons can be found) Learning Outcomes required for H1 (8873) & H2 (9729) Chemistry: Students should be able to: (a) identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses (b) deduce the behaviour of beams of protons, neutrons and electrons in an electric field (c) describe the distribution of mass and charges within an atom (d) deduce the numbers of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge) (e) describe the contribution of protons and neutrons to atomic nuclei in terms of proton number and nucleon number (f) describe the number and relative energies of the s, p and d orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p orbitals (g) describe the shapes of s, p and d orbitals [knowledge of wave functions is not required] (h) state the electronic configuration of atoms and ions given the proton number (and charge) (i) explain the factors influencing the ionisation energies of elements (j) deduce the electronic configurations of elements from successive ionisation energy data (k) interpret successive ionisation energy data of an element in terms of the position of that element within the Periodic Table All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the copyright owner. Copyright © 2023 National Junior College

National Junior College SH1 H2 Chemistry 2 1. INTRODUCTION The interactions between the valence electrons of 2 or more atoms lead to chemical combinations between them. Hence the chemical properties of an element are largely determined by the number of valence electrons each of its atoms possesses. The study of the electronic structure of atoms, i.e. the detaile d arrangement of electrons of an atom, is therefore of fundamental importance in the understanding of chemical behaviors of elements. Success criteria: • Identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses. • Define nucleon number (mass number) and proton number (atomic number). • Deduce the numbers of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge). Note: As the mass of electron is insignificant compared to mass of p & n. Nucleon number = mass number Note: Atoms are electrically neutral (no. of p = no. of e─) Loss of e─ gives rise to cation (no. of p > no of e─ ) Gain of e─ gives rise to anion (no. of e─ > no of p) 1.1 What are sub-atomic particles? Atoms are made up of 3 types of particles (known as sub-atomic particles). Sub-atomic Particle Relative charge Relative mass proton (p) +1 1 neutron (n) 0 1 electron (e─ ) –1 1/1840 1.2 Proton Number and nucleon Number Nucleon number (mass number) • total number of protons and neutrons in an atom Proton number (atomic number) • number of protons in an atom • determines the chemical identity of an atom. • indicates the number of electrons in an electrically neutral atom Collectively known as 'nucleons'. lC35 17 Chlorine-35

National Junior College SH1 H2 Chemistry 3 Note: When referring to a particular isotope, the nucleon number and the proton number must be indicated. e.g. if we want to refer to deuterium, we should write 𝐻1 2 for clarity. Success criteria: • Recognise that only the proton number determines the chemical identity of an atom. 1.3 Isotopes Atoms of the same element do not all have the same mass. Isotopes are atoms of the same element that have the same proton number but different nucleon number (different number of neutrons). Isotopes of an element have the same electronic configuration and chemical properties. They have different relative isotopic masses and physical properties. Checkpoint 1 1 State the number of protons, electrons and neutrons for the following particles: Particles Nucleon number No. of protons No. of neutrons No. of electrons P31 15 +240 20Ca −232 16 S Generally, except for 𝑯𝟏 𝟏 , number of neutrons  number of protons for other elements. 2 Which of the ions has more electrons than protons and more protons than neutrons? [Given: H]DO,H,He, 2 1 16 8 1 1 4 2 = A He+ B OH− C D3O+ D OD−

National Junior College SH1 H2 Chemistry 4 3 Oxygen has two isotopes, 16O and 18O. An oxide ion, −yxO8 has the same number of neutrons and electrons. What could be the values of x and y? x y A 16 1 B 16 2 C 18 1 D 18 2 4 In 1999 Russian chemists claimed to be the first to identify atoms of a new element of proton number 114. This was produced by bombarding atoms of plutonium, Pu, with the atoms of an isotope of a group 2 element, X. The reaction taking place is as shown below. 𝑃𝑢 + 𝑿 → [𝑛𝑒𝑤 𝑒𝑙𝑒𝑚𝑒𝑛𝑡] + 3 𝑛𝑒𝑢𝑡𝑟𝑜𝑛𝑠 ( 𝑛0 1 )𝟏𝟏𝟒 𝟐𝟖𝟗 94 244 What is X? A Mg B Ca C Sr D Ba [N03/1/4]

National Junior College SH1 H2 Chemistry 5 Note: e─ is deflected to a greater extent than p because of its much smaller mass. Success criteria: • Able to deduce the direction of subatomic particles (protons, neutrons and electrons) and charged particles in an electric field. • Able to compare the angle of deflection by considering their 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑎𝑠𝑠 ratio. 1.4 Effect of an electric field on protons, neutrons and electrons Protons and electrons, being charged particles, are deflected by an electric field. The angle of deflection, θ, is proportional to the charge mass ratio of the particles. Angle of deflection in an electric field depends on: • charge of particle: The greater the charge, the greater the extent of deflection. • mass of particle: The greater the mass, the smaller the extent of deflection. angle of deflection ∝ charge mass Worked Example 1 A sample of the element Americium (Am) was vaporised, ionised and passed through an electric field. It was observed that a beam of 241Am+ particles gave an angle of deflection of +2. Assuming an identical set of experimental conditions, by what angle would a beam of 32S− particles be deflected? θ = k × charge mass For 241Am+ , +2 = k × +1 241 k = 482 For 32S–, angle of deflection of 32S– = 481 × -1 32 = –15.1 Note: Ions are attracted to the oppositely charged plate and the angle has to be indicated as + or – relative to the reference line. e− n p θ + Source e−, n, p − α  > α _ + ⬚𝟐𝟒𝟏𝑨𝒎+ +𝟐𝒐 −

National Junior College SH1 H2 Chemistry 6 Success criteria: • Able to define terms relative atomic mass and relative isotopic mass. • Able to calculate the relative atomic mass of an element given the relative abundances of each isotope. 2 Quantifying the masses of atoms In section 1, we have looked at the composition of the atom. While the protons, neutrons and electrons have masses, they are so small that it is impossible to