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Atoms, Molecules, and Ions

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1 Atoms, Molecules, and Ions
Chapter 2 Atoms, Molecules, and Ions

2 Important Laws Law of Conservation of Mass: mass is neither created nor destroyed Law of Definite Proportion: a given compound always contains exactly the same proportion of elements by mass Law of Multiple Proportions: when two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

3 Dalton’s Atomic Theory
Each element is made up of tiny particles called atoms. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way(s) Chemical compounds are formed when atoms of different elements combine. A given compound always has the same relateive numbers and types of atoms Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction

4 Avogadro’s Hypothesis
At the same temperature and pressure, equal volumes of different gases contain the same number of particles

5 J.J. Thomson (1898) Used the cathode-ray tube to determine the charge-to-mass ratio of an electron Made electrodes of various metals and concluded that all atoms have electrons Plum pudding model: a positively charged cloud with electrons randomly dispersed throughout

6 Robert Millikan (1909) Oil drop experiment allowed him to determine the charge of an electron Caclulated the mass of an electron as 9.11 X kg

7 Types of Radioactive Emission
Gamma () Rays: high-energy “light” Beta () Particles: high-speed electron Alpha () Particles: 2+ charge and a mass 7300 times larger than an electron

8 Ernest Rutherford (1911) Tested Thomson’s plum pudding model with the Gold Foil Experiment Believed that most  particles (2+ charge) would pass through with some slight deflection when it came close to a pocket of negative charge Actually, many particles were deflected at large angles - showing that the plum pudding model could not be correct Concluded that there was a positively charged nucleus with electrons surrounding it

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10 Modern Atom Tiny nucleus with protons (+) and neutrons (neutral)
Electrons are located outside of the nucleus

11 PROTONS show what atom (also atomic number)…never changes
Li = 3 N = 7 Cd = 48 NEUTRONS represent isotopes Same number of protons, but different number of neutrons ELECTRONS represent ions Same number of protons, but different number of electrons causes a charge

12 Atomic # vs. Mass # Atomic # = number of protons (found on PT)
Mass # = protons + neutrons

13 Chemical Bonds - Introduction
Covalent bonds: atoms share electrons A molecule is formed (not ionic compounds) Usually formed between two nonmetals Ex: H2, H2O, O2

14 Formulas Chemical Formula: chemical symbols written with subscripts to show how many are present Ex: CO2 Structural Formula: bonds are shown with lines Space-filling model: shows relative size and orientation of atoms in a model Ball-and-stick model: shows basic structure with angles

15 Ions Charged atoms caused by transfer of electrons
Cation: LOST electron causes a positive charge Anion: GAINED electron causes a negative charge

16 Ionic Bonding Force of attraction between positively and negatively charged ions (metal/nonmetal) Solid ionic compounds are called ionic solids

17 Periodic Table Metals = left of stairs (conduct heat/electricity, malleable, ductile, high luster, like to LOSE electrons - become cations,) Nonmetals = right of stairs (characteristics unlike metals, like to GAIN electrons - become anions, usually form covalent bonds = molecular compounds) Groups/families - vertical Periods - horizontal

18 Group Trends Group 1A: Alkali Metals (form 1+ ions)
Group 2A: Alkaline Earth Metals (form 2+ ions) Group 7A: Halogens (form diatomic molecules, form 1- ions) Group 8A: Noble Gases (don’t usually react)

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20 Naming Binary Ionic Compounds
In ionic compounds, the cation (+) always comes first, anion (-) always comes second CATION: named as normal atom name UNLESS it is a transition metal (has more than one charge) Transition metals are either named with a Roman numeral in parentheses representing the charge OR by using endings -ous (lower charge) and -ic (higher charge)…book uses Roman numeral ANION: ends in -ide unless it’s a polyatomic

21 Polyatomic Ions MUST BE MEMORIZED FOR AP CHEMISTRY!
Including the new(ish) ones…follow same pattern

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23 Naming Binary Covalent (Molecular) Compounds
Compounds formed with two nonmetals First element has no “mono” and ends normally Second element ends in -ide When second element starts with a vowel, the final prefix vowel may be dropped ex. monooxide becomes monoxide

24 Common Names Used… H2O water NH3 ammonia H2O2 hydrogen peroxide
MEMORIZE THESE!

25 Acid Naming Rules Start with hydrogen Normal Ending Acid Rule -ide
Hydro___ic Acid -ate ___ic Acid -ite ___ous Acid

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