General Chemistry and Atomic Structure: Study Guide for Biology Students

General Chemistry Concepts

Classification of Matter

Matter can be classified based on its composition and properties. Understanding these classifications is essential for studying chemical reactions and biological processes.

• Pure Substance: A material with a constant composition (e.g., pure water, sodium chloride).

• Mixture: A combination of two or more substances that retain their individual properties. Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

• Examples:

  • Homogeneous mixture: 14 karat gold (gold alloy)

  • Heterogeneous mixture: Hydrogen gas and oxygen gas mixture

Chemical vs. Physical Changes

Chemical changes result in the formation of new substances, while physical changes do not alter the chemical identity of a substance.

• Chemical Change: Baking a cake (new substances formed)

• Physical Change: Melting chocolate (change of state, no new substance)

Properties and Classification of Elements

Elements are classified based on their properties and position in the periodic table.

• Alkali Metals: Group 1 elements (e.g., sodium, lithium)

• Alkaline Earth Metals: Group 2 elements (e.g., calcium, magnesium)

• Metalloids: Elements with properties intermediate between metals and nonmetals (e.g., boron, germanium)

• Nonmetals: Elements that lack metallic properties (e.g., sulfur, oxygen)

Atomic Structure and Periodic Table

Atomic Number, Mass Number, and Isotopes

The atomic number is the number of protons in an atom, while the mass number is the sum of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons.

• Atomic Number (Z): Number of protons

• Mass Number (A): Number of protons + neutrons

• Isotopes: Atoms with same Z but different A (e.g., Carbon-12 and Carbon-14)

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom. The ground state is the lowest energy configuration, while excited states have electrons in higher energy orbitals.

• Ground State: Electrons fill orbitals in order of increasing energy (Aufbau principle)

• Excited State: One or more electrons occupy higher energy orbitals than in the ground state

• Example: Sodium ion (Na+) ground state: $1s^2\ 2s^2\ 2p^6$

Valence Electrons and Ion Formation

Valence electrons are the outermost electrons involved in chemical bonding. Atoms form ions by gaining or losing electrons to achieve a stable electron configuration.

• Valence Electrons: Electrons in the outermost shell

• Ion Formation: Atoms lose electrons to form cations (+) or gain electrons to form anions (-)

• Example: A neutral atom with a valence shell configuration of $ns^2np^6$ will form a 1- ion

Chemical Calculations and Units

Significant Figures

Significant figures reflect the precision of a measurement. Calculations should maintain the correct number of significant figures.

• Example: 14.003 liters + 1.5 liters = 15.5 liters (3 significant figures)

Density, Volume, and Mass Calculations

Density is the mass per unit volume of a substance. It is used to calculate volume or mass when one is known.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Example: Volume occupied by 4.50 g of a substance with density 1.75 g/mL: $\text{Volume} = \frac{4.50\ g}{1.75\ g/mL} = 2.57\ mL$

Unit Conversions

Unit conversions are essential for scientific calculations. Common conversions include mass, length, and volume.

• Mass: 1 kilogram (kg) = 1000 grams (g)

• Length: 1 meter (m) = 100 centimeters (cm)

• Volume: 1 liter (L) = 1000 milliliters (mL)

• Example: 9.0 cubic miles to cubic inches: $9.0\ mi^3 \times \left(5280\ ft/mi\right)^3 \times \left(12\ in/ft\right)^3$

Specific Heat Calculations

Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

• Formula: $q = m \cdot c \cdot \Delta T$

• Example: If 394 calories are required to raise 100.0 g of a metal from 24.5°C to 1000°C, $c = \frac{394}{100.0 \times (1000 - 24.5)}$

Periodic Table Trends and Properties

Periodic Trends

Elements show trends in properties such as atomic radius, ionization energy, and electronegativity across periods and groups.

• Atomic Radius: Increases down a group, decreases across a period

• Ionization Energy: Decreases down a group, increases across a period

• Electronegativity: Tendency of an atom to attract electrons; increases across a period

Isoelectronic Species

Isoelectronic species have the same number of electrons but may be different elements or ions.

• Example: S2-, Ne, and Ca2+ are isoelectronic (all have 10 electrons)

Electromagnetic Radiation

Types and Energy

Electromagnetic radiation includes various types of waves, each with different energy and wavelength.

• Order of Energy (Highest to Lowest): Gamma rays > X-rays > Ultraviolet (UV) > Visible light > Infrared (IR) > Microwaves > Radio waves

• UV radiation has higher energy than visible light.

HTML Table: Classification of Elements

The following table summarizes the classification of selected elements based on their properties:

Element	Classification	Valence Electrons
Germanium	Metalloid	4
Calcium	Alkaline Earth Metal	2
Rubidium	Alkali Metal	1
Bismuth	Metal	5

Additional info:

• Some questions and examples were inferred to provide complete academic context.

• Topics such as electron configuration, periodic trends, and unit conversions are foundational for both general chemistry and biology students.