MATTER AND CHEMICAL CHANGE
Matter can be defined as anything that has mass and occupies space. The flow chart below shows how
matter is organized and can be classified.
A pure substance cannot be broken down into simpler substances. A mixture, however, can he separated
into component parts by physical means. Pure substances are grouped into elements, which are substances
composed of only one kind of atom, and compounds, which are substances composed of two or more
elements chemically combined. Hydrogen, oxygen and gold are examples of elements. Water and sugar are
examples of compounds.
Matter can be identified by physical and chemical properties. Physical properties are easily observable
and include characteristics such as melting point, density, color, and state. Chemical properties refer to
how the substance reacts with other substances. For example, iron is a reddish solid (physical properties)
that reacts with oxygen to form rust (chemical properties).
Safety is always a concern in a school lab. Eight important workplace hazardous materials information
system (WHMIS) symbols help identify potentially dangerous chemicals. In addition, hazardous symbols
enclosed in three different shapes appear on various product containers.
stands for DANGER-flammable
WHMIS Symbols:
ATOMIC STRUCTURE OF MATTER
Matter has been studied for many centuries. Metals such as gold and copper were the first to be identified.
It was in the early 18th century when considerable research was done and several theories about the atom
were proposed. Dalton described the atom in his Atomic Theory. Others, such a Rutherford, Thompson,
and Bohr, followed up with theories on the composition and structure of the atom.
Atoms are composed of three basic subatomic particles: protons, electrons, and neutrons (acronym PEN).
Each of these is identified by specific characteristics.
Particle
Charge
Size
Proton
+
Positive
Large-same as a neutron
Location
Nucleus
Electron
Negative
Small-about 1/1837 the
size of the proton
Orbits or Energy levels
Neutron
No Charge
Large-same as a proton
Nucleus
The atomic number (an) of an atom is the number of protons found in the nucleus. This also represents the
number electrons found in the orbits.
The atomic mass unit (amu) of an atom is the total mass of the protons and neutrons in the nucleus.
Example: copy chalkboard
Some atomic mass units may be written as a decimal (Carbon--12.01). The carbon atom can have a
different number of neutrons in its nucleus depending on which elements it combines with.
The electrons of an atom are arranged in energy levels. Each level has a maximum number of electrons.
Level One: maximum of 2 electrons
Level Two: maximum of 8 electrons
Level Three: maximum of 8 electrons
PERIODIC TABLE
All the elements have been grouped based on similar physical and chemical properties.
Mendelev, who developed the Periodic Table of Elements, grouped the metals on the left side and the nonmetals on the right side. Metals are solids at room temperature, shiny, malleable, and good conductors of
electricity. Non-metals can be a solid or gases at room temperature, are dull, and act as insulators.
Metalloids, found in a single "staircase" between the metals and nonmetals, have both metallic and nonmetallic properties.
The noble gases, located at the extreme right side of the table, are non-reactive and stable. Each horizontal
row in the Periodic Table is called a period. Each vertical row is called a group or family. The atoms in a
period have the same number of energy levels, and the atoms in a family have the same chemical
characteristics.
Information about each element in the Periodic Table is presented in a box.
FORMATION OF COMPOUNDS
When forming compounds, an atom can lose electrons from its outer ring or gain electrons to its outer ring.
When this happens, the atom becomes a charged particle called art ion.
Ions can appear as a single unit,
(
−2
S −2 , or as a group of atoms with an electrical charge, CO3
) . These are
called polyatomic ions.
Example: Aluminum would rather give up three electrons than have to find five to complete the third
€ in the presence of other compounds, aluminum would become a positive ion.
energy level Therefore,
€
Nitrogen, on the other hand, has five electrons in its outer ring (energy levels 2 and 5). It needs to pick up
three electrons to become stable as an eight-electron energy ring. When it picks up the three electrons,
−3
nitrogen is given the ionic charge of N .
In the formation of a compound, positively charged ions combine with negatively charged ions. The
positively charged ions (metals) retain the same name: whereas, negatively charged ions (non-metals) end
in "ide."
€
AlN is named aluminum nitride
MgCl2 is magnesium chloride
€
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Metals and non-metals come together because opposite charges attract. This is called ionic bonding, and
the compounds formed are called ionic compounds.
−
Molecular compounds are formed when atoms share electrons. For example, chlorine Cl will form
2
chlorine gas Cl . Even though they arc both negatively charged, they will share electrons so that both
atoms essentially have eight electrons in their outer shells.
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Molecular compounds are named using the following rule:
Prefix + First Element, Prefix + Second Element
(ending in "ide")
Example:
N 2O3 - dinitrogen trioxide
CHEMICAL REACTIONS
In a chemical reaction, the starting materials, which are called reactants, create new materials called
€products. The Law of Conservation of Mass states that the mass of the reactants equals the mass of the
products. Matter is neither created nor destroyed, but only changed. Oxidation reactions involving oxygen
are common in nature. Some can be rapid; whereas, others are very slow.
Chemical reactions can be represented in word equation form or symbol equation form.
The reaction of magnesium in hydrochloric acid can he written as:
Word Equation:
Magnesium + Hydrochloric Acid ⇒ + Magnesium Chloride + Hydrogen gas
Symbol Equation:
+
⇒
(Reactants)
+
(Products)
The rate of a chemical reaction can be increased or decreased by:
Using a catalyst
Changing the
temperature
Changing the surface
area
Changing the
concentration