Chem Unit 4

Question 1

A domain is:

Answer 1

the number of lone pairs and bonds (of any kind) in a compound

Question 2

What is a lone pair? Compare to a bond pair.

Answer 2

A pair of valence electrons that are not shared with another atom in a covalent bond. A bond pair is shared. All pairs want to be as far apart from each other as possible, but lone pairs more than bond pairs.

Question 3

What is electron vs. molecular geometry?

Answer 3

Electron geometry: Considers both bonding and non-bonding electron pairs. Consistent within a domain.
Molecular geometry: Only considers bonding electron pairs. Changes if lone pairs vs. bond pairs are present.

Question 4

What is electronegativity?

Answer 4

Electronegativity is defined as an atom’s ability to attract a covalently bonded pair of electrons.

Question 5

What units are used for electronegativity?

Answer 5

The most commonly used scale, the
Pauling scale, ranges from 0 to 4 and although the values are typically quoted as absolute numbers, if units are assigned then they are ‘Pauling units’.

Question 6

Differentiate between true covalent, polar covalent, non-polar, and ionic bonds.

Answer 6

True covalent: difference in electronegativity is 0

Non-polar: difference is 0-0.4

Polar covalent: difference is 0.4-1.7

Ionic: difference is 1.7-3.3

Question 7

What is a dipole?

Answer 7

The partial charge associated with a polar bond. Expressed negatively or positively (arrow pointing at negative, 6-looking symbol+/-…)

Question 8

What is VSEPR? Name and define.

Answer 8

Valence shell electron pair repulsion theory is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms.

Question 9

From 0 lone pairs to all lone pairs, what are the possible molecule shapes for a molecule with domain 2?

Answer 9

0 lone pairs: linear (180 degrees)
1: linear
2: N/A

Electron geometry is always linear.

Question 10

From 0 lone pairs to all lone pairs, what are the possible molecule shapes for a molecule with domain 3? Angles?

Answer 10

0 lone pairs: trigonal planar (120 degrees)
1: bent
2: linear
3: N/A

Electron geometry is always trigonal planar.

Question 11

From 0 lone pairs to all lone pairs, what are the possible molecule shapes for a molecule with domain 4?

Answer 11

0 lone pairs: tetrahedral (109.5 ish)
1: trigonal pyramidal (107.8)
2: bent
3: linear
4: N/A

Electron geometry is always tetrahedral.

Question 12

From 0 lone pairs to all lone pairs, what are the possible molecule shapes for a molecule with domain 5?

Answer 12

0 lone pairs: trigonal bipyramidal (90 degrees/120 degrees)
1: seesaw
2: t-shaped
3: linear
4: linear
5: N/A

Electron geometry is always trigonal bipyramidal.

Question 13

From 0 lone pairs to all lone pairs, what are the possible molecule shapes for a molecule with domain 6?

Answer 13

0 lone pairs: octahedral (90 degrees)
1: square pyramidal
2: square planar
3: t-shaped
4: linear
5: linear
6: N/A

Electron geometry is always octahedral.

Question 14

In Nick the Camel, what are consonants?

Answer 14

Oxygen #

Question 15

In Nick the Camel, what are vowels?

Answer 15

Charge (negative)

Question 16

Name 3 properties of ionic compounds.

Answer 16

1. Always form solid crystals
2. High melting/boiling points
3. Conduct electricity as aqueous electrolytes
4. Brittle (when same charge faces same charge, big repulsion = shatter)
5. Made of non-metal and metal
6. Readily dissolves into ions in water
7. Hard, because bonds resist stretching

Question 17

Name 3 properties of covalent molecules.

Answer 17

1. Usually gases with low melting/boiling points at room temp
2. Various textures
3. Don’t readily dissolve in water

Question 18

The smallest repeating unit in an ionic crystal is:

Answer 18

a formula unit

Question 19

Rule for drawing Lewis structure of a molecule?

Answer 19

1. Count total # of valence electrons of elements involved
2. Identify central atom
3. Distribute single bonds
4. Complete non-central atoms’ valence shells
5. Complete central atom’s valence shell

Question 20

Rule for drawing Lewis structure of an ionic compound?

Answer 20

1. Metal with square brackets and ionic charge
2. Non-metal with full octet and square brackets and ionic charge
3. Coefficient if needed

Question 21

Exceptions to octet rule?

Answer 21

Expanded octet: Xenon (12 valence), phosphorus (10 valence), sulfur (12 valence)… elements with an empty 3d orbital

Smaller octet: Beryllium (4 valence), Boron (6 valence)

Odd-electron: Nitrogen (just fill the other one out)

Question 22

Molecule polarity flowchart:

Answer 22

IF molecule has no polar bonds OR all polar bonds are symmetrical, non-polar. Otherwise, polar.

Question 23

Name the inter- and intramolecular forces in order of strength.

Answer 23

London dispersion force
Dipole-dipole
Hydrogen bond
Covalent
Ionic/metallic

Question 24

What increases as bond forces increase in strength?

Answer 24

Boiling point, surface tension, cohesion…

Question 25

Describe some features of London dispersion forces.

Answer 25

London dispersion forces: the random, continuous movement of electrons can create asymmetrical electron distribution which causes attraction between neighbouring atoms or molecules. This can occur in an atom or a molecule. The weakest force. Bigger molecules = stronger force. Present in all intermolecular bonds; the only force present in non-polar bonds.

Question 26

Describe some features of dipole-dipole forces.

Answer 26

This type of force will only exist between two asymmetrical molecules that each have a permanent dipole. Dipole–dipole forces are much stronger than London dispersion forces, but can act in unison with them.

Question 27

Describe some features of hydrogen bonds.

Answer 27

This intermolecular force only exists in molecules that have a bond between a hydrogen and a very electronegative element such as fluorine, oxygen or nitrogen (FON). The electronegative element must have a non-bonding pair of electrons. The hydrogen bond is not the intramolecular bond that exists between hydrogen and the FON in the same molecule.

Question 28

How do you predict the boiling point of an ionic compound?

Answer 28

SMALLER centrepoint distances and BIGGER charge = HIGHER boiling point (Coulomb's Law, [k(c1c2)]/r^2)

Question 29

What happens to the atomic radius of an anion and why?

Answer 29

Gets bigger because of electron repulsion

Question 30

Name the carbon allotropes in order of strength.

Answer 30

1. Graphite (layers of carbon) 2. Diamond (perfect tetrahedrons) 3. Bucky ball (C60), nanotube or whatever 4. Graphene (single layer of graphite, very very strong)

Question 31

Give a brief explanation of metallic bonding.

Answer 31

Delocalized electrons float around the lattice structure of a metal, sharing amongst all metal atoms in the structure. The delocalization of valence electrons turns the other metal atoms into cations, repelling each other and creating a neatly arranged lattice. This is metallic bonding. More delocalized electrons means better electric and thermal conductivity.

Question 32

Give a brief explanation of coordinate bonding.

Answer 32

A coordinate bond (also called a dative covalent bond) is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom.The atoms are held together because the electron pair is attracted by both of the nuclei. (e.g. NH3(g)+HCl(g)→NH4Cl(s))

Question 33

What is a fullerene?

Answer 33

A fullerene is an allotrope of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes and sizes.

Question 34

Silicon dioxide?

Answer 34

SiO2, sand/glass/fibreglass Same tetrahedral shape as diamond

Question 35

How is metallic bonding different from covalent or ionic bonding?

Answer 35

Metallic bonding is unique from its ionic and covalent counterparts as the bonding is not between atoms/ions. Instead, the bonding occurs between the cations within the lattice structure and the delocalised valence electrons. This type of bonding is non-directional because the electrostatic attractive force occurs in all directions .

Question 36

What are directional and non-directional bonds with examples?

Answer 36

Directional: atoms or molecules are arranged in a specific orientation, and the forces between them act in a particular direction. (Covalent, coordinate) Non-directional: the arrangement of atoms or ions is the same when viewed from any side, and the forces between them act in all directions. (Ionic, metallic)

Question 37

Three metal properties:

Answer 37

Shiny, sonorous, malleable (bendable), ductile (wireable), electrically conductive, thermally conductive (temperature)

Question 38

What is electron density? What is it, relative to metallic bonding?

Answer 38

The relative amount of electrons in a region of space. The radius and charge of a metal ion determine electron density. Bigger charge, smaller radius = stronger bond.

Question 39

Stronger metallic bond = greater ____

Answer 39

Hardness

Question 40

What is a free radical?

Answer 40

In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron.

Question 41

Acetate chemical formula?

Answer 41

CH2COOH (1-)