Ch 11 Introduction to Atoms
The Beginning of Atomic Theory
 Democritus & Aristotle
 Can you cut a piece of paper in half and cut those halves in half and
continue until you are left with 1 particle?
 If you could do this you would end up with what Democritus
called an _________= ______________________
 Aristotle _____________ with democritus’s idea. He
believed that ___________________________________
 Who was correct? Aristotle or Democritus??
The Beginning of Atomic Theory
 ____________________was correct!
 Matter is made of particles which we call ___________.

 Atom -
The Beginning of Atomic Theory
 Dalton – 1803
 Dalton’s atomic theory was based on _________________!
 All substances are made of ______
 Atoms are small particles that cannot be _____, _______, or
_________.
 Atoms of the same element are _________ and atoms of different
elements are _________.
 Atoms join with other atoms to make _____ substances.
The Beginning of Atomic Theory
 New information didn’t quite fit with _______ ideas.
His atomic theory had to be _________.
 Thomson- 1897
 Discovered the ____________ charged particles
 There are __________ inside the atom. Atoms can be
broken down further. (Dalton thought atoms were solid
spheres – so he’s wrong)
CATHODE-RAY TUBE
 A positively charged plate was attracted to a ______.
 Therefore, the beam must be made up of ________ charges.
 Thomson concluded these negative charges are _______ in every kind of
_______.
The Beginning of Atomic Theory
 ________- A subatomic
particle that has a negative
charge.
 Thomson described his model of
the atom like plum pudding.
Today you might call it the
______________ _____
model. (with electrons
represented by
_________________.)
The Beginning of Atomic Theory
 Rutherford- 1909
 Rutherford was a _____________ of Thomson’s. He tried to help
prove Thomson theory was _______ and ended up proving him
______!
 He aimed a beam of small, _________________ (α particles) at a
thin piece of gold foil.
 Photo paper behind the gold recorded where the charged particles hit.
 Surprising Results
 He thought the particles would _______________ the gold in a
straight line.
 Some particles were ________. Some shot right ______.
Rutherford’s Gold-Foil Experiment
 Rutherford determined an atom must be mostly ______
______ with a tiny part made of highly dense material.
Rutherford’s Model
 ________ – The centrally located, tiny, extremely dense
positively charged part of an atom.
The Beginning of Atomic Theory
 Bohr – 1913
 Niels Bohr proposed that electrons move around the nucleus
in _______________________________.
 Electrons can jump from path to path but cannot exist in
_____________ paths.
 Think of ________ on a ladder. You can stand on the rungs,
but not ________ the rungs.
 Or think of planets in our solar system – they do not stray off
the set path or ___________.
The Modern Atomic Theory
 Schrӧdinger and Heisenberg
 Electrons ________ travel in definite paths as Bohr suggested.
 The exact path of the electron ______ be predicted.
 There are regions where it is likely to be found called ______
__________.
4.2 The Atom
 How small is an _____?
 A penny contains __________ atoms.
(20,000,000,000,000,000,000,000 atoms)
 An atom is made up of _______, _______, and _________.
 The Nucleus
 Protons –
 The mass of protons are measured in atomic mass units
(amu). Each proton has a mass of __________
 _________- Particles in the nucleus that have ___ electrical
charge.
 Neutrons have a mass of 1 amu. (Same as _________)
The Atom
 Outside the nucleus
 _________ are found outside the nucleus. They have a
_______ charge. They have a mass of almost _____.
 If the number of protons __________ the number of
electrons, the atom is ______________
HOW DO ATOMS OF DIFFERENT
ELEMENTS DIFFER?
 Atoms of different elements have different numbers of
____________.
 No two elements have the same _____________.
 Atomic number is the number of ________ in an atom. All atoms of the
_____________ have the _________ atomic number.
HOW DO ATOMS OF DIFFERENT
ELEMENTS DIFFER?
 So how do we figure out the number of neutrons for an
atom?
 The number of _____________ = the number of
_______________
 Mass number –
 The mass number does not include the mass of ____________
because they are so ___________and have very little effect.
HOW DO ATOMS OF DIFFERENT
ELEMENTS DIFFER?
 Where do you find these numbers?
 On the ____________________ !
______
______ C
# __ + # __
# __
C
___
___
C

 # of neutrons = _________ - _________

 # of neutrons in C = ____ - ____
 C
P+ =
 No=
 E- =

HOW DO ATOMS OF DIFFERENT
ELEMENTS DIFFER?
Mass #
Li
Be
B
C
N
O
F
Na
k
Atomic #
Protons
Neutrons
Electrons
DRAWING BOHR MODELS OF ATOMS
 Draw the nucleus and label with #p & #n
 Draw electron orbitals
 1st orbital can have ______ electrons only
 2nd and 3rd ring can each have ______electrons
 Fill – _____________________
 Inner rings must be filled first before any electron enters a
higher ring!!!!!
 Examples:
Changing Atoms
 If you change a persons hair color does it change who they are?
Weight?
 What subatomic particle determines an atoms
identity?___________
 Therefore, the number of electrons and neutrons can change in the
atom and it is still the same atom.
 If the number of protons __________ the number of electrons, the
atom is ______________
 If the number of protons ___________ the number of electrons,
the atom becomes charged and we call it an _______.
 Positively charged ions –
 Negatively charged ions -
ISOTOPES
 _________- Atoms that have the same number of protons,
but have different numbers of neutrons.
 Examples:
 Hydrogen -1 and Hydrogen -2
 Naming Isotopes
 Write the __________ of the element, followed by a
hyphened and the _____________________ of the
isotope.
 Ex. A hydrogen atom with 1 proton and 0 neutrons
 A hydrogen atom with 1 proton and 1 neutron
ISOTOPES
 Mass Number – The sum of the _________________ in an atom.
(__________ are not included.)
 Mass # = protons + neutrons
 Atomic Mass – The _____________ of the masses of all the
___________ occurring isotopes of that element.
Solving the Atomic Mass
 Ex: Skittles consist of Orange – 1 which is 25% of the
Skittles and
Red – 2 which is 75% of skittles.
 Step1: change percents to decimals.
 Step 2: multiply the decimal by the mass
 Step 3: add the two answers together
Solving for Atomic Mass
 Ex: Chlorine-35 which is 76% of the Chlorine atoms and
Chlorine-37 which is 24% of Chlorine atoms.
 Step1: change percents to decimals.
 Step 2: multiply the decimal by the mass
 Step 3: add the two answers together