Chapter A1 – Particles & the structure of matter
Safety in the laboratory
Understanding the rules
 It’s not enough to remember the rules for conducting a
lab experiment safely – you need to understand WHY
those rules exist
 Like any lesson in science, you’ll remember it better if
you
 Understand the importance of the concept, or
 Experience the concept first-hand
 Since I’d rather you not learn the importance of safety
glasses by blinding yourself, focus on the WHY of the
following rules.
Rule #1 – Wear the proper safety
equipment
Rule #1 – Wear the proper safety
equipment
 QUESTION:
 What safety equipment is mandatory for every lab, and
what is optional?
Rule #1 – Wear the proper safety
equipment
 ANSWER:
 Safety glasses are mandatory, however, prescription glasses
are an acceptable replacement
 ** Safety glasses must be worn on the face, not as a hair
accessory, even if you find them uncomfortable. **
 ** We strongly discourage you from wearing contact lenses
into the lab, even if you are wearing safety glasses **
 Lab coats are mandatory any time chemicals are being used
(e.g. you don’t need them for a bio lab on microscopes)
 Closed-toe footwear is required – no sandals or flip flops
 Gloves are only needed during dissections, where you are
likely to be handling a biohazardous specimen
Rule #2 – Don’t eat or drink in the
lab
Rule #2 – Don’t eat or drink in the
lab
 QUESTIONS:
 Suppose you know your three solutions are salt water,
sugar water and vinegar, and that none of these
substances will hurt you. Why should you still not taste
them?
 Why is it not even a good idea to bring in a water bottle
or chewing gum?
Rule #2 – Don’t eat or drink in the
lab
 ANSWERS:
 We cannot guarantee that the solutions are pure, that the
glassware is clean, or that there are no chips in the beaker
 You shouldn’t stake your life on being 100% right about any
experiment
 You could reach for your water and get something else
 You don’t want anything else on your lab bench other than the
required materials
 Even water can be a dangerous chemical if mixed with the
right substance
 Gum can absorb fumes and increase your chance of ingesting
something
Rule #3 – Leftover chemicals
 QUESTION:
 What should be done with any used or unused chemical
once they have been taken from the original container
(the source container)?
Rule #3 – Leftover Chemicals
 ANSWER:
 ALWAYS put any chemicals you’ve taken from the stock
beaker in the waste beaker OR If it is safe to do so; with the
tap running to dilute it, you can pour it down the drain.
 WHY:
 The chemicals could have been contaminated by something
already in your beaker so it can never go back to the original
container
 The new chemical you made will have different properties
 Some solutions, such as those containing heavy metals, will
pollute local water supplies, or corrode the pipes
Rule #4 – Wash your hands
thoroughly
 QUESTION:
 When should you wash your hands in the lab?
 POSSIBLE ANSWERS:
 A) Before starting the experiment
 B) After handling each chemical
 C) At the end of the lab activity
 D) Before you eat your lunch
Rule #4 – Wash your hands
thoroughly
 CORRECT ANSWER:
 C) At the end of the lab activity


unless you spill anything on your hands while you’re working,
there’s no need to wash your hands in between each chemical
you should wash your hands at the end, even if they appear
clean, because some chemicals are invisible and others just
plain stink.
Rule #5 – Clean up any spilled
substances immediately
 QUESTION:
 Why should you check with your teacher first before you
clean something up?
 POSSIBLE ANSWERS:
 A) Because you should collect the spilled liquid and try to
reuse it
 B) Because your teacher wants as many reasons as possible to
yell at you
 C) Because there may be specific instructions for cleaning up
that particular solution
 D) Because your teacher spends less money on her clothes
than you, so she doesn’t mind the risk
Rule #5 – Clean up any spilled
substances immediately
 CORRECT ANSWER:
 C) Because there may be specific instructions for cleaning up
that particular solution

(Although your teacher does probably spends less money on her
clothes than you)
 For instance,
 if you spill an acid, we will first neutralize it with a basic solution
(baking soda solution)
 if you spill a base, we will first neutralize it with an acidic solution
(vinegar solution)
 some compounds should be diluted first before wiping them up
 some compounds stain your skin, and you don’t want to be known as
the “splotchy kid”
Rule #6 – Pour chemicals properly
 QUESTION:
 Which photo demonstrates the safe way of pouring
chemicals?
Rule #6 – Pour chemicals properly
 ANSWER:
 Actually none of them! (Photo #1
is the safest)
 If you spill something, immediate
stop pouring and check for a break
in your glassware
 Precise measurements are made at
eye level, not above or below your
line of sight
Rule #6 – Pour chemicals properly
 ANSWER:
 Don’t get your lab partner to hold on to
your glassware while you pour
 Especially with test tubes and graduated
cylinders (which are narrow), never pour
chemicals into containers held in your
hands – place the container on the counter
or use a test tube rack
Rule #7 – Always listen to the
teacher’s instructions
 QUESTION:
 You should know what you’re doing in the lab BEFORE
you go in, so what are some reasons why you should
listen to the teacher’s instructions during the lab?
Rule #7 – Always listen to the
teacher’s instructions
 ANSWERS:
 There may have been a change to the procedure due to a
lack of supplies
 There could be some kind of emergency
 Because your teacher charges a “stupid question tax” of 5
marks if you ask her something that is in the lab
procedure or was said out loud while you weren’t
listening
Rule #8 – Label any containers you
put chemicals in
 QUESTION:
 One of these solutions is sugar water, one is an acid
strong enough to dissolve concrete, and one will make
you go blind if you drink it. Which is which?
Rule #8 – Label any containers you
put chemicals in
 ANSWER:
 Actually, they’re all water, but hydrochloric
acid, methanol, and sugar water are all clear,
colourless solutions indistinguishable by sight.
 SO?
 Even if you think you can “keep track” of which
substance is which, label your containers to
minimize your risk, and your error
Rule #9 – What to do with broken
glassware
 QUESTION:
 What’s the proper procedure if you break glassware?
 ANSWER:
 1) Inform your teacher
 2) Make sure any other students in the area are alerted
 3) Your teacher will collect the large pieces, and we will
sweep up the smaller pieces
 4) If necessary, we will neutralize any spilled liquid
 5) Broken glass goes in a special bin – do not simply
throw it out into the garbage.
Rule #10 – Safely detect the odor
of a substance
 QUESTION: How should you go about safely detecting
the odor of a substance?
 ANSWER:
 You hold the container safely away from your face and
use your hand to “waft” the scent towards your nose.
 WHY:
 The smell may be too strong / irritating to get a nose-full
 You should never put your face directly over a container
in case of splattering or fumes
Rule #11 – Tie hair back and roll up
loose sleeves
Rule #11 – Tie hair back and roll up
loose sleeves
 QUESTION:
 What are three reasons why it could be dangerous to
have long hair or loose sleeves unsecured?
Rule #11 – Tie hair back and roll up
loose sleeves
 ANSWER:
 Both hair or clothing could catch on fire
 Loose sleeves can knock over glassware, resulting in
broken glass or spilling harmful chemicals
 Both hair and clothing can absorb chemicals and further
exacerbate a chemical burn/ irritation
Rule #12 – Mixing acids and water
 QUESTION:
 What’s the proper way of mixing an acid and water?
 POSSIBLE ANSWERS:
 A) Pour the acid into the water – it’s less likely for acid to
splash out of the container
 B) Pour the water into the acid – you’re less likely to get
acid on your hands this way
 C) It doesn’t matter what order you mix two chemicals
in, the result will be the same.
Rule #12 – Mixing acids and water
 CORRECT ANSWER:
 A) Pour the acid into the water – it’s less likely for acid to
splash out of the container
 You always pour any acids into water rather than vice
versa because it's much more likely that the liquid being
poured into will splash out of the beaker. If it's just
water, then it’s not a problem; but if acid gets on
your clothes or hands you can get burned badly.
Rule #12 – Mixing acids and water
 CORRECT ANSWER:
 There’s one other good reason why
acid goes in water, and not vice
versa  If you add water to acid, the first
drops of water will react
exothermically with the acid, and
bubble all over like it’s boiling
(very dangerous!)
 If you add the acid to the water,
the acid reacts/ mixes completely
with the water and dissipates.
 So: “Do like you oughta, add acid
to wat-ah”
Rule #13 – Using distilled water
instead of tap water
 QUESTION:
 What are three reasons why you get more accurate
results if you use distilled water instead of tap water?
 ANSWER:
 Tap water will have salts dissolved in it that can skew
your results
 Tap water is not necessarily neutral – in fact at O’Leary it
has a pH of about 8.5
 Tap water comes out at unpredictable rates, distilled
water is easier to control the flow
Practice problems:
1. List five steps that should be taken
BEFORE entering the lab to perform an
experiment?
2. List precautions you can take to prevent:
1. poisoning
2. scalding
3. eye damage
Practice problems:
3. The purpose of a lab is to determine what several
“mystery solutions are”. You pick up a fresh test tube,
and you pour some “mystery solution” into it and add
some solute. You give it a good shake by holding your
thumb over the opening and shake it up and down.
You put the test tube down into the rack and look
down into it to make your observations about the
reaction that took place.
List as many things as you can that were
performed unsafely in the lab. Suggest what
should have been done instead that would
improve the procedure.
Practice problems:
4. There are six pieces of emergency equipment in the
lab. What are they, where are they, and when/how
should they be used?
5. What should be done in the following two scenarios?


While your lab partner is boiling some water, the fire
alarm goes off.
Your lab partner has just poured some acid into what
you thought was a beaker of water. It starts to bubble
rapidly.
Practice problems (Solutions):
List five steps that should be taken BEFORE entering the lab or
starting to perform an experiment?
1.
read the lab COMPLETELY and prepare any pre-lab requirements








prepare a pre-lab – predictions, hypotheses, and observations tables
should be prepared in advance
come dressed in the appropriate clothing
bring only the necessary items to the lab (text book, pre-lab,
pen/pencil) NO purses, binders, jackets, or iPods
put on protective wear: goggles, lab coat, gloves (if necessary)
collect solutions/ materials from the front and bring them to your
station
LABEL all beakers/ materials…keep your station organized!
double check with your partners that you ALL understand the
procedure – once the lab begins you will lose marks for procedural
questions
Practice problems (Solutions):
List precautions you can take to prevent:
2.
poisoning
1.



always wash your hands after the lab,
don’t touch your face/ mouth during the lab
never use your mouth to open containers etc.
scalding
2.


never touch test tubes/ beakers that are sitting in water in case
they are hot
use “oven mitts” or tongs to handle any hot glassware
eye damage
3.


keep your safety glasses on at all times
do not wear contact lenses in chemistry labs (some fumes can
cause them to melt to your eyes)
Practice problems (Solutions):
3.
The purpose of a lab is to determine what several “mystery
solutions are”. You pick up a fresh test tube, and you pour some
“mystery solution” into it and add some solute. You give it a
good shake by holding your thumb over the opening and shake it
up and down. You put the test tube down into the rack and look
down into it to make your observations about the reaction that
took place.
 You shouldn’t mix chemicals unless you have a
reasonable idea how they will react
 You shouldn’t shake glassware vertically
 You shouldn’t use thumb as a stopper
 Never look directly into a test tube from above
(splatters/ fumes can get in your face).
Practice problems (Solutions):
Emergency equipment
Where it’s located
When & how to use
Emergency
shower
In the corner by the door
•Use it if you spill a large
amount of chemical on
your clothes
•Pull the handle, strip
down clothes and rinse
for 15 minutes
Eye wash station
Over the sink in the
second lab bench
•Use if you splash
chemicals in your eyes
•Place your eyes directly
over the two faucets, pull
the metal paddle towards
you, rinse for 15 minutes
Practice problems (Solutions):
Emergency equipment
Where it’s located
When & how to use
Fire extinguisher
In the prep room between •Use if the lab is on fire!
the Chem & Bio labs
•P – pull the pin
•A – aim at the fire
•S – squeeze the trigger
•S – sweep over the
flames
Fire blanket
In the corner by the green •Use if you are on fire –
cupboards
“stop, drop and roll” isn’t
enough
•Wrap yourself in the
blanket as tightly as
possible and roll on the
floor or get someone to
pat you out
Practice problems (Solutions):
Emergency equipment
Where it’s located
When & how to use
Emergency Spill Kit
On the wall by the fume
hood
•Use for a large spill, or
corrosive or oxidizing
substances, or if fumes
are escaping to other
rooms
•Alert your teacher, who
has received special
training
First Aid Kit
On the counter by the
green cupboards
•Alert your teacher, who
will assist you
Practice problems (Solutions):
What should be done in the following two scenarios?
5.
While your lab partner is boiling some water, the fire alarm
goes off.



Turn off the hot plate/ Bunsen burner.
Separate any chemicals that could possibly react while you’re out
of the room, then calmly leave the lab.
Your lab partner has just poured some acid into what you
thought was a beaker of water. It starts to bubble rapidly.




The two chemicals are now reacting.
Do not touch the beaker.
Come get the teacher/ lab tech and tell them what the two
chemicals could be
Safety symbols
 Two different systems of safety symbols have been
developed to warn users of potential hazards
What does the acronym
stand for?
Where is it used?
Number of symbols
Colour coded?
HSHS
WHMIS
Household Safety Hazard
Symbols
Workplace Hazardous
Materials Information
System
For household products
(the average consumer)
In labs & industry (people
with some understanding
of chemistry)
4
8
Yes, three shapes and
colours are used to
indicate degree of hazard
No, all symbols are in
circles and are printed in
black or red
HSHS
 Household Safety Hazard Symbols
CORROSIVE
POISONOUS
EXPLOSIVE
FLAMMABLE
The product can
burn your skin or
eyes. If swallowed,
it will damage your
throat and stomach
If you swallow, lick,
or in some cases,
breathe in the
chemical, you could
become very sick or
die.
The container can
explode if heated or
punctured. Flying
pieces from the
container can cause
serious injury.
The product or its
fumes will catch
fire easily if it is
near heat, flames or
sparks.
HSHS
 degree of hazard
CAUTION
WARNING
DANGER
Yellow inverted triangle
Orange diamond
Red octagon
LOWEST HAZARD
HIGHEST HAZARD
WHMIS
 the Workplace Hazardous
Materials Information System is a
national warning system for
dangerous chemicals
 WHMIS symbols are more
specific than HSHS, but require a
bit more understanding of
chemicals
WHMIS SYMBOLS
Symbol
Meaning
Description
compressed gas
gas is under pressure and
could explode
flammable
oxidizing
Examples
propane tank
helium tank
can burn or burst into
flames if placed near a heat
source or spark
natural gas
reacts with oxygen,
may not burn itself, but will
release gases that make a
fire worse
chlorine
ethanol
nitrogen
dioxide
WHMIS SYMBOLS
Symbol
Meaning
Description
poisonous,
causing
immediate toxic
effects
a substance that is highly
poisonous and will cause
immediate health hazards
poisonous,
causing other
toxic effects
a substance that is still
harmful, but will act over a
longer period of time (e.g.
carcinogens cause cancer)
corrosive
can attack (corrode) metals
or cause permanent damage
to human tissues on contact
burning, scarring, and
blindness may result
Examples
cyanide gas
some
pesticides
gasoline fumes
cigarettes
ammonia
hydrochloric
acid
sodium
hydroxide
WHMIS SYMBOLS
Symbol
Meaning
Description
dangerously
reactive
may react violently under
conditions of shock or an
increase in pressure or
temperature
they may also react
vigorously with water to
release a toxic gas.
biohazard
Examples
pure hydrogen
peroxide
aluminium
chloride
organisms or toxins released
blood
by organisms that causes
E. coli bacteria
disease in humans
WHMIS - purpose
 To ensure that all work places across Canada that work
with hazardous chemicals have a standardized way for
handling and labeling toxic chemicals.
 Provides:
 hazard identification
 product classification

ways of safely storing and organizing chemicals
 labeling methods & material safety data sheets
 standardized worker training and education
Practice problems:
7. For each room listed, suggest one
hazardous chemical that might be
found in it. Include the WHMIS
symbol that would be appropriate for
that hazard.





a) kitchen
b) bathroom
c) garage
d) bedroom
e) classroom
http://toxmystery.nlm.nih.gov/
Material Safety Data Sheets
 MSDS are detailed
information sheets describing
the particular properties,
hazards, and emergency
procedures for a specific
chemical
 Each and every single
chemical in the lab has its
own sheet, and they are
organized into binders
alphabetically
Material Safety Data Sheets
 Information that can be found on the MSDS:

material’s identity (e.g. Clorox bleach)



brand name
 e.g. Clorox
chemical name
 e.g. sodium hypochlorite
common name
 e.g. bleach
Material Safety Data Sheets

hazardous ingredients



lists ingredients as small as 1%
 e.g. sodium hypochlorite, 5.25%
unless listed, the rest of the substance is water
physical & chemical hazards / characteristics


stability, reactivity, flammability, explosiveness,
corrosiveness, compatibility with other materials
often listed using WHMIS symbols
 e.g. stable, incompatible with strong acids, toxic,
corrosive, oxidizing
Material Safety Data Sheets
 health hazards and information
 acute and chronic effects

e.g. corrosive, causes eye and skin burns, causes digestive tract
burns, harmful if inhaled, causes respiratory tract irritation
 carcinogen? (may include human and animal
summaries)
 exposure limits
 how it gets into the body, what organs it targets,
symptoms of overexposure

e.g. route: blood; organs: eyes, skin, lungs
Material Safety Data Sheets
 precautions for handling and storing
 any safety equipment required (e.g. gloves, eyewash
station) or monitoring equipment
 emergency and first aid procedures
 how to deal with cases of inhalation, ingestion, and eye
or skin contact

e.g. ingestion: do not induce vomiting
 specific fire-fighting information
 procedures for cleanup and spills
 identity of the organization responsible for creating
the MSDS, date of issue, contact number
Homework
 Safety worksheet
Properties and Classification of Matter
Properties of matter
 “Matter” includes anything that has mass and takes up
space
 To divide up this nearly infinite list of “stuff”, we classify
different types of matter based on their properties
 Properties: the physical and chemical characteristics of a
substance
 Physical properties: appearance and composition of a
substance, can usually be determined using the five senses
 Chemical properties: the reactivity of a substance, can be
determined by doing an experiment
Physical properties
Property
Description
boiling point
temperature of boiling (or condensing)
melting point
temperature of melting (or freezing)
malleability
can be flattened into sheets without crumbling
ductility
can be stretched into wires without breaking
colour
colour (or colourless)
transparency
clear (or opaque)
state
solid, liquid, or gas at room temperature
solubility
ability to dissolve (usually in water)
crystal
formation
formation of crystals, appearance of crystals
conductivity
ability to conduct heat or electricity
magnetism
magnetic attraction between objects
Chemical properties
Property
Description
ability to burn
combustion (causing flame, heat and light)
flash point
temperature needed to ignite a flame
behaviour in air
tendency to break down, react, tarnish
reaction with water tendency to corrode or dissolve
reaction with acids
corrosion, sometimes bubble formation
reaction to heat
tendency to melt or decompose
reaction to red and
blue litmus
blue  red - acid
red  blue - base
no colour change - neutral
Matter
Pure substances
Elements
Compounds
Mixtures
Homogeneous
Heterogeneous
Solutions
Mechanical
mixtures
Suspensions
Colloids
Classification of matter
Pure substances
Mixtures
 all the particles making up
 combination of pure
the substance are identical
 elements –cannot be
broken down into other
substances

e.g. carbon
 compounds – made up
of two or more elements
in fixed ratios

e.g. water
substances
 homogeneous mixtures
– the separate
components are not
visible
 heterogeneous mixtures
– the separate
components are visible
Classification of matter
 Homogeneous mixtures
 the prefix “homo” means “the same”, meaning all the
parts of the solution look the same
 Solutions
 one example of a homogeneous mixture
 in a solution, one substance is dissolved in another
 the substance dissolving is the solute and the substance
it’s dissolving in is the solvent
Classification of matter
Mechanical
mixtures
Suspensions
Colloids
 The different
 The components
 Similar to a
substances are
clearly visible
 E.g. trail mix
of the mixture are
in different states
 E.g. mud in water,
aerosol sprays
suspension but the
suspended
substance cannot
easily be separated
out
 E.g. whole milk
Classification of matter
 Not every substance can be easily classified because
some substances have features of several categories
 E.g. motor oil doesn’t have constant properties – it can
separate out over time so sometimes it behaves as a
solution and sometimes a colloid
 Pure substances are much easier to classify because
 Elements are classified in the periodic table
 Compounds are further classified according to the
elements that compose them
Physical change vs. chemical
change
 Physical change – does not alter the chemical
characteristics of the substances involved, e.g.
 phase changes  changing from solid to liquid to gas
 crystallization / dissolving  allowing a substance to
crystallize, then dissolve back into solution
 Chemical change – the substances produced have
different chemical properties than the substances that
reacted
Chemical reactions
 In a chemical reaction, chemical change occurs when:
 at least one new substance is formed, with new physical
and chemical properties


sometimes, those new substances can be observed with phase
changes such as bubbles or precipitates
sometimes, they can be observed with colour changes or new
odours,
 a change in energy occurs

this is often detected by a change in temperature (e.g. it gives
off heat)
Homework
 A1.2 – Check and Reflect
 Pg.17 #1-7, 9
Developing Ideas about Matter
Chemistry in our world
 Even before scientists fully understood the structure of
the atom or had the technology to study it, people
were using chemistry in their daily lives
 Food chemistry
 Metallurgy
 Alchemy
Food chemistry
 Methods of preserving food
 heating food – temporarily
sterilizes it (kills the microorganisms)
 canning – heating the food, then
sealing it in an air-tight container
 freezing – low temperatures
prevent the grown of microorganisms
Food chemistry
 salting – salt dries the water
out of the meat, but also
preserves it by drying the
water out of any bacteria
 fermentation – bacteria
naturally present on the
surface of living organisms
converts starches and sugars
into acid, preserving the food
and giving it a sour flavour
Metallurgy
 the science of producing
and using metals
 annealing
 the heating of a metal before
it’s hammered, which makes
it less brittle
 this technique has allowed
copper to be used for tools,
weapons and jewellery for
thousands of years
 copper works better than
other pure metals because of
its hardness and malleability
Metallurgy
 other techniques
include
 alloys – the heating
and combination of
two or metals to gain
the benefits of both

e.g. brass, bronze
 smelting – extracting
pure metal from its ore

e.g. getting iron from
iron ore
Alchemy
 early experiments involving a
combination of science and
magic
 was mostly schemes for
getting rich, or producing
“miracle cures” such as antiaging serums
 in the process, also resulted
in:
 the discovery of mercury
 a method for the production
of acids
 the improvement of
glassware and lab equipment
Our understanding of the atom
 Accurately describing matter in terms of its atomic
structure is something that scientists are still working on
today.
 This section deals with the evolution of our ideas on the
atom and its structure, from Aristotle (~400 BC) to today’s
theory on Quantum Mechanics
 As we go through each scientist’s contribution, try to
identify
 What was different about his view compared to previous
theory?
 How did this view contribute to our current understanding?
Our understanding of the atom
 What you learn in
Science 10 about the
actual structure of the
atom is still a
simplification of what
we believe to be true,
however we will
present the Bohr
model as being “close
enough”.
Our understanding of the atom
 Different elements are
simply different
combinations of the
same three particles
 What makes oxygen
different than nitrogen,
for instance, is that
oxygen has one more of
each of the particles, but
an oxygen proton looks
exactly the same as a
nitrogen particle.
Our understanding of the atom
 Features of this model
of the atom:
 Protons (p+)


Positively-charged
particles
Found in the nucleus
 Neutrons (n0)



Neutral particles
Found in the nucleus
Prevent the p+ from
repelling each other
Our understanding of the atom
 Electrons (e-)
 tiny negativelycharged particles
 in orbit around the
nucleus
 hardly have any mass
(about 1/2000th that of
a p+ or n0), but make
up most of the volume
of the atom
 How did we get to this
understanding?
Aristotle
400 B.C.
 all matter was composed of 4
DRY
elements: earth, air, water and fire
 what he got right:
 matter is made up of different
combinations of elements
 elements can be divided up based on
their properties
 what he got wrong:
 only 4 elements
 the elements were “continuous”, that
is, they weren’t composed of “parts”
COLD
HOT
WET
Democritus
400 B.C.
 working at the same time as Aristotle
 matter was made up of tiny particles, called atomos,
that could not be divided into smaller pieces
 what he got right:
 matter is composed of tiny particles
 the atoms determine the properties of the element
 what he got wrong:
 atoms are indivisible, that is, that they aren’t made up of
any smaller parts
John Dalton
early 1800s
 performed experiments by combining different
elements to form new substances (compounds)
 atoms are like small spheres that varied in size, mass
or colour
John Dalton
early 1800s
 what he got right:
 all matter is made of small particles called atoms
 all atoms of an element are identical in properties such as
size and mass
 atoms of different elements have different properties
 atoms of different elements can combine to form compounds
with new properties
 what he got wrong:
 atoms are solid and cannot be divided any further
J.J. Thomson
 experimented with beams of
particles produced in a vacuum
tube
 he passed electricity through
different samples of elements,
and found that a beam of
particles was emitted when the
element became “excited”
 showed that the beam was made
of negative charges, and that
different elements produced the
same type of beam
 thus credited with the discovery
of the electron
1890s
J.J. Thomson
 The “Plum Pudding”
Model
 In Thomson’s model, the
negatively charged
electrons are stuck in a
sphere of positive charge
 so named because it’s like
raisins in plum pudding
(or chocolate chips in a
cookie)
1890s
J.J. Thomson
 what he got right:
 atoms can be further
divided into smaller
particles
 one of those particles is
the electron, which carries
a negative charge
 the electrons in one
element are the same as
electrons in another
element, but in different
amounts
1890s
J.J. Thomson
 what he got wrong:
 the electrons are stuck in
the positive sphere,
instead of around it
 this was corrected by
Japanese Scientist H.
Nagaoka in 1904, who said
the electrons traveled
around the nucleus like
Saturn’s rings
1890s
Ernest Rutherford
 begun his research with Thomson,
but expanded on his ideas by
discovering the nucleus
 his experiment is called the Gold
Foil Experiment, and was so
designed:
 a sample of a radioactive element
was placed in a lead chamber
with a tiny opening
 through this opening, a beam of
positively-charged particles
would be emitted
 these particles were traveling at a
VERY high speed toward a thin
sheet of gold foil
1890s
Ernest Rutherford
 because the particles were
moving so fast, and the gold was
so thin, he expected the gold
foil not to slow the particles
down at all, and that they would
pass through


this would be like firing a
cannonball at a sheet of tissue
paper
most of the time, this is exactly
what happened, however…
 once in about every 10000th
time, the particle would bounce
back

this would be like the tissue
deflecting the cannonball – a
very surprising result!
1890s
Ernest Rutherford
 from this experiment, he
realized that the gold atoms
had to be made mostly of
empty space
 when the beam hit the
99.99% of empty space, it
passed right through
 however, 0.01% of the time,
the beam struck a positive
“spot” on the gold foil, which
he determined to be the tiny
nucleus of the atom
1890s
Ernest Rutherford
 what he got right:
 the nucleus is very small
compared to the empty space
around it
 the electrons occupy some of
the empty space
 the nucleus has a positive
charge
 what he got wrong:
 the electrons “swarmed”
around the nucleus like bees
around a beehive
1890s
Neils Bohr
 credited with discovering
the orbital levels of the
electrons, that is, that the
electrons don’t swarm
randomly, but rather occupy
specific energy levels
around the nucleus
 he discovered this by
passing electricity through
different elements to excite
them, then letting the
electrons release that energy
in the form of light
early 1900s
Neils Bohr
 he then noted the pattern
of light bands emitted
from the element
 since the light emitted
was related to the
electrons, he reasoned
that each element had a
different number of
electrons, and that the
electrons occupied certain
energy levels
early 1900s
Neils Bohr
early 1900s
 what he got right:
 electrons occupy set energy levels around the nucleus
 electrons cannot fall below the lowest energy level
Neils Bohr
early 1900s
 what he got wrong:
 electrons are not actually a solid particle, but actually a
cloud of negative charge – Quantum Mechanical Model
 there are two types of particles in the nucleus: the proton
and the neutron
Homework
 A1.3 Check and Reflect (page 25)
 #1, 5, 6, 7
 A1.0 Section Review (page 27)
 #3, 5, 9, 15, 17