Download Chapter 4: The Structure of the Atom &amp

Chapter 4: The Structure of the Atom &
Chapter 25: Nuclear Chemistry
CHAPTER 4
4.2 Subatomic Particles and the Nuclear Atom
 Subatomic atomic particles
o Proton – positive charge _________
 1.673x10-24 g
o Neutron – neutral charge ________
 About the same size as a proton: 1.675x10-24 g
o Electron – negative charge _______
 1/1840 the size of a proton or neutron (9.11x10-28 g). However has
equal (but opposite) charge of a proton.


ATOMS
o Electrically NEUTRAL
o Composed of protons, neutrons, and electrons
o Spherically shaped, with a tiny, dense NUCLEUS of POSITIVE charge
surrounded by one or more negatively charged electrons
o Most of an atom is empty space in which fast-moving ELECTRONS
travel.
o Electrons are held within the atom by their attraction to the positively
charged nucleus
o The nucleus (PROTONS + NEUTRONS) carries 99% of the mass of the
atom
o Since the atom is electrically neutral, the number of protons in the nucleus
equals the number of electrons outside of the nucleus.
4.3 How Atoms Differ
 ATOMIC NUMBER is the number of _______________ in the ___________.
o Each element has its own unique positive charge, so the atomic number
DEFINES THE ELEMENT
 Since atoms are electrically neutral, the number of protons is also the number of
_________________.
 Practice Problems p.99 11, 12, 13
 ISOTOPES are atoms of the same element (therefore same number of p+ and e-)
but they have different number of NEUTRONS
o Because the nucleus carries 99% of the mass of the atom, isotopes have
different mass numbers
o MASS NUMBER is PROTONS + NEUTRONS
o Practice Problems p.101 14
o Isotope symbols:
 Working with the masses of p+, no, and e- is very hard. Scientists created the
atomic mass unit (amu) to represent 1/12 of a carbon-12 atom.
o 1 proton = 1 amu
1 neutron = 1 amu
1 electron = .0005 amu
o Note that the electron has little impact on the mass of the atom
 ATOMIC MASS (not to be confused with the mass number) is the weighted
average mass of the isotopes of that element.
o Example: Element X has two isotopes X-6 (6.015 amu) and X-7 (7.016
amu). X-6 comprises 7.5% of all of element X. X-7 makes up the
remaining 92.5%. What is the atomic mass?
o NOTE: The % needs to be divided by 100 BEFORE putting it into the
equation!!
o Practice Problems p.104 15, 17
4.4 Unstable Nuclei and Radioactive Decay
 Chemical reactions involve only the atom’s electrons. The nucleus remains
UNCHANGED
 Nuclear reactions involve the nucleus, where atoms of one element are chanted
into an atom of another element by emitting RADIATION. [Process is called
RADIOACTIVITY]
 Why do some atoms emit radiation? Their nucleus is UNSTABLE.
 Three types of radiation
o Alpha radiation is made of ALPHA PARTICLES (2 protons and 2
neutrons)
 Equivalent of a Helium nucleus, therefore symbol is _________ or
___________
 _______ charge
o Beta radiation is made of BETA PARTICLES (fast moving electrons)
 Symbol is _________ or ________
 _______ charge
o Gamma radiation is made of GAMMA RAYS (high energy radiation)
 No mass or charge
 Symbol is _______________
 Nuclear equations are used to show the radioactive decay process
o Mass number and Atomic number are CONSERVED
Chapter 25: Nuclear Chemistry
25.1 Nuclear Radiation / 25.2 Radioactive Decay
 Characteristics or Chemical and Nuclear Reactions
CHEMICAL
1. Occur when bonds are broken and
formed
2. Atoms remain unchanged, though they
may be rearranged
3. Involve only valence electrons
4. Associated with small energy changes
5. Reaction rate is influenced by
temperature, pressure, concentration, and
catalysts
NUCLEAR
1. Occur when nuclei emit particles and/or
rays
2. Atoms are often converted into atoms of
another element
3. May involve protons, neutrons, and
electrons
4. Associated with large energy changes
5. Reaction rate is not normally affected
by temperature, pressure, or catalysts
 RADIOISOTOPES are isotopes of atoms with unstable nuclei that undergo
radioactive decay
 Ever wonder how positively charged protons can stay together in the nucleus?
STRONG NUCLEAR FORCE
o Helped by the presence of neutrons
o Band of Stability (ends at Bi-209; all elements with atomic numbers
greater than 83 are radioactive)
o Above the band of stability – too many _____________; Below the band
of stability – too many _______________ or too few ______________
o BETA DECAY: For elements above the band of stability (too many
neutrons)
 A NEUTRON will decay into a PROTON (stays in the nucleus)
and an ELECTRON (leaves the nucleus as a beta particle)
o ALPHA DECAY: Usually for elements with atomic number above 83
o POSITRON EMISSION / ELECTRON CAPTURE: For elements below
the band of stability
 POSITRON EMISSION: A PROTON in the nucleus is converted
into a NEUTRON (stays in nucleus) and a POSITRON (size of
electron but with positive charge – emitted from nucleus)

C B 





ELECTRON CAPTURE: ELECTRON from cloud moves into the
nucleus to combine with a PROTON to create a NEUTRON



 Rb e rX-ray
o Practice Problems p.814 6 – 9
photon
25.3 Transmutation
 Radioactive decay rates are measured in half-lives
 HALF LIFE is the time it takes for one half of a sample to decay into its products
o Every radioisotope has its own unique half-life
o Half-lives cannot be changed – you cannot speed up or slow down the
radioactive process!
 Practice Problems p.819 17-19
25.4 Fission and Fusion of Atomic Nuclei
 FISSION is the splitting of a large nucleus, releasing a large amount of energy
o Powers nuclear power plants

FUSION is the combining of two small nuclei, releasing even more energy than
fission
o Powers the sun