Ch. 7: Ionic Compounds & Metals Sec. 7.1: Ion Formation

Forming Chemical Bonds Objectives Define chemical bond. Relate ionic bond formation to electron configuration. Describe the formation of positive and negative ions.

Forming Chemical Bonds How do thousands of compounds form from the relatively few elements known to exist? How do we make all of the words we know out of 26 letters of the alphabet? The answer to this question lies in the electron structure of the atoms of the elements involved and the nature of the attractive forces between the atoms.

Forming Chemical Bonds Valence electrons are the electrons involved in the formation of chemical bonds between two atoms.

Forming Chemical Bonds A chemical bond is the force that holds two atoms together. Chemical bonds are due to: the attraction between a positive nucleus of one atom and the negative electrons of another (covalent), OR The attraction between a positive ion and a negative ion (ionic)

Forming Positive Ions Recall the octet rule …. Recall: metals have low ionization energy & electronegativity (meaning…?) Recall: metals form positive ions A positive ion forms when an atom loses one or more valence electrons in order to attain a noble gas configuration. Although Sodium now has the electron configuration of neon which makes it more stable it is not neon. It still has 11 protons which. Remember that the number of protons is what characterizes the element.

Example Neon 1s22s22p6 Sodium atom 1s22s22p63s1 Sodium ion 1s22s22p6 A positively charged ion is called a cation.

Forming cations Sodium atom (Na) Sodium ion (Na+) 11 protons 12 neutrons 11 electrons Sodium ion (Na+) 11 protons 12 neutrons 10 electrons SAME electron configuration as neon but it is NOT neon.

Reactivity of metals Depends on how easily they lose their valence electrons Group 1A (1+ ions): very easily ---> highly reactive Group 2A (2+ ions): relatively easy ---> very reactive Group 3A (3+ ions): easily ---> reactive

Transition Metals When forming positive ions, transition metals commonly lose their two “s” electrons, forming 2+ ions. It is also possible for the d electrons to be lost, forming other relatively stable electron arrangements. These are referred to as pseudo-noble gas configurations. Therefore, most transition elements can form more than one kind of ion For example, Fe can form a 2+ OR 3+ ion.

Forming Negative ions Recall octet rule; Recall the high ionization energy and electronegativity of nonmetals Nonmetals form a stable outer electron configuration by gaining 1 or more electrons.

Forming Anions Chlorine 1s22s22p63s23p5 Cl- 1s22s22p63s23p6 Argon 1s22s22p63s23p6 Chlorine 1s22s22p63s23p5 Cl- 1s22s22p63s23p6 By gaining a single electron, a chlorine atom attains the electron configuration of argon. With the addition of one electron, chlorine becomes a negatively charged ion called an anion.

Forming Anions To name an anion, the ending –ide is added to the root name of the element. The anion of chlorine is called chloride. What is the anion of nitrogen called? arsenic? nitride

Let’s look at nitrogen . . . Nitrogen atom (N) Nitride ion (N3-) 7 protons 7 neutrons 7 electrons Nitride ion (N3-) 7 protons 7 neutrons 10 electrons SAME electron configuration as neon but it is NOT neon

General Trends Group 5A/15: gain 3 e-’s and become 3- ions Group 7A/17: gain 1 e- and become 1- ions