Lecture 9A – Introduction to Chemical Bonding Roar

In nature, only the noble gases tend to exist as isolated atoms Monatomic – consisting of a single atom Example: Neigh Neon (Ne)

All other atoms like to join to other atoms to form compounds Depending on how the atom bonds, compounds can be considered 1 - molecules or 2 – ionic compounds

Properties of Ionic Compounds Introduction to Ionic Compounds Properties of Ionic Compounds Tend to have high melting / boiling points Most all exist as Solids at room temp. Example: NaCl (Salt)

Introduction to Ionic Compounds Ionic Compounds are composed of cations and anions. Cation – any atom or group of atoms with a positive charge. (metals lose electrons) Anion – any atom or group of atoms with a negative charge (non-metals gain electrons)

Cations: Anions: How can I remember? Cats have Pos (get it?) Are Negative IONS

Who loses, who gains? Cation – has a positive charge Metallic elements tend to lose electrons Cation – has a positive charge Example: Na has 11 protons, 11 electrons. To become more stable, Na loses one electron and becomes Na1+ Na1+ has 11 protons, 10 electrons (more like Neon) When writing this cation: Na1+ and Na+ are the same

If metallic elements lose electrons, what do nonmetallic elements tend to do? Nonmetallic elements tend to gain electrons Anion – has a negative charge Example: Cl has 17 protons, 17 electrons. Cl would like to be more stable so it gains one electron and becomes Cl1- Cl1- has 17 protons, 18 electrons (more like Argon) When writing this anion: Cl1- and Cl- are the same

There are many important chemical differences between atoms and their ions! Example: Na is a metal and reacts explosively with water Na+ is a cation and is unreactive in water

Naming ions Cations – Name of a cation is the same as the name of the element Example: Sodium (Na) , Sodium ion (Na+) Anions – The name of an anion typically ends in –ide. Example: Chlorine (Cl), Chloride ion (Cl-)

Molecular Compounds Many elements found in nature are in the form of molecules Molecule – smallest electrically neutral unit of a compound that still has the properties of the compound . . . Basically they are 2 or more atoms (nonmetals) that act as a unit

Examples of Molecules Ozone O3 Diatomic molecules: Composed of 2 atoms **Remember these: H2, O2, F2, Br2, I2 , N2, Cl2, Mr. HOFBrINCl Triatomic molecules: Composed of 3 atoms Example: Ozone, water, carbon dioxide Oxygen O2 Ozone O3

Molecular Compounds Molecular Compounds – compounds composed of molecules Mickey Mouse Just Kidding . . . Water (H20)

Properties of Molecular Compounds Tend to have low melting / boiling points Many exist as gas / liquid / solid at room temp. Most composed of atoms of 2 or more nonmetals Example: CO2 (Carbon Dioxide)

Remember . . . Molecular and Ionic Compounds differ. Table sugar – molecular compound Table salt – ionic compound Which one would melt the first? It is easy to melt a spoonful of table sugar over an open flame, but it is virtually impossible to do so with salt.

Putting it all together Characteristics of Molecular and Ionic Compound Molecular Compound Ionic Compound Composition Nonmetals Metal & Nonmetal Physical State Solid, Liquid, or Gas Solid Melting Point Low High

Give the name and symbol of the ion formed when: A nitrogen atom gains three electrons Nitride ion, N3- A calcium atom loses two electrons Calcium ion, Ca2+ A fluorine atom gains one electron Fluoride ion, F-