Chemistry Review 1
Name _________________________
Uncertainty in measurement

Accuracy vs. precision
accuracy (closeness)
% difference: % = 100|mean – true|
true

A X
Z
ionic charge = p – e
atomic symbol (# p)
A value = p + n
Z value = p

Isotopes: same Z, different A

Average atomic mass: 100mav = %1m1 + %2m2 + ...
Forms of matter
pure substances
mixtures
element
compound
homogeneous heterogeneous
measurements
mean
Atomic symbol
true
value
precision (spread)
% deviation: %  = 100 |trial – mean|
N(mean)
Significant figures: When are zeros significant?
0.00053000021000
never
always
with decimal
Round off calculations never measurements
x, : # of sf equals measurement with fewest sf
+, –: decimal position same as measurement with highest
Quantity of matter

Measured as mass (definition) or volume (liquids, gases)

Density: d = m/V

Molar mass: MM = sum of atomic masses in grams

Mole (6.022 x 1023 particles): n = m/MM
Atomic structure scientists

Dalton: atomic theory—elements made of indestructible,
identical atoms that combine to make compounds

J.J. Thomson: identified cathode rays as electrons and
measured charge-to-mass ratio

Millikan: measured electron charge with oil drops in a
vacuum chamber

Rutherford: characterized nucleus as dense and positive
with gold foil and alpha () radiation


Bohr: characterized electron region in terms of energy
levels and concentric "orbits"
Subatomic parts
Diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2
Molecular compound vs. crystalline compound
molecular: formula defines size
crystalline: formula shows ratio of atoms
Forms of natural radiation
Mass #
Charge
Relative
Type
Symbol
(A)
# (Z)
penetration
4
2
1
 42He
alpha
0 e
–
-1
100
0

-1
beta
0 e
+1
destroyed
0
+
1
positron
0 
0
0
10,000

0
gamma
Balance nuclear reactions

A and Z values are conserved

Nuclear symbol based on Z value
Nuclear decay





Rate of decay: rate = kNt
(k = rate constant, Nt = amount at time t)
Calculating Nt at time t: ln(No/Nt) = kt
Half-life: time when Nt = ½No: t½ = ln2/k
Photon energy

Light energy delivered as photon: Ephoton= hf = hc/
hc = 2.00 x 10-25 J•m  Ephoton = 2.00 x 10-25/ (J)

Energy proportional to frequency (color)  Violet > Red
(Inversely proportional to wavelength: 
Bohr model of hydrogen
En = -2.18 x 10-18/n2 (J)
Ephoton = 2.00 x 10-25/ (J)
E = E2 – E3 < 0
(ground state)
Particle
proton
neutron
electron
Location
nucleus
nucleus
outside
Charge
+
0
–
Mass
1
1
0
Symbol
1 p
1
1 n
0
0 e
-1
(excited states)
(n = : ionization, En = 0)
Chemistry Review 1
Uncertainty in measurement

Data "correctness" is measure by % ____________:
% = _______________

Data "precision" is measured by % ____________:
%  = ______________

Significant figures are all ________ digits, ________
zeros, and trailing zeros when a decimal point is ______

Leading zeros are _________ significant

Round off calculations never measurements
x, : _________________________________________
+, –: _________________________________________
Multiple massing of an object using the same balance
produces (12.3 g, 12.1 g, 11.9 g, 11.5 g, 11.3 g).
a. What is the mean?
b.
What is the % difference (true value is 12.0 g)?
c.
What is the % deviation?
d.
Is the balance more precise or accurate? Explain
Quantity of matter

Measured as mass (definition) or volume (liquids, gases)

Density: d _______

Mole: n = ___________ particles = __________

Molar mass: MM = __________________________
12.0 g of CO2 has a volume of 6.11 L.
a. What is the density of the CO2?
b.
What is the molar mass of CO2?
c.
How many moles of CO2?
d.
How many molecules of CO2?
Atomic structure scientists

____________; elements made of indestructible,
identical atoms that combine to make compounds

____________: identified cathode rays as electrons and
measured charge-to-mass ratio

____________: measured electron charge with oil drops
in a vacuum chamber

____________: characterized nucleus as dense and
positive with gold foil and alpha () radiation

____________: characterized electron region in terms of
energy levels and concentric "orbits"
Subatomic parts
Particle
Location
Charge
Mass
Symbol
proton
neutron
electron
Atomic symbol AZX

Atomic number Z: number of _______ (defines element)

Atomic mass A: sum of ________________________

Isotopes: ___________________________

Average atomic mass: 100mav = ___________________

Ions: # e  # p (e > p = _________, e < p = _________)
Magnesium has two common isotopes 24Mg, 25Mg.
a. How many protons, electrons & neutrons are in 2512Mg2+?
Name _________________________
b.
What is the average atomic mass if the abundance of
Mg-24 is 70.0 %?
Forms of matter

Pure elements: 1 type of atom
diatomic: ____________________________

Pure compound: _______________________________
molecular: formula _________________
crystalline: formula _________________

Mixture: group of pure substances in a container or object
______________: microscopic solute particles (solution)
______________: visible solute particles
Forms of natural radiation
Mass #
Charge
Relative
Type
Symbol
(A)
# (Z)
penetration

alpha

beta
positron


gamma
Rank alpha, beta & gamma in terms of
relative penetration:
and mass:
Balance nuclear reactions

A and Z values are conserved

Nuclear symbol based on Z value
Complete the nuclear equations.
231 Th  231 Pa +
16 O + 1 H  13 N +
90
91
8
1
7
Nuclear decay

Rate of decay: rate = kNt
(k = _______________, Nt = __________________)

Calculating Nt at time t: ln(No/Nt) = kt

Half-life: time when Nt = ½No: t½ = ln2/k
Co-60 has a half-life of 5.26 yrs.
a. What is rate constant for Co-60?
b.
What % of Co-60 is present after 6 years?
Photon energy

Light energy delivered as photon: Ephoton= hf = hc/
hc = 2.00 x 10-25 J•m  Ephoton = _______________ (J)

Energy proportional to _________ (color)  Violet > Red
(Inversely proportional to _______________
What is the energy of a 4.34 x 10-7 m photon?
Bohr model of hydrogen

Electron occupies an orbit around the nucleus

Orbits defined by energy level n: En = -2.18 x 10-18/n2 (J)

Ground state—lowest energy level (n = 1)

Excited state—electron absorbs photon energy and
moves to higher (n > 1) energy level

Eelectron = ____________ = _____________

+E when going to __________ energy level
(-E when going to __________ energy level)

Ionization—___________________ (n = ____, E = ____)
An n = 2 electron absorbs the photon energy from 4.34 x 10-7
m photon. What energy level does the electron move to?