Week 2 Cell chemistry: atoms, elements and their ions Dr Nicole Masters Introductory Bioscience, LFS103

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.

Atoms Subatomic Particles 2.1 Arranging electrons in atoms [4.6] Atoms Subatomic Particles Today we are going to talk about how the tiny electrons are organised in the electron cloud. This is called electron arrangement of atoms. We will study the first 20 elements (H to Ca)

Electron Arrangement in Atoms 2.1 Arranging electrons in atoms [4.6] Electron Arrangement in Atoms Every electron has a specific amount of energy. Electrons of similar energy are grouped in an energy level called a shell. The shells closest to the nucleus contain electrons with lowest energy. There are 7 shells that can orbit the nucleus We will study up to 4 shells

Electron Arrangement in Atoms 2.1 Arranging electrons in atoms [4.6] Electron Arrangement in Atoms Capacity of the first four electron shells. Electron Maximum Number Shell of Electrons 1 2 2 8 3 18 4 32 Increasing in energy levels Note: This is how many electrons each shell can hold in total, not the order in which the electrons are filled into the shells.

Electron Arrangement in Atoms The First Twenty Elements 2.1 Arranging electrons in atoms [4.6] Electron Arrangement in Atoms The First Twenty Elements There is a specific order for filling electrons into the shells of the first twenty (20) elements (Table 3.9). • Fill 2 electrons into shell 1 • Fill 8 electrons into shell 2 • Fill 8 electrons into shell 3 • Fill 2 electrons into shell 4 The electron order you need to remember is: 2 8 8 2

2.1 Arranging electrons in atoms [4.6] Shell 1 Hydrogen (Z = 1) H 1e- Hydrogen has 1 electron The first shell fills first it has a capacity for 2 electrons Hydrogen only has 1 shell, this is the outermost shell This means that in this form hydrogen is unstable i.e. reactive The outer most shell is where the chemistry takes place

2.1 Arranging electrons in atoms [4.6] Helium has 2 electrons The first shell fills first it has a capacity for 2 electrons Helium has 2 electrons in its shell, this is the outermost shell This means that this shell is now full. Full shells are very stable and un-reactive Helium is a noble gas and that is why noble gases very stable Shell 1 Helium (Z = 2) He 2e-

2.1 Arranging electrons in atoms [4.6] Helium has 2 electrons The first shell fills first it has a capacity for 2 electrons Helium has 2 electrons in its shell, this is the outermost shell This means that this shell is now full. Full shells are very stable and un-reactive Helium is a noble gas and that is why noble gases very stable Shell 1 Helium (Z = 2) He 2e-