Lesson Objectives To distinguish between ionic and covalent compounds. To define cation and anion and relate them to metal and nonmetal.

I. Molecules and Compounds Although there are only about 100 elements, there are millions of different compounds made from atoms. Therefore, when scientists exchange ideas, they must know exactly which compounds they are discussing. Thus, naming compounds is an essential skill in chemistry.

Elements that exist by themselves as single atoms are termed monatomic—they consist of a single atom and not bound to each other Examples: Noble gases He, Ne, Ar, Kr, Xe, Rn He Helium Argon Neon

Most elements, however, are found combined together in nature to form molecules. *A molecule is the smallest, electrically neutral unit of a substance that still has the properties of that substance.

Molecules are made up of two or more atoms that act as a unit. Example: Oxygen gas (the kind you breathe) is composed of 2 oxygen atoms each and is called a diatomic molecule. O 2 OO

Molecules are made up of two or more atoms that act as a unit. Examples: Ozone is a triatomic molecule —3 oxygen atoms. O 3 -- water is triatomic H 2 O O O O O H H

Atoms of different elements may combine chemically to form compounds which are made up of molecules. These compounds composed of molecules are termed molecular compounds.

Properties of molecular compounds: –Relatively low melting and boiling points –Exist as gas or liquids at room temperature –Molecules are composed of the atoms of 2 or more nonmetals.

CO 2 carbon dioxide H 2 O dihydrogen monoxide (Water) Examples of Molecules and Covalent Compounds Sketch these triatomic molecular compounds in your notes

II. Ions and Ionic Compounds A. Ions Not ALL compounds are covalent. Many are composed of ions instead of molecules. What are ions? Atoms or groups of atoms that have a positive or negative charge.

How does an ion form? An atom or loses or gains electrons. What is an ion anyway?

Cation + + Metallic elements tend to form cations by losing an electron. A cation is an atom or group of atoms that have a positive charge (+).

Nonmetallic elements tend to form anions by gaining one or more electrons. What is an anion? Atoms or groups of atoms that have a negative (-) charge.

B. Notation of ions: Na + Cl - Al 3+ An ionic charge is written as a number followed by a + or – sign The number 1 is usually omitted when writing the complete symbol for the ion Ex.Na 1+ and Na + are equivalent. Magnesium loses 2 electrons so its ionic symbol is written as Mg 2+

Ions tend to have completely different properties from their neutral atoms. –Sodium metal (Na) reacts explosively with water. –Sodium cations (Na+) are unreactive - salt in water.

Ionic Compounds are …… composed of cations and anions. composed of metal cations and nonmetal anions. usually solid crystals at room temperature and melt at high temperatures. Examples: sodium chloride (table salt) iron oxide (rust)

I.Valence Electrons A.The electrons in the highest occupied energy level on an element’s atoms. B. Valence electrons are the electrons that are usually active during chemical reactions. C. Lewis dot structures are depictions of the valence electrons around an atom.

Rules for Writing Lewis Dot Structures in TWO steps Step 1: Determine the number of valence electrons around the atom The number of valence electrons is the same as the A group number.

Rules for Writing Lewis Dot Structures: Step 1 Example Sulfur has ___ valence electrons sulfur atom

Rules for Writing Lewis Dot Structures: Step 1 Example Sulfur has _6_ valence electrons sulfur atom

Rules for Writing Lewis Dot Structures: Step 2. Put a dot for each valence electron, with no more that 2 electrons on each side of the element symbol. Example Sulfur has 6 valence electrons. :S:.

Draw the Lewis dot structure for aluminum. Draw the Lewis dot structure for bromine.

Draw the Lewis dot structure for aluminum. Draw the Lewis dot structure for bromine... Al.

Draw the Lewis dot structure for aluminum. Draw the Lewis dot structure for bromine... Al... :Br:.

Draw the Lewis dot structure for lithium. Draw the Lewis dot structure for oxygen.

Valence Electrons in atoms Lithium is in Group 1A, so it has 1 valence electron. Li –

Valence Electrons in atoms Lithium is in Group 1A, so it has 1 valence electron. Li – 1s 2 2s 1

Valence Electrons in atoms Oxygen is in Group 6A, so it has 6 valence electrons. O –

Valence Electrons in atoms Oxygen is in Group 6A, so it has 6 valence electrons. O – 1s 2 2s 2 2p 4

Valence Electrons in atoms How many valence electrons does silicon have? How many valence electrons does calcium have?

Valence Electrons in atoms How many valence electrons does silicon have?4 How many valence electrons does calcium have?2

Octet Rule Ionic Electron Configurations When an atom gains or loses electrons, its electron configuration is changed as well. Na – How many valence electrons does Na have? because the 3 rd energy level is the highest level with electrons. Will sodium lose or gain electrons when forming an ion? _________ an electron to become Na + -

Octet Rule Ionic Electron Configurations When an atom gains or loses electrons, its electron configuration is changed as well. Na – 1s 2 2s 2 2p 6 3s 1 How many valence electrons does Na have? 1 because the 3 rd energy level is the highest level with electrons. Will sodium lose or gain electrons when forming an ion? loses an electron to become Na + - 1s 2 2s 2 2p 6

Octet Rule Ionic Electron Configurations When an atom gains or loses electrons, its electron configuration is changed as well. Cl – How many valence electrons does Cl have? because the is the highest level with electrons. Will chlorine lose or gain electrons when forming an ion? an electron to become Cl - - 1s 2 2s 2 2p 6 3s 2 3p 6

Octet Rule Ionic Electron Configurations When an atom gains or loses electrons, its electron configuration is changed as well. Cl – 1s 2 2s 2 2p 6 3s 2 3p 5 How many valence electrons does Cl have? 2+ 5 = 7 because the 3 rd energy level is the highest level with electrons. Will chlorine lose or gain electrons when forming an ion? gains an electron to become Cl - - 1s 2 2s 2 2p 6 3s 2 3p 6

Octet Rule Ionic Electron Configurations We now have two atoms with opposite electric charges, each with 8 electrons in their outermost energy level. Na + - 1s 2 2s 2 2p 6 Cl - - 1s 2 2s 2 2p 6 3s 2 3p 6

Octet Rule Ionic Bonds In 1916, Gilbert Lewis formulated an explanation of why atoms form certain ions called the octet rule. Now each atom has the 8 outer electrons that they want.  sodium and chlorine

The Octet Rule: atoms tend to acquire 8 valence electrons when forming chemical compounds to look like noble gases.  Cl - Na +

How will an atom of fluorine form an ion? What will its ionic charge and symbol be?

How will an atom of calcium form an ion? What will its ionic charge and symbol be?

How will an atom of phosphorus form an ion? What will its ionic charge and symbol be?

Drawing Lewis Dot Structures for Ionic Compounds Practice