Atoms and the Atoms and the Periodic TablePeriodic Table

Atomic ModelsAtomic Models

Democritus (4Democritus (4thth century B.C.) century B.C.) thought all matter was made of thought all matter was made of particles he called the atomparticles he called the atom

Theory was modified when Theory was modified when subatomic particles were subatomic particles were discovereddiscovered

Atomic ModelsAtomic Models

Plum Pudding Model Plum Pudding Model (1904) developed (1904) developed by J.J. Thomsonby J.J. Thomson

Planetary Model Planetary Model (1911) developed by (1911) developed by Ernest Rutherford Ernest Rutherford

Newer ModelsNewer Models

Bohr’s Model (1913)Bohr’s Model (1913) Developed by Developed by Niels BohrNiels Bohr

Electron Cloud Electron Cloud Model (1925) Model (1925)

Protons (pProtons (p++))

Positively charged particles found Positively charged particles found in nucleus of atomin nucleus of atom

Have an electrical charge of +1Have an electrical charge of +1 Mass of 1 a.m.u.Mass of 1 a.m.u. Composed of quarksComposed of quarks Discovered by Ernest Rutherford Discovered by Ernest Rutherford

using Gold Foil Experiment using Gold Foil Experiment

ProtonsProtons The number of protons in an atom The number of protons in an atom

determines its identity determines its identity

All oxygen atoms have 8 protons, all All oxygen atoms have 8 protons, all uranium atoms have 92 protonsuranium atoms have 92 protons

If the number of protons change the If the number of protons change the identity of the atom changes.identity of the atom changes.

Neutrons (nNeutrons (n00))

Neutral particles found in nucleus Neutral particles found in nucleus of atomof atom

Have no electrical chargeHave no electrical charge Mass of 1 a.m.u.Mass of 1 a.m.u. Composed of quarksComposed of quarks Discovered by James ChadwickDiscovered by James Chadwick

NucleusNucleus

The nucleus is the positively charged The nucleus is the positively charged dense core in the center of the atomdense core in the center of the atom

Houses protons and neutronsHouses protons and neutrons Contains 99.9% of mass of atomContains 99.9% of mass of atom Extremely small compared to the Extremely small compared to the

entire size of the atom entire size of the atom

Electrons (eElectrons (e--))

Negatively charged particles found in Negatively charged particles found in electron cloudelectron cloud

Have an electrical charge of -1Have an electrical charge of -1 Constantly moving around outside Constantly moving around outside

nucleusnucleus Have essentially no massHave essentially no mass Discovered by J.J. Thomson during Discovered by J.J. Thomson during

cathode ray experimentcathode ray experiment

ElectronsElectrons

The number of electrons in a neutral The number of electrons in a neutral atom is equal to the number of atom is equal to the number of protonsprotons

Neutral oxygen has 8 protons, Neutral oxygen has 8 protons, therefore it has 8 electronstherefore it has 8 electrons

Neutral lead has 82 protons, therefore, Neutral lead has 82 protons, therefore, it has 82 electronsit has 82 electrons

Valence ElectronsValence Electrons

Electrons in the outermost energy Electrons in the outermost energy level of an atom are called valence level of an atom are called valence electronselectrons

These are the electrons furthest from These are the electrons furthest from the nucleusthe nucleus

SymbolsSymbols

Elements are identified by their Elements are identified by their chemical symbolschemical symbols

Symbols are usually either one capital Symbols are usually either one capital letter like C for Carbon, or one capital letter like C for Carbon, or one capital and one lowercase letter like Ne for and one lowercase letter like Ne for NeonNeon

Atomic Number (Z)Atomic Number (Z)

Whole number shown on periodic tableWhole number shown on periodic table Periodic table is arranged by atomic Periodic table is arranged by atomic

numbernumber

Atomic Number = # of Atomic Number = # of ProtonsProtons

*Also gives the number of *Also gives the number of electrons if the atom is neutral electrons if the atom is neutral

Atomic NumberAtomic Number

Mass Number (A)Mass Number (A)

The mass number is the sum of the total The mass number is the sum of the total number of protons and neutrons in the number of protons and neutrons in the atomatom

Mass # = # pMass # = # p++ + # n + # n00

The mass number is not found The mass number is not found on the Periodic Tablwon the Periodic Tablw

IsotopesIsotopes

Isotopes are atoms of the same Isotopes are atoms of the same element that have different numbers element that have different numbers of neutronsof neutrons

All atoms are isotopesAll atoms are isotopes

Each element has isotopes that are Each element has isotopes that are more common than othersmore common than others

Nuclear SymbolNuclear Symbol

Isotopes can be designated with their Isotopes can be designated with their nuclear symbolnuclear symbol

Hyphen NotationHyphen Notation

Isotopes can also be designated using Isotopes can also be designated using hyphen notationhyphen notation

Carbon-16Carbon-16

Element Name Mass Number

Write the Nuclear Symbol and Hyphen Write the Nuclear Symbol and Hyphen Notation for the Following IsotopesNotation for the Following Isotopes

Lithium isotope with 3 protons and 4 Lithium isotope with 3 protons and 4 neutronsneutrons

Sulfur isotope with 17 neutronsSulfur isotope with 17 neutrons

Lead with 122 neutronsLead with 122 neutrons

IonsIons

Ions are atoms or groups of atoms Ions are atoms or groups of atoms that have a net positive or negative that have a net positive or negative chargecharge

The charge results from an unequal The charge results from an unequal number of electrons and protons number of electrons and protons within atom of group of atomswithin atom of group of atoms

Ions Ions

AnionsAnions Ions with more electrons than Ions with more electrons than protons resulting in a negative chargeprotons resulting in a negative charge For each extra electron the negative charge For each extra electron the negative charge

increases by oneincreases by one

CationsCations Ions with less electrons than Ions with less electrons than protons resulting in a positive chargeprotons resulting in a positive charge For each missing electron the positive charge For each missing electron the positive charge

increases by oneincreases by one

Ions Ions

Ions are symbolized with a positive or Ions are symbolized with a positive or negative sign on the upper right side negative sign on the upper right side and number equal to the magnitude of and number equal to the magnitude of the chargethe charge

The number one is not included The number one is not included

-2OMagnitude

Charge

Ions Ions

FF-- 9 protons – 10 electrons = -1 charge 9 protons – 10 electrons = -1 charge

CaCa2+2+ 20 protons – 18 electrons = -2 20 protons – 18 electrons = -2 chargecharge

PP3-3- 15 protons – 18 electrons = -3 15 protons – 18 electrons = -3 chargecharge

Common Ions (Need to Common Ions (Need to memorize these) memorize these)

Column 1 (Li, Na, K, Rb, Cs): +1Column 1 (Li, Na, K, Rb, Cs): +1 Column 2 (Be, Mg, Ca, Sr, Ba): +2Column 2 (Be, Mg, Ca, Sr, Ba): +2 Column 13 (Al, Ga): +3Column 13 (Al, Ga): +3 Column 15 (N, P, As): -3Column 15 (N, P, As): -3 Column 16 (O, S, Se, Te): -2Column 16 (O, S, Se, Te): -2 Column 17 (F, Cl, Br, I): -1Column 17 (F, Cl, Br, I): -1

Average Atomic MassAverage Atomic Mass

The weighted average of The weighted average of the naturally occurring the naturally occurring isotopes of an element.isotopes of an element.

Found by averaging the Found by averaging the natural abundances of natural abundances of its isotopes its isotopes

Calculating Average Calculating Average Atomic Mass (amu)Atomic Mass (amu)

If abundance is given as percent If abundance is given as percent value:value:

If abundance is given as decimal If abundance is given as decimal value:value:

100

abundance) Isotope)(% of (Mass Mass Atomic

bundance)Isotope)(a of (Mass Mass Atomic

Average Atomic Mass Average Atomic Mass

Rubidium has two common isotopes, Rb-85 and Rb-87. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

amu 865.85100

)]8.27)(87[()]2.72)(85[(

Uranium has three common isotopes. If the abundance of 234U is 0.0001, the abundance of 235U is 0.0071, and the abundance of 238U is .9928, what is the average atomic mass of uranium?

amu 23897.238)]9928.238()0071.235()0001.234[(

Columbic AttractionColumbic Attraction

The attraction between oppositely The attraction between oppositely charged particlescharged particles

The greater the distance between the The greater the distance between the particles the weaker the attractionparticles the weaker the attraction

Columbic Attraction in Columbic Attraction in the Atomthe Atom

The electrons in the atom are attracted to The electrons in the atom are attracted to the protonsthe protons

Electrons closest to the nucleus feel a Electrons closest to the nucleus feel a stronger attraction force than electrons on stronger attraction force than electrons on the outermost energy levelthe outermost energy level

As you move in a row from left to right on As you move in a row from left to right on the Periodic Table the number of protons in the Periodic Table the number of protons in an atom increases and so the attractive an atom increases and so the attractive force on the outermost electrons increasesforce on the outermost electrons increases

Bohr Model of the AtomBohr Model of the Atom

Niels Bohr found that electrons occupy Niels Bohr found that electrons occupy distinct energy levels within the atomdistinct energy levels within the atom

Orbital DiagramsOrbital Diagrams

Represent the electrons within energy Represent the electrons within energy levels and sublevels using arrowslevels and sublevels using arrows

Orbital DiagramsOrbital Diagrams

Pauli Exclusion PrinciplePauli Exclusion Principle

Each sublevel can hold TWO electrons Each sublevel can hold TWO electrons

with opposite spins.with opposite spins.

Sub levelsSub levels

Each energy level has Each energy level has a different amount a different amount of sublevelsof sublevels

11ss

2 2 s, p s, p

33 s, p, d s, p, d

44 s, p, d, f s, p, d, f

55 s, p, d, f s, p, d, f

s has 1 sublevel s has 1 sublevel 2 e2 e--

p has 3 sublevels p has 3 sublevels 6 e6 e--

d has 5 sublevels d has 5 sublevels 10 e10 e--

f has 7 sublevels f has 7 sublevels 14 e14 e--

Orbital DiagramsOrbital Diagrams

Aufbau PrincipleAufbau Principle

Electrons fill the Electrons fill the lowest energy lowest energy level first.level first.

1s, 2s, 2p, 3s, 3p, 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 4d, 5p, 6s, 4f, 5d, 6p5d, 6p

RIGHTWRONG

Orbital DiagramsOrbital Diagrams

Hund’s RuleHund’s Rule Within a sublevel, place one eWithin a sublevel, place one e-- per orbital per orbital

before pairing them.before pairing them.

The last energy level being filled may not be The last energy level being filled may not be completely filled with arrowscompletely filled with arrows

FluorineFluorine

Germanium Germanium

B. NotationB. Notation

Electron ConfigurationElectron Configuration

An electron configuration is a shorthand An electron configuration is a shorthand description of how electrons are arranged description of how electrons are arranged around the nucleus of an atom. around the nucleus of an atom.

Electrons within each energy level and sub Electrons within each energy level and sub

level are represented with numbers in super level are represented with numbers in super

script rather than arrowsscript rather than arrows

S 16e-

Valence Electrons

Core Electrons

1s2 2s2 2p6 3s2 3p4

Electron ConfigurationElectron Configuration

Longhand ConfigurationLonghand Configuration

Electron Configuration ExceptionsElectron Configuration Exceptions ChromiumChromium

EXPECTEXPECT:: [Ar] 4s[Ar] 4s22 3d 3d44

ACTUALLYACTUALLY:: [Ar] 4s[Ar] 4s11 3d 3d55

Chromium gains Chromium gains stabilitystability with a half-full d- with a half-full d-sublevel.sublevel.

D. StabilityD. Stability

D. Lewis DiagramsD. Lewis Diagrams

Also called Also called electron dot diagramselectron dot diagrams Dots represent the valence eDots represent the valence e--

ExEx: Sodium: Sodium ExEx: Chlorine: Chlorine

Lewis Diagram for Oxygen

Steps to Draw Lewis Steps to Draw Lewis StructuresStructures

1.1. Determine how many valence are in the element.Determine how many valence are in the element.

2.2. Staring on the Right side of the element draw a Staring on the Right side of the element draw a dot to represent a valence electron.dot to represent a valence electron.

3.3. Place one dot on each side of the symbol. One Place one dot on each side of the symbol. One electron must be drawn around each side of the electron must be drawn around each side of the element before a second electron can be added element before a second electron can be added to any side.to any side.

Steps to Draw Lewis Steps to Draw Lewis StructuresStructures