The Structure of an Atom
Enviado por carvajal.ce • 23 de Abril de 2013 • 1.933 Palabras (8 Páginas) • 597 Visitas
1.1 The Structure of an Atom
An atom consists of a tiny dense nucleus surrounded by electrons that are spread
throughout a relatively large volume of space around the nucleus. The nucleus contains
positively charged protons and neutral neutrons, so it is positively charged. The
electrons are negatively charged. Because the amount of positive charge on a proton
equals the amount of negative charge on an electron, a neutral atom has an equal number
of protons and electrons. Atoms can gain electrons and thereby become negatively
charged, or they can lose electrons and become positively charged. However, the number
of protons in an atom does not change.
Protons and neutrons have approximately the same mass and are about 1800 times
more massive than an electron. This means that most of the mass of an atom is in its
nucleus. However, most of the volume of an atom is occupied by its electrons, and that
is where our focus will be because it is the electrons that form chemical bonds.
Li Be B C
the second row of the periodic table
N O F
4 CHAPTER 1 Electronic Structure and Bonding • Acids and Bases
Louis Victor Pierre Raymond duc
de Broglie (1892–1987) was born in
France and studied history at the
Sorbonne. During World War I, he
was stationed in the Eiffel Tower as a
radio engineer. Intrigued by his exposure
to radio communications, he returned
to school after the war, earned
a Ph.D. in physics, and became a
professor of theoretical physics at the
Faculté des Sciences at the Sorbonne.
He received the Nobel Prize in
physics in 1929, five years after obtaining
his degree, for his work that
showed electrons to have properties
of both particles and waves. In 1945,
he became an adviser to the French
Atomic Energy Commissariat.
Erwin Schrödinger (1887–1961)
was teaching physics at the University
of Berlin when Hitler rose to
power. Although not Jewish,
Schrödinger left Germany to return
to his native Austria, only to see it
taken over later by the Nazis. He
moved to the School for Advanced
Studies in Dublin and then to Oxford
University. In 1933, he shared the
Nobel Prize in physics with Paul
Dirac, a professor of physics at Cambridge
University, for mathematical
work on quantum mechanics.
The atomic number of an atom equals the number of protons in its nucleus. The
atomic number is also the number of electrons that surround the nucleus of a neutral
atom. For example, the atomic number of carbon is 6, which means that a neutral carbon
atom has six protons and six electrons. Because the number of protons in an atom
does not change, the atomic number of a particular element is always the same—all
carbon atoms have an atomic number of 6.
The mass number of an atom is the sum of its protons and neutrons. Not all carbon
atoms have the same mass number, because, even though they all have the same number
of protons, they do not all have the same number of neutrons. For example,
98.89% of naturally occurring carbon atoms have six neutrons—giving them a mass
number of 12—and 1.11% have seven neutrons—giving them a mass number of 13.
These two different kinds of carbon atoms and are called isotopes. Isotopes
have the same atomic number (i.e., the same number of protons), but different mass
numbers because they have different numbers of neutrons. The chemical properties of
isotopes of a given element are nearly identical.
Naturally occurring carbon also contains a trace amount of which has six protons
and eight neutrons. This isotope of carbon is radioactive, decaying with a half-life
of 5730 years. (The half-life is the time it takes for one-half of the nuclei to decay.) As
long as a plant or animal is alive, it takes in as much as it excretes or exhales.
When it dies, it no longer takes in so the in the organism slowly decreases.
Therefore, the age of an organic substance can be determined by its content.
The atomic weight of a naturally occurring element is the average weighted
mass of its atoms. Because an atomic mass unit (amu) is defined as exactly
of the mass of the atomic mass of is 12.0000 amu; the atomic
mass of is 13.0034 amu. Therefore, the atomic weight of carbon is 12.011 amu
The molecular weight is the
sum of
...