WashU Chemistry Review Flashcard

Precision
A measure of how closely individual measurements agree with one another.
Accuracy
Refers to how closely individual measurements agree with the correct or true value.
Significant Figures: Digits that are significant:

 

  1. Non-zero digits are always significant.
  2. Any zeros between two non-zero digits are significant.
  3. A final zero or trailing zeros in the decimal portion ONLY are significant.

Rules for Using Significant Figures: For addition and subtraction:

 the answer should have the same number of decimal places as the term with the fewest decimal places.

Rules for Using Significant Figures:

For multiplication and division:

 the answer should have the same number of significant figures as the term with the fewest number of significant figures.

Rules for Using Significant Figures:

In multi-step calculations:

 you may round at each step or only at the end.

Rules for Using Significant Figures: Exact numbers, such as integers, are treated as if…

…as if they have an infinite number of significant figures.

Rules for Using Significant Figures:

In calculations, round up if : 

 round down if:

 If the first discarded digit is 5, then round up if: 

 round down if:

In calculations, round up if the first digit to be discarded is greater than 5 and round down if it is below 5.

If the first discarded digit is 5, then round up if a nonzero digit follows it, round down if it is followed by a zero.

Significant Figures: Addition and Subtraction:

 12.793 + 4.58 + 3.25794 = 20.63094

sig figs?

With significant figures it is 20.63 since 4.58 has 2 decimal places, which is the least number of decimal places.

 

Significant Figures: Multiplication and Division.

56.937/0.46 = 130.29782609

sig figs?

With significant figures, the final value should be reported as 1.3 x 102 since 0.46 has only 2 significant figures. Notice that 130 would be ambiguous, so scientific notation is necessary in this situation.

Even though the _____ occupy most of the volume of the atom, they hold only a _____percentage of the atom’s mass.

The _____is incredibly dense and contains almost all of the mass of the atom. Actually nuclear densities are approximately 1014 times that of normal matter.

electrons occupy most of the volume of the atom, they hold only a very small percentage of the atom’s mass.

 The nucleus is incredibly dense and contains almost all of the mass of the atom. Actually nuclear densities are approximately 1014 times that of normal matter.

The ____/____occupies the majority of the atom.

 This ___ is actually over __% of the volume of the atom.

The electron cloud occupies the majority of the atom. This cloud is actually over 99% of the volume of the atom.

Masses of Atomic Components

in kg:

p+, proton mass:

no, neutron mass:

e, electron mass:

Masses of Atomic Components

p+, proton mass: 1.67262 x 10-27 kg
no, neutron mass: 1.67493 x 10-27 kg
e, electron mass: 9.1094 x 10-31 kg

Mass Number (A)

 

This is the total number of protons plus the number of neutrons (i.e., the total number of nucleons).

(A = # of protons + # of neutrons)

The atomic number (Z) is:

Z=is the number of protons.

The atomic number often is not included because the element name (or element symbol) also tells the number of protons.

If the number of protons changes, then it becomes a different element.

For example, helium will always have 2 protons; if you add a proton then it becomes lithium (Li).

A=
Mass Number
Z=
Atomic Number
In a neutral atom, the number of electrons must equal….

 the number of protons.

However if the atom has a non-zero charge, the number of electrons does not equal Z, and the atom is referred to as an ion.

 If an atom has a non-zero charge, the number of electrons does not equal Z, and the atom is referred to as an ___
ion
Ion:
a charged atom produced by adding or removing an electron or electrons to or from a neutral atom.
Cation
a positively charged ion.
Anion
 a negatively charged ion.
[image]
Atomic #, mass, chemical symbol, element name
[image]
The mass number (A = # of protons + # of neutrons) is four. This is the total number of protons plus the number of neutrons (i.e., the total number of nucleons). The atomic number (Z) is 2 and is the number of protons. T
[image]

 There are 35 protons, 45 neutrons and since it is neutral there are 35 electrons.

[image]
There are 47 protons, 61 neutrons and 44 electrons.
[image]
There are 34 protons, 45 neutrons, and 36 electrons.
[image]
There are 27 protons, 32 neutrons, and 23 electrons.
mass of a proton in amu
1.00728 u
mass of a neutron in amu
1.00867 u
mass of an electron in amu
5.5 *10^-4 u
Three processes that change the # of subatomic particles in an atom

1. Ion Formation (Ionization)

2. Isotope Conversion

3. Transmutation

Ion Formation (Ionization)
Changing the # of Electrons in an atom
Isotope Conversion
Changing the # of neutrons in the nucleus of an atom
Transmutation
Changing the # of protons in the nucles. This converts one element into another
Isotope Conversion and Transmutation occur only in _____reactions, not in normal _____reactions.
Isotope Conversion and Transmutation occur only in ___nuclear__reactions, not in normal __chemical___reactions.
chemical reactions
processes in which the # of electrons held or shared by an atom change
nuclear reactions
processes that involve changing the # of neutrons or protons held in the nucleus of an atom
missing mass
the difference between the experimental and calculated mass of an isotope
The missing mass has been converted into _____/___/____
nuclear binding energy
nuclear binding energy
energy that holds the nuclear particles together. This is the energy that would be required to separate the nucleus into its constituent protons and neutrons.
Avogadro’s #
6.022 x 1023 particles
1 mole contains the same number of particles as there are in ________.
12g of carbon-12 atoms by definition
1 mole contains the same number of particles as there are in 12g of carbon-12 atoms by definition.
This number is called;_______ and is equal to ______.
Avogadro’s number or Avogadro’s constant (NA) and is equal to 6.022 x 1023 particles.
The nuclear binding energy is related to the missing mass via Einstein’s famous equation (from the Theory of Special Relativity):
E=mc^2

E=mc^2

E=

m=

c=

E=nuclear binding energy

m=mass (in the case of nuclear binding energy equation it is the missing mass)

c=speed of light, 2.9979*10^8 m/s

c=speed of light=
 2.9979*10^8 m/s
The elemental atomic mass is the …….It is nothing more than a…..
The elemental atomic mass is the atomic mass that appears in the periodic table. It is nothing more than a weighted average of the isotopic masses of all the naturally occurring isotopes.
Isotope
atoms of the same element that differ in the number of neutrons in the nucleus and therefore they have different masses. Nevertheless isotopes have practically identical properties in terms of chemical reactivity.
Elemental Atomic Mass=
[image]
[image]

i=an index identifying each isotope for the element

f=fractional abundance of isotope i

m=mass of isotope i

The atomic mass of a specific atom or molecule is determined by using an experimental technique called_____.
Mass spectrometry
Mass spectrometry: this technique…..
separates the different isotopes of atoms to allow determination of the percent abundance or isotopic composition of the element in the given sample.
In a mass spectrum, each isotope appear as a ___in the mass spectrum. The ___(___) of each ____ depends on the _____of that isotope in the sample and the unique location of the ___on the x-axis indicates the ______of the isotope.
In a mass spectrum, each isotope appear as a _peak__in the mass spectrum. The _intensity__(__height_) of each __peak__ depends on the __abundance___of that isotope in the sample and the unique location of the __peak_on the x-axis indicates the ___mass-to-charge(m/q)___of the isotope.

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