A nearly-comprehensive list of vocabulary terms needed for introductory chemistry in grade 9 science, including a variety of source websites for reference.

1. Welcome to the grade 9 chemistry vocabulary list! Below you will find a comprehensive list
of the key ideas and concepts needed to successfully navigate our chemistry unit. You are
required to know all these definitions, and we may add other definitions and key words as
we progress through the unit. I’ve organized the list according to the major topics from the
unit.
Atomic Theory
Atomic Theory of Matter
1. All matter is made of atoms.
2. All atoms of an element are identical in mass and properties.
3. Compounds are formed by combining 2 or more kinds of atoms.
4. Chemical reactions are rearrangements of atoms.
Source: http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html
Atom
the smallest particle of an element which can exist by itself. A typical atom
consists of a nucleus of protons and neutrons with electrons orbiting this
nucleus. An atom is the defining structure of an element.
Source:
http://chemistry.about.com/od/chemistryglossary/a/atomdefinition.htm
Nucleus
(plural: nuclei)
the center of an atom, containing protons and neutrons. The atomic nucleus
contains a mix of positively charged protons and electrically neutral neutrons
Source: https://www.boundless.com/biology/definition/atomic-nucleus/
Valence shell
the outermost energy level where electrons orbit around the atomic nucleus
Source:
http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/valenceshe
ll.htm
Proton
A positively-charged particle in the center of atomic nuclei, with a relative mass
of 1 amu; the number of protons determines the chemical identity of an atom
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html
Electron
The lightest subatomic particle known. It carries a negative charge, which is
considered the basic unit of electric charge. Electrons orbit around the atomic
nucleus in shells of different energy levels.
Source: http://www.britannica.com/EBchecked/topic/183374/electron
Neutron
A particle in the center of atomic nuclei, which have no electrical charge.
Neutrons have a relative mass of 1 amu, like protons; however, atoms of the
same element may have different numbers of neutrons.
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c3
Isotopes
Forms of an element with the same number of protons but different numbers of
neutrons in the atomic nuclei. Isotopes of an element have the same chemical
properties but different atomic masses.
Source: http://ie.lbl.gov/education/info.htm
Ions
Forms of an element which have an electrical charge because they have either
gained or lost electrons. Ions which have gained electrons have a negative
charge and are called anions. Ions which have lost electrons have a positive
charge and are called cations.
Source:

2. http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/ionic_comp
ounds/ionicrev1.shtml
Anion
A negatively charged ion, produced when one or more electrons are added to
an atom.
Source:
http://chemistry.about.com/od/chemistryglossary/a/Aniondefinition.htm
Cation
A positively charged ion, produced when one or more electrons are lost from
an atom.
Source: http://chemistry.about.com/cs/glossary/g/cationdef.htm
Octet Rule
The tendency of atoms to gain or lose electrons in order to have 8 electrons in
their valence shell. The number of electrons gained or lost determines the
charge of the resulting ion.
Source: http://dl.clackamas.cc.or.us/ch104-08/octet.htm
Atomic symbol
A one-letter or two-letter abbreviation for a specific element. The first letter of
symbols is always capitalized, but the second letter of 2-letter symbols is never
capitalized.
Source: http://www.wisc-online.com/Objects/ViewObject.aspx?ID=GCH3404
Atomic number (Z)
the number of protons in one atom of a particular element, abbreviated as the
letter ‘Z’
Source:
http://www.colorado.edu/physics/2000/periodic_table/atomic_number.html
Atomic mass (A)
The combined number of neutrons and protons in the atomic nuclei of an
element, abbreviated by the letter ‘A’.
Source:
http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/atomic
massnumber.htm
Atomic Mass Unit (AMU)
The unit of measurement for subatomic particles. It is based on the average
mass of a proton or neutron, so that the mass of 1 proton = 1 amu.
Source:
http://www.colorado.edu/physics/2000/periodic_table/atomic_mass.html
Electron configuration
The way that electrons are arranged in different energy levels around the
nucleus of an atom. The energy levels correspond with electron shells in the
Bohr model of atoms.
Source:
Armstrong, Rick, Kevin Gaylor, and Jenny Sharwood. Chemistry 4/5 for the
International Student. South Melbourne, Vic.: Cengage Learning, 2010.
Print.
Electron shell
Electrons are arranged in shells at different distances around the nucleus.Each
shell represents a different energy level, with the lowest-energy shell closest
to the atomic nucleus. Each shell may hold a maximum number of electrons,
arranged in pairs as often as possible.
Source:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/perio
dic_table/electronsrev1.shtml

3. Periodicity and the Periodic Table
Periodicity
Repeating trends that are seen in elements’ properties, and which can be
predicted based on an element’s position in the periodic table. The major
properties we will study are electronegativity, electron affinity, atomic radius,
and ionization energy.
Source:
http://chemistry.about.com/od/periodicproperties/a/What-Is-Periodicity-On-T
he-Periodic-Table.htm
Group
A column of elements in the periodic table, sometimes also called a family of
elements. Each group has common chemical and physical characteristics based
on the elements’ electron arrangements.
Source:
http://chemistry.about.com/od/chemistryglossary/a/groupdefinition.htm
Period
A row of elements in the periodic table. Periods are based on the number of
energy levels where electrons orbit atomic nuclei.
Source:
http://chemistry.about.com/od/periodicproperties/f/What-Is-The-DifferenceBetween-An-Element-Group-And-Period.htm
Metal
a substance (such as gold, tin, or copper) that usually has a shiny appearance, is
a good conductor of electricity and heat, can be melted, and is usually capable
of being shaped.
Source: http://www.merriam-webster.com/dictionary/metal
Nonmetal
Elements which do not exhibit metallic properties, generally located in the
upper righthand corner of the Periodic Table. Nonmetals usually gain electrons
in ionic bonds, or they may share electrons with other nonmetals in covalent
bonds.
Source: http://chemistry.about.com/od/chemistryglossary/a/nonmetaldef.htm
Metalloid
Metalloids are the elements found along the stair-step line that distinguishes
metals from nonmetals. Metalloids have properties of both metals and
nonmetals. Some are semi-conductors.
Source: http://www.chemicalelements.com/groups/metalloids.html
Alkali metals
The elements in the first group (Group 1) on the left side of the periodic table.
Properties of Alkali metals are:
● highly reactive
● always found bonded with other elements
● 1 valence electron can be easily donated - become +1 cations
● form ionic bonds with nonmetals
● malleable and ductile
● extremely soft
● silvery color
● good conductors
● low boiling and melting points
● explosive reactions with water
Source:
http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Main
_Group_Elements/Group__1%3A_The_Alkali_Metals
Alkaline Earth metals
The elements in Group 2 of the periodic table. Properties of Alkaline Earth

4. metals:
● reactive, but less so than Alkali metals
● malleable
● soft
● silver color
● conductors
● 2 valence electrons are lost to become +2 cations
● form ionic bonds with nonmetals
● never found alone in nature
Source:
http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Main
_Group_Elements/Group__2%3A_The_Alkaline_Earth_Metals
Transition metals
The elements in the center of the periodic table, from Group 3 - Group 12. They
tend to lose electrons to form cations with charges from +1 to +7, and many
transition metals will form several different cations (Mn, for example, may be
Mn2+, Mn3+, Mn4+, Mn6+, or Mn7+. Properties of transition metals:
● form coloured compounds
● good conductors of heat and electricity
● hammered or bent into shape easily
● less reactive than alkali metals such
● high melting points - but mercury is a liquid at room temperature
● usually hard and tough
● high densities
Source:
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/patte
rns/transitionmetalsrev1.shtml
Noble Gases
The elements in Group 18 (the far right column) of the periodic table. They are
all gases, and they are almost totally non-reactive with other elements. They
have a full valence shell, so that they don’t gain or lose electrons.
Source:
http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Main
_Group_Elements/Group_18%3A_The_Noble_Gases
Halogens
The elements in Group 17 of the periodic table, the halogens all have 7 valence
electrons. This means they all gain 1 electron in order to fulfil the octet rule.
Properties of halogens:
● form anions with a 1- charge
● extremely reactive
● diatomic molecules
● poisonous
● react with metals to form salts
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/halog.html
Diatomic elements
Atoms of these elements will combine with atoms of the same element in order
to form stable molecules of the element. The molecules are formed when
atoms share one or more pairs of electrons. Diatomic elements are not diatomic
when they bond with different elements!The diatomic elements you have to
know are:
● H2
● N2
● O2
● F2

5. ● Cl2
● Br2
● I2
Source:
http://ths.talawanda.net/~BrambleN/classroom/Chemistry/Notes/Section%20
1B/DiatomicElements.htm
Oxygen group
All the elements underneath oxygen in the periodic table, which have 6 valence
electrons. They are less reactive than the halogens, but because they gain 2
electrons, are still fairly reactive.
Nitrogen group
All the elements under nitrogen in the periodic table (group 15), which have 5
valence electrons. They may form 3 covalent bonds, which are the strongest
type of covalent bond. Nitrogen and phosphorus are important for the growth
of producers.
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/ng.html
Lanthanides
The top row of the Rare Earth metals, which are the two rows separated from
the rest of the periodic table at the bottom. They dissolve in acids and tarnish
easily when exposed to air. They also react with water, but slowly.
Source:
http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Trans
ition_Metals_and_Coordination_Complexes/The_Lanthanides#Properties_and_
Chemical_Reactions
Actinides
The bottom row of the Rare Earth metals. All are radioactive (this is where
uranium is found in the periodic table!) because their nuclei are unstable, and all
are considered toxic. Most have been made synthetically and do not occur much
naturally.
Source:
http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Trans
ition_Metals_and_Coordination_Complexes/The_Actinides#Common_Propertie
s
Atomic radius
The distance from the nucleus of an atom to the valence shell, where the
outermost electrons orbit. One of the important trends we study in chemistry
because it relates to the strength with which atoms hold onto electrons when
bonding with other atoms. Atoms become smaller as we move to the right
across periods because the electrons are more strongly attracted to the
greater number of protons in the atomic nuclei. Atoms become larger as we
move down the groups because additional electrons are added in shells further
from the nuclei.
Source:
http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Atomic_radius.html
Melting point
The temperature at which a substance changes from a solid to a liquid. In theory,
this is the same temperature at which the liquid will turn into a solid, called the
freezing point.
Source:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/melting.php
Electronegativity
A measure of how strongly an atom holds electrons in a covalent bond. This is
important in determining polarity of substances.
Source: http://www.files.chem.vt.edu/RVGS/ACT/notes/electronegativity.html

6. Reactivity
A measure of how easily an element will bond with other elements to form
compounds. The trends are different for metals and nonmetals.
Source:
http://edtech2.boisestate.edu/lindabennett1/502/Periodic%20Table%20e%2
0config/PTable_trends%20around%20table.html
Bonding and Naming Compounds
Ionic bond
bond in which one or more electrons from one atom are removed and attached
to another atom, resulting in positive and negative ions which attract each
other.
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Covalent bond
bond in which one or more pairs of electrons are shared by two atoms. One
shared pair makes a single bond, two shared pairs make a double bond, and
three shared pairs make a triple bond.
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Element
A substance made of atoms with the same number of protons in their
nuclei. They are chemically the simplest substances and hence cannot be
broken down using chemical methods.
Source: http://www.chemicool.com/definition/element.html
Compound
A substance composed of 2 or more elements that are chemically combined
together. It can be split up into its original elements by running an electrical
current through it or by heating it.
Source:
Armstrong, Rick, Kevin Gaylor, and Jenny Sharwood. Chemistry 4/5 for the
International Student. South Melbourne, Vic.: Cengage Learning, 2010.
Print.
Mixture
A substance composed of 2 or more elements or compounds that are NOT
chemically combined. They can be separated by physical means such as filtration
or distillation.
Source:
Armstrong, Rick, Kevin Gaylor, and Jenny Sharwood. Chemistry 4/5 for the
International Student. South Melbourne, Vic.: Cengage Learning, 2010.
Print.
Diatomic element
elements which cannot exist as single atoms. They form molecules of 2 atoms of
the same element if they are isolated from other elements. There are 8
diatomic elements you must memorize for this unit:
● hydrogen (H2)
● nitrogen (N2)
● oxygen (O2)
● fluorine (F2)
● chlorine (Cl2)
● bromine (Br2)
● iodine (I2)
● astatine (At2)
Source:
http://ths.talawanda.net/~BrambleN/classroom/Chemistry/Notes/Section%20
1B/DiatomicElements.htm

7. Molecule
Atoms of 2 or more elements, which are covalently bonded together. The
atoms share one, two, or three pairs of electrons to form single, double, or
triple bonds respectively.
Source: http://education.jlab.org/qa/compound.html
Formula unit
The simplest repeating unit of a substance, showing all the elements within that
substance. It usually - but not always - refers to ionic compounds, in which
oppositely-charged ions are electrically attracted to one another.
Source: http://www.chemicool.com/definition/formula_unit.html
Balancing Equations
Law of Conservation of
Matter
All the atoms present at the start of a chemical reaction are still present at the
end of the reaction. They have simply been rearranged in new ways.
Source:
http://employees.oneonta.edu/viningwj/modules/CI_law_of_conservation_of_
matter_4_3.html
Reactant
One of the starting substances in a chemical reaction, which may be changed
during the course of the reaction. They are written on the left side of chemical
equations.
Source: http://chemistry.about.com/od/chemistryglossary/a/reactantdef.htm
Product
One of the substances made during a chemical reaction. It is assembled from the
atoms which make up the initial ingredients of the reaction. They are written on
the right side of chemical equations.
Source: http://www.chemprofessor.com/outline7b.htm
Reagent
a substance that is used to test for the presence of another substance by
causing a chemical reaction with it
Source: http://www.merriam-webster.com/dictionary/reagent
Yield
The amount of material produced in a chemical reaction, which depends on the
quantities of chemicals used and whether the reaction goes to completion or
not.
Source: http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH7504
Coefficient
The large number in front of a chemical symbol in reaction equations. It shows
the number of moles of a substance.
Source:
http://chemistry.about.com/od/chemistryquickreview/a/balanceequation.htm
Subscript
The small number after an individual element’s symbol in a chemical formula. It
shows how many atoms of that element are present in the compound.
Source: http://crescentok.com/staff/jaskew/isr/chemistry/class12.htm
Mole
The primary unit for measuring the amount of a substance present in chemical
reactions. Since atoms are so small, this makes it easier to calculate yields in
chemistry. It is based on the number of carbon atoms in 12g of pure carbon.
Source: http://www.files.chem.vt.edu/RVGS/ACT/notes/The_Mole.html
Avogadro’s number
The number of particles in one mole of any substance. Through experimental
observation it has been fixed at 6.02e23 (6.02 x 1023) particles per mole.
Source: http://www.files.chem.vt.edu/RVGS/ACT/notes/The_Mole.html

8. Molar mass
The mass (in grams) of 6.02e23 particles of a substance. It may be calculated by
adding the atomic masses of all elements in a given compound.
Source:
http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Molar_mass.html
Mole ratio
The relative number of moles, molecules, or formula units of substances
involved in chemical reactions. It is important in determining yields from the
reactions.
Source: http://www.occc.edu/kmbailey/Chem1115Tutorials/Molar_Ratios.htm
Mole-mass problem
Conversion between the number of particles and the number of grams of
various substances in chemical reactions.
Source: http://www.chemteam.info/Mole/Moles-to-Grams.html
Mass-mass problem
A type of conversion or problem which uses the mass and molar mass of one
substance to determine how many grams of another substance are produced
by a chemical reaction.
Source:
https://www.boundless.com/chemistry/mass-relationships-and-chemical-equat
ions/reaction-stoichiometry/mass-to-mass-conversions/
Types of Reactions
Synthesis
A type of reaction in which two or more substances combine to form a new and
chemically different substance. The general format is A + X → AX.
Source:
http://www.files.chem.vt.edu/RVGS/ACT/notes/Types_of_Equations.html
Decomposition
A type of reaction in which a single compound breaks down into simpler parts.
The general format is AX → A + X.
Source:
http://www.files.chem.vt.edu/RVGS/ACT/notes/Types_of_Equations.html
Single replacement
A type of reaction in which a more chemically reactive element takes the place
of another element in a compound and sets the less-reactive element free. The
general format is A + BX → AX + B or AX + Y → AY + X.
Source:
http://www.files.chem.vt.edu/RVGS/ACT/notes/Types_of_Equations.html
Double replacement
A type of reaction in which two ionic compounds ‘swap’ the partner ions with
each other. The general format is AX + BY → AY + BX.
Source:
http://www.files.chem.vt.edu/RVGS/ACT/notes/Types_of_Equations.html
Combustion
A type of reaction in which hydrocarbons react with oxygen gas to produce
carbon dioxide and water. The products always include CO2 and H2O.
Source:
http://www.files.chem.vt.edu/RVGS/ACT/notes/Types_of_Equations.html