Week 2: Cell chemistry: atoms and their ions 2.1 Arranging electrons in atoms [4.6] 2.2 Valence electrons [4.7] 2.3 Electron dot structures [4.7] 2.4 The formation of ions [6.1] 2.5 Cations and anions [6.1] Readings: Chemistry Textbook. Timberlake (2015). Chemistry (12th edn.). Pearson Australia. LFS103 Vol. 2 Custom textbook Ch 4: Concepts 4.6, 4.7 Ch 6: Concept 6.1

Week 2: Learning objectives Describe for the first 20 elements of the periodic table; the Z value, the valance electrons, the electron configuration and the electron dot structures. Explain if an element is stable or reactive using its electron configuration. Understand how an ion is formed. Use the octet rule to write the symbols of the simple ions for the first 20 elements. Explain which elements form cations and which elements form anions, and why.

Some Important Ions in the Human Body 2.4 The formation of ions [6.1] Some Important Ions in the Human Body There are a number of ions in body fluids that have important metabolic and physiological functions: Na+ for regulation and control of body fluid balance, and nerve conduction. K+ for heart muscle function. Ca2+ as a major component of bones and essential for muscle contraction. Mg2+ for certain enzymes and for nerve control. Cl- in gastric juices. Table 6.3 (Timberlake, 2015)

2.4 The formation of ions [6.1] What is an Ion? An ion is an atom that is electrically charged as a result of the loss or gain of electrons.

2.4 The formation of ions [6.1] Why Do Atoms Form Ions? The noble gases are the most un-reactive of all of the elements because they are so stable. They have the most stable of all electron configurations. All of the noble gases (except helium) possess eight valence electrons, which is the most stable number possible.

2.4 The formation of ions [6.1] Shell 1 Helium (Z = 2) He 2e- 2 valence electrons Shell 2 Neon (Z = 10) Ne 2e- 8e- 8 valence electrons

2.4 The formation of ions [6.1] Why Do Atoms Form Ions? We learnt before that atoms are neutral; that is, they have no overall charge. However, atoms adjust their valence electrons so they obtain the same electron configuration as a noble gas (i.e. nice and stable). This is called the Octet Rule. Remember: He only has 2 valence electrons

Q. An ion has a different number of ______ compared to its number of electrons, and hence causes the atom to have an overall charge? Neutrons Photons Protons Quarks ANSWER: C (protons stay the same in any atom of a particular element, and since the protons carry the complementary charge