UNIT 2UNIT 2Atomic StructureAtomic Structure

andandThe Periodic TableThe Periodic Table

(Chapters 4,5,6)(Chapters 4,5,6)

The smallest particle of an The smallest particle of an element that retains the element that retains the properties of that element.properties of that element.

Atoms consist of electrons, protons and neutrons.

These are called subatomic particles.

Sub Atomic ParticlesSub Atomic ParticlesElectronsElectrons (e-):(e-): negatively charged revolve around the nucleus in

electron cloudsmass much less than protons or

neutrons (mass = 0 a.m.u)Up to 2 electrons on 1st energy

level, up to 8 on each level after 1st.

Protons (p+): positive charge inside the nucleus Mass equals 1 a.m.uMass is 1840 times more than e- Neutrons (nNeutrons (n00):):Neutral (no) chargeNeutral (no) chargeinside the nucleus mass equals 1 a.m.u.

Central core of atomCentral core of atom Composed of Composed of protons and neutronsTiny (compared to atom as a whole)Very DenseContains most of the atoms mass

NucleusNucleus

ATOMIC NUMBERATOMIC NUMBERNumber of protons (p+) in the nucleusNumber of protons (p+) in the nucleus p+ = e- p+ = e- (in a neutral atom)(in a neutral atom) Each element contains a different # of Each element contains a different # of

protons (what makes each element protons (what makes each element different)different)

““the element’s address on the the element’s address on the periodic table”periodic table”

MASS NUMBERMASS NUMBER Total number of protons & neutrons in Total number of protons & neutrons in

an atoman atom nn00 + p + p++ = Mass # = Mass # Remember (atomic # = # of p+)Remember (atomic # = # of p+) Mass # - atomic # = nMass # - atomic # = n00

ISOTOPESISOTOPESAtoms of the same element that have:

• same number of protons

• different number of neutrons

• different masses

Atomic #

Mass #Chemical Symbol

How many neutrons does this atom have?How many neutrons does this atom have?

NOTE: Some periodic tables list the mass # on top and atomic # on the bottom while other periodic tables do the reverse. Remember, the smaller of the two numbers is always the atomic number!!

For about 50 years past the time of John Dalton, the atom was considered a solid indivisible mass. The later discovery of subatomic particles shattered this theory.

Dalton’s Atomic TheoryDalton’s Atomic Theory1. Elements are composed of tiny particles

called atomsatoms.2. Atoms of the same element are identical.

Different elements have different atoms.3. Atoms of different elements can

physically or chemically combine.4. Chemical Reactions (RXNs) occur when

atoms are separated, joined, or rearranged.

5. Atoms of one element never change into atoms of another element as a result of a chemical reaction.

He discovered the electron and proposed the plum-pudding model of the atom. This model said nothing about the number of protons and neutrons.

He discovered the nucleus and proposed a nuclear atom in which electrons surround a dense nucleus. He thought of the rest of the atom as empty space.

He had nothing to do with discovering a model of the atom but really likes teaching chemistry. (Just checking to see if you are paying attention!)

A student of Rutherford’s, he proposed that electrons are arranged in orbits around the nucleus. He explained that the electrons do not fall into the nucleus because they have fixed energy levels.

Development of Periodic Development of Periodic TableTable

70 elements known by 1800s70 elements known by 1800sDmitri Mendeleev discovered a Dmitri Mendeleev discovered a

way to systematically & logically way to systematically & logically group elementsgroup elements

What are some ways elements What are some ways elements are grouped?are grouped?

Mendeleev’s WorkMendeleev’s Work Arranged Arranged Elements in columnsElements in columns, so , so

elements w/ elements w/ similar properties were side similar properties were side by sideby side

Arranged in columns of Arranged in columns of increasing Atomic increasing Atomic MassMass

Left blank spacesLeft blank spaces in table because there in table because there were no known elements w/ the correct were no known elements w/ the correct properties and mass for that space.properties and mass for that space.

Moseley’s Periodic Table Moseley’s Periodic Table CorrectionsCorrections

Put table Put table according to atomic numberaccording to atomic number instead of atomic massinstead of atomic mass

PERIODIC LAWPERIODIC LAW

1)1) Elements arranged in order of Elements arranged in order of increasing atomic numberincreasing atomic number

2)2) Periodic Periodic Repetition ofRepetition of physical & physical & chemical chemical propertiesproperties

3)3) Elements with Elements with same properties in same properties in columnscolumns

Modern Periodic TableModern Periodic Table PeriodsPeriods – – horizontal rows horizontal rows going going

acrossacross the periodic table the periodic table 7 periods (each has its own energy 7 periods (each has its own energy

level)level) Properties of elements change as you Properties of elements change as you

move acrossmove across Pattern of properties repeats when Pattern of properties repeats when

you move from one period to the next.you move from one period to the next.

Groups/FamiliesGroups/Families–– elements in the elements in the periodic table periodic table going downgoing down in columns. in columns.

SimilarSimilar chemical & physical chemical & physical propertiesproperties

Classified by number and/or letterClassified by number and/or letter Ex: 1A, 2A, 3A…Ex: 1A, 2A, 3A…

Representative ElementsRepresentative Elements = = Group AGroup ATransition MetalsTransition Metals = Group B = Group B

METALSMETALS

a)a) Left side of periodic table (except H)Left side of periodic table (except H)b)b) High electrical conductivityHigh electrical conductivityc)c) High Luster (very shiny when clean)High Luster (very shiny when clean)d)d) Ductile (drawn into wires)Ductile (drawn into wires)e)e) Solid @ room temperature (except Solid @ room temperature (except

Hg)Hg)

1)1) Alkali Metals: Alkali Metals: Group 1A (not H)Group 1A (not H) Very ReactiveVery Reactive

2)2) Alkaline Earth Metals:Alkaline Earth Metals: Group 2A Group 2A3)3) Transition Metals: Transition Metals: Group B Group B

Middle of the periodic tableMiddle of the periodic table

NON-METALSNON-METALS

a)a) Upper right corner of periodic tableUpper right corner of periodic tableb)b) Non-lustrous (not shiny)Non-lustrous (not shiny)c)c) Poor conductors of electricityPoor conductors of electricityd)d) Some are gases at room temp.(O,N) Some are gases at room temp.(O,N)

--others --others brittle solids (S)brittle solids (S)

1)1) Halogens – Halogens – group 7Agroup 7A1)1) Very ReactiveVery Reactive2)2) 7 e- on outer energy level7 e- on outer energy level

2)2) Noble Gases -- Noble Gases -- group 8A group 8A1)1) Unreactive – Unreactive – Few to no chemical Few to no chemical

RXNsRXNs2)2) Full outer energy level Full outer energy level

Semi-Metals (metalloids)Semi-Metals (metalloids) Divides metals from nonmetalsDivides metals from nonmetals properties intermediate between metals properties intermediate between metals

and nonmetalsand nonmetals Ex: Si, Ge, ...Ex: Si, Ge, ... ““stair case”stair case” on right on right Side of periodic tableSide of periodic table

The Modern AtomThe Modern Atom Quantum Mechanical Model:Quantum Mechanical Model:The Energy level of an electron is

the region around the nucleus where the electron is likely to be moving.

Each period has its own principle energy level

principle energy levels are assigned values in order of increasing energy: n = 1, 2, 3, 4, and so forth

One Important RuleOne Important Rule Aufbau PrincipleAufbau Principle:: Electrons enter

orbitals of lowest energy first.

Energy SublevelsEnergy Sublevelseach principal energy level has

energy sublevels.sublevels are called atomic orbitals

and are represented by the letters: s, p, d, f.

n =1

n = 2

n = 3

n = 4

1

2

3

4

s

s, p

s, p, d

s, p, d, f

Principle Principle NRG LevelNRG Level

Number of Number of SublevelsSublevels

Orbital Orbital TypesTypes

An s orbital can contain 2 electrons.

A p orbital can contain 6 electrons

A d orbital can contain 10 electrons.

A f orbital can contain 14 electrons.

Each sub-orbital can hold a different number of electrons

s pd

f

3 QUESTIONS TO ASK3 QUESTIONS TO ASKWhat Row? What Row?

(principle energy level)(principle energy level)What section? What section?

(type of sub-orbital)(type of sub-orbital)What seat? What seat?

(how many electrons in that (how many electrons in that sub-sub-orbital)orbital)

Example 1:Write the electron configuration for nitrogen.

7N 1s22s22p3

Example 2:Write the electron configuration for Fe.

26Fe 1s22s22p63s23p64s23d6

s pd

f

S orbitalsS orbitals Starts in 1Starts in 1stst NRG level NRG level 1 orbital per energy level1 orbital per energy level Each can contain up to 2 electronsEach can contain up to 2 electrons Alkali and Alkaline Earth metalsAlkali and Alkaline Earth metals Spherical in natureSpherical in nature

P orbitalsP orbitals Starts in 2Starts in 2ndnd NRG level NRG level 3 orbitals per NRG level3 orbitals per NRG level Each orbital can contain up to 2 e- Each orbital can contain up to 2 e-

(6 e- total per sublevel)(6 e- total per sublevel) Groups 3A – 8AGroups 3A – 8A Dumbbell shapedDumbbell shaped

D orbitalsD orbitals Starts at 3Starts at 3rdrd NRG level NRG level 5 orbitals per NRG level5 orbitals per NRG level 2 e- per orbital (10 total e- per 2 e- per orbital (10 total e- per

sublevel)sublevel) Clover shapeClover shape Transition MetalsTransition Metals

F orbitalsF orbitals Starts in 4Starts in 4thth NRG level NRG level 7 orbitals per NRG level7 orbitals per NRG level 2 e- per orbital (14 e- total per 2 e- per orbital (14 e- total per

sublevel)sublevel) Complicated, unexplainable shapeComplicated, unexplainable shape LanthanideLanthanide & & ActinideActinide series series

2 Important Rules2 Important RulesPauli Exclusion Principle: An

atomic orbital may contain a maximum of two electrons. The electrons must have opposite spins.

Hund’s Rule: When electrons occupy orbitals of equal energy, one electron enters each orbital before they pair.

For Example:

2s 2p

After the s sublevel gets two electrons, three electrons enter the p orbitals before they pair.

What do we know about the table so far?

Trends in Atomic SizeTrends in Atomic Size radius of an atom cannot be

measured directly atomic radius is estimated as half of

the distance between the nuclei of two like atoms in a diatomic molecule.

Atomic size generally increases as you move down a group of the periodic table.More principal energy levels are added.

Atomic size generally decreases as you move from left to right across a period.

Increasing Nuclear charge pulls electrons in closer to nucleus

Trends in Ionization EnergyTrends in Ionization EnergyWhen an atom gains or loses an

electron, it becomes an ion. Ionization Energy is the amount of

energy required to remove an electron from a neutral atom.

The smaller the atom , the more ionization energy required.

Increases

Dec

reas

es

Trends in Ionic SizeTrends in Ionic SizeNonmetallic elements:

gain electrons to form negative ions. Negative ions (anions) are always

larger than the neutral atoms from which they form.

Metallic elements: lose electrons to form positive ions. Positive ions (cations) are always

smaller than the neutral atoms from which they form.

Trends in ElectronegativityTrends in Electronegativity tendency for an atom to attract

electrons when it is chemically combined with another atom.

decreases as you move down a group

increases as you go across a period from left to right.