Fundamental Concepts in Chemistry: Matter, Energy, and Measurement
Fundamental Concepts in Chemistry
Observations, Hypothesis, Experiment, and Theory
- Observations: Facts obtained by observing and measuring events in nature.
- Hypothesis: A statement that explains an observation.
- Experiment: A procedure that tests the hypothesis.
- Theory: A model that describes how the observations occur by using experimental results.
Significant Figures
- Leading zeros: Preceding non-zero digits in decimal numbers are not significant.
- Exact number: A number obtained by counting or by definition.
Rounding Rules
When the first digit dropped is 4 or less, the retained numbers remain the same.
To round 45.832 to 3 significant figures:
Drop the digits 32 = 45.8
When the first digit dropped is 5 or greater, the last retained digit is increased by 1.
To round 2.4884 to 2 significant figures:
Drop the digits 884 = 2.5 (increase by 0.1)
Multiplication and division: The final answer must be rounded to the same number of significant figures as the measurement with the fewest significant figures.
Prefixes and Equalities
A prefix in front of a unit increases or decreases the size of that unit, making units larger or smaller than the initial unit by one or more factors of 10. It indicates a numerical value.
Prefix Value
1 kilometer = 1000 meters
1 kilogram = 1000 grams
An equality states the same measurement in two different units and can be written using the relationships between two metric units.
Example: 1 meter is the same as 100 cm and 1000 mm.
1 m = 100 cm
1 m = 1000 mm
Several equalities can be written for mass in the metric (SI) system:
1 kg = 1000 g
1 g = 1000 mg
1 mg = 0.001 g
1 mg = 1000 µg
Equalities
Equalities use two different units to describe the same measured amount. They are written for relationships between units of the metric system, between U.S. units, or between metric and U.S. units.
Examples:
1 m = 1000 mm
1 lb = 16 oz
2.20 lb = 1 kg
Density
Density compares the mass of an object to its volume. It is the mass of a substance divided by its volume.
Density expression:
D = mass/volume = g/mL or g/cm3 = g/cm3
Note: 1 mL = 1 cm3
Energy
Energy makes objects move, makes things stop, and is needed to “do work.”
Potential energy is energy stored for use at a later time.
Examples: Water behind a dam, a compressed spring, chemical bonds in gasoline, coal, or food.
Kinetic energy is the energy of matter in motion.
Examples: Swimming, water flowing over a dam, working out, burning gasoline.
Temperature Conversions
The formula for the Fahrenheit temperature:
TF = (9/5)(TC) + 32°
Heat is measured in joules or calories. 4.184 joules (J) = 1 calorie (cal) (exact) 1 kJ = 1000 J 1 kilocalorie (kcal) = 1000 calories (cal)
The Kelvin temperature is obtained by adding 273 to the Celsius temperature:
TK = TC + 273
In the Kelvin temperature scale, there are 100 units between the freezing and boiling points of water.
100 K = 100 °C or 1 K = 1 °C
0 K (absolute zero) is the lowest possible temperature.
0 K = –273 °C
Matter
Matter is the material that makes up a substance. It makes up the things we see every day, such as water, wood, cooking pans, clothes, and shoes.
A pure substance is classified as matter with a specific composition: an element when composed of one type of atom, a compound when composed of two or more elements combined in a definite ratio.
Elements
Elements are pure substances that contain atoms of only one type.
Examples:
Copper (Cu)
Lead (Pb)
Aluminum (Al)
Compounds
Compounds contain two or more elements in a definite ratio.
Examples:
Salt (NaCl)
Table sugar (C12H22O11)
Water (H2O)
Mixtures
A mixture is matter that consists of two or more substances that are physically mixed, not chemically combined; two or more substances in different proportions; substances that can be separated by physical methods.
In a homogeneous mixture, the composition is uniform throughout, and the different parts of the mixture are not visible.
In a heterogeneous mixture, the composition is not uniform; it varies from one part of the mixture to another, and the different parts of the mixture are visible.
Physical and Chemical Properties
Physical properties are observed or measured without changing the identity of a substance. They include shape and color, melting point, and boiling point.
During a chemical change, reacting substances form new substances with different compositions and properties, and a chemical reaction takes place.
Heat = g x ΔT x cal (or J)/g °C = cal (or J)
Symbols, Groups, and Periods
A symbol represents the name of an element, consists of 1 or 2 letters, and starts with a capital letter.
Groups contain elements with similar properties and are arranged in vertical columns.
Periods are the horizontal rows of elements.
Metals are located to the left.
Nonmetals are located to the right.
Metalloids are located along the heavy zigzag line between the metals and nonmetals.
Atomic Structure
Protons have a positive (+) charge.
Electrons have a negative (–) charge.
Like charges repel, and unlike charges attract.
Neutrons are neutral.
Atoms
An atom consists of a nucleus that contains protons and neutrons, and electrons in a large, empty space around the nucleus.
The atomic number is specific for each element, is the same for all atoms of an element, is equal to the number of protons in an atom, and appears above the symbol of an element.
The mass number represents the number of particles in the nucleus and is equal to the number of protons + the number of neutrons.
Zinc Atom Example
How many protons are in this zinc atom?
1) 30 (atomic number 30)
How many neutrons are in the zinc atom?
2) 35 (65 – 30 = 35)
What is the mass number of a zinc atom that has 37 neutrons?
3) 67 (30 + 37 = 67)
Sublevels and Orbitals
A. 4s sublevel
One 4s orbital
B. 3d sublevel
Five 3d orbitals
C. n = 3
One 3s orbital, three 3p orbitals, and five 3d orbitals
Electron Configurations
A. Cl
1s22s22p63s23p5 [Ne]3s23p5
B. S
1s22s22p63s23p4 [Ne]3s23p4
C. K
1s22s22p63s23p64s1 [Ar]4s1
A. Zn
1s22s22p63s23p64s23d10 [Ar]4s23d10
B. Sr
1s22s22p63s23p64s23d104p65s2 [Kr]5s2
C. I
1s22s22p63s23p64s23d104p65s24d105p5 [Kr]5s24d105p5
Atomic Size
Atomic size is described using the atomic radius and is the distance from the nucleus to the valence electrons. It increases going down a group and decreases going across a period from left to right.
Select the element in each pair with the larger atomic radius.
A. K is larger than Li
B. K is larger than Br
C. P is larger than Cl