Chem Exam Review

Question 1

What is the Octet Rule?

Answer 1

A full valence = 8e^- (except helium-only2). Elements gain/lose e^- to achieve an octet, becoming ions.

Question 2

What are Cations/Anions?

Answer 2

Cation=positive ion

Anion=negative ion

Question 3

What is Ionization Energy

Answer 3

The quantity of energy required to remove an electron from an atom or ion in gaseous state.

Question 4

How do you write an I.E. equation?

Answer 4

Lewis Symbol + I.E. -> [Cation]^_++_e^-

Ex. Li• + I.E. -> [Li]¹⁺ + 1e^-

Question 5

What is Electron Affinity?

Answer 5

The quantity of energy change when an electron is added to the valence shell of an atom in gaseous state.

Question 6

How do you write an E.A. equation?

Answer 6

Lewis Symbol + #e^- -> [Anion]^_- + E.A.

Ex. S•^(x6) + 2e^- -> [S•^(x8)]^2- + E.A.

Question 7

What does Isoelectronic mean?

Answer 7

“Same electron configuration as”

Question 8

What are Isotopes?

Answer 8

Atoms of an element with same # p⁺ and e^- but differ in #n^o

Question 9

What is Average Atomic Mass? What are the unit?

Answer 9

Average of the masses of all the isotopes of an element. Units are “u” (atomic mass units)

Question 10

How do you calculate AverageAtomicMass?

Answer 10

AAM= mass(%abundance)+mass(%abundance)

Question 11

Half Life & Equation

Answer 11

Time taken for half original #atoms to decay.

M<sub>r</sub>=M<sub>o</sub>x(½)<sup>#of half lives</sup>
#half lives = total time / t (½)

Question 12

What are the two factors that affect attraction for valence e^-

Answer 12

Number of Orbits

Nuclear Charge

Question 13

of Orbits

Answer 13

Row#(period)=#of Orbits

Electrostatic attraction between valence e^- and the nucleus decrease as # of orbits increase (e^- are farther away from protons)

Question 14

Nuclear Charge

Answer 14

NC=# of protons in nucleus

Increases to the right of a period

Larger #= stronger electrostatic attraction

Question 15

Ionic Radius Trend

Answer 15

Cations are smaller than their neutral atom

Anions are larger than their neutral atom

Question 16

Multiple Ionization Energies Trend

Answer 16

First I.E.- energy to remove first e^- (weakest hold)

Second I.E.- energy to remove second e^- (more than 1^st I.E.-protons pulling on less e^-)

Third I.E. energy to remove third e^- (more than first two-protons pull on less e^-)

Question 17

What is Metallic Character?

Answer 17

The ability to lose e^-. Lower I.E. = more metallic

Question 18

Non-Metallic Character

Answer 18

Higher E.A. = more reactive non-metal (ability to attract e^-)

Question 19

Electronegativity

Answer 19

EN is a measure of how well an atom can attract a shared pair of e^- around it’s nucleus.

Question 20

Trends in the Periodic Table

Answer 20

Down a group : Atomic radius and ionic radius increases, Metallic Character increases,

Across a period : Ionization Energy increases, Electron Affinity increases, Non-Metallic Character increases, Electronegativity (EN) increases

Question 21

Expanded Octet

Answer 21

Elements in third row [and down] can be surrounded by more than 8 e^- in order to minimize formal charge.

Question 22

Guide to Balancing

Answer 22

1. Metals
2. Polyatomic ion groups
3. Non-metals
4. Hydrogen and oxygen

Question 23

Sig Figs & Zeros

Answer 23

• Leading zeros don’t count
• Captive zeros always count
• Trailing zeros count

If x and / take least # of sig figs

If + and - take least # of decimal places

Question 24

Law of Constant Composition

Answer 24

Any given compound has the same composition anywhere.

Adding or removing atoms changes compound into completely different substance.

H₂O is always 88.9% O and 11.1% H

Question 25

Percent Composition

Answer 25

% by mass of each element in a compound. (always the same no matter how large the sample)

%C = mass[Element] / total mass [Compound] x 100

Question 26

Dissociation Equation

Answer 26

Shows soluble ionic compound breaking into ions in solution.

Ex. NaCl_(s) -> Na⁺_(aq) + Cl^-_(aq)

Question 27

Dissolving Molecular Compounds

Answer 27

Most dissolve as molecules (except acids). Int.molec.forces are broken, bonds aren’t.

Therefore most molec.substances (except acids) are non-electrolytes [no mobile ions].

Question 28

Solvents / Solubility Rules

Answer 28

Rule: Like dissolves like.

Polar solvents dissolve polar molecules due to DD forces

Non-polar solvents dissolve non-polar molecules due to LDF

*H₂O - polar, C₈H₁₈ (gasoline) - non-polar*

Question 29

Percent Concentration

Answer 29

v/v *units must be the same (5ml/100ml)

m/v *units are g/ml (4% = 4g/100ml)

m/m *units must be the same (2g/100g)

Question 30

Low Concentrations

Answer 30

Parts per mil. - ppm: c_ppm= m/m x10⁶

Parts per bil. - ppb: c_ppb= m/m x10⁹

Parts per tril. - ppt: c_ppt= m/m x10¹²

Question 31

pH

Answer 31

Power of Hydrogen - indicates amount of H₃O⁺ in a solution

One unit of pH change means 10x change in H₃O⁺ concentration

Ex. pH of 5 is 10x more acidic than pH of 6

Question 32

How to calculate [H₃O⁺] / pH

Answer 32

[H₃O⁺] = 10^-pH

If [H₃O⁺] is _#x10^-_mol/L = -log#_x10^-_

Ex. 2.3x10^-2mol/L -> -log2.3x10^-2 = 1.6pH

*square brackets mean concentration*

Question 33

pOH

Answer 33

pOH=7

[OH^1-] = 10^-7mol/L

Question 34

Absolute Scale of Temperature

Answer 34

Celcius Kelvin

100^oC 373K

0^oC 273K

-273^oC 0 K

Question 35

Dalton’s Law of Partial Pressure

Answer 35

P_total = P₁ + P₂ + P₃ …

*Collecting gas over water includes water vapour, therefore the partial pressure of water must be subtracted.

Question 36

SATP and STP Values

Answer 36

SATP__STP

T : 25^oC = 298K 0^oC = 273k

P : 100kPa 101.3kPa

n : 1 mol 1 mol

V : 24.8L 22.4L

Question 37

Percent Ionization

Answer 37

%ionization (p) = [H₃O⁺] / [Acid] x100