Chemistry unit 4 (Originally: Chemistry lab quiz/properties of bonds)

Ionic bonds

Ionic bonds

forms when a metal loses an electron and gives it to a nonmetal

What shape do ions take when they form?

Crystal lattice structure

How is a crystal lattice structure made?

The negative anions are surrounded by the positive cations. Energy is released when the bonds are formed. When larger amounts of energy are released the bonds are stronger and more stable.

Ionic bonds properties

• High melting and boiling points: cations are strongly attracted to anions on all sides so it takes a large amount of energy to break the numerous bonds

• Hardness: ions in the crystal are locked in place by their bonds so the structure is very rigid and forms hard solids

• Brittle (not malleable or ductile): shifting ions in the crystal can cause similar charges to line up next to each other, repulsion forces the crystal to fall apart

More ionic bond properties

Ionic compounds do not conduct electricity when they are in solid form because the ions cannot move freely. However, when dissolved (or melted), ions are separated from each other and free to move. This allows an electrical current to flow easily through the metal or solution.

Covalent bonding

• In covalent bonding, electrons are shared to complete valence shells (usually octets)

• Covalent bonding usually occurs between two nonmetals

• Compounds that contain covalent bonds are called molecules

Covalent bonding and polarity

Polarity: unequal sharing of electrons in a covalent bond

Determined by differences in electronegativity

Intermolecular forces

• Intermolecular Forces: weak attractions between individual molecules

• Weaker than covalent bonds (and easier to break)

• Only forces that hold molecules together in the liquid and solid states

• These forces are what gives covalent bonds their properties, not the covalent bond itself

What happens when a covalent bond is dissolved in water?

The molecule is still not conductive; even when dissolved, no free-floating ions are produced

Covalent vs ionic bonds when dissolved in water, and how that effects their ability to conduct electricity (example uses salt and sugar, sugar being the covalent and salt being ionic)

Covalent properties

• Low melting and boiling points (compared to ionic compounds)

  • Molecules only held together by weak inter molecular forces

  • Many molecules are gases at room temperature

• Low hardness (covalent compounds tend to be soft)

  • Weak inter molecular forces allow molecules to move easily (not locked tightly into place like ionic compounds)

• Limited solubility in water

  • Water is polar and can only attach to and dissolve substances that are also polar or charged (ionic)

  • Many molecules are non-polar, so they don’t dissolve

• Poor conductors of electricity

  • Freely-moving ions needed to carry an electrical current

  • Many molecules do not separate into ions in water

Metallic bonding

Valence electrons are held weakly by the nucleus, and can easily move from atom to atom. Electrons are said to be delocalized and from a “sea of mobile electrons.” Strength of bonds determined by heat of vaporization.

Heat of vaporization

Heat of Vaporization: amount of energy required to turn a metal (usually a solid) into a gas

• positive energy values since it measures the energy required to break bonds

Metallic Bonding: Conductivity, MP and BP

High melting points (mp) and boiling points (bp): the positive nuclei are strongly attracted to many delocalized electrons surrounding it, so large amounts of energy needed to break bond

Conductivity: outer electrons move freely through a metal making them good conductors of heat and electricity.

Metallic Bonding: Malleability & Ductility

Malleable & Ductile: metals can be hammered into sheets or rolled into wires easily. The positive nuclei simply shift past one another through the sea of electrons, but do not lose their attraction to the electrons.

How to determine polarity of a molecule

1. Look at electronegativity

2. Look at the symmetry, if a molecule is symmetrical and has the same element surrounding the central atom, it must be non-polar

3. If a molecule is not symmetrical, it must be polar because there are some electrons somewhere (lone pairs) pushing the shape into a non-symmetrical shape

Why are the angles in a trigonal pyramidal smaller than the angles of a tetrahedral

Because the trigonal pyramidal is basically a tetrahedral but the top atom is replaced by a lone pair, which pushes on the atoms surrounding the central atoms a little more than an atom would, creating smaller angles (same goes for trigonal planar and bent). The electrons on the outside of the central atom just takes up more space.

What VSEPR shapes have lone pairs on the central atom?

Trigonal pyramidal and bent

What VSEPR shapes have no lone pairs on the central atoms?

Tetrahedral, linear, and trigonal planar

How to determine the number of bonds in a lewis structure?

1. add the max number of valence electrons each element can have (8 for most, 2 for hydrogen)

2. Add the number of valence electrons that each element has (adjust for ions)

3. #1-#2 (max number-current number)

4. divide the number you get by 2

5. this gives you the number of bonds you will have

Acid nomenclature for binary acid

Binary Acid

Hydrogen + nonmetal (monoatomic ion)

1. Change the –ide ending of the anion to -ic

2. Add the prefix hydro-

Examples:

•  HCl – hydrochloric acid 

  • chloride became chloric

  • Hydro- prefix added

Acid nomenclature for an oxyacid (mostly polyatomics)

Oxyacids (Ternary Acids)

Hydrogen + nonmetals (polyatomic ion)

1. Anions with –ate endings change to -ic

2. Anions with –ite endings change to –ous

   Do Not Add Hydro-

Examples:

•  HClO₃ –chloric acid 

  • chlorate became chloric

Covalent nomenclature

1. First element keeps its regular name

2. Second element gets –ide ending

3. Add numerical prefixes to both elements

   • Mono- only used on second element

   • Prefixes ending in “a” or “o” drop the last vowel if it’s followed by another vowel

Examples:

•  CO – carbon monoxide 

  • oxygen became oxide

  • Mono- became Mon- before oxide

S block metal and nonmetal (fixed charge metals)

1. metal retains its name

2. nonmetal retains its ionic name (-ide)

ex: Sodium chloride, Calcium chloride (CaCl2)

Variable charge metal +nonmetal

1. Metal get its charge written with roman number in () after name

2. nonmetal retains its ionic name

3. Variable charge metals are transition metals, d block, and elements under the staircase

Ex: Fe+3 + Cl- =iron(III) chloride

Lattice energy

Energy being released when bonds form (sometimes given in negative but just take absolute value to find strongest bonds)

Bond energy

Energy added to break bonds, number should be positive

Bond length and bond energy

Bond length decreases as you gain bonds, and as bond energy increases, attraction is stronger, so bond length goes down

Ammonium

(NH4)+

Hydroxide

(OH)-

Carbonate

(CO3)-2

Nitrate

(NO3)-

Phosphate

(PO4)-3

Sulfate

(SO4)-2

Acronym to remember polyatomics you need to memorize

Nick the Camel ate Supper in Phoenix

(Use the first letter to give the name of the polyatomic, count the number of consonants to give the number of O’s, and count the vowels to give the charge)

Ex Nitrate→ 3 consonants and 1 vowel in Nick → (NO3)-

examples this acronym doesn’t cover that you still need to know: Ammonium (NH4)+ and hydroxide (OH)-

What random elements look like they should have a roman numeral but instead have a fixed charge?

Al has a fixed charge of +3, Zn has a fixed charge of +2, and Ag has a fixed charge of +1