1 Atoms, Molecules and Ions. 2 Atoms Each element composed of atoms All atoms of a given element...

Atoms, Molecules and IonsAtoms, Molecules and Ions

AtomsAtoms

Each element composed of atoms All atoms of a given element are identical Atoms of an element are not changed during

a chemical reaction (the atoms just move from one chemical species to another)

Compounds are formed when atoms of more than 1 element combine

John Dalton• The Atomic Theory of Matter • Credited with developing Natural Laws

AtomsAtoms

Law of conservation of mass Law of constant composition

Law of multiple proportions: When two elements form different compounds, the mass ratio of the elements in one compound is related to the mass ratio in the other by a small whole number.

AtomsAtoms

Discovery and Properties of Discovery and Properties of ElectronsElectrons

Humphrey Davy (early 1800’s) - passed electricity through compounds• compounds decomposed into elements• compounds are held together by electrical forces

Michael Faraday - (1832-1833) - amount of reaction that occurs during electrolysis is proportional to current passed through compounds• Matter (atoms) is electrical in nature.

Cathode Ray Tubes - (late 1800’s & early 1900’s) • 2 electrodes in a glass tube with a gas at low

pressure• voltage applied to tube causing a glow discharge• “rays” emitted from cathode (- end) to anode (+

Cathode Rays must be negatively charged!

J.J. Thomson - (1897) - changed cathode ray tube experiments by adding two adjustable voltage electrodes into the experiment

measured charge to mass ratio of electrons• e/m = -1.75881 x 108 coulomb/g of e-

named cathode rays electrons Thomson is the “discoverer of

electrons”

Discovery and Properties of Discovery and Properties of ElectronsElectrons Robert A. Millikan - 1st American Nobel

Laureate• determined the charge and mass of the

electron (1909)• oil drop experiment

charge on 1 electron = -1.60219 x 10-19 coulomb

using Thomson’s charge to mass ratio we get that the mass of 1 electron is

9.11 x 10-28 g

Canal Rays and ProtonsCanal Rays and Protons

Goldstein (1886) - “Canal Rays”• streams of positively charged particles in

cathode rays • flow in opposite direction of cathode rays

must be positive• postulated existence of “proton”

Plum-Pudding?Plum-Pudding?

Thomson assumed all these charged species were found in a sphere.

Discovery of the Nuclear AtomDiscovery of the Nuclear Atom

Rutherford and the Nuclear AtomRutherford and the Nuclear Atom Ernest Rutherford - 1910 - basic picture

of atom Geiger & Marsden’s experiment on- particle

scattering from thin Au foils

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.

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.

Rutherford and the Nuclear AtomRutherford and the Nuclear Atom

Rutherford decoded the scattering information

Rutherford and the Nuclear AtomRutherford and the Nuclear Atom

atom is mostly empty space very small, dense center called nucleus nearly all of atom’s mass in nucleus nuclear diameter is 1/10,000 to 1/100,000

times less than atom’s radius nuclear density is 1015g/mL equivalent to 3.72 x 109 tons/in3

NeutronsNeutrons

James Chadwick - 1932 analyzed evidence from -particle

scattering off Be recognized existence of massive

neutral particles - “neutrons”

The atom consists of positive, negative, and neutral entities (protons, electrons, and neutrons).

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.

There can be a variable number of neutrons for the same number of protons. Isotopes have the same number of protons but different numbers of neutrons.

Electrons are located outside of the nucleus. Most of the volume of the atom is due to electrons.

The Modern View of Atomic StructureThe Modern View of Atomic Structure

Fundamental ParticlesFundamental Particles

Particle Mass (amu) Charge

Electron (e-) 0.00054858 -1

Proton (p,p+) 1.0073 +1

Neutron(n,n0) 1.0087 0

Three fundamental particles make up atoms. The following table lists these particles together with their masses and their charges.

Mass Number & IsotopesMass Number & Isotopes H.G. J. Moseley (1912-1914) - recognized

that atomic number is the defining difference between elements

new understanding of Mendeleev’s periodic law

Atomic NumberAtomic Number

Sometimes given the symbol Z number of protons in the nucleus determines the element • also determines number of electrons in a neutral atom

Isotopes, Atomic Numbers & Mass Isotopes, Atomic Numbers & Mass NumbersNumbers

All atoms of an element have the same number of protons in the nucleus

Isotopes of an atom have a different number of neutrons in the nucleus

Atomic number = # of protons Mass number = # protons + # neutrons

By convention, for element X, we write

Isotopes have the same Z but different A.

Isotopes, Atomic Numbers & Mass Isotopes, Atomic Numbers & Mass NumbersNumbers

IsotopesIsotopes

Give the number of protons, neutrons and electrons in each of the following species:

5656FeFe 5656FeFe3+3+ 3131PP 3131PP3-3-

IsotopesIsotopes

Give the number of protons, neutrons and electrons in each of the following species:5656FeFe 5656FeFe3+3+ 3535ClCl-1-1 3131PP3-3-

P P 2626

NN 3030

EE 2626

IsotopesIsotopes

P P 2626 2626

NN 3030 3030

EE 2626 2323

IsotopesIsotopes

P P 2626 2626 17 17

NN 3030 3030 18 18

EE 2626 2323 18 18

IsotopesIsotopes

P P 2626 2626 17 17 1515

NN 3030 3030 18 18 1616

EE 2626 2323 18 18 1818

Atomic WeightsAtomic Weights

weighted average of the masses of the constituent isotopes

lower number on periodic chart

The Periodic Table is used to organize the 114 elements in a meaningful way.As a consequence of this organization, there are periodic properties associated with the periodic table.

The Periodic TableThe Periodic Table

Columns in the periodic table are called groups (numbered from 1A to 8A or 1 to 18).

Rows in the periodic table are called periods..

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.

Some of the groups in the periodic table are given special names.These names indicate the similarities between group members:

Group 1A: Alkali metals.Group 2A: Alkaline earth metals.Group 6A: Chalcogens.Group 7A: Halogens.Group 8A: Noble gases.

Name the following elements. Indicate if each is a metal, nonmetal, or metalloid.

P Sn Mn K Cu Hg F As N Si Na Ca Fe Ag Mg

Name the following elements. Indicate if each is a metal, nonmetal, or metalloid.

P phosphorus Sn tin Mn manganese

K Potassium Cu copper Hg mercury

F fluorine As arsenic N nitrogen

Si silicon Na sodium Ca calcium

Fe iron Ag silver Mg magnesium

Molecules are assemblies of two or more atoms bonded together.

Each molecule has a chemical formula.

The chemical formula indicates •which atoms are found in the molecule•in what proportion they are found.

Compounds formed from molecules are molecular compounds.

Molecules and Molecular CompoundsMolecules and Molecular Compounds

Molecules and Molecular CompoundsMolecules and Molecular Compounds empirical formula - simplest molecular formula,

shows ratios of elements but not actual numbers of elements

molecular formula - actual numbers of atoms of each element in the compound

Molecules occupy three dimensional space.

However, we often represent them in two dimensions.

The structural formula gives the connectivity between individual atoms in the molecule.

The structural formula may or may not be used to show the three dimensional shape of the molecule.

Molecules and Molecular CompoundsMolecules and Molecular Compounds

If the structural formula does show the shape of the molecule, then either a perspective drawing, ball-and-stick model, or space-filling model is used.

Chemical FormulasChemical Formulas

show the ratio of the elements present in the molecule or compound

He, Au, Na - monatomic O2, H2, Cl2 - diatomic

O3, S8, P4 - more complex elements

H2O, C12H22O11 - compounds

Ions & Ionic CompoundsIons & Ionic Compounds

ions are atoms or groups of atoms that are charged

two basic types of ions• positive ions or cations

– one or more electrons less than neutral

• negative ions or anions– one or more electrons more than neutral

The number of electrons an atom loses is related to its position on the periodic table.Metals tend to form cations whereas non-metals tend to form anions.

Ions and Ionic CompoundsIons and Ionic Compounds

The majority of chemistry involves the transfer of electrons between species. (Ionic Bonding)Example:

To form NaCl, the neutral sodium atom, Na, must lose an electron to become a cation: Na+. The electron cannot be lost entirely, so it is transferred to a chlorine atom, Cl, which then becomes an anion: Cl-.The Na+ and Cl- ions are attracted to form an ionic NaCl lattice which crystallizes.

Ions and Ionic CompoundsIons and Ionic Compounds

Ions & Ionic CompoundsIons & Ionic Compounds

Sodium chloride - table salt is an ionic compound

Ion Names and FormulasIon Names and Formulas

Common Polyatomic Ions Can be found on my website Can be found as a table in your book

LEARN THEM!!!!

Ion Names and FormulasIon Names and Formulas

Naming of compounds, nomenclature, is divided into organic compounds (those containing C) and inorganic compounds (the rest of the periodic table).

NomenclatureNomenclature

Cations formed from a metal have the same name as the metal.

Example: Na+ = sodium ion.If the metal can form more than one cation, then the charge is indicated in parentheses in the name.

Examples: Cu+ = copper(I); Cu2+ = copper(II).

Cations formed from non-metals end in -ium.Example: NH4

+ ammonium ion.

Monatomic anions (with only one atom) are called ide.

Example: Cl is chloride ion.Exceptions: hydroxide (OH), cyanide (CN), peroxide (O2

Polyatomic anions (with many atoms) containing oxygen end in -ate or -ite. (The one with more oxygen is called -ate.)

Examples: NO3- is nitrate, NO2

- is nitrite.

Nomenclature Nomenclature

cations + anions must give neutral charge NaCl sodium chloride (+1 & -1) KOH potassium hydroxide (+1 & -1) CaSO4 calcium sulfate (+2 & -2)

Al(OH)3 aluminum hydroxide (+3 & -3)

Consider the formation of Mg3N2:

Mg loses two electrons to become Mg2+

Nitrogen gains three electrons to become N3-.

For a neutral species, the number of electrons lost and gained must be equal.However, Mg can only lose electrons in twos and N can only accept electrons in threes.

Therefore, Mg needs to lose 6 electrons (2 3) and N gain those 6 electrons (3 2).

3Mg atoms need to form 3Mg2+ ions (total 3x2+ charges) 2 N atoms need to form 2N3- ions (total 2x3- charges).

Therefore, the formula is Mg3N2.

Predict the chemical formulas when the following species combine:

Na with O Ca with Cl Fe(III) with Cl Ca with O Cu(II) with OH-

Na with O Na2O Mg with Cl Fe(III) with Br Ca with O Cu(II) with OH-

Na with O Na2O

Mg with Cl MgCl2 Fe(III) with Br Ca with O Cu(II) with OH-

Na with O Na2O

Mg with Cl MgCl2 Fe(III) with Br FeBr3

Ca with O Cu(II) with OH-

Na with O Na2O

Ca with O CaO Cu(II) with OH-

Na with O Na2O

Ca with O CaO Cu(II) with OH- Cu(OH)2

name of K2SO3

formula of ammonium sulfide

formula of aluminim sulfate

name of K2SO3

• potassium sulfite–What is charge on sulfite ion?

formula of ammonium sulfide

formula of aluminum sulfate

name of K2SO3

formula of ammonium sulfide• (NH4)2S–What is charge on ammonium ion?

formula of aluminum sulfate

name of K2SO3

formula of ammonium sulfide• (NH4)2S–What is charge on ammonium ion?

formula of aluminum sulfate• Al2(SO4)3

–What is charge on both ions?

Polyatomic anions containing oxygen with additional hydrogens are named by adding hydrogen or bi- (one H), dihydrogen (two H), etc., to the name as follows:

CO32- is the carbonate anion

HCO3- is the hydrogen carbonate (or bicarbonate)

anion.H2PO4

- is the dihydrogen phosphate anion.

Polyatomic anions containing oxygen with more than two members in the series are named as follows (in order of decreasing oxygen):

per-….-ate-ate-itehypo-….-ite

Binary molecular compounds have two elements.The most metallic element is usually written first (i.e., the one to the farthest left on the periodic table). Exception: NH3.If both elements are in the same group, the lower one is written first.Greek prefixes are used to indicate the number of atoms.

Naming Molecular CompoundsNaming Molecular Compounds

Name the following molecular compounds

CO2 Carbon dioxide

PF5 Phosphorus pentafluoride

CO2 Carbon dioxide

Cl2O7 dichlorine heptaoxide

CO2 Carbon dioxide

H2S dihydrogen sulfide

CO2 Carbon dioxide

H2S dihydrogen sulfide

SiH4 Silicon tetrahydride

The names of acids (molecules that lose H+) are related to the names of anions: Molecular acids

-ide becomes hydro-…..-ic acidIf acid has oxygen (oxoacids)

-ate becomes -ic acid;-ite becomes -ous acid.(keep the “per” and “hypo” if necessary)

Naming AcidsNaming Acids

Name the following AcidsName the following Acids

HCl H2SO4

Hydrobrombic acid Perchloric acid Hypochlorous acid

HCl Hydrochloric Acid H2SO4

Hydrobrombic acid Perbromic acid Hypobromous acid

HCl Hydrochloric Acid H2SO4 Sulfuric Acid

HNO3 Nitric Acid

H3PO4 Phosphoric Acid Hydrobrombic acid Perbromic acid Hypobromous acid

HNO3 Nitric Acid

H3PO4 Phosphoric Acid Hydrobrombic acid HBr Perbromic acid Hypobromous acid

HNO3 Nitric Acid

H3PO4 Phosphoric Acid Hydrobrombic acid HBr Perbromic acid HBrO4

Hypobromous acid

HNO3 Nitric Acid

H3PO4 Phosphoric Acid Hydrobrombic acid HBr Perbromic acid HBrO4

Hypobromous acid HBrO

1 Atoms, Molecules and Ions. 2 Atoms Each element composed of atoms All atoms of a given element...

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