Chemistry – Dr. May Notes
Describing Matter
According to make-up, matter exists as mixtures, elements, or compounds.
Mixture – Matter that consists of two or more substances mixed together but not
chemically combined. Matter that can be physically separated into component
parts is a mixture.
Heterogeneous mixture – A mixture that does not appear to be the same throughout
Homogeneous mixture – A mixture that appears to be the same throughout
Colloid – Homogeneous mixtures where the particles are mixed together but not
dissolved.
Solution – A type of homogeneous mixture of two or more substances in a single
physical state (solid, liquid, gas). Solutions are homogeneous mixtures and
have no visible evidence of the components. Solutions can usually be
separated by distillation.
Solute – The substance that is dissolved
Solvent – The substance that does the dissolving
Soluble – A property of a substance that dissolves in another substance
Insoluble – A substance that does not dissolve in another substance
Solubility – The amount of a solute that can be completely dissolved in a given amount
of solvent at a given temperature
Alloy – Metal solutions or solids dissolved in solids
Characteristics of pure substances
Pure substance – A substance where all the particles are alike. When the components
can no longer be separated into simpler substance, we are dealing with
a pure substance.
Boiling point, freezing point, and melting point are distinct and reproducible for
pure substances.
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Compounds can be chemically decomposed into new substances.
Electrolysis is a decomposition process that will convert a pure substance into
new matter. Electrolysis will decompose water to the new compounds, hydrogen and
oxygen (both elements). Hydrogen forms at the negative electrode and oxygen forms at
the positive.
Electrolysis of molten (melted) NaCl (table salt) (m.p. = 801 oC) (b.p. = 1413 oC)
will decompose NaCl to sodium metal and chlorine gas. Sodium forms at the negative
terminal and chlorine forms at the positive.
Decomposition is a chemical change.
Elements cannot be decomposed further.
Elements are the building blocks of compounds.
Element – A substance that cannot be changed into a simpler substance
Atom – The simplest particle of an element that has the properties of the element
Elements are made up of atoms. All the atoms of a given element are the
identical. An atom of sodium is described on the periodic table as having 11 protons and
an atomic mass of 23. All the mass of a sodium atom is in the nucleus, which is made up
of the 11 protons and the 12 neutrons (11 + 12 = 23). Sodium has 11 electrons, which are
in a cloud outside the nucleus. The electrons are involved in chemical reactions.
Atomic mass 
23
Atomic number
11
Sodium is represented:
Na
One mole (23 grams) of sodium contains 6.02 x 1023 atoms of sodium. An atom is
the smallest particle that can participate in a chemical reaction. When 23 grams of
sodium react with water, 6.02 x 1023 atoms of sodium react with 6.02 x 1023 atoms of
water.
Compounds have a definite composition
Compounds are made by combining elements in definite composition.
Compounds are made up of two or more kinds of atoms.
Compound – A pure substance that is made of more that one element.
Molecule – A molecule is the smallest particle of a compound that has the properties of
that compound.
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Mixtures can have any composition while compounds have a fixed (definite)
composition. (Law of Definite Composition)
It is possible to have different compounds containing the same elements, but each
will have a definite composition. Examples: H2O (water) and H2O2 (hydrogen peroxide),
CO2 (carbon dioxide) and CO (carbon monoxide). This is called the Law of Multiple
Proportions.
Symbols and names of molecular compounds
Chemical symbol – A shorthand way of representing the elements (Na)
Chemical formula – A shorthand way of representing chemical substances (NaCl)
Subscript – Gives the number of atoms of the element in a compound (CaCl2)

Coefficient – The appropriate number placed in front of a chemical formula to indicate
how many molecules are present (3 NaCl)

Rules for writing formulas:
1. Use the proper symbol for each element
2. Use subscripts (except 1) to show the number of atoms
3. Write the most metallic (+) element (or hydrogen) first
Formulas and names of covalent compounds (between two or more nonmetals)
The name of a compound tells which elements are present
Guidelines for naming covalent compounds are:
1. Name the elements in the same order as in the formula
2. Drop the last syllable or two of the final element and add –ide
3. Add Greek prefixes to each element name to indicate number. The prefix
mono- is frequently omitted.
Possible prefixes:
1. Mono6. Hexa-
2. Di7. Hepta-
3. Tri8. Octa-
4. Tetra9. Nona-
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5. Penta10. Deca-
Formulas and names of ionic compounds (between a metal and a non-metal)
Ions - particles that have lost or gained electrons and have an electrical charge
Ionic charges depend on the oxidation number of the elements. This is dependent
on the number of valence electrons in the outer orbits. Some charges to remember are:
1.
2.
3.
4.
5.
Group 1
Group 2
Group 13
Group 16
Group 17
(e.g. Sodium)
(e.g. Calcium)
(e.g. Aluminum)
(e.g. oxygen)
(e.g. chlorine)
+1
+2
+3
–2
–1
The sum of charges in a compound is zero (0)
Ions are written as: Ca+2 while the atom is written as: Ca
Ionic compounds can dissociate from the ionic network. When dissolved in water the
compound CaCl2 dissociates into ions of Ca+2 and Cl–1.
Predicting formulas containing polyatomic ions
Polyatomic ions are two or more non-metallic elements covalently bonded
together and having an overall charge.
Some common polyatomic ions are:
OH–1
CO32
NO3–1
SO4–2
NH4–1
PO4–3
, hydroxide
, carbonate
, nitrate
, sulfate
, ammonium
, phosphate
Predicting ion charge from a chemical formula
As an example, you can determine the ion charge of iron by looking at FeCl2 and
FeCl3. In the first case, iron has an oxidation number of +2 while in the latter; iron has an
oxidation number of +3. The ion Fe+2 is called iron II (ferrous) and Fe+3 is called iron III
(ferric).
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