Chemistry Chapters 4 & 5 Visual Study Guide

Atoms, Elements, & Chemical Nomenclature Chemistry Chapters 4 & 5 Visual Study Guide 1. FOUNDATIONS OF ATOMIC THEORY & STRUCTURE Ancient vs. Modern Atomic Theory What you need to know: Democritus and Leucippus first theorized in ancient times that matter is made of tiny, indestructible particles called atomos (indivisible). In 1808, John Dalton formalized his 3-part Atomic Theory: (1) each element is composed of tiny, indestructible atoms; (2) all atoms of a given element have the same mass and properties; (3) atoms combine in simple, whole-number ratios to form compounds. Today, scanning tunneling microscopes (STM) provide direct visual proof of atoms, as featured in the IBM film 'A Boy and His Atom' where individual Xenon atoms are moved precisely on a surface. ■ Simple explanation: Think of dividing a piece of paper. Democritus said you can't cut it forever; eventually, you reach an uncuttable piece: the atom. Dalton proved this scientifically. Today we can actually 'write' with atoms using advanced microscopes, like building structures with Lego bricks on a microscopic scale. Thomson's Electron & Plum-Pudding Model What you need to know: J. J. Thomson discovered the electron (negatively charged, much smaller and lighter than the atom, present in all substances). He proposed the 'plum-pudding' model, suggesting that these negatively charged electrons are held within a uniform sphere of positive charge to maintain overall electrical neutrality. ■ Simple explanation: Imagine a chocolate chip muffin (or blueberry pudding). The muffin cake is a sphere of positive charge, and the chocolate chips embedded in it are the negative electrons. Chemistry Foundation Course • Study Guide & Review Page 1 Figure 1.1: Comparison of J. J. Thomson's Plum-Pudding model (left) and Rutherford's Nuclear model (right) showing alpha-particle scattering behavior. Chemistry Foundation Course • Study Guide & Review Page 1 ATOMS, ELEMENTS, & CHEMICAL NOMENCLATURE VISUAL STUDY GUIDE 2. RUTHERFORD'S EXPERIMENT & SUBATOMIC PARTICLES Rutherford's Gold Foil Experiment What you need to know: Ernest Rutherford directed tiny, positively charged alpha-particles at a thin sheet of gold foil. Instead of passing straight through as the plum-pudding model predicted, a few alpha-particles deflected at sharp angles and some bounced directly back. This led to the Nuclear Theory of the Atom: (1) most of the atom's mass and all positive charge are in a small core called the nucleus; (2) most volume is empty space with dispersed electrons; (3) protons equal electrons, keeping the atom neutral. Nuclear matter is incredibly dense: a sand grain of solid atomic nuclei would mass 5 million metric tons (5 billion kg), similar to neutron stars. ■ Simple explanation: Imagine shooting bullets at a piece of tissue paper, and some of them bounce back at you! That means there must be a tiny, super-dense boulder hidden inside that paper—this 'boulder' is the nucleus. Figure 2.1: Subatomic mass comparison: Proton/Neutron (baseball) vs. Electron (rice grain). 3. THE PERIODIC TABLE & CHEMICAL SYMBOLS Chemical Symbols from Latin and Greek: While most element symbols match their English names, several are based on historic Latin or Greek names, which you must memorize for the exam. Element Name Chemica l Symbol Latin/Greek Name Element Name Chemica l Symbol Latin/Greek Name Potassium K Kalium Iron Fe Ferrum Sodium Na Natrium Silver Ag Argentum Lead Pb Plumbum Tin Sn Stannum Mercury Hg Hydrargyrum Copper Cu Cuprum Element Classifications: The periodic table divides into: (1) Metals (left, malleable, ductile, shiny, conductors, lose electrons to form cations); (2) Nonmetals (upper right, poor conductors, gain electrons to form anions); (3) Metalloids (zigzag boundary, semiconductors like Silicon (Si), Germanium (Ge), and Arsenic (As), with controlled electrical conductivity). Chemistry Foundation Course Page 3 Generated by Gemini Notebook ATOMS, ELEMENTS, & CHEMICAL NOMENCLATURE VISUAL STUDY GUIDE 4. PREDICTABLE GROUPS, ISOTOPES, & MASS CALCULATIONS Main Group Periodic Families: Main-group elements (Group A columns) have highly predictable properties: (1) Alkali Metals (Group 1A): highly reactive, violent with water; (2) Alkaline Earth Metals (Group 2A): fairly reactive; (3) Halogens (Group 7A): highly reactive nonmetals; (4) Noble Gases (Group 8A): inert, chemically stable. Note: Hydrogen is NOT an alkali metal, despite being in Group 1A. Isotopes & Atomic Mass Calculation What you need to know: Isotopes are atoms of the same element with identical protons (atomic number Z) but different neutrons, resulting in different mass numbers (A = protons + neutrons). Every element has a unique natural abundance of isotopes. The average atomic mass on the periodic table is a weighted average: Sum of (fractional abundance x isotopic mass). Fractional abundance = percent abundance / 100. ■ Simple explanation: Think of calculating your final grade. If exams are 70% and homework is 30%, you do a weighted average. For Chlorine (75.77% Cl-35 and 24.23% Cl-37), the average mass is weighted heavily towards Cl-35, resulting in 35.45 amu. Figure 3.1: Standard Isotope symbol notation vs. hyphen notation. 5. MOLECULES, COMPOUNDS, & MIXTURES Compounds vs. Mixtures & Law of Constant Composition What you need to know: In a compound, elements combine in fixed, definite proportions (Law of Constant Composition). In a mixture, components combine in variable proportions. Joseph Proust formulated this law: all samples of a given compound have the same proportions of their constituent elements. For example, water always has an O-to-H mass ratio of 8.0 to 1.0 (16.0g O to 2.0g H); ammonia has an N-to-H mass ratio of 4.7 to 1.0 (14.0g N to 3.0g H). ■ Simple explanation: A mixture is like a salad—you can add more or fewer tomatoes and it's still a salad. A compound is like a car—it must have exactly 4 wheels and 1 steering wheel; if you change that ratio, it isn't a functional car anymore. Chemistry Foundation Course Page 4 Generated by Gemini Notebook ATOMS, ELEMENTS, & CHEMICAL NOMENCLATURE VISUAL STUDY GUIDE Figure 3.2: Microscopic comparison of a mixture (left) with variable gas proportions and a pure compound (right) with a fixed 2:1 ratio of atoms. Chemistry Foundation Course Page 5 Generated by Gemini Notebook ATOMS, ELEMENTS, & CHEMICAL NOMENCLATURE VISUAL STUDY GUIDE 6. CHEMICAL FORMULAS & VISUAL VIEWS Types of Formulas: (1) Empirical Formula: simplest whole-number ratio of atoms (e.g., HO for hydrogen peroxide); (2) Molecular Formula: actual number of atoms in a molecule (e.g., H2O2); (3) Structural Formula: represents bonds as lines, showing connectivity. Classifications: (1) Atomic elements (exist as single atoms, e.g., Hg); (2) Molecular elements (exist as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2); (3) Molecular compounds (nonmetals only); (4) Ionic compounds (metal + nonmetal forming an alternating 3D array of formula units). 7. WRITING & NAMING IONIC COMPOUNDS Formulas for Ionic Compounds: The sum of charges of cations must equal the sum of charges of anions to ensure electrical neutrality. We use the criss-cross method (the charge of one ion becomes the subscript of the other) and always reduce subscripts to the smallest whole-number ratio (e.g., Al3+ and O2- becomes Al2O3; Mg2+ and O2- becomes Mg2O2 which reduces to MgO). Type I and Type II Ionic Systems: • Type I Compounds: Contain a metal with a constant, invariant charge (Group 1A, 2A, Al3+). Exceptions: Zn2+, Ag+, Sc3+ are transition metals but have fixed charges and are named as Type I (no Roman numerals!). Naming: [Metal Name] + [Anion Stem + -ide] (e.g., NaCl is sodium chloride). • Type II Compounds: Contain a metal with a variable charge (transition metals). Exceptions: Lead (Pb2+ / Pb4+) and Tin (Sn2+ / Sn4+) are main-group metals but form variable charges and MUST be named as Type II (using Roman numerals!). Naming: [Metal Name] (Roman numeral of charge) + [Anion Stem + -ide]. Determine the charge from the negative anion. E.g., FeCl3 has three Cl- ions (-3 total), so iron must be Fe3+: iron(III) chloride. Polyatomic Oxyanion Series: When naming oxyanions (polyatomic ions containing oxygen), use a systematic naming pattern based on the oxygen count: • per-_______-ate (most oxygen, e.g., ClO4-: perchlorate) • _______-ate (more oxygen, e.g., ClO3-: chlorate) • _______-ite (less oxygen, e.g., ClO2-: chlorite) • hypo-_______-ite (least oxygen, e.g., ClO-: hypochlorite) Everyday Chemistry Formulas to Memorize: 1. Sodium Hypochlorite (NaClO): Active ingredient in bleach, decomposes colors and kills bacteria. 2. Sodium Bicarbonate (NaHCO3): Baking soda, acts as a CO2 gas source in baking. 3. Calcium Carbonate (CaCO3): Active ingredient in antacids (Tums), neutralizes stomach acid. 4. Sodium Nitrite (NaNO2): Food preservative in packaged meats, inhibits botulism-causing bacteria. Naming Molecular Compounds (Two Nonmetals): Name using Greek prefixes for both elements to show the number of atoms. Drop prefix vowels sometimes (e.g., monoxide, but keep dioxide and triiodide). Never use mono- on the first element (e.g., CO2 is carbon dioxide). Prefixes: 1=mono, 2=di, 3=tri, 4=tetra, 5=penta, 6=hexa, 7=hepta, 8=octa, 9=nona, 10=deca. Chemistry Foundation Course Page 6 Generated by Gemini Notebook ATOMS, ELEMENTS, & CHEMICAL NOMENCLATURE VISUAL STUDY GUIDE 8. NAMING ACIDS & CALCULATING FORMULA MASS Acid Classification: Acids are molecular compounds containing hydrogen (written first in the formula) that form ions in water. They are classified into two groups: Binary Acids (H + Nonmetal) What you need to know: Naming: hydro- + [nonmetal base name] + -ic acid. They must have the '(aq)' subscript indicating they are dissolved in water. E.g., HCl(aq) is hydrochloric acid (while HCl(g) is hydrogen chloride gas, not an acid). H2S(aq) is hydrosulfuric acid. ■ Simple explanation: To name a binary acid, open with 'hydro-', write the nonmetal's stem ending with '-ic', and add 'acid' (e.g., hydro-chlor-ic acid). Oxyacids (H + Polyatomic Oxyanion) What you need to know: Oxyacids combine hydrogen with an oxygen-containing polyatomic ion. Their names depend on the oxyanion's suffix: • If the oxyanion ends in -ite, the acid becomes -ous acid (e.g., HNO2 containing nitrite is nitrous acid; H2SO3 with sulfite is sulfurous acid). • If the oxyanion ends in -ate, the acid becomes -ic acid (e.g., HNO3 containing nitrate is nitric acid; H2SO4 with sulfate is sulfuric acid; HC2H3O2 with acetate is acetic acid; H2CO3 with carbonate is carbonic acid). ■ Simple explanation: Use the mnemonic: 'I mitey mouse had an ous house; I ate something slick.' This connects '-ite' to '-ous' and '-ate' to '-ic'. No 'hydro-' prefix is used for oxyacids! Formula Mass Calculations What you need to know: The formula mass of any compound is the sum of the atomic masses of all the atoms in its chemical formula, expressed in atomic mass units (amu). Formula Mass = (number of atoms of 1st element x atomic mass) + (number of atoms of 2nd element x atomic mass) + ... ■ Simple explanation: Think of calculating the total weight of a basket of fruit. If you have 2 apples (24.3g each) and 1 orange (16.0g), the total basket weight is (2 x 24.3) + 16.0 = 64.6g. It's the same for compounds like MgCl2. MUST KNOW FOR THE EXAM (PRIORITIZED CHECKLIST) ■ ■ MUST MEMORIZE: The 7 Diatomic Elements (H2, N2, O2, F2, Cl2, Br2, I2); Latin element symbols (K, Na, Pb, Hg, Fe, Ag, Sn, Cu); Fixed transition charges (Zn2+, Ag+, Sc3+); Main-group variable charge exceptions (Pb and Sn); Prefix vowels rules; Everyday chemical formulas (bleach, baking soda, antacid, meat preservative). ■■■■ VERY IMPORTANT: Naming flowcharts for Ionic (Type I & II), Molecular, and Acids; Common polyatomic ion formulas and charges (especially Sulfite/Sulfate, Nitrite/Nitrate, Carbonate/Bicarbonate); Predicting main-group ion charges based on Group Number (1A=1+, 2A=2+, 3A=3+, 5A=3-, 6A=2-, 7A=1-). ■■■ ■■■ UNDERSTAND: Rutherford's Gold Foil Experiment observations vs predictions; Dalton's Atomic Theory parts; Law of Constant Composition and elements in fixed mass ratios; Difference between Mass Number (A), Atomic Number (Z), and Average Atomic Mass. Chemistry Foundation Course Page 7 Generated by Gemini Notebook