The Study of Chemistry The Atomic and Molecular Perspective of Chemistry Matter is the physical material of the universe. Matter is made up of relatively few (ca. 100) elements. Elements are the building blocks of matter. On the nano (ultramicroscopic) level, matter consists of atoms. An atom is a “nano-basketball” -- nano = Atoms usually are found in the combined state, either molecules, salts, or alloys. Molecules may consist of the same type of atoms or different types of atoms.

Elements Classification of Matter The next five elements are: Na 2%, K 2%, Mg 2%, H 1%, Ti 0.5%. The next six elements are: N 3%, Ca 1.5%, P 1%, K,S,Na 0.75%

Elements in the Human Body – including trace elements including trace elements

The Periodic Table Bring your Periodic Table to each class!

Properties of Matter When a substance undergoes a physical change, its physical appearance changes, but its chemical nature does not. Physical and Chemical Changes Example: the melting of ice (physical change) results in a solid being converted into a liquid, but it is still water. Physical changes do not result in a change of composition. When a substance changes its composition, it undergoes a chemical change Example: when pure hydrogen and pure oxygen react completely, they form pure water. In the flask containing water, there is no oxygen or hydrogen left over.

Units of Measurement Powers of ten are used for convenience with smaller or larger units in the SI system. What is a GigaByte?

Units of Measurement - Temperature There are three temperature scales: Kelvin Scale (used in science) Same temperature increment as Celsius scale. Lowest temperature possible (absolute zero) is zero Kelvin. Absolute zero: 0 K = o C. Celsius Scale (used in science) Also used in science. Water freezes at 0 o C and boils at 100 o C. To convert: K = o C Fahrenheit Scale (used in US engineering and commerce) Water freezes at 32 o F and boils at 212 o F. To convert:

Units of Measurement - Temperature

A user-friendly way to view the Celsius Scale: 0° - Cold! (coat) 10° - Cool (sweat shirt) 20° - Pleasant (long sleeves) 25° - Room temperature (short sleeves) 30° - Very warm (T-shirt) 40° - Hot! (swimming pool!) Units of Measurement - Temperature

Units of Measurement - Density Used to characterize substances. Defined as: density = mass /volume. Units: g/cm 3, also known as specific gravity. Originally based on mass -- the density was defined as the mass of 1.00 g of pure water.

John Dalton: Elements are composed of atoms. –All atoms of an element are identical (chemically). (Dalton stressed “identical in weight” but he didn’t know about isotopes) –In chemical reactions, the atoms are not changed. –Compounds are formed when atoms of more than one element combine. The Atomic Theory of Matter (e.g., H 2 O, C 6 H 6, C 12 H 22 O 11 but not H 2, Cl 2 )

The ancient Greeks were the first to postulate that matter consists of indivisible constituents. Later scientists realized that the atom consisted of charged (+ or -) entities. The Discovery of Atomic Structure Cathode Rays and Electrons A cathode ray tube (CRT) is a hollow vessel with an electrode at either end. A high voltage is applied across the electrodes. A charged particle will have its path bend in either an electric or magnetic field.

The ancient Greeks were the first to postulate that matter consists of indivisible constituents. Later scientists realized that the atom consisted of charged (+ or -) entities. The Discovery of Atomic Structure Cathode Rays and Electrons A cathode ray tube (CRT) is a hollow vessel with an electrode at either end. A high voltage is applied across the electrodes. A charged particle will have its path bend in either an electric or magnetic field.

The Discovery of Atomic Structure a spot which is not affected by the electric field, Three spots are noted on the detector: a spot in the direction of the positive (+) plate, a spot in the direction of the negative (-) plate.

 -radiation: Large deflection toward the positive plate corresponding to radiation which is negatively charged and of low mass. These  particles are light and of low mass.  particles are electrons.  -radiation: No deflection; neutral (zero charge) radiation.  -radiation: Small deflection toward the negative plate corresponding to high mass, positively charged radiation.

The Nuclear Atom From the separation of radiation we conclude that the atom consists of neutral, positively, and negatively charged entities. J. J. Thomson assumed all these charged species were found in a sphere. The Discovery of Atomic Structure

The Nuclear Atom Rutherford’s  -particle experiment: The Discovery of Atomic Structure

The Nuclear Atom In order to get the majority of  -particles through a piece of foil to be undeflected, the majority of the atom must consist of a low mass, diffuse negative charge  the electron. The Discovery of Atomic Structure To account for the small number of high deflections of the  -particles, the center or nucleus of the atom must consist of a dense positive charge.

The Nuclear Atom Rutherford modified Thomson’s model as follows: assume the atom is spherical but a massive positive charge must be located at the center, with a diffuse light negative charge surrounding it. The Discovery of Atomic Structure

The atom consists of positive, negative, and neutral entities (protons, electrons, and neutrons). The Modern View of Atomic Structure Protons and neutrons are located in the nucleus of the atom, which is small. Most of the mass of the atom is due to the nucleus. Electrons are located outside of the nucleus. Most of the volume of the atom is due to electrons.

(1Å = cm = m) The Nucleus Ångstrom unit:

Columns in the periodic table are called groups (numbered from 1A to 8A or 1 to 18). The Periodic Table Metals are located on the left hand side of the periodic table (most of the elements are metals). Non-metals are located in the top right hand side of the periodic table. Elements with properties similar to both metals and non-metals are called metalloids and are located at the interface between the metals and non-metals. Rows in the periodic table are called periods.

Some elements occur naturally as diatomic molecules (Most elements can be viewed as uniatomic; but there are unusual elemental molecules, e.g., P 4, S 8, C 60.)

Some of the groups in the periodic table are given special names. The Periodic Table These names indicate the similarities between group members: Group 1A: Alkali metals - “al kali” = “the ashes” (of a fire) Group 2A: Alkaline earth metals (“earths” historically were oxides that were difficult to reduce to the metal). Group 6A: Chalcogens - “ore formers” Group 7A: Halogens - “salt formers” Group 8A: Noble gases - “unreactive” gases At the bottom are the lanthanides (“rare earths”) and the actinides.

The Periodic Table Metals Non-Metals Metalloids “semiconductors”

COMPARISON OF METALS AND NONMETALS PROPERTY METALS NONMETALS Appearance Metallic luster Flat, matte appearance Conductivity of electricity High Low Conductivity of heat High Low Change of form Malleable Brittle Affinity for electrons Loses electrons Gains electrons Oxide chemistry Oxide forms bases Oxide forms acids MO + H 2 O → MOH XO + H 2 O → HXO Examples: Na 2 O + H 2 O → 2NaOH SO 3 + H2O → H 2 SO 4

Alkali Metals Alkaline Earths Noble or Inert Gases HalogensChalcogens Lanthanides (rare earths) Actinides Transition Metals Navigating the Periodic Table

Different Kinds of Compounds A salt, formed by ionic bonding, is formed between a metal and a nonmetal, (e.g., NaCl, Ag 2 O).

A molecule, formed by covalent bonding, is formed between a nonmetal and a nonmetal, (e.g., CO 2, PBr 3, H 2 O). Different Kinds of Compounds

An alloy, formed by metallic bonding, is formed between a metal and a metal, (e.g., brass or nickel-steel)

The Wave Nature of Light

Na H Bohr’s Model of the Hydrogen Atom Line Spectra Colors from excited gases arise because electrons move between energy states in the atom. These are called line spectra.

Absorption Emission E1E1 E2E2 E3E3 E4E4 Bohr’s Model of the Hydrogen Atom

The Mole The mole connects the visible with the invisible. A fluorine molecule (F 2 ) weighs amu. A mole of fluorine molecules weighs grams. The number of fluorine molecules in a mole is an incredibly large number, called Avogadro’s Number, N, which is x We will be using the mole concept very often. Amedeo Avogadro

The Mole Examples: A mole of H is grams. A mole of H 2 is grams. A mole of CO 2 is grams. A mole of CO is grams. A mole of octane (C 8 H 18 ) is grams. A mole of copper (Cu) is grams. A mole of table salt (NaCl) is grams. A mole of sodium bicarbonate (NaHCO 3 ) is grams. A mole of Ag 2 O is grams. A mole of glucose (C 6 H 12 O 6 ) is grams. A mole of chlorophyll (C 55 H 72 MgN 4 O 5 ) is grams.

Picturing Molecules Molecules and Molecular Compounds

When an atom or molecule loses electrons, it becomes positively charged. Ions and Ionic Compounds For example, when Na loses an electron, it becomes Na +. Positively charged ions are called cations.

When an atom or molecule gains electrons, it becomes negatively charged. Ions and Ionic Compounds For example when Cl gains an electron it becomes Cl . Negatively charged ions are called anions. An atom or molecule can lose more than one electron.

12p + 12 e - lose 2 e - 12p + 10 e - Ions and Ionic Compounds When an atom or molecule loses two electrons, it becomes doubly positively charged. For example, when Mg loses two electrons, it becomes Mg 2+ Mg atom Mg 2+ ion “magnesium atom” “magnesium ion”

16 p + 16 e - gain 2 e - 16p + 18 e - Ions and Ionic Compounds When an atom or molecule gains two electrons, it becomes doubly negatively charged. For example, when S gains 2 electrons, it becomes S 2- S atom S 2- ion “sulfur atom” “sulfide ion”

Important: note that there are no easily identified NaCl molecules in the ionic lattice. Therefore, we cannot use molecular formulas to describe ionic substances. Ions and Ionic Compounds

Ionic Compounds I.e., 3Mg atoms need to form 3Mg 2+ ions (total 3x2+ charges) and 2 N atoms need to form 2N 3- ions (total 2x3- charges). Therefore, the formula is Mg 3 N 2. Ions and Ionic Compounds Mg N N 3- Mg Be careful! what’s the ionic compound formed between magnesium and oxygen?) MgO

Lavoisier: mass is conserved in a chemical reaction. Chemical equations: descriptions of chemical reactions. Two parts to an equation: reactants and products: Chemical Equations 2H 2 + O 2 2H 2 O ReactantsProduct

H2H2 O2O2 H2OH2O

Stoichiometric coefficients: numbers in front of the chemical formulas give numbers of molecules or atoms reacting (and numbers being produced).

CH 4 + O 2 CO 2 + H 2 O Count atoms: Reactants: Products: 1 C 4 H2 H 2 O 3 O is not balanced. (Why?) Law of Conservation of Mass: All reactions must be balanced

Balance reactions only by changing coefficients, not by altering chemical formula