Exam #1 Review: Chemistry Fundamentals, Atoms & Elements, Ionic Compounds

Study Guide - Smart Notes

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Chemistry in Our Lives

The Scientific Method

The scientific method is a systematic approach used in scientific investigations to acquire new knowledge. It involves several key steps that ensure observations and experiments are conducted logically and objectively.

Observation: Gathering information through the senses or instruments.
Hypothesis: A testable explanation for an observation.
Experiment: A procedure to test the hypothesis under controlled conditions.
Conclusion: Analysis of experimental results to support or refute the hypothesis.

Example: Observing that a metal rusts when exposed to water, hypothesizing that water causes rust, and testing this by exposing different metals to water.

Definition of Chemistry

Chemistry is the study of matter, its properties, how and why substances combine or separate to form other substances, and how substances interact with energy.

Matter: Anything that has mass and occupies space.
Chemical: Any substance with a definite composition, such as water (H2O), sodium chloride (NaCl), or glucose (C6H12O6).

Example: Table salt (NaCl) is a chemical because it has a specific composition.

Atoms and Elements

The Periodic Table

The periodic table organizes all known elements by increasing atomic number and groups elements with similar properties together.

Element: A pure substance consisting of only one type of atom.
Symbol: One- or two-letter abbreviation for an element (e.g., H for hydrogen, Na for sodium).

Classification of Elements

Representative Elements: Groups 1, 2, and 13-18 (main group elements).
Transition Metals: Groups 3-12, located in the center of the table.
Metals: Located on the left and center; shiny, good conductors, malleable.
Non-metals: Located on the right; dull, poor conductors, brittle.
Metalloids: Border between metals and non-metals; have properties of both.

Special Groups

Alkali Metals (Group 1): Highly reactive metals.
Alkaline Earth Metals (Group 2): Reactive metals, less so than alkali metals.
Halogens (Group 17): Very reactive non-metals.
Noble Gases (Group 18): Non-reactive gases.

Example: Sodium (Na) is an alkali metal, chlorine (Cl) is a halogen.

Structure of the Atom

An atom consists of three main subatomic particles:

Proton: Positively charged, located in the nucleus.
Neutron: Neutral, located in the nucleus.
Electron: Negatively charged, orbits the nucleus.

Atomic Number and Mass Number

Atomic Number (Z): Number of protons in the nucleus; defines the element.
Mass Number (A): Total number of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons.

Formula:

Number of neutrons = Mass number - Atomic number

Atomic Symbol/Isotopic Notation

Isotopic notation shows the element's symbol, mass number, and atomic number:

Where X is the element symbol, A is the mass number, and Z is the atomic number.

Determining Abundance of Isotopes

The most abundant isotope of an element is usually the one whose mass number is closest to the atomic mass listed on the periodic table.

Ionic and Molecular Compounds

Formation of Ions

Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net charge.

Cation: Positively charged ion; formed when an atom loses electrons.
Anion: Negatively charged ion; formed when an atom gains electrons.

Example: Sodium atom (Na) loses one electron to become sodium ion (Na+).

Writing Ion Symbols

The symbol for an ion includes the element symbol and its charge:

Na+ (sodium ion)
Cl- (chloride ion)

Naming and Writing Formulas for Ionic Compounds

Ionic compounds are formed from cations and anions, and their formulas must have a net charge of zero.

Fixed charge metals: Metals that always form the same charge (e.g., Na+, Mg2+).
Variable charge metals: Metals that can form more than one charge (e.g., Fe2+, Fe3+).
Polyatomic ions: Ions composed of two or more atoms covalently bonded (e.g., NO3-, SO42-).

Example: Sodium chloride (NaCl) is formed from Na+ and Cl-.

Steps to Write Ionic Compound Formulas

Write the symbol and charge for each ion.
Balance the charges so the total charge is zero.
Combine the ions in the lowest whole number ratio.

Example: Magnesium chloride: Mg2+ and Cl- combine to form MgCl2.

Table: Common Polyatomic Ions

Name	Formula	Charge
Nitrate	NO3	-1
Sulfate	SO4	-2
Phosphate	PO4	-3
Ammonium	NH4	+1
Hydroxide	OH	-1

Additional info: Polyatomic ions are important in many biological and chemical processes.

Properties of Ionic Compounds

Form crystalline solids at room temperature.
High melting and boiling points.
Conduct electricity when dissolved in water.

Example: Table salt (NaCl) is an ionic compound with these properties.