1.1 Atoms, Molecules, and Compounds
Atoms- fundamental unit of a chemical substance.
- Extremely small, not visible to the eye.
Atoms – basic particles from which matter is composed.
Atoms consist of a nucleus (protons and neutrons) and electrons.
Atoms may be combined with others (of the same or different
element) to form molecules.
Atoms in molecules are associated by
sharing electrons in covalent bonds. We will study this in Chapter 7:
Theories of Chemical Bonding. Other types of associations include
coordinate covalent bonds and ionic bonding. More about that in
Chapter 6: Fundamentals of Chemical Bonding!
Atoms are often represented by spheres, with different colours
differentiating the different elements.
Your textbook uses the following convention:
Molecules- atoms when come together in orderly ways become
molecules. (only takes two atoms to make one molecule, which is
- Chemical compound: contains more than one type of element in
fixed, relative amounts.
- This ratio is expressed as a chemical formula
- Chemical formulas are composed of each element type present
(chemical symbol) followed by a whole-number subscript which
represents the number of atoms of the type in the molecule.
- There are different ways to represent molecules, different shapes
and colours depending on what is being analyzed and why. 1.2 Measuring in Chemistry
Physical Properties- length, area, and volume measure the size of an
object. Every object possesses a certain quantity of matter called
mass. Time is also used to know how long it takes for chemical
transformation to occur. Temperature is the property of matter that
determines the direction of heat flow.
- each measurement gives a numerical result that has three aspects:
1. a numerical magnitude
2. an indicator of scale called a unit
3. a precision
Physical changes – do not alter the chemical composition of a
Chemical changes- result from processes that change the chemical
composition of a substance.
Magnitude- values range from vanishingly small to astronomically
Units- scientists use an international sustem of units (SI). It consists
of seven base units that can be used to derive other units and prefixes
that are used as decimal base multipliers.
Liters are not included in the SI however, 1L= 1dm 3
Temperature – kelvin to Celsius is -273.15 and Celsius to kelvin is
Precision and Accuracy
- the exactness of a measurement is precision.
- how close a measurement is to the true value is accuracy.
1. When adding or subtracting, the number of decimal places in the
result is equal to the least number of decimal places of the numbers
being added or subtracted
2. when multiplying or dividing, the number of sig.figs in the result is
equal to the least number of sig.figs of the numbers being multiplied
3. postpone adjusting result to the correct number of sig.figs until a
calculation is complete.
1.3 Chemical Problem Solving
Step 1: Determine what is asked for.
- What type of problem is it? What are you asked to find?
Step 2: Visualize the problem.
- Draw pictures that illustrate what takes place.
- Is chemical changes occur, draw molecular pictures.
Step 3: Organize the data.
- What data are available? - How are the data related to what is asked for?
Step 4: Identify a process to solve the problem.
- What concepts are required? What equations apply?
Step 5: Manipulate the equations.
- If necessary, do calculations in step. Solve for what is asked for.
Step 6: Substitute and calculate.
- Keep track of units.
- Use the correct number of sig.figs
Step 7: Does the result make sense?
- Are the units consistent? Is the result sensible?
1.4 Counting Atoms: The Mole
Mole- the amount of substance that contains as many elementary
entities ( atoms, molecules, or other particles) as there are atoms in
exactly 12g of C.
Avogadro’s number- 6.022142 x 10 atoms/mol
Molar mass- of an element is a weighed avg. of the masses of all the
isotopes of one element. Once calculated, it is the mass of one mole of
atoms of the elements.