CHEMISTRY_MIDTERM 1

What does each letter stand for?

A = the mass number (#p+n): can describe isotope

Z = the atomic number (#p): describes element

X = Chemical symbol for the element

Neutral atom

#electrons = # protons

The atom's total electric charge is zero, and it is said to be neutral.

Charged ion

#electrons ≠ #protons

Cation

positive charge

Anion

negative charge

#neutrons equation

Atomic number - #protons

(ex: Lutetium-177 has 71 protons;

#neutrons = 177-71 = 106

The sum of all oxidation numbers in a molecule or ion must…

equal the overall charge of the molecule or ion

A pure element always has an oxidation number of

0

Fluorine has an oxidation number of

-1 (typically all halogens do)

An alkali metal ion (Gr 1) has an oxidation number of

+1

An alkaline earth metal has an oxidation number of

+2

What is an oxidation number?

The number of electrons an atom can donate or accept to form a bond with another atom

Hydrogen oxidation number is typically

+1

If hydrogen forms a compound with a metal or boron, it behaves as a hydride and its oxidation number is

-1

Oxygen’s oxidation number is

-2 (sometimes -1 when there is a -O-O-)

In a compound with metalloids and metals, which are positively charged, non metals are typically (charge wise)

negatively charged

In a compound with metalloids and non metals, which are negatively charged, metals are typically (charge wise)

positively charged

What is the oxidation state of carbon in 3CO2

+4

Ionic compounds

compounds made up of ions that form charged particles when an atom (or group of atoms) gains or loses electrons

Binary molecular compounds

a molecular compound that is composed of two elements

Polyatomic ions

a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero.

Oxoacids

an acid that contains oxygen

Mols

A mole is defined as 6.02214076 × 10²³ of some chemical unit, be it atoms, molecules, ions, or others. The mole is a convenient unit to use because of the great number of atoms, molecules, or others in any substance

How do you find each quantity?

m = M x n (g)

M = m / n (g / mol)

n = m / M (mol)

How do you find each quantity?

N = n x Na (particles / atoms)

Na = avogadro’s # (N / n) mol

n = N / Na (mol)

1 mL =

1 cm³

How do you find each quantity?

n = C x V (mols)

C = n / V (mols / dm³)

V = n / C (dm³)

How do you find each quantity?

m = d x V (g)

d = m / V (g / cm³ or kg / L^-1)

V = m / d (L)

% by mass =

(mass of solute / mass of solution) x 100

% by volume =

(volume of solute / volume of solution) x 100

Acid-base reactions

The reaction of an acid with a base is called a neutralization reaction.

The products of this reaction are a salt and water.

Redox reactions

a chemical reaction in which electrons are transferred between two reactants participating in it

Reduction: gains electron

Oxidation: loses electron

Decomposition reactions

the process or effect of simplifying a single chemical entity into two or more fragments.

Precipitation reactions

one in which dissolved substances react to form one (or more) solid products

Displacement reactions

occurs when a more reactive element displaces, or pushes out, a less reactive element from a compound that contains the less reactive element

To find the limiting reagent

1. Determine the balanced chemical equation for the chemical reaction.

2. Convert all given information into moles (most likely, through the use of molar mass as a conversion factor).

3. Calculate the mole ratio from the given information. Compare the calculated ratio to the actual ratio.

4. Use the amount of limiting reactant to calculate the amount of product produced.

5. If necessary, calculate how much is left in excess of the non-limiting reagent.

Boyle

VOLUME is inversely proportional to PRESSURE

Charles

VOLUME is proportional to TEMPERATURE

Avogadro

VOLUME is proportional to MOLS

PV = nRT rearranged for density

PM = dRT (V = m / d) (m = M x n)

Partial Pressure

partial pressure of a gas describes its contribution to the total pressure.

Ptotal = P1 + P2 + P3 + Pn

P1 = Ptotal x x1 (mol fraction of 1)

v =

frequency

lambda (wavlength) =

c / v

E =

energy (J)

E is proportional to

frequency (s^-1)

E is inversely proportional to

wavelength (nm)

E = (formula)

hv and hc / lambda

v = (formula)

c / lambda

Quantum mechanics describe

electrons

Electrons behave as

waves and particles

Orbitals are

regions of space where electrons are likely to be found (probability clouds)

Quantum numbers

describe orbitals

Quantum theory

energy is quantized (discontinuous)

Bowls of flame =

electronic transitions

emitted light consists of certain wavelengths

The photoelectric effect (Albert Einstein)

When light of a certain minimum frequency called threshold frequency shines on a metal surface, electrons are ejected from the metal surface.

Higher wavelength =

lower energy

Ionization

Quantity of energy that must be absorbed to discharge an electron (resulting in cation)

Generally increases from left to right and bottom to top.

Emission

the process that creates a photon and takes the atom or molecule in an excited state back to the ground state.

ΔE < 0

Absorption

The process that consumes a photon and puts the atom or molecule in an excited state.

ΔE > 0

wavelength graph for hydrogen emission

Lyman = UV

Balmer = Visible, UV

Paschen = IR

Brackett = IR

Exposure to UV radiation

• shortwave radiation (especially uvc) is largely screened by small molecules (N2, O2) in the atmosphere.

• most UVA, UVB radiation is absorbed by O3, but some reaches the earth’s surface; harmful to biological molecules.

Body’s response to radiation

produces melanin to filter UVB radiation

Aufbau rule

electrons occupy the lowest energy level orbital that will receive it.

Hunds rule

electrons will occupy empty orbitals first, before occupying half filled orbitals.

Pauli exclusion rule

No 2 electrons in an atom may have the same 4 quantum numbers

Absorption and emission of energy between the same 2 energy levels are equal in

magnitude

Physical sunscreens

reflect UV rays

Chemical sunscreens

molecules absorb UV rays and then lose energy by falling back to ground state.

no atom is ionized

Wave-particle duality (J.J. Thompson and. George Thompson)

Waves display particle-p (like properties

Particles display wave-like properties

p (momentum) =

mu

Diffraction occurs when

radiation and object spacing are similar

Broglie wavelength is used for

photoelectric effect questions

λ (wavelength) = c (speed of light) / v (frequency)

applies to light (any electromagnetic radiation)

λ (wavelength) = h (plank’s constant) / mu (mass x speed) or p (momentum)

applies to particles

Principal quantum number (n)

• described orbital energy and average distance from nucleus.

• Determines size of the atomic orbital.

• Larger n = orbital extend further from nucleus

Angular momentum quantum number (l)

• describes orbital shape

• number of l values = number of subshells in a given n

• (n-1)

• ex: n=3; l= 0,1,2

Magnetic quantum number (ml)

• describes orbital orientation

• (2l + 1) values

• sml = 0

• pml = -1,0,1

• dml = -2,-1,0,1,2

S orbitals

spherical

1s, 2s, 3s, 4s

P orbitals

• possible in n>=2

• 1 angular node (0 probability of finding electrons)

• (px, py,pz)

• 3 orbitals

d orbitals

• possible in n>=3

• 2 angular nodes

• (dxy, dxz, dyz, d2², dx²-y²)

• 5 orbitals

Degenerate

subshell energies are the same (ex: hydrogen)

Electron screening, effective nuclear charge

subshell energy differ (multi-electron atoms)

Electron spin quantum number (ms)

• electrons have spin generating magnetic field

• ms = +1 / 2 or - 1 / 2

Diamagnetic

all paired electrons

Paramagnetic

unpaired electron (even just one)

Electron configuration

lowest energy configuration

What is this group?

Alkali metals

What is this group?

Alkaline Earth metals

What is this group?

Transition metals

What is this group?

Post-transition metals

What is this group?

Metalloids

What is this group?

Nonmetals

What is this group?

Halogen

What is this group?

Noble gas

What is this group?

Lanthanides

What is this group?

Actinide

Shielding

electrons shield one another from the nucleus causing them to be repelled, despite their attraction to the protons in the nucleus

Z =

full attractive charge from the nucleus

Zeff =

effective nuclear charge

Z-S (where S is shielding)

Increases from left to right

Increases slightly from top to bottom (because shielding is not 100%)

S is approximately equal to

number of core electrons (+ small contribution from other valence electrons)