Chapter 4 Section 1: Introduction to
atoms
• Key Concepts:
– How did atomic theory
develop and change?
– What is the modern
model of the atom?
• Key terms:
–Atom
–Electron
–Nucleus
–Proton
–Energy level
–Neutron
–Atomic number
–Isotope
–Mass number
Atoms and atomic theory
• Atoms (as you know) are the smallest
particles of elements
• Atomic theory grew as a series of models
(models- you know them from chapter 1)
that developed from experimental
evidence. As more evidence was
collected, the theory was revised.
• Everything… is made of atoms.
• (not on the test… If you made a tiny dot with
the tip of a sharp pencil, and the pencil lead
were made of carbon, the tiny dot would have
about 4 billion billion carbon atoms.”
John Dalton
• English chemist. Proposed an atomic theory
and model for atoms. With only a few
changes, the theory is still widely accepted.
“my spectacles are
the bomb foshizzle”
Dalton’s theory (yes, you need to know it, because it is
true and it will help you understand atoms)
• All elements are composed of atoms that cannot
be divided
• All atoms of the same element are exactly alike
and have the same mass. Atoms of different
elements are different and have different
masses.
• An atom of one element can’t be changed into
another.
• Every compound is composed of atoms of
different elements, combined in a specific ratio.
So true.
Smaller parts of atoms
• Scientists realized that atoms are composed of
even smaller parts.
• 1897, JJ Thompson found that atoms contain
negatively charged parts (they later became
known as electrons)
• 1911 – Ernest Rutherford found the nucleus
and protons
• (you will not be tested on this, this is
background info – you should know it, tho )
Evolving models
• Scientists created better and better models
of atoms as they got new information. (this
you should know)
• 1913 – Niels Bohr revised it again. He showed
that electrons could only have specific
amounts of energy, leading them to move in
certain orbits
– (this is just background info)
Structure of atoms
as we know it today
• Nucleus – the tiny, positively charged, center of
an atom. It contains protons and neutrons.
• Protons – positively charged particles inside the
center (+)
• Electrons – negatively charged particles (form a
cloud-like region around the nucleus) (-)
• Neutrons – electrically neutral particles inside
the center (no charge)
Atoms
• Have an equal number of positively charged
protons and negatively charged electrons.
Hence (heh, hence), they USUALLY have no
charge.
• http://www.youtube.com/watch?v=QbWKF9u
DF7w
The electron cloud
• The “cloud” is a visual model. It symbolizes
where electrons are likely to be found. They’re
moving all the time within this region.
• An electron’s movement is related to its
energy level, or the specific amount of energy
it has.
Particle masses and size of atoms
• It takes almost 2000 electrons to equal the
mass of just one proton. Together, protons and
neutrons make up nearly all the mass of an
atom. Protons and neutrons have about the
same mass.
• Atoms are… small. A tiny speck of dust may
contain 10 million billion atoms. No, that’s not
a made up number like “Oh yeah? I’m 10
million billion times sure I’m right…”
Atomic number
• Every atom of an element has the same
number of protons. Example: every carbon
atom has 6 protons. Every oxygen atom has 8
protons.
• This number of protons is called the atomic
number.
Isotopes and mass number
• Atoms with the same number of protons and a
different number of neutrons are called isotopes.
All atoms of an element have the same number of
PROTONS, but neutron number can vary.
• Examples: Carbon 13 has 7 neutrons, carbon 14
has 8 neutrons.
• Isotopes are identified by mass number, which is
the sum of protons and neutrons. Some isotopes
are more common than others: Carbon 12 is more
common than 13 or 14.
OMG What should I know??
• OMG KNOW IT ALL! I will help you  start by
learning what I ask you in the review questions…
• If you are confused, use the book to review.
Reading the chapter, regularly, will help you
retain information. At any point, if you have
questions, are unsure, want to improve your test
grades, ask me. I am here to help you. Email me.
If you don’t have email, I will give you my digits
bruh.
Review questions
• What is atomic number?
• What is an isotope?
• Where do you find electrons, neutrons, and protons?
(specifically)
• How are atom parts (electrons, neutrons, protons)
charged?
• Draw an atom and label its parts
• What are the four parts of Dalton’s theory?
• THIS IS WHAT I WILL ASK YOU ON THE ASSESSMENT
TOMORROW. KNOW IT KNOW IT KNOW IT KNOW IT
KNOW IT! STUDY THESE THINGS TONIGHT! WHILE
YOU ARE BRUSHING YOUR TEETH! WHILE YOU ARE
INSTAGRAMING!