Science 9 Unit B Matter and Chemical Change
Topic 2.0
An understanding of the nature of matter has developed through observations over time.
Evolving Theories of Matter
Copper Age - 5000 – 3000 BC
Bronze Age - 3000 – 1000 BC
Iron Age - from 1000 BC
Humans in the Stone Age could make only simple stone and bone tools like these.
Stone Age people improved their lives when they discovered how to start and control fires.
They used fire mainly for cooking and warmth.
STONE AGE CHEMISTS
The first chemists lived before 8000 B.C. in an area now called the Middle
East. This period is known as the Stone Age because humans used only
simple stone tools at the time. Metals had not been discovered.
Once these first chemists learned how to start and control fire, they learned
how to change a range of substances to their advantage.
For example, they could cook their food, fire-harden mud bricks to
strengthen them, and make tougher tools.
Eventually this ability to control fire led to the production of glass and ceramic material.
The first metals to be used were gold, silver, and copper.
They became highly valued because of their properties – attractive color and
lustre.
Gold, Silver, and copper exist in their elemental state without combining with
other metals
Copper Age
Copper became valuable because it could be used to make pots, coins, tools,
and jewelry. In its natural state copper is brittle – breaks easily . When copper is
heated it can be rolled into sheets or stretched into wires
Bronze Age
Bronze became very important in the making of stronger weapons.
Bronze is made by melting two different metals and mixing them.
The two metals used are copper and tin.
Copper, by itself would be too soft to make statues from.
Tin is much too brittle and breaks too easily.
But if you mix a little bit of tin into the copper it becomes bronze which is much harder and at the
same time much less brittle
Iron Age
A group of people in the Middle East called Hittites discovered how to extract iron from rocks
and turn it into a useful material.
The Iron Age began.
Eventually, people learned to combine iron with carbon to produce an even harder material steel.
Steel meant sharper blades could be fashioned for hunting and stronger armour could be
built to protect soldiers in battle.
Egyptian Mummies
The ancient Egyptians developed techniques for extracting and purifying juices and oils
to use in mummifying bodies
Chemistry – from the Greek word khemieia meaning the ’juice of a plant’
Democritus (460-370 BCE.)
Democritus used the word atomos to describe the smallest particles a substance
could be broken down into and still be that substance.
Atomos is the Greek word for indivisible.
Aristotle 350 BC – believed that matter was made up of earth, fire, air, and water.
Each of these elements had 2 main features.
For example:
water was wet and cold
Earth was dry and cold.
Fire was hot and dry
Air was hot and wet
Alchemists.
For the next 2000 years experiments with matter were carried out by Alchemists.
They were trying to turn common metals into gold.
Andreas Libau
In 1597, he wrote the first systematic chemistry textbook, Alchymia
Robert Boyle - (1627-1691)
In the 1660s, Robert Boyle experimented with the behaviour of gases and noted that the
mercury fell as air was pumped out.
He also observed that pumping the air out of a container would extinguish a flame and
kill small animals placed inside, as well causing the level of a barometer to drop.
He was interested in what happened when gases were placed under pressure.
He presented Boyle’s Law, which states that pressure varies inversely as volume at
constant temperature
He was also interested in determining the composition of gases and other substances.
Through his experiments and observations, Boyle became convinced that matter was made up of tiny
particles, just as Democritus had suggested in about 400 B.C.
Boyle believed that the tiny particles, existing in various shapes and sizes, would group together
in different ways to form individual substances.
Boyle felt that the purpose of chemistry was to determine the types of particles making up each
substance.
Antoine Laurent Lavoisier
In the 1770s, the French scientist Antoine Laurent Lavoisier studied chemical
interactions.
By the late 1780s, he had developed a system for naming chemicals.
Now all scientists could use the same words to describe their observations.
That made it easier to compare the results of their experiments.
Using his naming system, Lavoisier defined some of the substances discovered to
that time, including hydrogen, oxygen, and carbon.
Because of his experimental and theoretical work,
Lavoisier is called the “father of modern chemistry.”
Unfortunately, he supported the losing side during the French Revolution and was executed by
guillotine in 1794.
He established the Law of Conservation of Mass.
Demonstrated that burning wood caused no change in mass
John Dalton
(1766-1844)
In 1808, John Dalton was the first scientist to define an element as a pure
substance that contained no other substances
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All matter is made of atoms. Atoms are indivisible and indestructible.
All atoms of a given element are identical in mass and properties
Compounds are formed by a combination of two or more different kinds
of atoms.
A chemical reaction is a rearrangement of atoms.
Billiard Ball Model
J.J. Thompson
In 1897, Thomson showed that cathode rays were composed of a previously unknown
negatively charged particle, and thus he is credited with the discovery and
identification of the electron; and, in a broader sense, with the discovery of the first
subatomic particle.
In 1897 he developed his raisin bun model of an atom with a positively charged
sphere in which electrons are embedded like raisins in a bun.
Cathode rays are produced when a piece of metal
is heated at one end of a tube containing a gas.
The heated metal sends out a stream of electrons
toward the opposite end of the tube, causing the end of the
tube to glow.
Early scientists used a simple tube like the one shown here.
Cathode ray tubes are used in electrical devices such as
televisions.
Hantaro Nagaoka
In 1904 Hantaro Nagaoka developed an early planetary model of the atom.
In this model electrons orbited around the positively charged center.
He proposed an alternative model in which a positively charged center is surrounded by a number of
revolving electrons, in the manner of Saturn and its rings.
Ernest Rutherford
Ernest Rutherford won a Nobel prize in 1908 for his work in Radioactivity at McGill
University in Montreal.
Rutherford discovered the nucleus by bombarding the atom with high speed particles.
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Mostly empty space
Small, positive nucleus
Contained protons
Negative electrons scattered around the outside
Niels Bohr
Danish researcher Niels Bohr worked with
Rutherford suggested that electrons do not orbit
randomly in an atom.
He said they moved in circular orbits or electron
shells.
He believed electrons jump between these
shells by gaining or losing energy.
Bohr won the Nobel prize for physics in 1922.
James Chadwick
In 1932 James Chadwick added to the Bohr atomic model.
He discovered neutral particles in the nucleus called neutrons.
A Neutron has the about same mass as a proton.
An electron has only 1/1837th the mass of a proton or neutron.
Today most people still use the Bohr model to describe particles that make up the atom
but further research in the area of quantum mechanics has found the structure of an
atom is different again.
Quantum Mechanics Atomic Model
The principal quantum number n describes the average distance of
the orbital from the nucleus — and the energy of the electron in an
atom.
It can have positive integer (whole number) values: 1, 2, 3, 4, and so on.
The larger the value of n, the higher the energy and the larger the
orbital. Chemists sometimes call the orbitals electron shells.
Organizing the Elements
Finding a pattern in an unknown helps scientists to organize ideas and information. It also helps
scientists to interpret what the information means and explain these ideas, based on what they have
learned.
- Early chemists used symbols of the sun and the planets to identify the metallic elements known to
them.
Choose Your Carbon
Some elements exist in different forms as a solid. Carbon can be a soft black substance called
graphite. Or it can be a hard, clear substance called diamond.
This later became a problem, when more elements were discovered, because they ran out of planets.
John Dalton developed a new set of symbols in the early 1800’s to improve communication between
chemists.
Dalton’s symbols were later modified by Swedish chemist Jöns Jacob Berzelius.
In 1814, Berzelius suggested using letters rather than pictures to represent each element.
The first letter (capitalized) of an element would become the symbol. For elements with the same
first letter, such as hydrogen and helium, a small second letter would be added.
Thus, “H” came to stand for hydrogen and “He” for helium.
The new system - which remains the one used today - enabled scientists to communicate with each
other in a precise and understandable manner.
An Order for the Elements
It was soon realized that the elements could be listed in order of increasing atomic mass.
Atomic mass is the mass of one atom of an element.
Scientists were able to determine the average mass of an atom of other elements by comparing it with
the mass of a carbon atom (which is 12.0).
Atomic mass is measured by atomic mass unit (amu).
In 1864, the English chemist John Newlands recognized a pattern when elements were listed by
increasing atomic mass. He noticed that properties of elements seemed to repeat through this list at
regular intervals. He called this pattern the “law of octaves,” as the pattern was similar to the octave
scale on a piano or other musical instrument. Many other scientists thought this law was silly and
refused to accept the idea.
Not until 1869 did a clearer understanding of how to arrange the elements emerge. Russian chemist
Dmitri Mendeleev was able to organize the elements in a way that reflected the patterns in the
properties of the elements.
Mendeleev collected the 63 elements known to exist in his time (the mid -1800s). These included
lithium, carbon, nitrogen, oxygen, fluorine, sodium, silicon, phosphorus, sulfur, and chlorine.
He then wrote down the properties of each element on a card, such as melting point, density, and
colour.
Using these cards, he tried to sort the elements into a pattern based on their properties.
He also wanted to find a pattern that would allow him to predict the properties of elements not yet
discovered. He felt that the ability to predict properties of new elements would prove that his pattern
accurately reflected nature.
PREDICTING NEW ELEMENTS
Mendeleev noticed some gaps in his chart of the elements, yet was convinced that his organization
of the elements was correct. He predicted that new elements would be discovered that would have
the properties and atomic mass needed to fit into the gaps.
Many scientists didn’t agree with Mendeleev’s ideas and criticized his work.
Within 16 years, however, the gaps were filled through the discovery of new elements that had the
properties Mendeleev had predicted.
Dmitri Mendeleev (1869)
In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical
classification schemes for elements known to date. The periodic table is base on
the similarity of properties and reactivities exhibited by certain elements.
HOW HIS WORKED…
• Put elements in rows by increasing atomic number.
• Put elements in columns by the way they reacted
SOME PROBLEMS…
• He left blank spaces for what he said were undiscovered elements. (Turned out he was right!)
• He broke the pattern of increasing atomic weight to keep similar reacting elements together.
The Periodic Table Today
Dmitri Mendeleev’s periodic table included the 63 known elements of his time. Since then, many
more elements have been discovered.
All elements from atomic numbers 1 (hydrogen) to 118 (ununoctium) have been discovered or
reportedly synthesized, with elements 113, 115, 117, and 118 having yet to be confirmed. The first 98
elements exist naturally although some are found only in trace amounts and were synthesized in
laboratories before being found in nature.[n 1] Elements with atomic numbers from 99 to 118 have only
been synthesized, or claimed to be so, in laboratories. Production of elements having higher atomic
numbers is being pursued
One of the first important finds using Mendeleev’s table was the element gallium.
Discovered in 1875, gallium fit into one of the positions in the periodic table where Mendeleev had
placed a question mark. It matched almost exactly his prediction of the properties of an element that
would fit in that position.
Another question mark in the table wasn’t filled until 1939 when the element francium was discovered
by the French chemist Marguerite Perey. This element also matched Mendeleev’s prediction almost
exactly. This proved once again that the periodic table was a useful tool for organizing the elements.
Today, more new elements are being discovered, but many of these are not stable.
They have been created in laboratories with special equipment and have never been found in nature.
Still, no matter how the elements are identified, they all have their place in the periodic table.
Element Symbol and Name
The large letter or letters in each box show the symbol for the element. In the figure, you can see that
oxygen’s symbol is O.
For most elements, the symbol is an abbreviation derived from the element’s modern chemical name.
For example, the symbol for silicon is Si, and the symbol for manganese is Mn.
However, there are exceptions. For example, the symbol for gold is Au, which is from aurum, the Latin
word for gold.
The symbol for iron is Fe, which is from ferrum, the Latin word for iron.
The following table shows the word origin for several common elements.
Other Names for Elements
Not all elements are named for Latin words.
Some elements are named after the location in which they were first discovered. For example,
californium was discovered in 1950 at the University of California.
Other elements are named after scientists who made important contributions to their field of study.
For example, einsteinium, fermium, and curium are
named after Albert Einstein, Enrico Fermi, and Marie Curie.
Atomic Number
The number above the element’s symbol on the left is the atomic number.
It shows how many protons are in the nucleus of one atom of the element.
An oxygen atom, for example, always has eight protons. If you found six protons in an atom, the
periodic table would show you that you were looking at
carbon. Because atoms are neutral, the number of protons
equals the number of electrons. Therefore, the atomic number
also tells you how many electrons are in an atom of a
particular element. Notice that the atomic number increases
by one for each element as you read across the periodic table
from left to right.
Atomic Mass
The number below the element’s name is the atomic mass.
The atomic mass tells you the total mass of all the protons and neutrons in an atom.
(Electrons are so tiny that they have very little effect on the total mass of the atom.)
This is the average mass of the element’s atoms.
Not all atoms in an element have exactly the same mass: some have slightly higher values than others,
and some have slightly lower values.
This difference occurs because of the different number of neutrons from atom to atom.
Atomic mass is measured by atomic mass unit (amu). One amu is defined as 1/12th the mass of a
carbon-12 atom.
Associated with atomic mass is mass number.
It represents the sum of the number of protons and neutrons in an atom.
For example, the most common form of carbon atom has six protons and six neutrons. Its mass
number is therefore equal to 12. Not all carbon atoms are carbon -12, however.
About 1% of carbon atoms have seven neutrons. The mass number of each of those atoms is 13.
There is also one more naturally occurring form of carbon atom, and its mass number is 14.
How would you find out how many neutrons it has?
Subtracting the atomic number (6) from the mass number (14) shows you there are 8 neutrons in the
nucleus of this type of carbon atom:
mass number (14) - atomic number (6) = number of neutrons (8)
Carbon -14 is present in nature in very low concentrations.
That’s good, because carbon-14 is radioactive, which means the atom is unstable and falls apart easily
in a mini-nuclear reaction, releasing energy.
Carbon -14 is present in small amounts in all living things. Scientists use it to find the age of biological
materials, such as animal fossils.
This technique is called carbon dating.
The Current Periodic Table
Now the elements are put in rows by increasing ATOMIC NUMBER!!
The horizontal rows are called periods and are labeled from 1 to 7.
The vertical columns are called groups are labeled from 1 to 18.
Elements in the same group have similar chemical and physical properties! Why?
• They have the same number of valence electrons.
• Valence electrons are the electrons in the outer shell.
• They will form the same kinds of ions.
Non - Metals -
Orange area - Solid or gas - Dull, brittle
All non-metals except Carbon do not conduct electricity - insulators
Metals -
Green area - Shiny, Malleable, and ductile.
They are all solid at room temperature except for Mercury and are conductors
Metalloids -
Purple area
They have both metallic and non-metallic properties.
They can be conductors or insulators
Periods - The rows in the periodic tables are called periods.
The left side of the period is a metal the right side is a non-metal.
Generally as you move left to right the elements get less reactive.
Families on the Periodic Table
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Columns are also grouped into families.
Families may be one column, or several columns put together.
Families have names rather than numbers. (Just like your family has a common last name.)
All the elements in these groups have similar chemical properties and valence electrons
Hydrogen
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Hydrogen belongs to a family of its own.
Hydrogen is a diatomic, reactive gas.
Hydrogen was involved in the explosion of the Hindenberg.
Hydrogen is promising as an alternative fuel source for automobiles
Group 1 – not including Hydrogen - Akali Metals
The Akali metals are the most reactive of the metals.
They react with air or water. Lithium is the first element.
• 1st column on the periodic table (Group 1) not including hydrogen.
• Very reactive metals, always combined with something else in nature (like in salt).
• Soft enough to cut with a butter knife
• More reactive as you move down the periods
Group 2 – Akaline-earth metals
The Akaline-earth metals are less reactive than Group 1 elements. They also react with air or water.
Beryllium is the first element.
• Second column on the periodic table. (Group 2)
• Reactive metals that are always combined with nonmetals in nature.
• Several of these elements are important mineral nutrients
(such as Mg and Ca)
Groups 3 – 12 Transition Metals
Because they possess the properties of metals, the transition elements are also known as the transition
metals.
• Elements in groups 3-12
• Less reactive harder metals
• Includes metals used in jewelry and construction.
• Metals used “as metal.”
• These elements are very hard, with high melting points and boiling points
Group 13 - Boron Family
• Elements in group 13
• Aluminum metal was once rare and expensive, not a “disposable metal.”
Group 14 - Carbon Family
• Elements in group 14
• Contains elements important to life and computers.
• Carbon is the basis for organic chemistry.
• Silicon and Germanium are important semiconductors
Group 15 - Nitrogen Family
• Elements in group 15
• Nitrogen makes up over ¾ of the atmosphere.
• Nitrogen and phosphorus are both important in living things.
• Most of the world’s nitrogen is not available to living things.
• The red stuff on the tip of matches is phosphorus.
Group 16- Oxygen Family or Chalcogens
• Elements in group 16
• Oxygen is necessary for respiration.
• Many things that stink, contain sulfur (rotten eggs, garlic, skunks,etc.)
Group 17 - The Halogens
They are the most reactive non-metals.
• Elements in group 17
• Very reactive, volatile, diatomic, nonmetals
• Always found combined with other element in nature .
• Used as disinfectants and to strengthen teeth.
Group 18 - The Noble gases
They are the most stable and un-reactive elements.
• Elements in group 18
• VERY unreactive, monatomic gases
• Used in lighted “neon” signs
• Used in blimps to fix the Hindenberg problem.
• Have a full valence shell.
• They are the most stable and un-reactive elements
• The outer shell is full of electrons
• Noble gases will not lose or gain electrons
Rare Earth Elements - lanthanides and actinides (30)
One element of the lanthanide series and most of the elements in the actinide series are synthetic or
man-made. All of the rare earth metals are found in group 3 of the periodic table, and the 6th and 7th
periods.
The Periodic Table: the Bulk Earth
A small number of elements make up more than 99% of the solid Earth
O = oxygen
Na = sodium
Mg = magnesium
Al = aluminum
Si = silicon
S = sulfur
Ca = calcium
Fe = iron
Ni = nickel
Atomic Weight: It’s all in the Nucleus
Since electrons weigh virtually nothing, the mass of an atom is concentrated in its nucleus.
Each atom can be described by its atomic weight (or mass),
which is the sum of the protons and neutrons.
lithium:
atomic number = 3
3 protons
4 neutrons
atomic weight = 3 + 4 = 7
BUT... although each element has a defined number of protons, the number of neutrons is not fixed.
Atoms with the same atomic number but variable numbers of neutrons are called isotopes.
Isotopes
Carbon (atomic # 6) has three natural isotopes
with atomic weights of 12, 13 and 14.
Tin (Sn, atomic # 50) has ten natural isotopes with atomic masses of 112, 114, 115, 116, 117, 118,
119, 120, 122 and 124. How many protons and neutrons do these isotopes have?
Radioactive or Stable?
Radioactivity is a nuclear phenomenon: it comes as a result of a particular structure in a nucleus.
A radioactive atom is considered unstable.
All unstable atoms emit radioactivity
(usually by ejecting nuclear particles)
in order to reach a stable configuration.
This is the process of radioactive decay
So, not all atoms will be radioactive, just a small proportion of isotopes with unstable nuclei.
The bulk of isotopes are stable, or non-radioactive.