Transcript Atoms - Images

Bell-ringer


Who were the two scientists we discussed
yesterday that helped shape our modern
atomic theory?
What were the three laws we discussed
yesterday that helped formulate the atomic
theory?
Section 3-2
The Structure of the Atom
Coach Kelsoe
Chemistry
Pages 72–76
What is an atom?


Even though not all of John
Dalton’s ideas about the
atom were true, many of
them were.
An atom is the smallest
particle of an element that
retains the chemical
properties of that element.
Atomic Pioneers



Joseph John Thomson concluded that
electrons were found in all atoms.
Robert Millikan confirmed the negative
charge of the electron and suggested a
possible mass.
Ernest Rutherford determined that most of
the mass of an atom is found in the nucleus
and that the nucleus occupies very little
space within the atom.
Regions of the atom
Nucleus

There are two basic
regions of the atom:


Electron
The nucleus – found near
the center of the atom and
contains protons and
neutrons.
Surrounding the nucleus
are the electrons
Composition of the Atomic Nucleus




All nuclei (except for one hydrogen) have two
types of particles: protons and neutrons.
The positive charge of a proton is equal to
the negative charge of an electron.
Atoms are electrically neutral because they
contain equal numbers of protons and
electrons.
A neutron is electrically neutral.
Masses of Atomic Particles



A proton has a mass of
1.673 x 10-27 kg.
The mass of a neutron is
1.675 x 10-27 kg.
The mass of an electron is
about 1836 times less than
that of a proton, so they are
usually neglected when
calculating mass.
Forces in the Nucleus


Normally particles with
the same charge repel
each other, but there are
strong attractions
between protons.
The short-range forces
between protons and
neutrons that hold the
nucleus together are
called nuclear forces.
The Sizes of Atoms


The radius of an atom is the distance
from the center of the nucleus to the
outer portion of the “electron cloud.”
Since atomic radii are so small, they
are expressed in picometers (10-12 m).