Matter, Measurement, and Atoms

Pure Substances vs. Mixtures

Understanding the distinction between pure substances and mixtures is fundamental in chemistry.

• Pure Substances: Materials with a fixed composition; can be elements (e.g., O2) or compounds (e.g., H2O).

• Mixtures: Combinations of two or more substances that retain their individual properties; can be homogeneous (solutions) or heterogeneous (e.g., sand and water).

• Example: Salt water is a mixture; table salt (NaCl) is a pure substance.

Periodic Table Regions and Group Names

The periodic table is organized into regions and groups with distinct properties.

• Regions: Metals, nonmetals, metalloids.

• Group Names: Alkali metals (Group 1), alkaline earth metals (Group 2), halogens (Group 17), noble gases (Group 18).

• Example: Group 1 elements are highly reactive metals.

Scientific Notation

Scientific notation expresses numbers as a product of a coefficient and a power of ten.

• Format:

• Example: 0.00045 =

Significant Figures

Significant figures reflect the precision of a measured quantity.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros in a decimal are significant.

• Example: 0.00450 has three significant figures.

Mathematical Operations with Significant Figures

When performing calculations, report answers with the correct number of significant figures.

• Addition/Subtraction: Result has the same decimal places as the least precise measurement.

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

Metric Prefixes and Multiples

Metric prefixes indicate multiples or fractions of units.

• Kilo (k):

• Deci (d):

• Centi (c):

• Milli (m):

• Micro (\mu):

Unit Conversion

Unit conversion uses conversion factors to change from one unit to another.

• Set-up: Use dimensional analysis.

• Example: Convert 5.0 cm to mm:

Temperature Scales

Three common temperature scales are Fahrenheit (°F), Celsius (°C), and Kelvin (K).

• Conversion Equations:

• Example: 25°C = K

Subatomic Particles of the Atom

Atoms are composed of protons, neutrons, and electrons.

• Protons: Positive charge, located in nucleus.

• Neutrons: Neutral, located in nucleus.

• Electrons: Negative charge, orbit nucleus.

Atomic Number and Mass Number

Atomic number and mass number describe the composition of an atom.

• Atomic Number (Z): Number of protons.

• Mass Number (A): Number of protons plus neutrons.

• Example: Carbon-12: Z = 6, A = 12.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Representation: (where X is the element symbol, A is mass number, Z is atomic number).

• Example: is an isotope of carbon.

Calculating Protons, Neutrons, and Electrons

To determine the number of subatomic particles in an isotope:

• Protons: Equal to atomic number (Z).

• Neutrons:

• Electrons: Equal to protons in a neutral atom.

• Example: : 11 protons, 12 neutrons, 11 electrons.

Valence Electrons

Valence electrons are the outermost electrons involved in chemical bonding.

• Main-group elements: Number of valence electrons equals group number (for Groups 1-2 and 13-18).

• Example: Oxygen (Group 16) has 6 valence electrons.

Covalent Bonding and Molecules

Covalent Bonds

A covalent bond is a chemical bond formed by the sharing of electron pairs between atoms.

• Occurs: Typically between nonmetals.

• Example: In H2O, oxygen shares electrons with two hydrogen atoms.

Binary Covalent Compounds: Names and Formulas

Binary covalent compounds consist of two nonmetal elements.

• Naming: Use prefixes to indicate the number of atoms (mono-, di-, tri-, tetra-, penta-, etc.).

• Example: CO2 is carbon dioxide; N2O is dinitrogen monoxide.

Lewis Dot Symbols

Lewis dot symbols represent valence electrons around an element's symbol.

• Example: For oxygen: O with six dots around it.

Drawing Lewis Structures

Lewis structures show how atoms share electrons in a molecule.

• Steps:

  1. Count total valence electrons.

  2. Arrange atoms and connect with single bonds.

  3. Distribute remaining electrons to satisfy octet rule.

• Example: Water (H2O): Oxygen in center, two hydrogens attached, four lone electrons on oxygen.

Additional info: Academic context and examples were added to expand brief points into full explanations and to make the notes self-contained for study purposes.