WashU Chemistry Review – Flashcards

A measure of how closely individual measurements agree with one another.

Refers to how closely individual measurements agree with the correct or true value.

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

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

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

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

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

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.

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

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.

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

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

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

(A = # of protons + # of neutrons)

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).

Mass Number

Atomic Number

 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.

ion

a charged atom produced by adding or removing an electron or electrons to or from a neutral atom.

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

There are 47 protons, 61 neutrons and 44 electrons.

There are 34 protons, 45 neutrons, and 36 electrons.

1.00728 u

1. Ion Formation (Ionization)

2. Isotope Conversion

3. Transmutation

Changing the # of Electrons in an atom

Changing the # of neutrons in the nucleus of an atom

Isotope Conversion and Transmutation occur only in ___nuclear__reactions, not in normal __chemical___reactions.

the difference between the experimental and calculated mass of an isotope

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.

6.022 x 1023 particles

Avogadro’s number or Avogadro’s constant (NA) and is equal to 6.022 x 1023 particles.

E=mc^2

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.

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Mass spectrometry

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 _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.