Chemical Bonding September 4, 2015

What do we already know? Where are protons? Neutrons? Electrons? What is an electron shell? How many electrons fill the first shell? How many electrons fill the second? Fifth? What is a valence shell? What is a valence electron? How many valence electrons do Group 1 elements have? Group 5? Group 17?

Do we know more…? Which group is considered to be ‘inert’? Why? Which group gives up an electron most readily? Which group gains an electron most readily? What is the name given to an atom which has given up an electron? Gained? How many valence electrons remain when sodium gives an electron?

Octet Rule An element’s valence shell is full and stable when it contains 8 electrons. This stability is the reason the Noble Gases are so inert. Atoms of elements tend to combine in such a way that they each have 8 valence electrons. This gives them the same configuration as a noble gas.

Chemical Energy This is the potential energy resulting from the electrical attractions and repulsions that occur within atoms, molecules, and ions. When particles rearrange and form bonds some of this energy is transformed into heat, light or motion. (lost to surroundings) Reactions between atoms generally result in the formation of bonds that lower the overall chemical energy of participating atoms.

Chemical Energy Potential energy – from electrical attractions and repulsions Ionization energy – the energy required to remove electrons from their atoms High electron affinity – large amounts of potential energy are released when electrons are obtained by neutral atoms Lattice energy – lowering of the potential energy when ions form crystal structures

Ionic Bonding These bonds are the result of the forces of attraction between positive and negative ions. Metals in Groups 1, 2, and 3 tend to form ionic bonds with non-metals in Groups 16 and 17. Groups 1 and 2 require less energy to remove electrons from their atoms (ionization energy)  cations Groups 16 and 17 have a high affinity for electrons, releasing a large amount of energy when electrons are obtained  anions

Ionic Bonding Ionic Bonding Animation 1 Ionic Bonding Animation 2 Summarize what you see happening in the animations between sodium and chloride atoms.

Covalent Bonding This is also known as ‘electron sharing.’ Covalent bonds occur between atoms when electron transfer is too energetically “expensive.” Shared electrons attract the positive nuclei of the atoms involved which leads to a lowering of potential energy as the covalent bond forms.

Covalent Bonding Electrons have lower energy in pairs. Electrons generally become paired in single, double, and triple covalent bonds (the sharing of 1, 2, or 3 electron pairs) between atoms. Elements in Groups 14, 15, and 16 often participate in this form of bonding.

Covalent Bonding Covalent Bonding Animation 1 Covalent Bonding Animation 2 Summarize what you see happening in the animation between hydrogen and oxygen atoms.

Remember… Even though there are different ways in which atoms bond, all atoms bond for the same reason – to lower their overall energy and become more stable.