Chapter 8 - Atoms and Periodic Properties

Will turn to a study of the properties of matter why materials have certain properties

chemistry - composition, structure and properties of substances and thetransformations they undergo

consider world - many objects with many propertiestrees bark, leaves, woodcar wheels, dash, hood

all substances made of combinations only

about 113 known elements

element - pure substance that cannot be decomposed into simpler substances by a chemical or physical process

well-defined properties

Water - H2O

Salt - NaCl

Periodic Table - lists all known elements

currently about 108 known elements

88 naturally occurring

others made in lab

Some substances known for long timehow to describe?

alchemists - “lead into gold”

antimony Sbconfusing

STANDARDIZATION - modern symbols

used world-wide now

how did we get these symbols?

+

HgAgAuNaFeSnPb

H HeC ClB BeO OsP PtS SeN Ni

Where do the names come from?

Pu Es AmU Fm FrHg Md EuNp Bh Cf

Cl - light greenTc - artificialNe - newHe - sunTe - Earth

Elements named after planets, people, places and descriptions!

Names passed by international council“Commission on the Nomenclature

of Inorganic Chemistry”

Names agreed upon worldwide standardized

Elements made up of large collection of atoms

Atom - smallest unit with the same chemical

identity as element (10-10 m, 10-24 g) chemical identity - physical and chemical

properties of a pure substance

structure of the atom: protons, neutrons, and electrons

+

-

+ ++

+

-

-

-

-

protonpositive chargestrong nuclear force

electron - negative charge (same as proton)-swarm around nucleus (electron cloud)-can be attracted away or added w/o chemical change -very light 1/1837 mass of proton (negligible)

neutronno chargesame mass as protondoes not affect chemical identity

NUCLEUS - fixed central part of atom

contains:

these are also called

nucleons-reside in nucleus

neutral atom-same number of p+ as e- (zero net charge)remember ion: atom with net charge

How to determine atomic structure

History: Ancient Greeks

Democritus-matter is discontinuous

cannot divide indefinitely

“atom” - Greek for uncuttable

Aristotle & Plato disagreed with this view

(wrongly) thought matter was continuous

John Dalton (1800’s) revisited idea of Atoms

1. All matter = indivisible atoms

2. An element is made up of identical atoms

3. Different elements have atoms with different masses

4. Chemical compounds are made of atoms in specific integer ratios

5. Atoms are neither created nor destroyed in chemical reactions

Dalton’s Atomic Theory

MODERN IDEAS – discoveries leading to atomic structure – indirect observations

J.J Thompson (late 1800’s) – discovery of electrons

cathode ray tubes – eject particles from plates

-cathode rays found to be negative

(opposites attract-not light)

-deflect in magnetic field (current-moving charge)

- measured charge-to-mass ratio

(crossed electric&magnetic fields)

Robert Millikan (1906) Oil drop experiment-charged oil drops in electric field-electric force opposed gravity – drop floats-droplet charge in multiples

of electron charge qe=1.6x10-19 C-found electron mass by using q/m from Millikan

me=9.11x10-31 kg very very small

Early model of the atom

Plum pudding modelElectrons embedded in blob of positively charged matter like “raisins in plum pudding”

But what is the positive charge that cancels tiny electrons?

Rutherford –alpha particle positive helium nucleus scattering- shoot alpha particle at gold sheet

Result : -most of the alpha particles passed through sheet -some alpha particles back-scattered

Conclusion: -atom contains small central part most of mass nucleus -electrons orbit at distance 100,000

times the size of the nucleus

the atom is mostly made up of EMPTY SPACE

Nucleus later found to be made of protons (Rutherford split nucleus) and neutrons (Chadwick-1932)

Describing the Modern Atom

atomic number – number of protons in nucleus-describes identity of element

-neutral atom number of e- = number of p+

mass number – number of protons and neutrons in nucleusindicates mass since the electrons are negligible

new mass scale – STANDARDIZEatomic mass units (amu, dalton) 1 amu is about mass of a proton

amu defined by mass of carbon-12:carbon 12: 6 protons and 6 neutrons

define to have mass of exactly 12 amuATOMIC MASS STANDARD

But mass number does not define elementcan have different numbers of neutrons

For example: Lithium

++ +

ATOMIC NUMBER: 3 3 3

MASS NUMBER: 3 amu 4 amu 5 amu

Li+

+ ++

+ +

Isotope: elements with the same number of protons, but different numbers of neutron – different mass numbers

How do we study isotopes?

Mass Spectrometer

oven

N SIons accelerated in electric field

Curve of ions depends on the charge-to-mass ratio-isotopes have different masses

Each isotope will form a spotAt different places on the screen

Natural Abundance-what percentage of each isotope exists for each element

Mass number –refers a particular isotope - specific atoms

Atomic Weight (Mass) – weighted average of the masses for different isotopes in a sample of an element for the element in general (all isotopes)

Notation: describes atomic structure: for an isotopenumber of protons, neutrons and electrons

11278Pt

mass number

atomic number

Means atomic number=78 and mass number =112 amu

Atomic structure-protons: 78electrons: 78 neutralneutrons: 112-78=34Example:

3517Cl

An important isotope : H lightest element

H D Thydrogen deuterium tritium

11H 2

1H 31H

normal heavy radioactivehydrogen hydrogenhydrogen-1 hydrogen-2 hydrogen-3

Natural 99.98% 0.015% < 0.005%Abundance

atomic weight: 1.008 amu

Remember atomic model: SOLAR SYSTEM MODEL

massive nucleus surrounded by electronsproblem: electron circles atom -

centripetal acceleration classical charge radiates if acceleratedloses energy e- falls into nucleus

New Theory needed -- F=ma didn’t workPlanck & Einstein :

matter absorbs discrete amounts of energyQUANTA

BOHR MODEL: tried to match experiments involving

absorption and emmision of light from hot solids

and gases - line spectra

not derived but phenomenological

Bohr’s Theory:

1. Electrons orbit the nucleus at

specific distances from the nucleus

-allowed orbits

2. Electrons in allowed orbits

do not radiate energy

-contrary to classical theory

3. Electrons gain energy by “jumping” to

a higher energy (further) orbit

-lose energy by falling to a lower energy

-energy loss or gain in

the form of a photon- particle of light

“Qnantum Leap”

n=1n=2

n=3

Explained line spectra - electrons in matter gain (absorb) or lose (emit) photons to make

quantum leaps

Wave-Particle duality : light travels like particles and waves

de Broglie : matter also travels like waveselectrons travel like waves

-normal objects have very small wavelength-electron motion governed by wave properties

STANDING WAVESOLUTION

Only certain wavelengths (energies) will fit correctly around nucleus

ALLOWED ORBITS

Led to the development of QUANTUM MECHANIC THEORY

Schrodinger Equation-solve with linear algebra and differential equations

Solution: electron orbital - 3D region surrounding nucleus where there is the greatest probability of finding an electron

Consequences of quantum mechanics

PROBABILITY DENSITY - probality at a particular position

Cannot isolate position of an electronHEISENBERG UNCERTAINTY PRINCIPLE

cannot measure momentum (motion) and position of electron exactly

Solution gives energy levels of electrons surrounding nucleus -gives electron configuration

-the arrangement of electrons in orbitals and suborbitals about the nucleus of an atom -describes properties of atom

“fingers of the atom” interact through electrons

SOLUTION TO WAVE EQUATION GIVES QUANTUM NUMBERS

-describe energies of the electrons-determine properties of electrons in atom-gives framework to “build” atoms-similar electron configuration gives similar properties-restrictions on what numbers can be

QUANTUM NUMBERS - n,m,l,sdescribe energy levels of electrons

Principal Quantum Number ( n ) main energy level of electron

-describes orbit-how far electron is from nucleus-similar to allowed Bohr orbit-restriction: whole number

greater than 0n=1,2,3,4,…

closest furthest

n=1n=2

n=3

Angular Momentum Quantum Number ( l ) shape of electron orbit

-how spread out the orbital is-restriction: l= 0 to (n-1)

l = 0sphere

l = 1hourglass

Magnetic Quantum Number ( m ) orientation of electron orbital

-the way the electrons are oriented about nucleus-restriction: -l > m > +l

Example : n=2 electronsl=0 electrons have possible m=0

only one wayto orient sphere

l=1 electrons have possible m= -1, 0, +1

oriented in y-dir m=-1

oriented in x-dir m=+1

oriented in z-dir m=0

n, l, m describe spatial properties of electronhow the electron cloud looks

each quantum number describes electron with specific energy in nucleus!

Spin Quantun Number (s) magnetic properties of the electron

electron - electric chargespin clockwise spin counterclockwise

spin up spin down

electron magnets interact with magnetic fieldsplit into two beams in magnet

- restriction s = +1/.2, -1/2

ELECTRON CONFIGURATION determined by the values of quantum numbers n, l, m, s

“fingers of the atom” how the electrons interact with their environment

PHYSICAL AND CHEMICAL PROPERTIES(CHEMICAL IDENTITY)

-- -- -- -

-S

N

N

S

CAN NOW BUILD ATOMS

Need some rules before building electron configurations

Electrically neutral atoms - same number of e- as p+have no net charge

Ground state atom - electrons occupy only the lowest

energy levels in atom

as opposed to excited state - electrons occupy higher energy states

lower energies unoccupied

Will add electrons up to atomic number-but how do we add electrons?

TWO WAYS TO ADD PARTICLES:1. Put all electrons in lowest energy level

{n=1, l=0, m=0, s=1/2} cannot do for e- only for BOSONS (photons)

2. Pauli Exclusion Principle: no two electrons in the same atom can have the same set of

quantum numbers n, l, m, s

Law of nature for fermions (spin=1/2)

BUILD TABLE OF ELEMENTSFirst note: for the spatial orbital

n, l, m describe position in spacetwo values of s for each nlm combination

Start building - add electrons successively to each lowest energy orbital

H : atomic number = 1 one electronput electron in lowest energy

Electron configuration:n=1, l=0, m=0, s=1/2

He : atomic number = 2 two electrons Electron configuration:

n=1, l=0, m=0, s=1/2 still lowestn=1, l=0, m=0, s=-1/2 -different atom

just change to s=-1/2 (next energy)

LI : atomic number = 3 three electrons Electron configuration:

n=1, l=0, m=0, s=1/2n=1, l=0, m=0, s=-1/2 n=1 full, next n=2 n=2, l=0, m=0, s=1/2 electron capacity

Be to Ne are filled by adding two e- to each n, l, m

Electron capacity - maximum number of electrons that can be added to each orbital

Connections to Periodic TableNote: row (period) determined by highest

principal quantum number

electron capacity met at end of row: NOBLE GASES

outer shell not full - chemically reactive outer shell full - no electrons to interact

with other elements chemically inert NOBLE GAS

INERT GAS

get to next element by adding electron to next level in orbital up to electron capacity

Electron properties determined by principle (n) and angular momentum (l) Q.N

Electron orbital notation:specify n, l, and number of electrons

in the orbital (superscript)electron capacity

s orbital l =0 2p orbital l =1 6 electronsd orbital l =2 10 allowed in thef orbital l =3 14 orbital

Example : 3d2 n=3, l =2, 2 e- in orbital

Rewrite electron configuration in new notation

H Li Na KBe Mg CaB AlC SiN PO SF Cl

He Ne Ar

Sc next: things are different, but first

Periodic (Moseley’s) Law - electron configurations repeatproperties of elements repeat when ordered by increasing atomic number

periodic function of atomic number similar outer shell, similar properties

First column : Alkali metals s1 orbitalvery reactive - single electron

Second column: Alkaline Earth Metals s2 orbital

Last column : (Inert) Noble Gases s2p6 (s2 for He) very stable - octet (eight outer e- except He)

Electron configuration repeats, chemical properties repeat

Led to Periodic Table

Mendelev thought to be the father of the Periodic Table

Periodic Table – table of all know elements listed in order of atomic number

-periodicity in properties along rows (density, melting/boiling, hardness, etc)

DIVIDED INTO:Families (Groups) – vertical column of elements

these elements exhibit similar properties have same outer electron configuration

Eight main groups : Group IA to Group VIIIA MAIN GROUP or REPRESENTATIVE GROUPS

show similarities in outer e- shell ( want octet )

Group IA – Alkali Metals (react violently w/H2O) s1

never uncombined in nature

Group IIA – Alkaline Earth Metals (also reactive) s2

Group IIIA s2p1

Group IVA s2p2

Group VA s2p3

Group VIA s2p4

Group VIIA –Halogens (salt former w/metal) s2p5

Group VIIIA - Noble (Rare)Gasses s2p6

never bond with others

explains Periodic Law{

Periods – row groupings of the Periodic Tableproperties repeat as you go from one period to the next -periods begin reactive (IA) and end stable (VIIIA)

Transition Metals – B groups

Group IB to Group VIIB

fill inner electron orbitals

like Sc: 1s22s22p63s23p64s23d1 skips energy

change in orbital energies

higher orbitals have lower energy

i.e., 4s is lower than 3d

shows gap in periodic table

electron energy level order:

1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p6f7dincreasing energy

can write any electron configuration

Example 1. Write configuration for:

Zr

V

Example 2. Identify element electron configuration

1s22s22p63s23p64s23d7

1s22s22p63s23p4

Note: Period and Group of element identified propertiesHistorically: some elements undiscovered-

chemists knew properties before it even existed

How to read Periodic Table

Magnesium12Mg

24.31

Name Group II (family): 2 e-Atomic number group: # of outer e-SymbolAtomic weight Period 4

Electron dot notationKERNEL – nucleus and inner electrons

-dots represent the outermost electrons-shows what’s available for the other

atoms to interact withC group IV 4 outer electrons

Metals non-metals and semiconductors (semimetals)

METALS- conducts heat and electricity- metallic luster (shiny)- maleable pond into sheets- ductile draw into wires (extrusion) -form positive ions by losing electronsLi 1s22s1 Li+ stable [He] config

Mg 1s22s22p63s2 Mg+2 stable [Ne] octet

NONMETALS- insulators - dull appearance - brittle - form negative ions to complete octet

Cl 1s22s22p63s23p5+1 Cl- stable [Ar] config

XX