Chapter 6: Ionic and Molecular Compounds

Ionic bond

Ionic bond

A bond that occurs when valence electrons of a metal are transferred to the atom of a nonmetal

Covalent bond

A bond that occurs when 2 nonmetal atoms share electrons to attain a noble gas arrangement

What is the net charge of an ionic bond?

zero

What are the charges like in an ionic bond?

One side is more negative, and the other is more positive

How many valence electrons do most elements want?

8 - octet

How many valence electrons do Hydrogen and Helium want?

2 - duet

Ion

The number of protons does not equal the number of electrons

Cation

Positive ion

Anion

Negative ion

What ion of Magnesium would give it 8 valence electrons? What type of ion is this?

Mg → 1s²2s²2p⁶3s² - 2 electrons

1s²2s²2p⁶ = [Ne] = stable Mg²⁺ = cation

What ion of Chlorine would give it 8 valence electrons? What type of ion is this?

Cl → 1s²2s²2p⁶3s²3p⁵ + 1 electron

1s²2s²2p⁶3s²3p⁶ = [Ar] = stable Cl⁻ = anion

Do metals want to loose or gain electrons?

Loose

Do nonmetals want to loose or gain electrons?

Gain

What count of electrons do anions and cations form to?

Anions → 8 electrons

Cations → 0 electrons

How do you name cations and anions?

Cations → same name that’s on the periodic table

Anions → use the first syllable, and add “ide“ to the end

How do you draw Lewis structures for ions, polyatomic ions?

You subtract the necessary electrons, make octets, put brackets around it, and write the charge

How do you draw an atomic symbol?

Use the element symbol

• Top left = mass # (protons + neutrons)

• Bottom left = atomic number (protons)

• Top right = charge (if no charge, don’t write anything)

When calcium looses two electrons what would you call it?

When chlorine gains an electrons, what would you call it?

Calcium

Chloride

Ionic Compound

Consist of positive and negative charges (ions) held together by the strong electrical attraction between oppositely charged ions

Specifics of ionic compounds

• Have ionic bonds

• High melting points

• Solids at room temperature

Chemical Formula

No charges in the formula

• The symbols and subscripts are written in the lowest whole # ratio of the atoms or ions

• Net charge should be 0

  • Total positive charge = Total negative charge

Naming ionic compounds

Metal and then nonmetal =

cations and anion meaning the second word will end with an “ide“

No capitals

What is the difference between superscript number and subscript number in an ionic compound?

Superscript = charges

Subscript = # of atoms

What are the charges for these groups?

1

2

3

15

16

17

18

1 = 1+ cation

2 = 2+ cation

3 = 3+ cation

15 = 3- anion

16 = 2- anion

17 = 1- anion

18 = 0

What are the net charges of…

• Aluminum

• Zinc

• Cadmium

• Silver

These, we must have memorized

• Aluminum = 3+ cation

• Zinc = 2+ cation

• Cadmium = 2+ cation

• Silver = 2+ cation

For any transition metal, or any element that we have not memorized the charge for, what do you do?

We use a roman numeral; by looking at what its bonded to

What is the name of FeCl₂?

Fe = iron; we don’t know the charge

Cl₂ = 2 chlorine and we know that chlorine has a charge of 1- and since there are two of them, the overall is -2 and we would call it chloride

Now, we need to balance out the ion with the iron. We can do this by creating a +2, so we will choose iron II.

iron(II) chloride

What are the formulas?

• nickel (II) sulfide

• zinc chloride

• nickel (II) sulfide

  Nickel, we are given the two, so we know the charge is 2+ now we just have to figure out the sulfide. Sulfur’s charge is 2-, as we can tell using the periodic table, and we need 2- to combat the 2+, which works perfectly here NiS

• zinc chloride

  Zinc is one the elements we memorized, so we know it has a 2+ charge. Chlorine has a charge of -1, as shown on the periodic table, and since we need a 2- to combat the 2+ we add another atom of chlorine! ZnCl₂

Polyatomic Ions

Group of covalently bonded atoms w/ an ionic charge

What types of charges do polyatomic ions usually have?

1-, 2-, 3-

• Negatives

What types of atoms are usually in polyatomic ions?

Nonmetals such as P, S, C, N, O

Which polyatomic ions are the only positive ones?

Hydronium (H₃O⁺) and Ammonium (NH₄⁺)

What do polyatomic ions end in? What are the exceptions?

-ate or -ite

• OH⁻ and CN⁻ (Hydroxide and Cyanide)

How would you combine a magnesium ion and and a nitrate ion?

Magnesium = 2+ (from periodic table)

Nitrate = polyatomic ion NO₃⁻ aka 1-

So, just like we would do with any ionic compound, we need to balance out the charges. Here, we can do this by adding a nitrate ion.

Now, we need to add a subscript 2 to represent the amount of nitrate atoms, BUT since there is already a subscript, we put parenthesis around the NO₃.

Remember, no charges! Mg(NO₃)₂

Name FePO₄

Fe = Iron and we don’t know the charge

PO₄ is a polyatomic ion!, we have these memorized, so we know its phosphate and the charge is 3- meaning we need a 3+ to combat it! So we simply use that charge for the iron giving us Iron(III) Phosphate

Molecular Compounds

Have covalent bonds

• No charge

• Between 2 nonmetals

• Valence electrons shared by nonmetal atoms to achieve stability

Molecule

A discrete group of atoms in a definite proportion

• H₂O = always in that proportion and doesn’t go on, merge with other H₂O to make a larger H₂O

Naming Covalent or Molecular Compounds

Like ionic compounds, the first word stays the same as on the periodic table

Second work, needs an “ide“

Difference:

• PREFIXES

If there is only one of the first atom, then keep the name, but if there are any more, use the proper prefix that corresponds to the number.

For the second word, even if there is one, use the proper prefix, one being mono-

Prefixes (1-10)

1 = mono-

2 = di-

3 = tri-

4 = tetra-

5 = penta-

6 = hexa-

7 = hepta-

8 = octa-

9 = nona-

10 = deca-

What is the rule with o and a when naming molecular compounds?

If there is either oo, ao, oa, aa, then you drop the first vowel.

Name these:

• N₂O

• Cl₂O₇

• CO₂

• N₂O = dinitrogen monoxide

• Cl₂O₇ = dichloride heptoxide

• CO₂ = carbon dioxide

What is diphosphorus pentoxide’s formula?

P₂O₅

Which polyatomic ion can form an ionic bond with other nonmetals and why?

NH₄⁺ (Ammonium) because the entire charge is positive, creating ionic bonds with negatively charged nonmetals

What are the types of pairs in Lewis Structures

Double bonds

• Bonding pairs

• Nonbonding pairs/lone pairs

How are the two types of bonds portrayed in Lewis Structures?

Bonding pairs = lines

Lone pairs = two dots side-by-side

Electronegativity

An atom’s ability to attract the shared electrons in a chemical bond

What is the trend of electronegativity on the periodic table?

Left to right = increases

Top top to bottom = decreases

When drawing Lewis Structures, what must you always form?

Octets!

• Hydrogen and Helium = duets

Diatomic Molecules

Double bonded pairs of atoms

• H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

What type of molecule are diatomic molecules?

Covalent, Nonpolar

Formulas for methane, ammonia, and water

Methane = CH₄

Ammonia = NH₃

Water = H₂O

What is a central atom?

The atom to which the other atoms are attached to

• The one in the center

How do you calculate the number of valence electrons when making Lewis Structures?

Number of valence electrons x number of atoms of that element

Do for each element and add up the values

Double Bonds

When atoms share two pairs of electrons

Triple Bonds

When atoms share three pairs of electrons

Why do double and triple bonds form?

When there aren’t enough electrons to create octets

What do halogens like to have, and where in a molecule do they like to be?

3 lone pairs, terminal = on the ends

What does carbon like to do in molecules?

Like to bond to itself, wants to be in the center, have 4 bonds somehow

What can hydrogen not have in a molecule, and where can’t it be?

Can’t handle more that 2 electrons, cannot be in the middle

If you have a cation, what did you do with electrons

subtract electrons

If you have an anion, what did you do with electrons

add electrons

What are the electronegativity ranges?

TOTAL = 0.0 - 4.0

Non-polar Covalent = 0.0 - 0.4

Polar Covalent = 0.5 - 1.8

Ionic = 1.9 - 4.0

Electronegativity: Which element is the most attractive and which is the most generous?

Attractive = Fluorine

Generous = Cesium

Is electronegativity higher for metals or nonmetals?

Nonmetals

How can you determine the polarity of a compound?

• Use general

  • Uneven/unsymmetrical = polar

  • Even/symmetrical = nonpoalr

• Find the dipole

  • Difference in electronegativity

Dipole

Separation of charges in a charged molecule (usually polar)

• A bond or molecule whose ends have opposite charges

What happens as the electronegativity increases in a polar bond?

The bond becomes more polar

What does VSEPR Theory stand for?

Valence Shell Electron-Pair Repulsion Theory

What does the VSEPR Theory state?

Electron groups are arranged as far apart as possible around the central atom

What does the VSEPR Theory show/describe?

Shape

Linear: types of pairs and angle degree

Pairs: 2 bonded atoms, 0 lone pairs

Angle: 180°

Trigonal Planar: types of pairs and angle degree

Pairs: 3 bonded atoms, 0 lone pairs

Angle: 120°

Bent (Trigonal): types of pairs and angle degree

Pairs: 2 bonded atoms, 1 lone pairs

Angle: <120°

Tetrahedral: types of pairs and angle degree

Pairs: 4 bonded atoms, 0 lone pairs

Angle: 109°

Trigonal Pyramidal: types of pairs and angle degree

Pairs: 3 bonded atoms, 1 lone pairs

Angle: <109°

Bent (Tetrahedral): types of pairs and angle degree

Pairs: 2 bonded atoms, 2 lone pairs

Angle: <<109°

Can nonpolar molecules have polar bonds?

Yes, as long as their dipoles cancel out

What happens if dipoles point to the same molecule?

They do not cancel out and instead add up

• Reinforce eachother

Intermolecular Forces

Forces between two atoms/molecules

Are intermolecular forces covalent or ionic?

Covalent

What are the three types of intermolecular forces?

Dipole-Dipole Attractions, Hydrogen Bonds, Dispersion Forces

Dipole-Dipole Attractions

Polar molecules

• Hydrogen bonds are part of this; don’t always occur

Hydrogen Bonds

Polar molecules

• First, we check for Dipole-Dipole

• If H is bonded to F, N, or O, then it is a Hydrogen bond

Dispersion Forces

Non-polar Molecules

• Only type of non-polar bond

• Enables non-polar molecules to form solids and liquids

Which intermolecular force is weakest, which is the strongest?

Weakest = dispersion forces

Strongest = hydrogen bond

Are ion bonds/ ion dipoles stronger than intermolecular forces?

Yes, they are extremely strong

How do intermolecular forces correspond with melting points?

The stronger the force, the more energy it will take to break those bonds, and vice-versa

• Non-polar molecules have a lower melting point than polar molecules due to their intermolecular forces

Between NH₃ and PH₃, which has the higher melting point?

Both of them are polar molecules, however, NH₃ has a hydrogen bond while PH₃ only has dipole-dipole

Therefore, NH₃ has the higher melting point