Chemistry Basics and Properties of Matter

Ever wonder why some substances change completely when mixed while others just blend together? It all comes down to understanding the basic properties of matter.

Matter is anything that has mass and takes up space. When describing matter, we use two types of data: qualitative data (descriptions without numbers like color or smell) and quantitative data (measurable information with numbers).

Properties of matter can be either intensive or extensive. Intensive properties don't depend on the amount of material (like density, color, or luster), while extensive properties do (like mass, volume, or length).

States of matter have different properties: solids have definite shape and volume, liquids have indefinite shape but definite volume, and gases have both indefinite shape and volume.

💡 When identifying chemical vs. physical changes, remember this: If a new substance forms (like iron rusting), it's a chemical change. If the substance remains the same (like ripping paper), it's a physical change.

Metals, nonmetals, and metalloids are classified by their properties. Metals are typically hard, shiny, malleable (can be hammered into shapes), ductile (can be drawn into wires), and good conductors. Nonmetals lack these metallic properties, while metalloids show characteristics of both.

Scientific Method, Measurements and Mixtures

When you measure your height in inches but need it in centimeters, how do you convert it? Understanding measurement units and conversions is crucial in chemistry!

The scientific method is the process scientists use to answer questions about the world. It helps us understand concepts like the difference between mass (the amount of matter in an object) and weight (the measure of gravitational force on that matter).

Measurements in chemistry use specific units: meters for length, kilograms for mass, seconds for time, liters for volume, and Kelvin for temperature. These can be modified with prefixes like kilo (10³), centi (10²), milli (10⁻³), micro (10⁻⁶), nano (10⁻⁹), and mega (10⁶).

Converting between units requires understanding the relationships between them. For example, to convert 4 m/s to cm/h, you multiply by 100 cm/1 m and 3600 s/1 h to get 1,440,000 cm/h.

🔍 When working with mixtures, remember this key distinction: homogeneous mixtures have uniform composition throughout $like Kool-Aid$, while heterogeneous mixtures have varying composition in different regions.

Pure substances cannot be separated into other types of matter by physical means, unlike mixtures, which are made by combining different substances. The composition of a mixture determines whether it's homogeneous (consistent throughout) or heterogeneous (varies throughout).

Atomic Structure and Laws of Matter

Did you know that everything you touch is made of atoms that are mostly empty space? Understanding atomic structure helps explain why materials behave the way they do!

Proportions in chemistry follow specific patterns. In a direct proportion, variables increase together, while in an inverse proportion, one increases as the other decreases. These relationships appear frequently in chemistry formulas.

The structure of atoms includes three main subatomic particles: protons (positive charge, 1 amu), neutrons (no charge, 1 amu), and electrons (negative charge, negligible mass). The atomic number defines an element and equals the number of protons in the nucleus.

Several fundamental laws govern chemical reactions:

• The Law of Conservation of Mass states that matter cannot be created or destroyed, only rearranged
• The Law of Definite Proportions states that elements in compounds exist in fixed ratios by mass
• The Law of Multiple Proportions states that when two elements form multiple compounds, the ratios of one element to a fixed amount of the other are simple whole numbers

💡 Ever wonder why atomic masses on the periodic table aren't whole numbers? They're weighted averages of all naturally occurring isotopes of that element!

Isotopes are atoms of the same element (same number of protons) that have different masses due to different numbers of neutrons. For example, carbon-12 and carbon-14 are isotopes of carbon with different numbers of neutrons.

Electrons, Orbitals, and the Periodic Table

The arrangement of electrons in an atom determines how that element will behave chemically. It's like knowing the seating arrangement at a party to predict who will talk to whom!

Light travels as waves and is a form of electromagnetic radiation. Light with shorter wavelengths (like purple) has more energy than light with longer wavelengths (like red). Similarly, gamma rays have much more energy than microwaves because of their shorter wavelength.

Photons are packets or bundles of electromagnetic radiation. The energy of these photons varies based on the wavelength of light, following the principles of quantum mechanics.

Electrons occupy specific energy levels around the nucleus. These are described by quantum numbers which determine the position and energy of electrons. Electrons fill orbitals following specific rules:

• The Aufbau Principle states electrons fill lower-energy orbitals before higher ones
• Pauli's Exclusion Principle states that two electrons in the same orbital must have opposite spins

⚡ Electron configurations are like atomic fingerprints - they help explain why elements in the same column of the periodic table behave similarly!

Different orbital shapes can hold different numbers of electrons. The s orbital is sphere-shaped and holds 2 electrons, while the p orbital can hold 6 electrons. The d orbitals are found in the transition metals section of the periodic table.

Periodic Table Trends and Atomic Properties

As you move across the periodic table, elements' properties change in predictable patterns. These trends are like roadmaps that help chemists predict how elements will behave!

The periodic table organizes elements into rows (called periods) and columns (called groups). Elements in the same group have similar properties because they have the same number of valence electrons (outer electrons that participate in bonding).

Key groups on the periodic table include:

• Noble gases (Group 18): colorless, odorless, nonflammable gases
• Alkali metals (Group 1): highly reactive metals with good conductivity
• Alkaline earth metals (Group 2): reactive metals with low ionization energy
• Halogens (Group 17): highly reactive nonmetals that form acids
• Transition metals $Groups 3-12$: good conductors with high melting points

Several important trends exist across the periodic table:

• Atomic radius (size of atoms) increases down and to the left
• Ionization energy (energy needed to remove an electron) increases up and to the right
• Electronegativity (tendency to attract electrons) increases up and to the right

🧪 When calculating average atomic mass, you multiply each isotope's mass by its abundance (as a decimal) and add them together. This is why atomic masses aren't whole numbers!

A cation has a positive charge because it has lost an electron. The average atomic mass of an element is calculated by multiplying each isotope's mass by its abundance percentage and adding the products together.

Chemical Bonding and Compounds

Chemical bonds are like relationships between atoms - some share equally, some take more than they give, and some completely transfer electrons to their partner!

Chemical bonds form between atoms to achieve stability. The two main types of bonds are:

• Ionic bonds: form between a metal and nonmetal when electrons are transferred
• Covalent bonds: form between nonmetals when electrons are shared

When naming ionic compounds, you state the metal name followed by the nonmetal with an "-ide" ending (like sodium chloride for NaCl). For covalent compounds, you use prefixes to indicate the number of atoms (like diphosphorus trioxide for P₂O₃).

Electronegativity plays a crucial role in determining bond types. Elements with higher electronegativity (like fluorine) attract electrons more strongly than elements with lower electronegativity (like hydrogen).

💡 To quickly predict bond type, look at the elements involved: metal + nonmetal = ionic bond; nonmetal + nonmetal = covalent bond.

Ionic compounds typically have high melting points, form crystalline solids, and conduct electricity when dissolved or melted. Covalent compounds often have lower melting points and many are soluble in water.

Polar covalent bonds form when electrons are shared unequally between atoms (electronegativity difference of 0.5 or more), while nonpolar covalent bonds form when electrons are shared equally (little to no electronegativity difference).

Measurements, Compounds, and Bonds

Reading scientific measurements accurately and understanding different types of bonds are essential skills in chemistry. They help you make sense of everything from lab data to molecule behavior!

When reading measurements from graduated cylinders, you need to look at the bottom of the meniscus (curved surface of the liquid). The correct reading for the picture shown would be 63 ml, as you need to read from the bottom of the curve.

Naming compounds follows specific rules:

• For covalent compounds like P₂O₃ (diphosphorus trioxide), prefixes indicate the number of atoms
• For ionic compounds like NaCl (sodium chloride), you name the metal first, then the nonmetal with an "-ide" ending

The properties of compounds depend on their bond types:

• Ionic compounds typically have high melting points, form crystalline solids, and conduct electricity in solution
• Covalent compounds often have lower melting points and many are water-soluble

🔬 When measuring liquids in a graduated cylinder, always read from the bottom of the meniscus (the curved surface) for the most accurate measurement!

Polar covalent bonds form when electrons are shared unequally between atoms with different electronegativities. A difference of 0.5 or more in electronegativity results in a polar bond, while smaller differences create nonpolar bonds where electrons are shared equally.

Scientific Notation and Radioactivity

Scientific notation makes working with very large or small numbers manageable, while understanding radioactivity helps explain how elements can transform over time!

Scientific notation expresses numbers in the form a × 10ᵇ, where 1 ≤ a < 10 and b is an integer. For example:

• 34,567 becomes 3.4567 × 10⁴
• 0.123 becomes 1.23 × 10⁻¹
• 0.045 becomes 4.5 × 10⁻²

The electromagnetic spectrum ranges from low-energy radio waves to high-energy gamma rays. Energy is inversely proportional to wavelength and directly proportional to frequency—as wavelength decreases, energy increases.

Accuracy refers to how close a measurement is to the true value, while precision refers to how close repeated measurements are to each other. A target analogy helps visualize this:

• High accuracy, low precision: shots scattered around the bullseye
• High precision, low accuracy: shots clustered together but away from the bullseye

⚛️ During radioactive decay, the number of radioactive atoms decreases by half after each half-life. After 3 half-lives, you'll have only 1/8 of the original amount!

Radioactive decay follows a predictable pattern called half-life. Starting with 48 radioactive pennies, after one half-life you'd have 24, after two half-lives 12, and after three half-lives only 6 pennies would remain radioactive. The decay curve is exponential, not linear.