Chapter 4 – Atoms and Bonding 4.2 Ionic Bonds

I. Essential Question: How do ions form? How are the formulas and names of ionic compounds written? What are the properties of ionic compounds?

Key Vocabulary Ion: an atom or group of atoms that has an electric charge Polyatomic ion: ions made from more than one atom Ionic bond: the attraction between two oppositely charged ions Ionic compound: a compound made up of positive and negative ions

Key Vocabulary Chemical formula: group of symbols that shows the ratio of elements in a compound Subscript: tell the ratio of elements in a compound; smaller numbers Crystal: orderly, three dimensional arrangement of atoms

Key Concepts When a neutral atom loses an electron, it becomes more positively charged. When a neutral atom gains an electron, it becomes more negatively charged. Metals (alkali and alkaline) like to lose their electrons; nonmetals (especially halogens) like to gain them.

Key Concepts Because they are becoming charged, the ions will now attract to one another. Negative and positive charges will attract.

Key Concepts To write the formula for an ionic compound, write the symbol of the positive ion first and then the symbol for the negative ion. Then, add the subscripts that are needed to balance the charges. Positive charges must be equal to negative charges.

Key Concepts To name an ionic compound, first name the positive ion and then the negative ion. If the negative ion is a single element, its name ends with an –ide. If the negative ion is polyatomic, then it usually ends with –ate or –ite.

Key Concepts Ionic compounds form hard crystals that have high melting points. They conduct electricity when dissolved in water or melted. The ions must be able to move around in order to carry an electric current.

Chapter 4 – Atoms and Bonding 4.3 Covalent Bonds

I. Essential Question: How are atoms held together in a covalent bond? What are properties of molecular compounds? How do bonded atoms become partially charged?

II. Key Vocabulary Covalent bond: chemical bond formed when 2 atoms share electrons Molecule: a neutral group of atoms joined by covalent bonds Double bond: when two atoms share two pair of electrons Triple bond: when two atoms share three pair of electrons

II. Key Vocabulary Molecular compound: a compound that is made up of molecules Nonpolar bond: a covalent bond in which electrons are shared equally Polar bond: a covalent bond in which electrons are shared unequally

III. Key Concepts Covalent bonds usually form between nonmetals. By sharing electrons, nonmetals can become surrounded by 8 valence electrons.

III. Key Concepts Molecular compounds do not usually conduct electricity. They generally have lower melting points and boiling points. The forces between these molecules is not as strong as they are in ionic compounds.

III. Key Concepts Unequal sharing (polar bonds) causes covalent bonds to have a slight electric charge. Nonpolar bonds – when identical atoms bond

III. Key Concepts In polar bonds, the atom with the stronger pull is slightly negative; the weaker pull is slightly positive. van der Waals forces: polar molecules attract to one another because of their slightly charged particles.