Chemistry Unit 1
Topic 1.1 Elements and the
Periodic Table
Essential Knowledge
All matter is made from about 100 different chemical elements. The Periodic Table
of the Elements (PTOE) shows all of the known elements, arranged by increasing
atomic number.
Periods (1-7), or rows run horizontally. Groups (1-18), or columns run vertically.
Each element on the PTOE is located in a specific group and period, and has a symbol.
The symbol for many of the elements is one capital letter. In two-letter symbols
for elements, the first letter is always an upper case letter, the second one a lower
case.
The smallest particle of an element is an individual atom. Some elements commonly
exist as two atoms joined together as diatomic molecules. Example: hydrogen H2
(g), nitrogen N2, oxygen O2(g) and all of the elements in group 17.
1.2 Compounds and Bonding
Atoms of different elements can join together by chemical bonds to form a
compound. A compound has different properties from its elements. The
smallest particle in a compound is called a molecule or formula unit.
Compounds and elements (individual molecules and atoms) are both pure
substances. Pure substances contain only one type of particle and all particles have
the same composition.
 H2O, water, is a pure substance because its elements are bonded together to form
one particle (molecule) and all of the particles in water are the same with the
same properties. (The properties of water, H2O, are very different from the
properties of either the element hydrogen or the element oxygen.)
Chemical formulas show the ratio or number of atoms of each element in a
compound. Example: 2 hydrogen atoms bonded to one oxygen atom make a water
molecule (H2O).
1.3 Kinetic Theory
Atoms and molecules are in constant motion. Therefore, all matter has Kinetic
Energy (energy of motion).
Particles of a gas move fastest; particles in a liquid move slower and particles in a
solid move slowest.
Temperature measures the average Kinetic energy (movement of particles).
There is a direct relationship between temperature and speed of the particles.
When the temperature increases, particles move faster. When temperature is
decreased particles move slower.
Temperature can be expressed in Celsius or Kelvin. On the Celsius scale, water
freezes at 0C and boils at 100C.
On the Kelvin (K) scale, water freezes at 273K and boils at 373K.
273K = 0o C (K=oC + 273)
Density is the mass per unit of volume, D = mass/volume. In general solids are
most dense and gases are least dense. The densities of solids and liquids are
expressed in g/ml while gases are in units of g/L. Using this equation, you can
determine the density, mass and/or volume of a substance.
1.4 The Mole and
Stoichiometry
Atoms and molecules are too small to be seen and measured directly. The mole is the
unit used to count how many particles are in a certain amount of a substance. A mole
is 602,000,000,000,000,000,000,000 particles.
Expressed in scientific notation, a mole is 6.02 x 1023 particles. This is a very large
number because individual atoms are so small. Given the number of particles in a
sample, be able to determine how many moles or what part of a mole it contains. For
example, 2 mol = 1.20 x 1024 particles and 0.5 mol = 3.01 x 1023 particles.
The atomic mass of an element is found on the Periodic Table of Elements. The
molar mass of an element represents the mass of one mole of the element. It is
equal to its atomic mass in grams, i.e. 1 mole of carbon equals 12.01 grams.
The molar mass for a compound is the sum of the atomic masses of each atom in the
compound.
1.5 Chemical Reactions
Chemical changes occur when atoms interact and rearrange to form new
substances. The new substances formed have different properties from the
substances that reacted. Chemical reactions result in both chemical and physical
changes.
Individual substances can also undergo physical changes, the physical properties of
a substance change, but the identity (chemical composition) of the substance does not
change. Steam, liquid water and ice have different physical properties, but they are all
the same substance, H2O.
Physical properties describe a substance without changing the identity or
composition of that substance. Examples are density, melting point, boiling point,
specific heat, state of matter, color and odor.
1.6 Solutions
Chemical properties such as flammability, stability and reactivity describe the ability
of substances to react together.
If a substance contains different types of particles, then it is called a mixture.
Mixtures are NOT pure substances. (Example: Soapy water is a mixture of many
water molecules and a few soap particles.)
In a heterogeneous mixture, the different particles are unevenly distributed and
the different parts can be easily seen (like salad dressing or concrete).
In a homogeneous mixture the particles are distributed evenly and mixed so well
that the separate parts cannot be seen (like salt dissolved in water or Kool–aide.).
Homogeneous mixtures are called solutions.
1.7 Experimentation
Know the proper use of laboratory safety equipment and the laboratory safety
rules and procedures that are described in your Safety Contract. (goggles,
aprons, gloves, safety shower, eyewash, broken glass container, fume hood and fire
blanket)
The independent variable (IV) in an experiment is the variable that the
experimenter changes. The dependent variable (DV) is the variable that responds
to the changes. For example: What is the effect of temperature (the IV) on how
many drops of water (the DV) fit on a penny?
On a graph the IV is located on the x–axis (horizontal) and the DV is on the y–axis
(vertical).
Know the prefixes kilo-, centi-, and milli– for metric units (g, ml, L and meter).