1. Forming Chemical Bonds

2. Compounds Remember compounds are two or more different elements that combine chemically – Can be broken down by chemical means – Have properties different from those of its component element – Thousands of compounds exist

3. Chemical Bonds A chemical bond is a force that holds two atoms together Chemical bonds usually only involve valence electrons

4. Chemical Bonds Ionic bonds Covalent bonds Share electrons transfer electrons

5. Valence Electrons Valence electrons are electrons in the highest occupied s and p energy level. The number of valence electrons largely determines the chemical properties of an element. To find the number of valence electrons in a representative (group A) element, simply look at its group number.

6. Diagrams that show valence electrons as dots Lewis dot diagram

7. Why do elements react? Noble Gases typically do not react and are chemically stable because they have eight valence electrons called an octet Elements tend to react in order to acquire a full octet or “eight is great” (gain stability) Octet rule –when forming compounds, atoms tend to achieve the stable electron configuration of a noble gas

8. Formation of Positive Ions-Cations A cation is an atom or group of atoms with a positive charge because of a loss of valence electrons. Ca “+” ion Metals only form cations Reactivity of metals is based on the ease in which they lose a valence electron to achieve a stable octet. Brainiac Alkali Metals Video

9. Electron Configuration of Positive Ions-Cations All of the above metal ions have electron configurations of the noble gas neon, Ne. 8 is great! Na atomNa1s 2 2s 2 2p 6 3s 1 Na ion (lost 1 electron)Na + 1s 2 2s 2 2p 6 Mg atomMg1s 2 2s 2 2p 6 3s 2 Mg ion (lost 2 electrons)Mg 2+ 1s 2 2s 2 2p 6 Al atomAl1s 2 2s 2 2p 6 3s 2 3p 1 Al ion (lost 3 electrons)Al 3+ 1s 2 2s 2 2p 6 Ne atom (noble gas)Ne1s 2 2s 2 2p 6

10. Cation Charges Group 1A lose 1 electron, making a 1 + ion Group 2A loses 2 electrons, making a 2 + ion Group 3A loses 3 electrons, making a 3 + ion

11. Formation of Negative Ions-Anions An anion is a negative atom or group of atoms that gain electrons Nonmetals tend to gain electrons egativeegative

12. Electron Configuration of Negative Ions-”Anions” Cl ion and S ion have the noble gas configuration of argon. 8 is great! Cl atomCl1s 2 2s 2 2p 6 3s 2 3p 5 Cl ion (gain 1 electron)Cl - 1s 2 2s 2 2p 6 3s 2 3p 6 S atomS1s 2 2s 2 2p 6 3s 2 3p 4 S ion (gain 2 electrons)S 2- 1s 2 2s 2 2p 6 3s 2 3p 6 Ar atomAr1s 2 2s 2 2p 6 3s 2 3p 6

13. Anion Charges 5A tend to gain 3 electrons, making a 3 - ion 6A tend to gain 2 electrons, making a 2 - ion 7A tend to gain 1 electron, making a 1 - ion The ion produced when atoms of halogens (group 7A) gain electrons are called halide ions