[CHEM] Chapter 2.2 - Atomic Structure

1 DARRELL ER (COPYRIGHTED) TOPIC 2.2: ATOMIC STRUCTURE DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Relatively straight forward chapter • 2 key concepts • 1 advanced concept • Usually tested in MCQs or Section A • Tested as add-on to other chapters 🡪 Chemical Bonding, Periodic Table • Light overall weightage • Constitute to 1% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 BASICS BASICS DARRELL ER (COPYRIGHTED) © Subatomic particle Charge Relative mass Symbol Location Proton +1 1 p Nucleus Neutron 0 1 n Nucleus Electron -1 1 / 1836 (negligible mass) e Electron shell

4 BASICS BASICS Must know: 2,8,8 electronic configuration *For elements after calcium, the third shell is able to hold a maximum of 18 electrons.  transition metals DARRELL ER (COPYRIGHTED) © First shell: Maximum of 2 electrons Second shell: Maximum of 8 electrons Third shell: Maximum of 8 electrons Ar atom: 18- protons 22 - neutrons

5 BASICS BASICS Proton number: The total number of protons in an atom (number of electrons as well) Nucleon number: The total number of protons and neutrons in the nucleus of an atom Identity of an element is dependent on its proton number, not its nucleon number.  To review later: Isotopes DARRELL ER (COPYRIGHTED) © Proton number / atomic number Ca 40 20 Nucleon number (protons + neutrons) Symbol of element

6 FORMATION OF POSITIVE IONS When atoms that lose electrons, there are now more protons than electrons, hence they become positively charged. They would become a cation. The sodium atom achieves a stable electronic configuration by losing one electron. It becomes a sodium cation with a charge of +1 and is written as Na+. ‘plus’ sign DARRELL ER (COPYRIGHTED) ©

7 FORMATION OF NEGATIVE IONS When atoms gain electrons, there are more electrons than protons now, they become negative ions, called an anion. The chlorine atom fully completes its valence shell by gaining one electron. It is now a chlorine anion with a charge of -1 and is also written as Cl-. Negative DARRELL ER (COPYRIGHTED) ©

8 ELECTRICALLY NEUTRAL  ATOM ELECTRICALLY STABLE  ION CHEMICALLY STABLE  COMPOUND Let’s explore the WHY. We will explore why atoms turn into ions and subsequently into compounds. WHY DARRELL ER (COPYRIGHTED) ©

9 ATOM ELECTRICALLY NEUTRAL protons = electrons ION IONIC FORM octet structure COMPOUND CHEMICALLY STABLE Ionic bond formation WHY Electrically neutral = normal person But everyone wants to be attractive, especially to an opposite gender. Turn into an ion and seeking a partner. The end goal is to be in a relationship=) Compound. DARRELL ER (COPYRIGHTED) ©

10 ISOTOPES SAME NUMBER OF PROTONS DIFFERENT NUMBER OF NEUTRONS Let’s delve deeper into the understanding of isotopes, a common killer question at ‘O’ levels. KEY CONCEPT DARRELL ER (COPY