Unit 2: Matter and Chemical Change
Lesson 1: Properties of Matter
All chemicals should be handled very carefully.
WHMIS (Workplace Hazardous Materials Information System) has been developed to provide guidelines for handling, storage and disposal of reactive materials (chemicals).
Some materials are CAUSTIC - will burn, corrode or destroy organic tissue
MATTER: Matter is anything that has mass. All matter is described in terms of its properties
PROPERTIES - are characteristics you can use to describe or identify different substances. Ex. Color, luster, state, taste, melting point, and behavior
Properties can be classified as:
1. QUALITATIVE PROPERTIES
- Those properties, which describe a quality of matter that has no numerical value (no number)
- Usually involves one of the senses
Ex. Taste, odor, texture, color, luster
2. QUANTITATIVE PROPERTIES
-Those properties, which describe a quantity of matter
- Have a number associated with the property
Ex. Melting point of water is 00 C
· Freezing point, boiling point, number of legs, density etc.
CHEMICAL PROPERTIES – those properties that involve the formation of a new substance. Chemical properties cannot be tested without destroying the substance.
Ex. Rust is formed when iron reacts with oxygen
Magnesium burns to produce a white powder
Paper burns to produce carbon dioxide and water
PHYSICAL PROPERTIES – do not involve the formation of a new substance. Physical properties can be tested without destroying the substance.
Ex. Melting point – temperature at which something changes from a solid to a liquid
Boiling point – temperature at which something changes from a liquid to a gas
Malleability – can be pounded or rolled into sheets
Ductility – can be stretched into a wire
Density – the amount of mass in a given volume of a substance
Conductivity – ability of a substance to conduct electricity
Solubility – ability to be dissolved in another
The Particle Model of Matter states that:
1. All matter is made up of extremely tiny particles.
2. Each pure substance has its own kind of particle, different from the particles of other pure substances.
3. Particles attract each other.
4. Particles are always moving.
5. Particles at a higher temperature move faster on average than particles at a lower temperature.
All matter can be classified according to its state as a
1. Solid – has a definite shape and a definite volume
- Particles are close together and the forces between the particles are strongest
2. Liquid - has a definite volume but takes the shape of its container
- Are said to be fluid because they flow
- Particles are further apart and the forces between the particles are weaker
3. Gas - has neither a definite shape nor a definite volume
- Expands to fill the container
- Gases are fluids because they also flow
- Particles are furthest apart and the forces between the particles are very weak
CHANGES OF STATE
1. Melting
2. Freezing
3. Boiling/Vaporizing
4. Condensation
5. Sublimation
Classification of Matter
Matter can also be classified according to its composition:
Matter
Pure Substances Mixtures
Elements Compounds Mechanical Solutions
Mixtures (homogeneous) (heterogeneous)
Suspension Colloids
PURE SUBSTANCES have properties that are always the same.
Ex. Table salt is a white solid that melts
at 801 °C and boils at 1465 °C.
Water, vinegar, sugar etc.
Elements
-Pure substances that cannot be broken down into any simpler substances - most elements are solids but several are gases and two are liquids
-All of the elements have been arranged on the Periodic Table according to certain properties.
- Contains only one type of atom
Ex. Silver, Oxygen, Iron, Carbon, Mercury
Compounds
- Pure substances that contain two or more
different elements, combined in a definite
fixed proportion.
- Can be broken down chemically into different substances since it is made up of different kinds of atoms
Ex. Water - 2 hydrogen + 1 oxygen ---> H2O
Salt - 1 sodium + 1 chlorine ---> NaCl
MIXTURES contain at least two different substances. Properties are variable
Solutions -Homogeneous are a mixture in which one substance is dissolved in another. It is a uniform mixture that appears the same throughout.
Ex. Salt water, apple juice, and air
Mechanical - Heterogeneous are mixtures that do not appear the same throughout. The different components are visible.
Ex. Soil, chocolate chip cookies, chicken noodle soup
Suspensions
– Heterogeneous mixture made of large particles that are uniformly mixed but will settle if left undisturbed
Ex. Sand in water, powdered chalk in water
Colloids
- Heterogeneous mixture composed of fine particles evenly distributed throughout a second substance
Ex. Hair gel
Emulsions
- Type of colloid in which liquids are dispersed in liquids
- Many will separate quickly to form layers of the original liquids (oil and vinegar)
Lesson 2: Chemical and Physical Changes
Physical Changes
- No new substance produced
- Change of size, shape or state
- Ex. Cutting, freezing, molding, boiling, dissolving
Chemical Changes
- Starting material is used up
- New substance formed with different properties
- Atoms are rearranged to form new molecules
- Changes cannot be reversed
- Ex. Cooking an egg, rusting, burning
Evidence of a Chemical Change
(a) Color Change
(b) Gas Formed – bubbling
(c) Solid material, called a precipitate is formed.
- two solutions are combined and a solid is formed
(d) Energy Change - energy is the ability to do work
- Ex. Light, heat, mechanical, sound, electrical
There are 2 types of energy change:
1. Endothermic – energy is required.
- Energy is added to the starting materials
- Ex. cooking
2. Exothermic – energy is released.
- Ex. Burning
Identify the following substances as pure substances (element / compound) or as a mixture (homogeneous / heterogeneous):
1. zinc 6. vinegar
2. carbon dioxide 7. tossed salad
3. orange juice 8. aluminum
4. nitrogen 9. kool-aid
5. sugar 10. windex
Lesson 3: History of the Atomic Theory
Aristotle: (350 BC) – Greek philosopher
- Believed that everything was made of
1. Earth (dry and cold)
2. Air (wet and hot)
3. Fire (dry and hot)
4. Water (wet and cold)
Robert Boyle: (1660’s) – England
Recognized that elements could be combined to form compounds
Lavoisier: (1770-1780) – France
1. Defined elements as pure substances that cannot be decomposed (broken down into simpler substances)
2. Developed a system for naming chemicals, so that all scientists could use the same words
3. Identified 23 pure substances as elements
4. Discovered that in a chemical change, “the mass of the new substances is always the same as the mass of the original substances” – LAW OF CONSERVATION OF MASS.+
John Dalton: (1808) – England
Atomic Theory:
1. All matter is made up of small particles called atoms
2. Atoms cannot be created, destroyed or divided into smaller particles
3. All atoms of the same element are identical in mass and size. Atoms of one element are different in mass and size from the atoms of other elements
4. Compounds are created when atoms of different elements link together in definite proportions.
Dalton’s Theory led to the current definitions:
Element – a pure substance made up of one type of particle, or atom.
Compounds – pure substances that are made up of 2 or more elements chemically combined together. Compounds can be broken down into elements again by chemical means.
J.J. Thompson: (1897) England
- Raisin bun model (plum pudding)
- Atom is a sphere, which is positive, with negative electrons embedded in it like raisins in a bun
Ernest Rutherford: (1911) McGill University, Canada
- Atoms have a nucleus which is positive
- Most of the atom is empty space occupied by the moving negatively charged electrons
- Proposed the existence of protons in a nucleus
Neils Bohr: (1913) – Danish
-Electrons move in circular orbits around the nucleus
- Like a miniature solar system
James Chadwick: (1932)
- showed that the nucleus must contain heavy neutral
particles to account for all of the atom's mass
- proposed the existence of neutrons
Lesson 4: Element Symbols
- All elements have been given an atomic symbol
(a) A single capital letter – O – oxygen
(b) Capital letter & a lower case letter – Co – cobalt
(c) Capital letter & 2 lower case letters – Uun – ununnilium
- In the 1860’s Dmitri Mendeleev, a Russian chemist arranged the elements in order of increasing ATOMIC MASS and created the PERIODIC TABLE
- ATOMIC MASS is the average mass of an atom of an element
Ex. Oxygen = 16.00 g/mol
- Mendeleev found that the properties of the elements repeated at definite, or periodic intervals (ex. Lithium, sodium and potassium have similar properties so he placed them in the same family or vertical row)
- He left blanks in the table where he predicted elements should be and predicted what their properties would be, based on where they were on his table
- After the development of atomic theory, the periodic table was rearranged in order of increasing ATOMIC NUMBER
- ATOMIC NUMBER is the number of protons an element has in its nucleus
Ex. Fluorine – atomic number = 9, therefore it must have 9 protons in its nucleus.
The Periodic Table contains a lot of information about the different atoms. For example:
Atomic number Symbol
Name
Atomic Mass
The horizontal rows on the periodic table are called Periods.
The vertical rows on the table are called Groups or Families.
Elements in the same family have similar properties (behave in a similar manner)
There are 18 Groups or Families.
The key on the periodic table will indicate the state of each element. Ex. White box – solid
Grey box – gas
Black box - liquid
- All elements can be classified as metals, non-metals or metalloids depending on their properties
Metals Non-metals
- Found to the left of the - located to the right of
staircase line of the staircase line
- 80% of all elements - 20 % of all elements
- Lustrous (shiny) - dull
- Ductile (stretched into wire) - non-ductile
- Malleable (hammered/shaped) - brittle
- Conduct electricity - non-conductors
- All solids, except mercury - Mostly gases, some metals, 1 liq.
- Ex. Sodium, iron Ex. Oxygen, bromine
Metalloids - these elements have properties of both metals and non-metals
Ex. Silicon – shiny like a metal, poor conductor like a non-metal
There are 4 special named groups in the table:
Group 1 – Alkali Metals
- Most reactive metals
- Never found in pure form in nature
Ex. Lithium, sodium, potassium
Group 2 – Alkaline Earth Metals
- React fairly vigorously with some substances
Ex. Magnesium, calcium, barium
Group 17 – Halogens
- Most reactive non-metals
Ex. Fluorine, Chlorine
Group 18 – Noble Gases
- Most non-reactive elements
- Used to be called “Inert” gases until 1963 when a
Canadian chemist at UBC, made some of them react
- Different noble gases produce different colors
Ex. Argon – blue
Helium – yellow-white
Lesson 5: ATOMIC STRUCTURE
q Atom - the smallest part of an element (which retains the chemical and physical properties of the element). Atoms are made up of 3 sub-atomic particles
1. Electron (e)
-Smallest particle in an atom
-Has a negative charge
-Located in the extra nuclear region of the atom - outside the nucleus
2. Proton (p)
-Has a large mass
-Has a positive charge
-Located inside the nucleus
3. Neutron (n)
-Same mass as a proton
-Has a neutral charge (no charge)
-Located inside the nucleus
Nuclear Notation
- Atomic number is the number of protons in the nucleus
- The number of protons equals the number of electrons in a neutral atom (#p = #e)
- Atomic Mass Number is the total number of protons and neutrons in the nucleus
And,
Atomic # = #p = #e
Example:
Find the number of protons, electrons and neutrons
for iron and sodium.
Fe Atomic # = 26
Atomic mass = 55.85 = 56 (round the mass)
Therefore: # of p = 26
# of e = 26
# of n = 56 – 26 = 30
Note: when finding the number of neutrons we round the atomic mass to the nearest whole number.
Na Atomic # = 11
Mass # = 22.99 = 23
p = 11
e = 11
n = 23 – 11 = 12
Au Atomic # = 79
Atomic mass = 196.96 = 197
p = 79
e = 79
n = 197 – 79 = 118
Lesson 6: Bohr’s Model of the Atom
- Bohr’s model states that electrons can be found only in certain energy levels or orbits around the nucleus
- He also stated that only a certain maximum number of electrons are allowed in each orbit.
Orbit # Max. # of electrons
1st 2
2nd 8
3rd 8
4th 18
5th 18
6th 32
When one orbit is filled the remaining electrons go to the next orbit – you cannot exceed the maximum allowed.
We can draw the Bohr diagram for any element. It must
have a nucleus showing the number of protons and neutrons and circles outside the nucleus showing the number of electrons.
Reminder: # of protons = # of electrons = atomic #
e.g. Draw the Bohr model for the following elements:
a) Lithium
Step 1 – Look up the atomic number
It’s 3.
So, # of p = 3