Chemistry Essentials: Last-Minute Review

What is Chemistry?

• Chemistry: the science of the properties, reactions, composition, and structures of matter.
• Or: the study of matter and energy and the interactions between them.

Why Study Chemistry?

• Involved in every aspect of our lives: food, medicines/drugs, clothes/materials, electronics, and many more.

Chemistry in the Health Care Industry

• Manufacture of current drugs
• Development of new drugs (synthesis of new pharmaceutical compounds)
• Clinical laboratory tests (e.g., blood glucose, cholesterol)
• Discovery of new instruments/tools: synthetic skin grafts, stitches, sterile materials

Matter and Particulate Nature

• Matter is anything that has mass and occupies space
• Matter is composed of discrete, tiny fundamental particles called atoms
• The surface of a penny is made up of tiny identical copper atoms packed together

Physical States of Matter

• Solid: definite shape and volume; strong attractive forces; essentially incompressible
• Liquid: definite volume; indefinite shape; mobile particles; strong attractions
• Gas: no definite shape or volume; compressible; particles far apart; weak attractions

Solids

• Crystalline solids: regular, repeating 3D geometric patterns
• Amorphous solids: lack regular internal geometric pattern (e.g., wax, plastics, glass)

Liquids

• Indefinite shape, definite volume; particles are mobile; strong forces hold them together

Gases

• Indefinite shape and volume; highly compressible; particles far apart; weak attractions

Classifying Matter

• Pure substance: definite fixed composition; cannot be decomposed into simpler substances by chemical means
• Elements: cannot be decomposed by chemical means; building blocks of matter
• Compounds: can be decomposed into elements by chemical means; fixed ratios
• Mixtures: two or more substances
• Homogeneous mixtures (solutions): one phase
• Heterogeneous mixtures: two or more phases

Elements and Compounds in Nature

• Elements: building blocks; smallest unit is an atom
• Compounds: composed of two or more elements in fixed proportions; can be decomposed

Elements

• There are ${118}$ known elements
• Elements are named from various sources (origins may be geometric, historical, geographic, etc.)
• Elements have symbols (one- or two-letter abbreviations) and a periodic table organization

Symbols of the Elements

• Fourteen elements have single-letter symbols; the rest have two-letter symbols
• The first letter of a symbol is always capitalized; a second letter (if any) is lowercase

Introduction to the Periodic Table

• Designed by Dmitri Mendeleev in ${1869}$ to organize elements by properties
• Elements are arranged in order of increasing atomic number
• Elements with similar properties are placed in columns called groups
• Four groups have special identifying names (e.g., noble gases)

Periodic Table Organization by Group

• Elements can be classified by their Group (columns) and by their properties

Metals, Metalloids, and Non-metals

• Metals: malleable, conduct heat and electricity, ductile, high density, high melting points
• Non-metals: brittle, poor conductors, non-ductile, low density, low melting points
• Metalloids: properties intermediate between metals and nonmetals; some are semiconductors

Elements in Nature

• Atomic vs. Molecular elements shown in nature: Ar (atomic), N₂ (molecular)
• Seven elements exist as diatomic molecules (two atoms per molecule): $ext{H}<em>2, ext{N}</em>2, ext{O}<em>2, ext{F}</em>2, ext{Cl}<em>2, ext{Br}</em>2, ext{I}_2$
• Many elements exist as compounds in nature

Elements that Exist as Compounds

• Compounds are formed from two or more elements in definite proportions
• Elements combine in whole-number ratios (e.g., $ext{Al}<em>2 ext{O}</em>3, ext{KNO}<em>3, ext{CaCl}</em>2$)
• Compounds can be decomposed chemically into simpler substances
• Each compound has properties different from its constituent elements

Molecular vs Ionic Compounds

• Molecular (covalent): usually two or more nonmetals; held together by covalent bonds
• Ionic: typically a metal and a non-metal; held together by electrostatic forces between ions

Molecules vs Ions

• Molecules: smallest unchanged unit of a compound formed by two or more atoms; cannot be divided without changing identity
• Ions: charged atoms or groups; cation = positive, anion = negative

Chemical Formulas

• Formula shows the symbols of all elements in a compound
• If only one atom of an element, no subscript is needed
• If more than one atom, use a subscript after the symbol (e.g., $ext{H}<em>2 ext{O}$, $ext{NaCl}$, $ext{CaCl}</em>2$)
• Parentheses group a unit when there are multiple groups (e.g., $ext{Zn}( ext{CH}<em>3 ext{COO})</em>2( ext{H}<em>2 ext{O})</em>2$)
• Formulas indicate the number and kinds of atoms, not connectivity

Chemical Formulas Practice (types of formulas to identify)

• Examples include: $ext{H}<em>2 ext{CO}</em>3, ext{ Ca}<em>3( ext{PO}</em>4)<em>2, ext{ NH}</em>4 ext{NO}<em>3, ext{ C}</em>2 ext{H}<em>3 ext{O}</em>2 ext{N H}<em>4, ext{ Zn}( ext{CH}</em>3 ext{COO})<em>2( ext{H}</em>2 ext{O})<em>2, ext{ Na}</em>2( ext{B}<em>4 ext{O}</em>5( ext{OH})<em>4)( ext{H}</em>2 ext{O})_8$

The Scientific Method and Problem Solving

• A scientific approach to problem solving includes:
  • Define the problem
  • Propose possible solutions (hypothesis)
  • Decide which way to proceed (design experiments)
  • Perform experiments to test the hypothesis
  • Draw conclusions to support or deny the hypothesis
• Hypothesis: tentative explanation that can be tested
• Theory: well-tested hypothesis
• Law: statement of natural phenomena with no known exceptions

Matter and The Particulate Nature of Matter

• Matter is composed of discrete, tiny fundamental particles called atoms
• Atoms are the smallest units that retain the properties of an element

Physical Properties vs Chemical Properties

• Physical properties: can be observed without changing chemical composition (color, odor, density, melting/boiling points, etc.)
• Chemical properties: describe a substance's ability to react and form new substances (e.g., sodium reacts with water)

Naming and Symbols: Elements

• Names of elements come from various sources (historical, geographic, Latin/Greek roots)
• Symbols: one- or two-letter abbreviations; first letter capitalized, second letter if present is lowercase

Naming Elements and Their Symbols: Examples

• Antimony: symbol $ext{Sb}$; former name stibium
• Copper: symbol $ext{Cu}$; former name cuprum
• Gold: symbol $ext{Au}$; former name aurum
• Iron: symbol $ext{Fe}$; former name ferrum
• Lead: symbol $ext{Pb}$; former name plumbum
• Mercury: symbol $ext{Hg}$; former name hydrargyrum
• Potassium: symbol $ext{K}$; former name kalium
• Argon: symbol $ext{Ar}$; (name origins vary)
• Sodium: symbol $ext{Na}$; former name natrium
• Tin: symbol $ext{Sn}$; former name stannum
• Tungsten: symbol $ext{W}$; former name wolfram

Symbols of the Elements

• Each element has a symbol; 14 elements have single-letter symbols; others have two letters
• First letter capitalized; second letter if present is lowercase

The Periodic Table

• Organized by atomic number; groups (columns) with similar properties
• Concept of metals, metalloids, non-metals

Metals, Metalloids, and Non-metals

• Metals: malleable, good conductors, ductile, high density and melting points
• Non-metals: brittle, poor conductors, low density and melting points
• Metalloids: intermediate properties; semiconductors

Elements in Nature and Diatomic Elements

• Some elements exist as diatomic molecules in nature: $ext{H}<em>2, ext{N}</em>2, ext{O}<em>2, ext{F}</em>2, ext{Cl}<em>2, ext{Br}</em>2, ext{I}_2$
• Others exist as individual atoms or as compounds

Summary of Key Points

• Chemistry connects matter, energy, and their interactions across health, industry, and everyday life
• Matter exists as solids, liquids, or gases with distinct properties
• Elements and compounds form the basis of materials; mixtures introduce variable compositions
• The periodic table provides a concise map of element properties and relationships