Time taken for half original #atoms to decay. ``` Mr=Mox(½)#of half lives #half lives = total time / t (½) ```

Chem Exam Review Flashcards by Geraldine Lopez

What is the Octet Rule?

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

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What are Cations/Anions?

Cation=positive ion

Anion=negative ion

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What is Ionization Energy

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

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How do you write an I.E. equation?

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

Ex. Li• + I.E. -> [Li]¹⁺ + 1e^-

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What is Electron Affinity?

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

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How do you write an E.A. equation?

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

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

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What does Isoelectronic mean?

“Same electron configuration as”

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What are Isotopes?

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

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What is Average Atomic Mass? What are the unit?

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

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How do you calculate AverageAtomicMass?

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

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Half Life & Equation

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)

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

Number of Orbits

Nuclear Charge

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of Orbits

Row#(period)=#of Orbits

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

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Nuclear Charge

NC=# of protons in nucleus

Increases to the right of a period

Larger #= stronger electrostatic attraction

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Ionic Radius Trend

Cations are smaller than their neutral atom

Anions are larger than their neutral atom

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Multiple Ionization Energies Trend

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^-)

What is Metallic Character?

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

Non-Metallic Character

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

Electronegativity

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

Trends in the Periodic Table

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

Expanded Octet

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

Guide to Balancing

Metals
Polyatomic ion groups
Non-metals
Hydrogen and oxygen

Sig Figs & Zeros

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

Law of Constant Composition

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

Percent Composition

% 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

Dissociation Equation

Shows soluble ionic compound breaking into ions in solution. Ex. NaCl_(s)-\> Na⁺_(aq) + Cl^-_(aq)

Dissolving Molecular Compounds

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].

Solvents / Solubility Rules

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\*

Percent Concentration

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)

Low Concentrations

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

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

How to calculate [H₃O⁺] / pH

[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\*

pOH

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

Absolute Scale of Temperature

Celcius Kelvin 100^oC 373K 0^oC 273K -273^oC 0 K

Dalton's Law of Partial Pressure

P_total= P₁ + P₂ + P₃ ... \*Collecting gas over water includes water vapour, therefore the partial pressure of water must be subtracted.

SATP and STP Values

_SATP__STP_ T : 25^oC = 298K 0^oC = 273k P : 100kPa 101.3kPa n : 1 mol 1 mol V : 24.8L 22.4L

Percent Ionization

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