CHEMICAL FORMULAS AND

BONDING Ions and Molecules

Learning Target

➢Understand octet rule and how it applies to oxidation state of an ion.

➢What do all atoms need in order to be stable?

OCTET RULE

➢ Elements will gain or lose electrons in order to obtain a noble gas valence (full shell)

Remember….

➢ It takes energy to gain or lose electrons➢ Nature wants to move towards the path of

least resistance…..

……because it requires less energy

Gain or Lose Electrons?

➢ Depends on the nearest noble gas.

Noble Gases

OXYGEN

➢ Oxygen has 6 valence electrons➢ Is it easier to gain 2e- or lose 6e-?➢ Easier to gain 2e-

SODIUM

➢ Sodium has 1 valence e-

➢ Is it easier to gain 7e- or lose 1e-?➢ Easier to lose 1e-.

Try some……

➢ Sulfur➢ Fluorine➢ Potassium➢ Argon➢ Carbon➢ Hydrogen➢ Calcium

Gain

Gain

Lose

Neither

Both

Lose

Lose

Lose

OXIDATION NUMBER

➢ The possible charge an atom could obtain by gaining or losing electrons or the number of electrons an element will donate/accept in a bond.

● Remember electrons are negative

OXYGEN

➢ Oxygen gains 2e-

● So its charge is 2-

O2-Oxidation Number

SODIUM

➢ Sodium loses 1e-

● So its charge is 1+

Na+

TRY SOME…..

➢ Magnesium➢ Boron➢ Bromine

Loses 2e-, Mg2+

Loses 3e-, B3+

Gains 1e-, Br-

2 TYPES OF CHEMICAL BONDS WE WILL TALK ABOUT

➢Ionic compounds ➢Covalent compounds

➢2 terms that go with the ionic and covalent:➢Empirical➢Molecular

Review

1. What is the oxidation number for Rubidium? Selenium?

2. Do metals have (+) or (–) oxidation numbers?

3. Do non metals have (+) or (–) oxidation numbers?

Review1. What rule states that elements will gain or lose electrons to obtain a noble gas valence?

o Octet Rule

2. Do non metals have (+) or (–) oxidation numbers?

• (-)

3. Do metals have (+) or (–) oxidation numbers?• (+)

5. What is the oxidation number for barium? Iodine?

➢ Ba2+ and I-

Goal of Today

➢Know how to write formulas for Ionic Compounds.

Ionic Bond

➢ Electrons are everywhere – static is a good example

➢ Positive ion is attracted to a negative ion in an ionic bond

➢ What kind of elements?

Ionic Compound

➢ Made up of ions➢ Electrically neutral➢ Charges must equal each other➢ Bonds between metals (+ charge) and

nonmetals (- charge)

Ionic Bonding➢ Ionic bonds occur

between positive metal ions (cations) and negative nonmetal ions (anions)

➢ Made up of ions➢ Electrically neutral➢ Charges must equal

each other

Properties of Ionic Compounds

➢ Strong bonds➢ High melting points➢ Brittle➢ Soluble in water➢ Their solutions are

good conductors of electricity

➢ Solids at 20°C

Formation of Ionic Compounds

➢ Use ● The Octet rule● Lewis Dot Diagrams● Crisscross Method

Monatomic Cations

➢ Positive 1, 2, or 3➢ Transition metals can vary, and even have

a charge of 4+➢ Use element name➢ Use a Roman numeral with any metal that

varies in charge➢ Example Copper(I) is Cu+1 and Copper (II)

is Cu2+

Monatomic Anions

➢ Can be negative 1,2, or 3➢ Change element name to “-ide” ending➢ Example: chloride

Polyatomic Ions

➢ Two or more atoms that are bonded together and carry a single charge

➢ Names are on the handout➢ Most are negative with one positive➢ Usually end in “-ate” or “-ite”➢ Example: NO3

- is nitrate

Formulas for Binary Compounds

➢ Contain a monatomic cation (metal) and a monatomic anion (nonmetal)

➢ Metal is first➢ Charges must add to “0”➢ Use subscripts to get the value to “0”➢ Why is sodium chloride NaCl?➢ Try some

Write the formulas for the following

➢potassium iodide

➢barium chloride

➢lithium bromide

➢calcium hypochorite

➢chromium (III) sulfide

➢gold (III) bisulfate

Review

1. What are negative ions called?

2. What are positive ions called?

3. Write the formula for niobium(V) phosphate

Goal of Today

➢Understanding naming of Ionic Compounds and begin our “Ionic Bonding Puzzle Lab”

Naming Ionic Compounds

➢ Use NaCl as a good example➢ Metal first, then nonmetal➢ Ends in “-ide” if binary (2 elements only)➢ Use polyatomic name➢ Use Roman numeral if necessary➢ Suspect every transition metal to possibly

have a Roman numeral

Review Questions

1. Write the formulas for:beryllium carbonatesilver nitrate

2. Name the following ionic compound:Cu(HSO4)2

GOAL OF TODAY

Understand how covalent bonds form and know how to draw Lewis structures to represent covalent compounds.

COVALENT BONDING

➢ A covalent bond is formed by a shared pair of electrons between two atoms.

➢ A group of atoms that are united by covalent bonds is called a MOLECULE

➢ Most of what you see is covalently bonded

Describing a molecular bond

➢ Molecular formula: tells you how many atoms and which kind are in each molecule. Glucose C6H12O6

➢ Empirical formula: gives you the ratio of the atoms in a molecule. Glucose: C1H2O1

Covalent Bonding

➢ Single bonds share 2 electrons. Example:

Ammonia (H-N-H) H

➢ Double bonds share 4 electrons:

Formaldehyde H-C=O

H ➢ Triple bonds share 6

electronsEthyne H-C=C-H

Exit Questions

1.What is the difference between ionic bonds and covalent bonds?

2.Draw the Lewis structure for N2H2

GOAL OF TODAY

➢Know that there are exceptions to the octet rule.

➢Know how to determine and notate polarity of chemical bonds.

Exceptions to the Octet Rule

➢ Some elements are satisfied with fewer than 8 electrons (6 or 4)

➢ Some structures can only be drawn with 7 electrons

➢ Compounds with Beryllium (Be) and Boron (B) may have less than an octet BCl3

➢ 3rd Row elements or lower may exceed octet rule. SF4.

➢ Odd number of electrons cannot follow the octet rule. I.e., NO or CO

➢ These substances can be short-lived and reactive – called free radicals

Chloroform CHCl3

Draw the Lewis structure for chloroform

➢Draw the Lewis structure for PF3

Properties of Covalent Bonds

➢ Electrons are not necessarily shared equally. This depends on the electronegativity of an atom (atom’s attraction for electrons)

Polar and Nonpolar Covalent Bonds

➢ Polar bonds: 1 atom is significantly more electronegative than the other one. One side of the bond is slightly positive the other negative. Example: Water

➢ Nonpolar bonds: Both atoms have similar electronegativities. Example:

Bond Type by Electronegativity

➢ First, Find the difference of electronegativities of the atoms.Then apply the information of the table below

Electronegativity Difference

Bond type

< 0.4 Non-polar covalent

Between 0.4 and 2.0 Polar covalent

> 2.0 Ionic bond

Goal for Today

➢Review bond polarity➢Know the difference in naming ionic and covalent compounds.

Look at the table on page 241.

➢ What is the electronegativity difference between hydrogen and oxygen (H20)?

● 1.4 (polar covalent)➢ What is the electronegativity difference

between sodium and chlorine (NaCl)?● 2.1 approximately (ionic)

➢ What is the electronegativity difference between 2 nitrogen atoms (N2)?

● 0 (non polar covalent)

Properties of Molecular Substances

• Weak bonds

• Can be solids, liquids, or gases at 20°C

• Lower melting points

• Poor conductors of electricity

• Soft, not hard and brittle

• Some are soluble in water.

Naming Molecular Compounds

• Similar to naming ions• Numerical prefixes are used. Example:

CO2=Carbon Dioxide• Do not use a prefix for one• - ide is added to the more electronegative

element• Some elements have common names: Diatomics like O2= oxygen; not dioxide NH3= ammonia; not Nitrogen tetrahydride

H2O is water not dihydrogen monoxide

HYDRATES

Ionic compounds that absorb water into their solid structures.

Example:

CuSO4. 5 H2O (s)

Copper (II) Sulfate pentahydrate