1. Chemical Bonding

2. Basic Atom Information Atoms are neutral Atoms are the smallest particles of an element Elements are arranged on the table by increasing atomic number The atomic number tells you the proton number The mass number tells you the number of protons and neutrons

3. Basic Information (continued) The group number tells you the number of valence electrons The period number tells you the number of energy levels Group 1 is the most reactive group on the periodic table Group 17 is the most reactive non-metal on the periodic table

4. Ionic Bonding Occurs when electrons are transferred from one atom to another, forming two ions The ions stay together because of electrostatic attractions (opposites attract) Ionic bonds NEVER form molecules The metal becomes a cation because it loses valence electrons. The non-metal becomes an anion because it gains valence electrons.

5. The Octet Rule Atoms tend to gain, share, or lose valence electrons in order to obtain a full set of valence electrons (in most cases this equals 8) Exceptions: Those elements where energy level 1 is the outermost energy level

6. Example Na + ClNa+Cl + -

7. Properties of Ionic Compounds Ionic compounds do not form molecules; they form a crystal lattice, which is an alternating arrangement of cations and anions The green spheres are Na + and the red spheres are Cl -

8. This is a crystal of CaCl 2. Each ion is held rigidly in place by strong electrostatic forces that bond it to several oppositely charged ions. The crystal lattice is what gives ionic compounds most of their properties.

9. Other Ionic Properties Normally form between metals and nonmetals, usually forms a salt Ionic compounds have ions that form very strong bonds, which makes them hard and brittle They have high melting points and high boiling points When dissolved in water, the solution will conduct electricity

10. Names of Charged Particles When electrons are lost, the ion has an overall positive charge and is called a cation Examples: Na +, Ca 2+ When electrons are gained, the ion has an overall negative charge and is called an anion Examples: F -, S 2- The anion will attract the cation and form a bond. The anion takes on the ending –ide example: Sodium Fluoride NaF All ionic compounds are electrically neutral

11. Ionic Compounds Writing formulas for binary ionic compounds  Compounds composed of two elements are called binary compounds When the formula is written, the charge of the cation must be balanced by the charge of the anion The overall charge of the ion combination must be zero The cation is always written first in the formula

12. How to Determine the Charge on an Ion An atom is neutral because the proton number equals the electron number Ions are not neutral. If an ion has more electrons than protons, it is negative (anion) If an ion has more protons than electrons it is positive (cation)

13. Example of How to Determine the Charge on an Ion Mg has 12 protons (+) and 12 total electrons (-). Mg has 2 valence electrons. If it gives them away it now has 12 protons (+) and 10 electrons (-). There are 2 more positive charges than negative charges so the charge on the Mg ion is +2.

14. Example of How to Determine the Charge on an Ion N has 7 protons (+) and 7 total electrons (-). N has 5 valence electrons. It is a non- metal. It will not give these valence electrons away because the energy of ionization is too high. N will share with another non-metal or take from a metal. If it takes 3 from a metal it will now have 7 protons (+) and 10 electrons (-). There are now 3 more negative charges so the charge on the N ion is -3.

15. Energy of Ionization For a metal to lose an electron and become a cation energy is required. The more electrons it needs to lose the greater the amount of energy required. Whenever an electron is accepted by its new atom, forming an anion, energy is released. If the energy released is greater than the energy needed to take the electron, the ionic bond easily forms.

16. Covalent Bonding Covalent bonds form between non-metals that are very reluctant to give away their valence electrons Most reactive non-metals have 5, 6, or 7 valence electrons (there are some with 4) Too much ionization energy is required to remove these valence elctrons from the non-metals

17. Molecules Covalently bonded substances contain molecules. Molecules are particles that contain 2 or more covalently bonded atoms. These atoms may be alike or different.

18. Properties of Covalently Bonded Substances Low boiling/melting point Soluble, but not in water Since they do not form ions in water, covalent substances do NOT conduct electricity Examples: carbon dioxide, carbon monoxide

19. Diatomic Elements There are 7 elements that when found pure in nature will always be covalently bonded to another one of themselves. This covalent bond results in the formation of a molecule. Diatomic elements: H, O, N, F, Cl, Br, I Examples of diatomic molecules: H 2 Cl 2

20. Electron Dot Diagrams The dots around each element symbol represent the valence electrons for that element.

21. Electron Dot Diagrams Showing Covalent Bonds

22. Electron Dot Diagram Showing an Ionic Bond