FORMING COMPOUNDS

What is a compound? A substance made of two or more elements CHEMICALLY combined. A substance made of two or more elements CHEMICALLY combined.

How are compounds formed? Electron Transfer (Ionic Bonds) Elements gain or lose electrons Elements gain or lose electrons Formed between a metal and nonmetal Formed between a metal and nonmetal Definition: The attraction between 2 oppositely charged ions. Definition: The attraction between 2 oppositely charged ions.

Why do compounds form? Elements want to be stable Elements want to be stable What is a stable element? What is a stable element? An element that has a full or empty valence shell An element that has a full or empty valence shell Usually 8 electrons to be full Usually 8 electrons to be full Always take the easiest way to 8. Always take the easiest way to 8.

What are valence electrons? Electrons on the outside energy level. How do we know how many valence electrons? How do we know how many valence electrons? EASY WAY: EASY WAY: Look at what family or group they are in on the Periodic Table. Look at what family or group they are in on the Periodic Table.

Forming Ionic Bonds What is an Ion? What is an Ion? An atom or group of atoms with a charge (positive or negative) An atom or group of atoms with a charge (positive or negative) How is an ionic bond formed? How is an ionic bond formed? One atom wants to lose an electron(s) One atom wants to lose an electron(s) One atom wants to gain an electron(s) One atom wants to gain an electron(s)

How do atoms get a charge? Gain or lose electrons Gain or lose electrons What do you already know about protons and electrons? What do you already know about protons and electrons?

Example #1: Ionic Bonds Sodium (Na) and Chlorine (Cl) Na: lost 1 e- so it has a charge of +1 Cl:gained 1 e- so it has a charge of -1 Compound formed: NaCl (positive element always goes first) NaCl +1

Nomenclature (naming compounds) 4 Basic Rules: 1. Name compounds in same order written. 2. First element name doesn’t change (just read it off the Periodic Table)

3. Second element: change the end of the element name to “-ide” Examples: Examples: Chlorine  Chlorine  Bromine  Bromine  Oxygen  Oxygen  Sulfur  Sulfur  Fluorine  Fluorine  Nitrogen  Nitrogen  Iodine  Iodine  Carbon  Carbon 

4. Polyatomic ion names never change. Just read the names off the list. Just read the names off the list. Nomenclature examples: KCl KCl MgF 2 MgF 2 NaI NaI Ca(OH) 2 Ca(OH) 2

Ionic Bonds: Shortcut Method Determine CHARGE on ion Determine CHARGE on ion Write + ion first - ion second Write + ion first - ion second Criss-cross the charge # & drop sign Criss-cross the charge # & drop sign If #s are the same, cancel them out If #s are the same, cancel them out Don’t write “1” Don’t write “1” Example: Example: Mg +2 Br -1 Mg +2 Br -1

Polyatomic Ions An ion that is made of more than one atom, but acts like one atom. An ion that is made of more than one atom, but acts like one atom. See list. See list. Writing Formulas: Writing Formulas: Same shortcut method, but… Same shortcut method, but… Use ( ) if you are adding a subscript. Use ( ) if you are adding a subscript. Ca +2 NO 3 -1 Ca +2 NO 3 -1

Covalent Bonds Elements share Valence electrons Elements share Valence electrons Formed between 2 nonmetals Formed between 2 nonmetals Definition: A bond formed when two atoms share valence electrons. Definition: A bond formed when two atoms share valence electrons.

Example: Covalent Bonds Example: Example: Hydrogen (H) andOxygen (O) Hydrogen (H) andOxygen (O) Elements share electrons to make full shells O H H H2OH2O