Covalent bond lewis structureMolecule

electronegativityIntermolecular forces sigma bondPi bond orbitalChemical bond exothermic reactionEndothermic reaction bond lengthBond dissociation energy octet ruleResonance VSEPR modelPolar covalent bond structural formula

Vocab quiz moved to tomorrow - you have 20 minutes to work on them today

Warm up: Write the molecular formula for:

Trinitrogen pentoxideAluminum nitrideCopper (II) sulfate

Write the names for:NO2

PCl3CaI2

Chapter 8

Covalent compounds consist of what? Only nonmetals

When naming, we use … Prefixes: mono, di, tri, tetra… Prefix = number of atoms (subscript)

N2O7

Why are there no charges (like in ionic compounds)?

In ionic compounds, electrons are _______________, so atoms gain or lose charge

In covalent compounds, electrons are _____________, so no charges are formed

What does the octet rule state? In order to be stable, an atom wants a full outer

shell (which generally means 8 valence electrons) Which nonmetal is the only exception to this rule?

Hydrogen – how many does he need to be full?

transferred

shared

When neither atom wants to give up their electrons, they will just share

When 2 electrons are shared between atoms, they form a single bond

When 2 or more atoms bondcovalently, this is called

a molecule

Consider ionization energy and electronegativity– when 2 elements are near each other on the periodic table, these values will be very near each other

Ionization energy Energy required to remove an electron

Electronegativity How well an element attracts electrons in

a bond

If both atoms have very similar strengths (for holding on to their electrons) then….

Neither one will be strong enough to take electrons away from the other

Lewis structures – using electron dot diagrams, shows the arrangement of the atoms in a molecule

How many valence electrons does carbon have? How many more electrons does it need to be “happy”? How many times do you think carbon will bond? How about hydrogen? Oxygen? Generally, the # of “missing” electrons is equal to

the number of times an element will bond HONC 1234

Calculate the number of valence electrons Arrange the atoms in the molecule

○ Generally, the atom you have one of will go in the middle

○ Hydrogen only bonds once, bonds on the outside○ How many times will carbon bond? Oxygen? (look

at their valence electrons)

Put pairs of electrons between the central atom and all of the outer atoms

Put electrons to fill the central atom Put remaining electrons around outer

atoms Check to see that every atom is “happy”

When you are finished with the quiz, bring it up front and take out your notes from yesterday

CCl4

PH3

H2S

SiH4

When 2 electrons are shared between atoms, you draw a line to show the bond

All other electrons that are not shared are called lone pairs and are included in the structure

Single covalent bonds are also called sigma bonds

Orbitals – the area where you will most likely find an electron

When these orbitals overlap, they form a sigma bond (σ)

Let’s try carbon dioxide…

Sometimes, atoms may share more than 2 electrons

If 4 electrons are shared, how many bonds would there be?

This is called a double bond How many electrons would a triple bond share?

Double or triple bonds consist of sigma and pi bonds (π)

Don’t start using double bonds in every molecule, it is a last resort

Bond everything first, use up the rest of your electrons, THEN see if you need to double or triple bond

Try SO2

Draw the Lewis structures for SO2 and OF2

Look at the word… Molecules that contain how many atoms?

H. BrONClIF

In nature, when these elements are not bonded to another element, they like to exist with 2 of themselves. They are more stable that way.

Draw: F2 O2 N2

What do you notice about the bonds? Bond length : the distance between two

bonding nuclei Which of these 3 do you think would have

the shortest bond length?

As the number of bonds increases, the bond length becomes shorter

Which bond would be the strongest? Shorter = stronger

Bond dissociation energy : energy required to break a bond in a molecule

What is the relationship between bond length and dissociation energy? Shorter = more energy

PO43- what is this called?

When an ion has a charge, that means it has lost or gained ______________

What has phosphate done?

Start the lewis structure like we did for the others – add up all valence electrons

Now we have 3 extra electrons

ClO4-

NH4+

CO32-

H3O+

Be careful ! a negative

charge means we are gaining electrons, while a positive charge means we have lost electrons!

H2SO4

C2H4

N2H2

Determine the chemical formula and draw the Lewis structures for the following compounds or ions:

Carbon disulfide

Phosphorus trihydride

Sulfate ion

What does it mean when something resonates?

Resonance structures are different ways to draw Lewis structures for a molecule or ion

Only the arrangement of the electrons is changed – keep the skeleton structure

Let’s draw the structure for NO3-

How many resonance structures do each of these have?

O3

NO2-

SO2

CO3-2

Sometimes an atom may not obey the octet rule

1. Odd number of valence electrons (NO2)

2. Less than 8 electrons present around an atom (BH3)

3. Expanded octet: happens with elements in period 3 and below – d orbital electrons Generally, the central atom gets the extra

electrons PCl5

SF6

If you have a 75 or lower on your progress report, you must get it signed by a parent and returned to me by Wednesday

Try the following, and refer to notes from yesterday:

ICl3

ClF5

More than an octet on chlorine

ICl4 -1

More than an octet on iodine

BeH2

Less than an octet - Beryllium and boron generally follow the less than 8 exception

NO Odd number of valence - Nitrogen generally

takes the odd number of electrons

Draw the Lewis structure for the following:

ICl3

BeCl2

NS2

Any progress reports?

Valence Shell Electron Pair Repulsion – used to determine the shape of a molecule

What determines how a molecule will arrange itself? What part of the atom are we generally

concerned about?... ELECTRONS

Something to keep in mind: lone pair electrons occupy more space than bonded electrons

Draw the Lewis structures for each of the compounds on the handout (1st one is already done)

Let’s see how many things the central atom is bonded to, and how many lone pairs on the central atom there are

Linear

Bent

Trigonal planar

Tetrahedral

Trigonal pyramidal

Trigonal bypramidal

Octahedral

107.3o

104.5o

120o

109.5o

90o/ 120o

180o

90o

NCl3 OCl2 HOF NHF2

CO2

H2Se CH2O NH4

+1

Pick one of the VSEPR shapes and build a molecule

Include: label the type, an example of a specific molecule, the angle between the atoms, represent lone pairs (if there are any)

Use anything you would like to build this – no drawings, and the model must be an accurate representation of the shape

Due Friday, Feb. 12th

If something is polar, it means it has opposing ends

Need to know electronegativity and shapes

Influenced by the electronegativities of atoms in a molecule

What is electronegativity? How well an atom attracts electrons in a bond

What is the trend for electronegativity? (remember shielding and nuclear strength) Increases up and over

Who has the highest electronegativity value? Fluorine

Ionic: Look at the electronegativities of Na and Cl – who has more attraction for the electrons?

Covalent: look at the values for the nonmetals Polar covalent – unequal sharing of the

electrons in a bond Nonpolar covalent – equal sharing of

electrons in a bond

Electronegativity Difference Bond Type

Less than 0.4 Nonpolar covalent

0.5 to 1.9 Polar covalent

Greater than 2.0 Ionic

What kind of bond would carbon and oxygen form?

Phosphorus and fluorine? Chlorine and chlorine?

C – OSi – OGe – OC – ClC - Br

Draw the Lewis structure for water What is water’s shape? Who is stronger? Who will the electrons be closer to?

This makes partial charges.

Draw carbon tetrachloride and label the partial charges

Compare carbon tetrachloride’s structure to water’s Polar molecules are asymmetric, while

nonpolar are symmetrical Which one of these would you consider

symmetrical?

Determine if the following molecules/ion are polar:

H3O+

NCl3H2S

oxygenCF4

CS2

SF6

Solubility (what is this?) is determined by polarity

What is the universal solvent?

Are most substances polar or nonpolar?

Write the formulas for the following compounds:

Aluminum sulfate Iron (III) phosphide Hydronitric acid Sulfurous acid Dicarbon trisulfide

Grab a chemistry book, and work on the following questions –

p. 274 83, 85, 89, 96, 98, 101, 108, 112 (don’t worry about hybrid orbitals), 114, 120, 127

Be sure to look through my powerpoints and study guide on my website

Draw the Lewis structure for SO3 and draw its resonance structures

Draw the Lewis structure for ClF3

Name the following compounds: ZnCl2

KNO3

H2S

NF3