Chemical Bonds

CH. 18: PG. 552-571

Today’s Learning Objectives

•How does a compound differ from the elements that make it up?

•What is a chemical bond?

•Know how to determine the number of valence electrons for elements in groups 1, 2, and 13-18.

•Draw electron dot structures.

Valence Electrons (18-1)

•Remember NaCl?

–Made of Na and Cl…

–The properties of a compound differ from the elements that make it up.

Valence Electrons

•There are just over 100 elements, yet millions of substances exist. How?

Valence Electrons

•Chemical bond – The force of attraction that holds two atoms together

–Such as those binding NaCl or H2O

•Electrons are the keyto understanding chemical bonds

•Electrons drawn in energy levels

–First energy level –can hold 2 electrons

–Second energy level –can hold 8 electrons

–Third energy level –can hold 18 electrons

Remember these??

Valence Electrons

• Only the outermost energy level is important in bonding

– They are the only ones available to bond!

• Valence electrons – The electrons in the outermost energy level of an atom

– How many valence electrons in the drawings on the board?

Valence Electrons

•Determining # of valence electrons–Method 1: Draw the atom

–Method 2: Use the periodic table

• Ignoring the transition metals:

• Groups 1 & 2:

–valence electrons = group number

• Groups 13-18:

– valence electrons = group number minus 10

• Every element in a group has the same number of valence electrons!

Valence Electrons

•Electron dot diagrams

–Great for drawing valence electrons!

–Draw the symbol for the element, surrounded by one dot for each valence electron

Today’s Learning Objectives

•Be able to predict the ion formed by metals in groups 1-2, and all of the nonmetals.

•Know how to properly write the symbol and charge for an ion.

•Be able to name ions.

Ions (18-2)

• The secret to chemical bonds

– Every atom “wants” to have 8 valence electrons

• (that is the most stable number)

• Exception: H, He, Li, Be & B are happy with 2

– Atoms will take, lose, or share electrons to get their total of 8 valence electrons

– Draw Lithium, Fluorine, Neon, and Carbon (electron dot notation). Predict how many electrons they will gain, lose, or share.

Ions

• Ions – Charged particles formed when the number of protons and electrons are not equal

Ions

•Forming ions:

–Metals lose electrons and become positive ions• Ex. Na+, Mg2+, Al3+

–Nonmetals gain electrons and become negative ions• N3-, O2-, F-

Ions–You can easily predict the charges of

elements in groups 1, 2, and 13-17.

• Find the element on the periodic table

• Determine the closest path to a noble gas, counting the elements you pass as you go

• Go to the right… you are addingelectrons, thus becoming negative

• Go to the left (around the back of the table)… you are losing electrons, thus becoming positive

Ions

•Don’t forget what is actually happening…

o Atoms gain or lose electrons to achieve 8 valence electrons

o If the number of protons ≠ electrons, the atom becomes an ion with a positive or negative electric charge

o Charge = # protons - # electrons

o Practice

IonsTime out – writing info…

–Superscript – writing above the line, indicates charge

–Subscript – writing below the line, indicates quantity

–Ions written with the atomic symbol followed by the charge in superscript• Ex. Na+, Mg2+, O2-, F-

Ions

• Ion Review: What ions are made by the following elements:

–Na

–Al

–N

–Cl

–S

•Answers: Na+, Al3+, N3-, Cl-, S2-

Ions

•Naming Ions:

–If positive, just use the element name• Complication: If it is a transition metal,

it is the element name followed by the charge in parenthesis.

–Ex. Fe3+ = Iron(III)

–If negative, add an “-ide” to the end of the element name• Practice

Today’s Learning Objectives

•Why does chemical bonding occur?

•List the 3 types of chemical bonds.

•Describe an ionic bond.

•Be able to determine the formula of an ionic compound.

Ionic Bonds and Compounds (18-3)

3 types of chemical bonds1. Ionic bonds

2. Covalent bonds

3. Metallic bonds

Ionic Bonds and Compounds

• Ionic bond – Bond made by gaining or losing electrons, between metal & nonmetal

– Animation

Ionic Bonds and Compounds

•Bonding of ions:

–Opposites attract (like magnets)

–Ions will continue to attract other ions until the net charge is zero• Ex: Na+ + Cl- → NaCl

• Ex: Mg2+ + Cl- + Cl- → MgCl2

–The final compound always has a net charge of zero!

–Animation

Ionic Bonds and Compounds

•Writing formulas

–Always written positive ion before negative ion

–Subscripts indicate simplest ratio of ions to make it neutral overall• Mg2+, Br- form MgBr2

Ionic Bonds and Compounds

•You need to balance the charges of each ion when forming the compound

• How many Cl- do you need to balance out one Mg2+?

• Answer: 1 Mg2+ + 2 Cl- → 1 MgCl2

–Try matching Na+ and N3-

–Try matching Ca2+ and P3-

–Try matching Li+ and F-

Ionic Bonds and Compounds

• Crossing-over technique –– For writing the formula made by 2 ions

1. Write the ions down (positive first)

2. Below them, write just the symbols for the elements

3. Cross over the absolute value of the charges as subscripts

4. Simplify if possible

5. Erase the number if it is “1”

• Try it with Magnesium and Nitrogen

• Try it with Potassium and Oxygen

Today’s Learning Objectives

•How do you determine the oxidation number of an element?

•How do you write formulas for compounds (ionic and covalent)?

•How do you name ionic compounds?

Ionic Formulas & Names (18-4)

If you had to go into the store room and pick out sodium hydroxide from the following chemicals, could you do it?

1) Na2O

2) NaH

3) NaOH

4) Na2O2

Ionic Formulas & Names

•To write a formula, you need to know the elements involved and the number of electrons they gain, lose, or share to be come stable

•Oxidation number – a positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable

•The number at the top of each column is the most common oxidation number of elements in that group.

Ionic Formulas & Names

•For ions, this is easy –Just use the charge of the ion

–If the ion is a transition metal, the charge is given to you in the name of the compound – in Roman numerals

–Ex. Iron(III) oxide

Ionic Formulas & Names

•Rules for naming compounds can get quite complicated.

•We’ll focus only on ionic compounds for now.

•Binary ionic compounds–Made up of two ions (one positive and

one negative)

–Name the compound by naming the two ions!

Ionic Formulas & Names

•First, name the cation

–Cations – positive ions

• just use the element’s name–Ex. Na+ is sodium

• When multiple ions possible for same element, put the charge in roman numerals–Ex. Cr 2+ is chromium(II),

Cr 3+ is chromium(III)

Ionic Formulas & Names

•Second, name the anion

–Anions – negative ions• change the end of the name to “-ide”

• Ex. F- is fluoride, N3- is nitride

• Ionic compounds –2 words: cation, anion…

Ionic Formulas & Names

•Practice: Determine the formulaand write the name of the compounds from these ions

–Na+ and O2-

–Cu2+ and Br-

–Fe3+ and O2-

–Games

Ionic Formulas & Names

•Easy so far, right?

•Minor complication – polyatomic ions

–Polyatomic ion – an ion formed by a group of covalently bonded atoms with a charge• Ex. OH- is hydroxide

• You don’t need to memorize the list of polyatomics, but must recognize them when they appear.

Polyatomic ions to recognizeIon Name Ion Formula

Ammonium NH4+

Acetate C2H3O2-

Carbonate CO32-

Chlorate ClO3-

Hydroxide OH-

Nitrate NO3-

Phosphate PO43-

Sulfate SO42-

Ionic Formulas & Names

•Naming the ionic compound doesn’t change

–Still name the cation, then the anion

•But writing formulas has one change

–If have multiple copies of the same polyatomic ion in formula, put parenthesis around them

–Ex. Mg(OH)2

Ionic Formulas & Names

• Give it a try:• Polyatomic ions

• Ionic compounds with polyatomics

• Practice Naming:

– Ions First

– Formula First

– Name First

Today’s Learning Objectives

1) What is a covalent bond?

2) Compare and contrast a molecule and a compound.

3) What is the difference between polar & nonpolar?

4) Be able to name covalent compounds.

Covalent Bonds & Compounds (18-5)

•The ionic bonds we’ve been discussing only work between metals & nonmetals

•What if two nonmetals come into contact, can they bond with each other?

Covalent Bonds & Compounds

•Covalent Bonds – Force of attraction between atoms that result from sharing electrons – Between two or more nonmetals

Covalent Bonds & Compounds

•Molecule –

–Neutral group of atoms held together by covalent bonds• Ex. H2O

–Molecules are the smallest particle into which a covalently bonded substance can be divided and remain that substance

–Link 1, Link 2 (start at 50 s)

molecules

•Range from “diatomic” to very complex

Covalent Bonds & Compounds

•Single and multiple bonds

–If only 1 pair of electrons is shared, it is a single bond. Ex. H2

–If multiple pairs of electrons are shared, it is a multiple bond. Ex. O2

and N2

Covalent Bonds & Compounds

•Two types of covalent bonds

–Nonpolar bond – a covalent bond in which electrons are shared equallybetween atoms• Ex. H2

–Polar bond – a covalent bond in which electrons are shared unequally• Ex. HCl

Covalent Bonds & Compounds

•Nonpolar & polar bonding result in two types of molecules

•Nonpolar molecule – a molecule that does NOT have oppositely charged ends

–This type of molecule is symmetrical

–May have polar ornonpolar bonds

–Ex. CO2

Covalent Bonds & Compounds

•Polar molecule – unequal sharing of electrons within a molecule, and nonsymmetrical shape, result in oppositely charged ends of the molecule

–Ex. H2O

•Spoon Activity

•Simulation(look at polar/nonpolar, & model differences)

Covalent Formulas & Names (18-6)

•We’ve named:

–Monoatomic ions

–Polyatomic ions

–Binary ionic compounds…

•Now:

–Binary molecular compounds

Covalent Formulas & NamesNaming Binary Molecular Compounds

• When 2 non-metals combine, usually get Binary Molecular Compound

• Name is 2 words

– First word is name of the element listed first.

• A Greek prefix is used to show the number of atoms present (only if >1)

• Know all 10 Greek prefixes

Covalent Formulas & Names

•Greek prefixes:

1 = mono-

2 = di-

3 = tri-

4 = tetra-

5 = penta-

6 = hexa-

7 = hepta-

8 = octa-

9 = nona-

10 = deca-

Covalent Formulas & Names

•Second word consists of:

–The appropriate Greek prefix showing the number of atoms of that element

–The stem name of the 2nd element

–The suffix “-ide”

•Ex. N2O4 is “dinitrogen tetroxide”

•Game