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Chemistry Vocabulary

Important Chemistry Vocabulary
Atomic Theory
Atomic Theory of Matter
Nucleus (plural: nuclei)
Valence shell
Octet Rule
Atomic symbol
Atomic number (Z)
Atomic mass (A)
Atomic Mass Unit (AMU)
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.
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.
the center of an atom, containing protons and neutrons. The atomic
nucleus contains a mix of positively charged protons and electrically
neutral neutrons
the outermost energy level where electrons orbit around the atomic
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
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.
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
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
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
A negatively charged ion, produced when one or more electrons are
added to an atom.
A positively charged ion, produced when one or more electrons are
lost from an atom.
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.
A one-letter or two-letter abbreviation for a specific element. The
first letter of symbols is always capitalized, but the second letter of 2letter symbols is never capitalized.
the number of protons in one atom of a particular element,
abbreviated as the letter ‘Z’
The combined number of neutrons and protons in the atomic nuclei
of an element, abbreviated by the letter ‘A’.
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
Important Chemistry Vocabulary
Electron configuration
Electron shell
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
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
Periodicity and the Periodic Table
Alkali metals
Alkaline Earth metals
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.
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
A row of elements in the periodic table. Periods are based on the
number of energy levels where electrons orbit atomic nuclei.
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
Elements which do not exhibit metallic properties, generally located
in the upper right-hand corner of the Periodic Table. Nonmetals
usually gain electrons in ionic bonds, or they may share electrons
with other nonmetals in covalent bonds.
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
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
The elements in Group 2 of the periodic table. Properties of Alkaline
Earth metals:
● reactive, but less so than Alkali metals
● malleable
● soft
● silver color
● conductors
Important Chemistry Vocabulary
Transition metals
Noble Gases
Diatomic elements
Oxygen group
Nitrogen group
● 2 valence electrons are lost to become +2 cations
● form ionic bonds with nonmetals
● never found alone in nature
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 colored 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
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
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
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
● Cl2
● Br2
● I2
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.
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
Important Chemistry Vocabulary
Atomic radius
Melting point
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.
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.
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
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.
A measure of how strongly an atom holds electrons in a covalent
bond. This is important in determining polarity of substances
A measure of how easily an element will bond with other elements to
form compounds. The trends are different for metals and nonmetals.
Bonding and Naming Compounds
Ionic bond
Covalent bond
Diatomic element
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
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.
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.
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.
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.
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
Important Chemistry Vocabulary
Formula unit
● O2
● F2
● Cl2
● Br2
● I2
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.
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.
Balancing Equations
Law of Conservation of
Avogadro’s number
Molar mass
Mole ratio
Mole-mass problem
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.
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.
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.
a substance that is used to test for the presence of another substance
by causing a chemical reaction with it
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.
The large number in front of a chemical symbol in reaction equations.
It shows the number of moles of a substance.
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
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.
The number of particles in one mole of any substance. Through
experimental observation it has been fixed at 6.02e23 (6.02 x 10 23 )
particles per mole.
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
The relative number of moles, molecules, or formula units of
substances involved in chemical reactions. It is important in
determining yields from the reactions.
Conversion between the number of particles and the number of
grams of various substances in chemical reactions.
Important Chemistry Vocabulary
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
Types of Reactions
Single replacement
Double replacement
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
A type of reaction in which a single compound breaks down into
simpler parts. The general format is AX → A + X
A type of reaction in which a more chemically reactive element takes
the place of another element in a compound and sets the lessreactive element free. The general format is A + BX → AX + B or AX +
Y → AY + X
A type of reaction in which two ionic compounds ‘swap’ the partner
ions with each other. The general format is AX + BY → AY + BX.
A type of reaction in which hydrocarbons react with oxygen gas to
produce carbon dioxide and water. The products always include CO2
and H2O.