Atoms, Molecules, and IonsAtomic Theory of Matter

John Dalton – earliest version of the atomic theory

1. Elements are composed of small particles called atoms.

2. Atoms of a given element are identical

3. 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 StructureSimilar charges repel each otherOpposite charges attract each other

A. RadioactivityErnest 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 AtomJ.J. Thomson – atoms are a uniform positive

sphere with electrons embedded in it.

“Plum Pudding Model”

Nuclear AtomRutherford – 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 = 2.6 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; 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

N2 O2 F2 Cl2 Br2 I2H2

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