Download Chapter 1 Learning Objective Summary

Chapter 1
The Structure and Stability of Atoms
LEARNING OBJECTIVE SUMMARIES
1. Understand the fundamental properties and behavior of substances, including:
a. Matter is composed of atoms that combine in whole number ratios to form molecules
This fact, called Dalton’s atomic theory, historically was deduced from the Law of Definite
Proportions and the Law of Multiple Proportions.
Law of Definite Proportions:
Different samples of a pure chemical compound always contain the same proportion of
elements by mass. Example:
- If 1 g hydrogen + 8 grams oxygen = 9 g H2O, how much oxygen will combine
with 3 g hydrogen to form H2O?
- Since elements combine in definite proportions, tripling the amount of
hydrogen means the amount of oxygen that combines with it will be tripled to
24 g, giving triple the amount of water (27 g).
Law of Multiple Proportions:
Elements can combine in different ways to form different chemical compounds, whose mass
ratios are simple whole-number multiple of each other. Example:
- Carbon and oxygen can combine to form two compounds, CO and CO2
- CO is formed from a 6:7 carbon:oxygen ratio
- CO2 is formed from a 6:14 carbon:oxygen ratio
⁄
a simple whole number ratio
⁄
b. The conservation of mass in chemical reactions, which involve only a rearrangement of
atoms
This is called the Law of Mass conservation, which means that in any chemical reaction, the
sum of the masses of the reactants equal the sum of the masses of the products.
2. Learn the structure of atoms and the properties of each of the subatomic particles
Particle
Electron
Proton
Neutron
Mass (kg)
9.109383 × 10–31
1.672622 × 10–27
1.674927 × 10–27
Charge
–1
+1
0
Location
Delocalized around nucleus
Nucleus
Nucleus
3. Learn how atoms are characterized by the number of protons, neutrons, and electrons
Atomic number = # of protons
Mass number = # of protons + # of neutrons
Atomic charge = # of protons – # of electrons
4. Learn the relationship between the number of atoms, their atomic masses, and the number of
moles
Since
anythin
then a mole of atoms = 6.022
anythin s
atoms
The masses of individual atoms are expressed in atomic mass units, or amu, where 1 amu = ⁄
such that if an atom had a mass of 13.00335 amu, then 1 mole of that atom weighs 13.00335 grams.
,
5. Convert between atomic masses, atomic weights, and isotope abundances
Not all atoms of a particular element are identical. They can exist in different isotopes, defined by their mass
number, which changes based on how many neutrons are in the nucleus.
Isotopes of Hydrogen
Symbol:
Name:
Protons:
Neutrons:
Atomic mass:
Hydrogen
1
0
1.007825
Deuterium
1
1
2.014102
Tritium
1
2
3.016049
The atomic weight of an element is what is found on the periodic table, which is actually an average of the
atomic masses of all of the existin isotopes of the element, wei hted by their abundances in the earth’s
crust. This is called a weighted mean, and can be calculated using fractional abundances:
For example, if an isotope is 67.5 % abundant, its fractional abundance is 0.675. The sum of the fractional
abundances of all known isotopes must be equal to 1 exactly.
The equation to calculate the atomic weight is then as follows:
6. Learn to balance common nuclear reactions, know the common radioactive particles involved,
and understand fission and fusion
Chemical reactions involve the gain, loss, or sharing of the outer electrons, whereas nuclear reactions involve
changes to the composition of the nucleus. This means that alchemy is possible (though not economical!),
because transmutation of one element into another can be accomplished via radioactive decay or
bombardment with another particle. Many isotopes are unstable, and undergo spontaneous radioactive
decay to form more stable elements. Additionally, nuclear physicists have learned to perform nuclear
reactions to use as weapons, to produce energy, or to research subatomic particles.
Balancing Nuclear Reactions
- The sum of the superscripts (mass numbers) of all the species on the left must equal the sum of
those on the right in a nuclear equation
- The algebraic sum of the subscripts (atomic numbers) must be equal on each side of the arrow
in a nuclear equation. For example:
In the above reaction, 241 = x + 237, and 95 = y + 93
So x = 4 and y = 2, meaning that the decay product Z must have 2 protons and 2 neutrons,
otherwise known as an alpha particle (
). The possible nuclear decay reactants and products
are shown below:
Fission and Fusion
The energy harnessed in nuclei can be released in nuclear reactions. Fission is the splitting of a
heavy nucleus into lighter daughter nuclei and is used in nuclear power plants, while fusion is the
combining of nuclei to form bigger and heavier nuclei.