Atoms, Molecules, and Ions Atomic Theory of Matter John Dalton – earliest version of the atomic theory Elements are composed of small particles called atoms. 2. Atoms of a given element are identical Law of Conservation of Matter/Energy – matter/energy cannot be created or destroyed 4. Two or more elements that combine chemically form compounds

Atomic Theory of Matter Element – one kind of atom Compound – 2 or more elements chemically bonded. Chemically different than elements Mixture – 2 or more substances together, each maintains its chemical identity

Discovery of Atomic Structure Similar charges repel each other Opposite charges attract each other Radioactivity Ernest Rutherford – 3 types of radiation Alpha (α) – positively charged particle Beta (β) – negatively charged particle Gamma (γ) – no charge; dangerous Alpha particle (α) is the core of a helium atom

Nuclear Atom J.J. Thomson – atoms are a uniform positive sphere with electrons embedded in it. “Plum Pudding Model”

Nuclear Atom Rutherford – fired alpha particles at gold foil to study scattering, most went straight through, some bounced straight back.

Rutherford – the Nuclear Atom Deduced that: most of an atom is empty space center of atom has a positive charge The nucleus – small and dense contains the majority of the mass of an atom Rutherford Gold Foil Animation

2.3 Modern View of Atomic Structure Atoms are composed of 3 particles Proton – positive charge (+) Neutron – neutral charge Electron – negative charge (-) Mass of an atom – all in nucleus sum of protons and neutrons

Modern Atomic Structure Size of an Atom – Between 1-5 Angstroms (Ǻ) Angstrom (Ǻ) = 1 x 10-10 m Electron Cloud – area around nucleus where electrons spend most of their time - makes up most of the size of an atom - mostly empty space

How many copper atoms (DCu atom = 2 How many copper atoms (DCu atom = 2.6 Ǻ) fit across the edge of a penny (19 mm)?

Isotopes, Atomic #, Mass # Isotopes, atomic #, and mass # - bookkeeping of subatomic particles All atoms of an element have the same number of protons Isotopes – Atoms of the same element with differing #’s of neutrons - affects mass #

Atomic Number (Z) – number of protons Mass Number (A) – # of protons + neutrons Examples:

2.4 Periodic Table (developed in 1869) Your new best friend!!!! Periodicity – repeating patterns of chemical and physical properties Vertical Columns – family or group; similar chemical behavior Horizontal Rows – Periods

Metals – Left of staircase; except Hydrogen; Metals – Left of staircase; except Hydrogen; most are _________ at room temp. Nonmetals – Right of staircase; includes H most are _______ at room temp. Metalloids – lie along staircase,behave as metal and nonmetal Elements Song Meet the Elements

2.5 Molecules and Ions Molecule – Two or more nonmetal atoms bonded together 7 Diatomic molecules: Horses Need Oats For Clear Brown Irises H2 N2 O2 F2 Cl2 Br2 I2

7 Diatomic Molecules

Subscripts – represent the # of atoms of the element just before it Ex: H2O C6H12O6 CaSO4 Mg3(PO4)2

Molecular, Empirical, and Structural Formulas Molecular Formula – Actual # of atoms Example: C6H12O6 , H2O2 Empirical Formula – Relative # of atoms smallest whole # ratio usually for ionic compounds Example: CH2O , HO , NaCl

Formula Types (con’t) Structural Formula – lines represent bonds; indicates which atoms are bonded to each other

Ions – form when an atom gains or loses electrons Cation – metal atom loses electrons to form a positive ion Anion – nonmetal atom gains electrons to form a negative ion Metals are losers (shhhhhh!)

Symbol 17O2- 52Cr3+ Protons 38 34 Neutrons 50 45 74 Electrons 36 54 Net Charge 2+ 1-

Polyatomic Ions Polyatomic Ions – many atoms with a charge See test packet for a list of common PAI’s Covalently bonded (nonmetals)

Predicting Ionic Charge Predicting Ionic Charge - use the staircase metals – lose electrons, form cations nonmetals – gain electrons; form anions Atoms will gain or lose electrons to have the same number of electrons as the nearest noble gas (for the main group [A] elements only) NOBILITY IS STABILITY

Ionic vs. Covalent Ionic Compounds – electrons are transferred from the metal (loser) to the nonmetal Empirical formula shows ratio – ionic compounds form large 3-D crystals. Covalent molecule – electrons are shared between 2 or more nonmetals