Vocabulary Isotope – atoms of a given element that have different numbers of neutrons and different mass numbers Ion – an atom or group of atoms that has a positive or negative charge Molecule – a neutral group of atoms that are joined together by one or more covalent bonds (will define covalent bonds later) Valence electron – an electron that is in the highest occupied energy level of an atom

Vocabulary Metal – elements that are good conductors of heat and electric current Metalloid – elements with properties that fall between those of metals and nonmetals Nonmetal – elements that are poor conductors of heat and electric current

Two primary forms of molecular bonding Covalent bonding – a chemical bond in which two atoms share a pair of valence electrons (will discuss more later) Ionic bonding – the force that holds cations and anions together Cation – a positively charged ion Anion – a negatively charged ion

Properties of Ionic Compounds Form crystals. When struck, ionic compounds shatter. Salt is an example of an ionic bond. The subscripts indicate a ratio of one element to another. Salt is NaCl. It has one part sodium per one part chlorine.

Ionization Energy Amount of energy it takes for a neutral atom to become charged (i.e. an ion) The more valence electrons the greater the ionization energy. Cations form in groups 1A, 2A, and 3A. Anions form in groups 5A, 6A, and 7A. These are the groups that typically form ionic compounds.

Criss-cross The charge indicates what ionic compound will form. It will always be with one form of cation and one form of anion. Example: Mg 2+ Cl - MgCl 2

Assignment Form various ionic compounds of these elements:

Molecule Maker Oxidation number – the charge that is formed when an atom ionizes (loses or gains electrons to form a stable outer shell of 8 electrons) – e.g. Lithium’s is +1, calcium’s is +2, oxygen’s is -2 Polyatomic ion – a covalently bonded group of atoms that has a positive or negative charge and acts as a unit In the Molecule Maker, blue represents a cation, red represents an anion. The number of slots indicates their oxidation number.

Magnesium has an oxidation number of +2, therefore it has two “male” slots. Chlorine has an oxidation number of - 1, therefore it has one “female” slot.

The Rules A molecule is only correct when the cards form a rectangle. The number of atoms of each element is written in the space below the line and to the right of the symbol (the subscripts, the 2 in MgCl 2 ). When the number of atoms is one, we do not write anything and the “one” is understood.

Covalent Bonds Covalent bond – a chemical bond in which two atoms share a pair of valence electrons – “Co-” meaning it shares – “-valent” referring to valence electrons

Common covalent bonds

Molecules Molecule – a neutral group of atoms that are joined together by one or more covalent bonds The attraction between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond

Polar vs. Nonpolar Polar covalent bond – a covalent bond in which the electrons are not shared equally When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge.

Polar vs. Nonpolar Water is polar. It has a positive charge on one side, and a negative charge on the other.

Polar vs. Nonpolar The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar.

Polar vs. Nonpolar Attractions between polar molecules are stronger than attractions between nonpolar molecules. Surface tension.

Naming Compounds and Writing Formulas The name of an ionic compound must distinguish the compound from other ionic compounds containing the same elements. The formula of an ionic compound describes the ratio of the ions in the compound. Cations in the 1A, 2A, and 3A families retain their element name. Anions change their name. Metals form various ions and must be distinguished.

Common Anions

Some Metal Cations

Polyatomic Ions Polyatomic ion – a covalently bonded group of atoms that has a positive or negative charge and acts as a unit

Naming Covalent (Molecular) Compounds The name and formula of a molecular compound describe the type and number of atoms in a molecule of the compound. More metallic element appears first (the leftmost element). The second element ends in –ide Use Greek number prefixes to indicate number.

Prefixes for Covalent Compounds

Examples CO 2 – carbon dioxide N 2 O 4 – dinitrogen tetroxide H 2 O – dihydrogen monoxide P 2 F 4 – diphosphorus tetrafluoride In Book, page 175, #1-10

TEST ON THURSDAY, FEBRURARY 28 Test on the last day of February It will be on – Ionic bonding – Covalent bonding – Molecular polarity – Polyatomic ions – Naming molecules