Study Notes: Components of Matter and Atomic Theory

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Chapter 2: The Components of Matter

Elements, Compounds, and Mixtures: An Atomic Overview

This topic introduces the fundamental types of matter: elements, compounds, and mixtures, and explains their atomic-level distinctions.

Element: The simplest type of substance with unique physical and chemical properties. An element consists of only one type of atom and cannot be broken down into simpler substances by physical or chemical means.
Molecule: A structure consisting of two or more atoms chemically bound together, behaving as an independent unit.
Compound: A substance composed of two or more elements that are chemically combined.
Mixture: A group of two or more elements and/or compounds that are physically intermingled.
Example: Oxygen gas (O2) is an element; water (H2O) is a compound; air is a mixture.

Properties of Elements and Compounds

Elements and compounds have distinct physical and chemical properties, which can be compared to understand their behavior.

Property	Sodium	Chlorine	Sodium Chloride
Melting point	97.8°C	-101°C	801°C
Boiling point	881.4°C	-34°C	1413°C
Color	Silvery	Yellow-green	Colorless (white solid)
Density	0.97 g/cm3	0.0032 g/cm3	2.16 g/cm3
Behavior in water	Reacts	Dissolves slightly	Dissolves freely

Mixtures: Heterogeneous and Homogeneous

Mixtures are classified based on the uniformity of their composition and the visibility of boundaries between components.

Heterogeneous mixture: Has one or more visible boundaries between the components. Composition varies from one region to another. Example: sand mixed with water.
Homogeneous mixture (Solution): Has no visible boundaries; components are mixed at the molecular level. Example: salt dissolved in water.
Aqueous solution: A solution in which water is the solvent.

Heterogeneous Mixtures	Homogeneous Mixtures (Solutions)
One or more visible boundaries among the components. The composition is not uniform throughout the mixture. Boundaries may be visible only with a microscope. Example: sand mixed with water.	No visible boundaries. Uniform composition. Components are uniformly intermingled at the molecular level. Example: copper(II) sulfate dissolved in water.

The Distinction Between Mixtures and Compounds

Mixtures can be separated by physical means, while compounds require chemical reactions for separation.

Physical mixture: Elements retain their individual properties and can be separated (e.g., iron and sulfur mixture separated by a magnet).
Chemical compound: Elements are chemically bonded and cannot be separated by physical means (e.g., iron sulfide, FeS).

Basic Separation Techniques

Several laboratory techniques are used to separate mixtures based on physical properties.

Filtration: Separates components based on differences in particle size.
Crystallization: Separation based on differences in solubility.
Distillation: Separation based on differences in volatility.
Chromatography: Separation based on differences in solubility between a solvent and a stationary phase.

The Atomic Theory and Laws of Chemical Combination

Law of Mass Conservation

The total mass of substances does not change during a chemical reaction.

Statement: Mass is conserved in chemical reactions; atoms are rearranged but not created or destroyed.
Equation Example:

Law of Definite (Constant) Composition

A particular compound always contains the same elements in the same proportion by mass.

Example: Calcium carbonate (CaCO3) always contains 40% calcium, 12% carbon, and 48% oxygen by mass.
Table:

Element	Mass (g/20.0g)	Mass Fraction	Percent by Mass
Calcium	8.0	0.40	40%
Carbon	2.4	0.12	12%
Oxygen	9.6	0.48	48%

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Example: Carbon oxides I and II: For a fixed mass of carbon, carbon oxide II contains twice as much oxygen as carbon oxide I.

Dalton’s Atomic Theory

John Dalton proposed a model to explain the laws of chemical combination.

All matter consists of atoms, which are indivisible and indestructible.
Atoms of one element cannot be converted into atoms of another element.
Atoms of an element are identical in mass and properties, and differ from atoms of other elements.
Compounds are formed by the chemical combination of atoms in specific ratios.

Structure of the Atom

Subatomic Particles

Atoms are composed of protons, neutrons, and electrons, each with distinct properties.

Particle	Symbol	Charge	Relative Mass (amu)	Absolute Mass (g)
Proton	p+	+1	1	1.6726 × 10-24
Neutron	n0	0	1	1.6749 × 10-24
Electron	e-	-1	0.00055	9.1094 × 10-28

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

Mass Spectrometry and Atomic Mass

Mass spectrometry measures the relative masses and abundances of isotopes, allowing calculation of atomic mass.

Atomic mass: Weighted average of the masses of naturally occurring isotopes.
Equation:
Example: Silver (Ag) atomic mass calculation using isotopic abundances.

The Periodic Table and Classification of Elements

Periodic Table Organization

The periodic table arranges elements by increasing atomic number and groups elements with similar properties.

Main group metals: Groups 1, 2, and 13.
Transition metals: Groups 3-12.
Nonmetals: Groups 14-18 and hydrogen.
Metalloids: Elements with properties intermediate between metals and nonmetals.

Chemical Bonding and Formulas

Ionic Compounds

Ionic compounds form by the transfer of electrons from metals to nonmetals, resulting in cations and anions.

Cation: Positively charged ion (metal loses electrons).
Anion: Negatively charged ion (nonmetal gains electrons).
Monatomic ions: Ions formed from single atoms (e.g., Na+, Cl-).
Polyatomic ions: Ions composed of two or more covalently bonded atoms (e.g., SO42-).

Naming Ionic Compounds

Ionic compounds are named by listing the cation first, followed by the anion. The anion name ends with "-ide" for monatomic ions.

Example: NaCl is sodium chloride.
Metals with multiple ions: Use Roman numerals to indicate charge (e.g., FeCl2 is iron(II) chloride).

Naming Compounds with Polyatomic Ions

Polyatomic ions retain their names in compounds. Hydrates are named with prefixes indicating the number of water molecules.

Example: Ba(OH)2·8H2O is barium hydroxide octahydrate.

Naming Acids

Binary acids: Use "hydro-" prefix and "-ic" suffix (e.g., HCl is hydrochloric acid).
Oxoacids: Suffix changes from "-ate" to "-ic" and "-ite" to "-ous" (e.g., HNO3 is nitric acid).

Naming Binary Covalent Compounds

Binary covalent compounds are formed by two nonmetals. Prefixes indicate the number of atoms.

Example: CO2 is carbon dioxide; N2O4 is dinitrogen tetroxide.

Molecular and Formula Masses

Calculating Molecular Mass

The molecular mass is the sum of the atomic masses of all atoms in a molecule.

Equation:
Example: For H2O: amu

Formula Mass for Ionic Compounds

For ionic compounds, the term "formula mass" is used since they do not consist of discrete molecules.

Example: NaF: amu

Representing Molecules

Chemical Formulas and Models

Chemical formulas use element symbols and numerical subscripts to indicate the type and number of atoms in the smallest unit of a substance.

Example: H2O, CO2, NH3

Summary Table: Classification of Matter

Type	Description	Example
Element	One type of atom	O2, Fe
Compound	Two or more elements chemically combined	H2O, NaCl
Mixture	Two or more substances physically intermingled	Air, seawater

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