CH. 7 IONS

WHY: Everything around us is made up of compounds and molecules. It is important to know the properties of these compounds/molecules and the impact they have on us.

Valence electrons• Electrons in the highest occupied energy level of an

elements atoms• Electrons used in bonding• Responsible for determining chemical properties of the

element• To find valence electrons:

• When dealing with representative elements, simply look at group number

Electron Dot Structure• Diagrams that show the valence electrons of an element• Example: see board

• On your own: write the electron dot structure for:

• Magnesium• Sulfur• Fluorine• Potassium

Octet Rule• Noble Gases are unreactive in chemical reactions (stable)• In forming compounds, atoms tend to achieve the electron

configuration of a noble gas (8 VE)• Metallic atoms will lose valence electrons, leaving an octet in the

next lowest energy level• Nonmetallic atoms will gain (or share with another nonmetallic

atom) valence electrons to achieve a complete octet

Cations/Anions• Ion- forms when an atom gains or loses electrons

• CATIONS• Formed when an atom loses valence electrons• Metal- monatomic ions• What is the charge of a cation? • Positively charged ion• Name stays the same• Charges? How many VE are being lost?• Transition metals don’t follow rep. element rules

Cations/Anions cont.• Anions

• Formed when an atom gains valence electrons• Nonmetal – monatomic ions• What is the charge of an anion?• Negatively charged ion• Name changes to end in -ide• Charges? How many VE are being gained?

• Monatomic ions vs Polyatomic ions?

Identify if the following form cations or anions

- Ca -Ba - He

- I - N - S

- Zn - Co - Ar

Formation of Ionic Compounds• Cation + Anion = Ionic Compound

• Opposites attract

• Metal + Nonmetal• Even though ionic compounds are composed of ions, they

are electrically neutral

• https://www.wisc-online.com/learn/natural-science/chemistry/gch2204/atomic-structure-and-ionic-bonding

Properties of Ionic Compounds• Crystalline solids at room temperature

• Crystals in repeating 3-d patterns

• Strong attractive forces result in a high melting and boiling point –lots of energy needed to break bonds

• Hard and Brittle• Conduct an electric current when melted or dissolved in

water• Often are soluble in water (can dissolve)• Alloy- mixture of two or more elements, at least one of

which is a metal- properties are superior to those of component elements

Bonding in Metals

• Metals made up of closely packed together cations• Valence electrons modeled as a “sea of electrons”• Valence electrons can drift from one part of metal to another

• Mobile

• Metallic Bonds•attraction of free- floating valence electrons for positively charged metal ions

•Good conductors of electricity•Malleable•Ductile

Ionic Bonds• Chemical Formula- shows the kinds and numbers of

atoms in the smallest representative unit of a substance• NaCl

• Formula Unit- lowest whole-number ratio of ions in an ionic compound• 1:1

Electrostatic Forces that hold ions together in ionic compounds are called ionic bonds

Ch. 8 Covalent Bonds• A chemical bond in which a pair of electrons are shared

between 2 atoms• Tug of war

• Molecule- group of atoms joined together by covalent bonds• Molecular compound- compound composed of molecules

• How different from Ionic compounds??

• Diatomic molecule- a molecule consisting of two atoms• Must memorize : H2, N2, O2, F2, Cl2, Br2, I2

Properties of molecular compounds• Lower melting and boiling points than ionic compounds

• Weaker bonds

• Many molecular compounds are gases or liquids at room temp

• Mostly composed of two or more non-metal atoms• Generally have little to no electrical conductive properties

***Properties of molecular compounds vary greatly***

Molecular formula• Shows how many atoms of each element a molecule

contains• Ex- Ethane= C2H6

• Does not show how atoms are arranged within the molecule

Structural formula- represents covalent bond by dashes and shows the arrangement of covalently bonded atoms

- Lewis Dot Diagrams show bonded and unbonded pairs of electrons

See Board

Octet Rule• Remember me????• In forming covalent bonds, electron sharing usually

occurs so that atoms attain the electron configuration of noble gases• There are exceptions to this rule

• Molecules with odd # of valence electrons• Molecules which contains atoms with more or less than a complete octet

• 2 shared electrons = “shared pair”• 2 unshared electrons = “unshared pair”

• Example: Water=??

Rules for drawing Lewis Structures• DRAWING LEWIS STRUCTURES

1. SUM THE VALENCE ELECTRONS FROM ALL ATOMSA. Don’t worry about keeping track of which electrons come from which atoms. Only the total number is important.

• 2. WRITE THE SYMBOLS FOR THE ATOMS TO SHOW WHICH ATOMS ARE ATTACHED TO WHICH, AND CONNECT

THEM WITH A SINGLE BOND ( - ).• Remember a ( - ) equals 2 electrons

A. Atoms are often written in the order in which they are connected in the molecule or ion, as in HCN. When the central atom has a group of other atoms bonded to it, we usually write the central atom first, as in CO3

2- and SF4.

A. Atom with the most bonding sites is usually the central atom

Cont.

3. COMPLETE THE OCTETS OF THE ATOMS BONDED TO THE CENTRAL ATOM.

A. Remember, however, that hydrogen can only have only two electrons.

4. PLACE ANY LEFTOVER ELECTRONS ON THE CENTRAL ATOM, EVEN IF DOING SO RESULTS IN MORE THAN AN OCTET.

5. IF THERE ARE NOT ENOUGH ELECTRONS TO GIVE THE CENTRAL ATOM AN OCTET, TRY MULTIPLE BONDS. A. Use one or more of the unshared pairs of electrons on the atoms bonded to the central atom to form double or triple bonds.

Single Covalent Bond• When two atoms share a single pair of electrons

Examples: F2, H2O, PCl3 , NH3,

Double Covalent Bond• When noble gas configuration is achieved by sharing two

pairs of electrons• Example: CO2

Triple Covalent Bond• When noble gas configuration is achieved by sharing

three pairs of electrons• Example: N2

Answer Me• What is the difference between a molecular formula and a

structural formula?

• Why do you think molecules have different shapes?

Molecular orbital• Atoms have atomic orbitals, molecules have molecular

orbitals• When two atoms are shared in these molecular orbitals, they

become bonding orbitals

VSEPR (Valence shell electron pair repulsion) Theory-

-explains the 3-d shapes of small molecules

-repulsion between the electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible

Prove your knowledge

According to VSEPR, how are the bonded electron pairs oriented within a molecule?

Which molecular shape contains :

- 3 bonded pairs and 1 unbonded pair?

- 2 bonded pairs and 1 unbonded pair?

- 3 bonded pairs?

Bond length and energy

• Single bonds are longer than double or triple bonds• It takes more energy to break a triple bond than a double

or single bond

Non-polar vs. Polar Bond• In covalent bonds, the bonding pair of electrons are pulled

in a tug or war manner• Non-Polar = when the electrons in the bond are pulled equally• Polar = when the electrons in the bond are pulled unequally, giving

one atom a slight negative charge and the other a slight positive charge• If pull of electrons is so strong an ionic bond forms

• The greater the difference in electronegativity the more polar the bond• 0.0 – 0.4 = Nonpolar covalent• 0.4 – 1.0 = moderately polar covalent• 1.0 – 2.0 = very polar covalent• Greater than 2.0 = Ionic Bond

Intermolecular attractions• Van der Waals forces- weakest attractions between

molecules• Dipole interactions

• Polar Molecules have one end with + charge and one end with – charge• Determined by polarity of bonds and shape of molecule

• When polar molecules are attracted to one another

• Dispersion forces• Due to movement of electrons within molecule

Hydrogen Bond-attractive force in which a hydrogen covalently bonded to an atom is also slightly attracted to another semi-negatively charged atom

Bond Strength=

Ionic > Covalent > Intermolecular attractions(Van der Waals)