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.

2.2 Valence electrons [4.7] Valence Electrons The electrons in the outer shell have an important role in determining the chemical properties of an atom. These electrons are referred to as valence electrons.

Hydrogen (Z = 1) Helium (Z = 2) Shell 1 H 1e- 1 valence electron 2.2 Valence electrons [4.7] Shell 1 Hydrogen (Z = 1) H 1e- 1 valence electron Shell 1 Helium (Z = 2) He 2e- 2 valence electrons

Lithium (Z = 3) Shell 2 Li 2e- 1e- 1 valence electron 2.2 Valence electrons [4.7] Shell 2 Lithium (Z = 3) Li 2e- 1e- 1 valence electron Lithium has 3 electrons The first shell fills first it has a capacity for 2 electrons The third electron is placed in the second shell, this is the outermost shell This second shell has the capacity for 8 electrons This means that in this form lithium is unstable ie reactive The outer most shell is where the chemistry takes place

Boron (Z = 5) Boron has 5 electrons 2.2 Valence electrons [4.7] Boron has 5 electrons The first shell fills first it has a capacity for 2 electrons The fourth and fifth electrons are placed in the second shell, this is the outermost shell This second shell has the capacity for 8 electrons This means that in this form boron is unstable i.e. reactive The outer most shell is where the chemistry takes place Shell 2 Boron (Z = 5) B 2e- 3e- 3 valence electrons

Neon (Z = 10) Neon has 10 electrons 2.2 Valence electrons [4.7] Neon has 10 electrons The first shell fills first it has a capacity for 2 electrons Neon has 2 electrons in this shell, This means that this shell is now full. The second shell has the capacity for 8 electrons, this shell is full also Full shells are very stable and un-reactive Neon is a noble gas and that is why noble gases very stable Shell 2 Neon (Z = 10) Ne 2e- 8e- 8 valence electrons

Sodium (Z = 11) 1 valence electron Shell 3 Na 2e- 8e- 1e-

2.2 Valence electrons [4.7] Calcium (Z = 20) Remember shell 3 has the capacity to hold 18 electrons 2 valence electrons Shell 4 Ca 2e- 8e- 8e- 2e- Electron configuration? 2,8,8,2

Electron Arrangement in Atoms The First Twenty Elements 2.2 Valence electrons [4.7] Electron Arrangement in Atoms The First Twenty Elements A couple of points to note: notice that elements in the same Group of the Periodic Table have the same number of valence electrons. They also have similar chemical properties. you can use the old system for numbering the Groups in the Periodic Table (1A, 2A, 3A ….. ) to easily work out the number of valence electrons for the first 20 elements.

Write the electron configuration for Fluorine

Q. Which group of elements on the Periodic Table have 2 valence electrons? Alkali metal Alkali earth metal Halogen Nobel gas ANSWER: Group 2A: alkali earth metals