Chemical Foundations: Elements, Atoms, and Ions

Chemical Foundations: Elements, Atoms, and IonsUnit 2 The ElementsAbundances of ElementsThere are about 118 different known elements with 88 of them occurring naturally.

The names and symbols of each element are listed on the periodic table in your book. Names and Symbols for the ElementsNames for elements come from many different sources.Many have Latin or Greek originsHowever, more recent discoveries are named for descriptions, Famous Scientists, or Place of discovery

We use abbreviations to simplify when writing called Element Symbols.

Names and Symbols for the ElementsExamples:Berkelium (Bk)- named for place of discovery-Berkeley, CaliforniaCopper (Cu)- Latin- cuprum or cyprium, discovered in CyprusLead (Pb)- Latin,- plumbum, meaning heavyOxygen (O)- French, oxygene, generator of acid, derived from the Greek, oxy and gene meaning acid formingOxygen was thought to be part of all acids, but its not. Can you guess which element is part of all acids?Names and Symbols for the ElementsElement Symbols- First or first two letters of the element names. The first letter is always capitalizedThe second letter is always lowercase

O- oxygen, C- carbon, Ne- neon, Si- siliconNames and Symbols for the ElementsElement Symbols- Sometimes the first two letters are not the first two letters of the name.Symbols are from the old namesSymbols are from other letters in the name

Gold- Aurum- Au Lead- Plumbum- PbZinc- ZnCadmium- Cd

Atoms and CompoundsDaltons Atomic TheoryLaw of Constant Composition: A given compound always contains elements in exactly the same proportion by mass.

This observation along with others became the basis for Daltons Atomic Theory.Daltons Atomic Theory1. Elements are made of tiny particles called Atoms. All matter is made of atoms. Atoms are indivisible and indestructible particles.

2. All atoms of a given element are identical, both in mass and in properties.

3. The atoms of a given element are different from those of any other element.

Daltons Atomic Theory4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative number and types of atoms.5. Atoms are the units of chemical change. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.Formulas of CompoundsChemical Formula: a way of writing a compound using only symbols and numbers. The atoms are indicated by he element symbols and the number of each type of atom is indicated by a subscript.

Water- H2OWater contains 2 hydrogen atoms and 1 oxygen atomCarbon dioxide- CO2Carbon dioxide contains 1 carbon atom and 2 oxygen atoms Atomic StructureThe Structure of the AtomThe atom is composed of 3 subatomic particles called:

1. Protons (p+) 2. Neutrons (n0) 3. Electrons (e-)

Protons and Electrons are always equal in number in neutral atomsThe Structure of the AtomNuclear Atom: An atom with a dense center of positive charged around which tiny electrons move in a space that was otherwise empty.

Nucleus: The relatively small, dense center of positive charge in an atom.Made of Protons and Neutrons

The Structure of the AtomProton: A positively charged subatomic particle located in the atomic nucleus.

Neutron: A subatomic particle with no charge located in the atomic nucleus.

Electron: A negatively charged subatomic particle located outside of the nucleus.The Structure of the AtomParticleSymbolRelative ChargeRelative MassElectrone-1-1 amuProtonp+1+1836 amuNeutronN01839 amuIsotopesAtomic Number: The number of protons intside the nucleus of an atom.Generally given the symbol ZMass Number: The sum of the number of protons and neutrons in the nucleus of an atom.Generally given the symbol AThe element symbol is given the symbol X

AZX=Na2311IsotopesIn natural samples of an element you may find atoms with different masses. This phenomena can be explained by isotopes Isotopes: Atoms with the same number of protons, but with different numbers of neutrons.Most atoms have at least two stable isotopesExceptions: Aluminum, Fluorine, and Phosphorus have only 1Tin has 10

IsotopesWhen we refer to an isotope we use its name and mass numberWe dont have to give the atomic number because it is the same in all isotopes of a given element

Example: Boron-10 (10B)Boron- 11 (11B)IsotopesHydrogen is an exception to the name and mass number ruleThe isotopes of hydrogen are so important that they have special symbols and names

Protium (P)- hydrogen with no neutronsDeuterium (D)- hydrogen with 1 neutronTritium (T)- hydrogen with 2 neutronsIsotope AbundancesPercent abundance of each isotope can be calculated if the masses of the isotopes is found using a mass spectrometer

Using a mass spectrometer we find that the mass of 10B is 10.0129 amu and 11B is 11.0093 amuIsotope Abundance10B is 10.0129 amu11B is 11.0093 amuAverage Atomic Mass is 10.811 amu

By looking at the information, which isotope occurs in the greatest abundance?Isotope Abundance10.811= (%10B 10.0129) + (%11B 11.0093)

We know from algebra that when you add two percents they must equal 100We reduce this to two decimals equal to 1% 10B + % 11B = 1, where % 10B = x and % 11B = ySo, x + y = 1We need to have the equation in terms of one variable so, y = 1 - x10.811= (x 10.0129) + ((1 x) 11.0093)

Isotope AbundancesWe find that 10B has an abundance of 19.91% and 11B has an abundance of 80.09%

This means that in an average natural sample of 10,000 boron atoms you would find that 1,991 would be 10B atoms and 8,009 would be 11B atomsIsotope AbundancesAntimony, Sb, has two stable isotopes with experimentally determined masses of 120.904 amu (121Sb) and 122.904 amu (123Sb). What are the relative abundances of these isotopes ?Using the Periodic TableIntroduction to the Periodic TablePeriodic Table: A chart that shows all the known elements and gives you information about each one.

Elements are listed on the periodic table in order of increasing atomic number

One of the most useful tools in chemistryIntroduction to the Periodic TableElements are arranged in vertical Groups and horizontal Periods.

Periodic tables used in the United States have groups numbered 1-8 followed by the letter: A or B.

Introduction to the Periodic TableA groups are main group elements

B groups are transition elements

Group 1A- Alkali MetalsGroup 2A- Alkaline Earth MetalsGroups 3B-12B Transition MetalsGroup 7A- HalogensGroup 8A- Noble Gases

Introduction to the Periodic TableThe horizontal periods are numbered from 1-7

Period 1 contains only H and HePeriods 2 & 3 contain 8 elementsPeriods 4 & 5 contain 18 elementsPeriods 6 & 7 contain 32 elements

Introduction to the Periodic TableThe table is split into 3 basic parts:

1. Metals2. Non-metals3. Metalloids/semimetals

Introduction to the Periodic Table1. Metals: high electrical conductivityhigh luster (shininess)high ductility (can be drawn into wires)high malleability (can be rolled into sheets)can form alloys (solutions of one or more metals in another metal)

All metals are solids except for Mercury

Introduction to the Periodic Table2. Non-metals: Nonlustrous poor conductors of electricityAll lie to the right of the diagonal line that stretches from B to Te in the periodic table

Some are solids; bromine is a liquid, and a few, like nitrogen and oxygen are gases at room temp.Introduction to the Periodic Table3. Metalloids/ semimetals: display characteristics of both metals and nonmetals.Only silicon, germanium, arsenic, antimony, and tellurium are in this category

Natural States of the ElementsMost elements are reactive and are not found naturally in pure form

However, there are a few exceptionsNatural States of the ElementsGold, Silver, and Platinum are called Noble Metals because they are relatively unreactive

Group 8 elements are called Noble Gases because they do not combine readily with other elements.He, Ne, Ar, Kr, Xe, RnNatural States of the ElementsDiatomic Molecules: Molecules made up of two atoms. H2, O2, N2, Cl2, F2, Br2, and I2 are diatomic molecules in pure, elemental form.

All the elements of Group 7 are diatomic molecules

Natural States of the ElementsAllotropes: Different forms of elements where there are the same atoms, but they are structured differently.Carbon comes as Diamond, Graphite, and Buckminsterfullerene.

Ions and Their CompoundsIonsIon: An atom or group of atoms that has a positive or negative charge.

Taking a neutral atom and adding or subtracting one or more electrons can result in a charged ion.IonsPositive ions are called Cations.Produced when an electron is lost from a neutral atom.Mg2+ and Na+ are examples of cations.

Magnesium normally has 12 protons and 12 electrons, but when 2 electrons are lost it becomes a cation with a 2+ charge.

IonsNegative ions are called Anions.Produced when an electron is gained to a neutral atom.Cl- and O2- are examples of anions

Chlorine normally has 17 protons and 17 electrons, but when it gains an electron it becomes an anion with a 1- charge.IonsIndividual atoms that have lost or gained electrons are called Monatomic ions

Na+ 11 protons, 10 electrons

O2- 8 protons, 10 electrons

Al3+ 13 protons, 10electronsIonsGroups 1A- 3A form positive ions with a charge equal to the group number of the metal

1A Na 1 electron lost Na +2A Ca 2 electrons lost Ca2+3A Al 3 electrons lost Al3+IonsNonmetals often form ion with a negative charge equal to 8-(group #) of the element.

5A N 8-5= 3 electrons gained N3-6A S 8-6= 2 electrons gained S2-7A B 8-7= 1 electron gained B-IonsThere is no easily predictable pattern for determining charges on transition metals

Many of them also form several different ions

Iron can be Fe2+ or Fe3+IonsPolyatomic ions contain two or more atoms with the resulting compound having an electric charge.

NH4+ Four hydrogen atoms surround a nitrogen atom, and the group has a 1+ charge.Compounds That Contain IonsMany chemical compounds contain ions.We know this because electric currents can run through them.

Substances can only conduct electric current if the ions can move freely

Salt water has ions, however pure salt and pure water cannot conduct electricity.Compounds That Contain IonsIonic Compounds: A compound that results when a metal reacts with a nonmetal to form cations and anions.The result must have a net charge of zero.

1. Both positive and negative ions must be present.2. The numbers of cations and anions must be such that the net charge is zero.Compounds That Contain IonsNa+ + Cl- = NaCl

Mg2+ + Cl- = MgCl2

Li+ + N3- = Li3N