Structure of an Atom
Atoms are too small to be seen with the naked eye. But scientists using high powered electron
microscopes have photographed atoms. They look like fuzzy white dots.
Rutherford’s model describes a nucleus which is a tiny core that is very small in volume, dense
compared to the rest of the atom, and positively charged. Also that there is an “envelope” that is
very large in volume, light compared to the nucleus, and negatively charged.
Bohr’s model compared the nucleus to the Sun, and the electrons to the planets . The Sun exerts
an enormous gravitational pull on the planets, but they do not spiral inward and crash. Why?
Because they revolve at just the right speed to remain in their orbits. Similarly, the atom’s
positive nucleus exerts a strong force of attraction on the negative electrons. The electrons do not
spiral inward and crash, however, because they are moving rapidly in fixed regions around the
nucleus. These regions are moving rapidly in fixed regions around the nucleus. These regions are
three-dimensional and sphere-like. For this reason, they are called electron shells. (page 242textbook)
The Bohr-Rutherford model of an atom uses aspects of both models.
The central part of an atom
of protons and neutrons.
Protons – positively charged particles
Neutrons – no electrical charge
Electrons – negatively charged particles
is called the nucleus. The nucleus is made
They are all constantly in motion.
Electrons move rapidly around the atom’s nucleus in a region called the
Electron cloud.
An atom is the smallest particle of an element that still is that element.
The atom is made up of several parts. It has a center part called the nucleus. The nucleus
is made up of a positively charged particle called a proton and a particle that does not
have a charge called a neutron. The nucleus is surrounded by negatively charged
particles called electrons that move in orbits around the nucleus. Most of the mass of
the atom is contained in the nucleus and the mass of the proton and neutron are about
the same. However, the nucleus is a small portion of the total amount of space the atom
takes up. Different types of atoms can be identified by: the numbers of protons,
neutrons and electrons they contain and their atomic mass.
The negatively charged electrons are very light in mass. The electrons that are
outermost can combine with other atoms by giving up or taking on electrons
The atomic number of an atom is the number of protons it has.
The atomic weight or mass of the atom is the total number of protons and
in the atom's nucleus.
neutrons