Download 3.1 - cmpascience

Ch. 3: “Atoms and the
Periodic Table”
Section 3.1: “Atomic Structure”
Objectives
1.
2.
3.
Explain Dalton’s atomic theory, and
describe why it was more successful
than Democritus’s theory.
State the charge, mass, and location of
each part of an atom according to the
modern model of the atom.
Compare and contrast Bohr’s model with
the modern model of an atom.
Dalton’s Theory
Every element is made of tiny, unique particles
called atoms that cannot be subdivided.
2. Atoms of the same element are exactly alike.
3. Atoms of different elements can join to form
molecules.
 Dalton’s theory was widely accepted because,
unlike Democritus’s theory, there was
evidence to support it.
1.
Parts of an Atom

proton (p+) = a positively charged subatomic
particle in the nucleus of an atom
(mass = 0.00000000000000000000000000167 kg)

neutron (n◦) = a neutral subatomic particle in the
nucleus of an atom
(mass = 0.00000000000000000000000000167 kg)


nucleus = the center of an atom; made up of
protons and neutrons
electron (e-) = a tiny negatively charged
subatomic particle moving around the outside of
the nucleus
(mass = 0.000000000000000000000000000000911 kg)
The Bohr Model vs the Modern
Atomic Theory

In both theories, electrons orbit the nucleus
and each electron has an energy level
associated with its location. In Bohr’s model
of the atom, electrons were thought to orbit
the nucleus in set paths, much like planets
orbiting the sun. In the modern atomic
theory, the region in an atom where electrons
are likely to be found is called an orbital. But,
the exact location of an electron cannot be
determined according to this model.
Electron Configuration





The higher the energy level, the farther from the
nucleus the electrons tend to be, and the more
energy they have.
Rules for filling energy levels:
The first electrons enter the K shell, up to a
maximum of 2.
The next electrons enter the L shell, up to a
maximum of 8.
The next electrons enter the M shell, up to a
maximum of 18, but are stable with 8.
Electron Configuration
Electron Configuration




Valence:
Whichever shell is currently most outward is the
valence shell, even if it only has one electron.
Valence electrons are those electrons that an
atom uses in forming a bond with another atom.
Generally, these electrons are found in the
outermost shell of an element.
How many valence electrons are in the first 18
elements?