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 the
transformations they undergo
consider world - many objects with many properties
trees
bark, leaves, wood
car
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 time
how to describe?
alchemists - “lead into gold”
antimony +
Sb
confusing
STANDARDIZATION - modern symbols
used world-wide now
how did we get these symbols?
Hg
Ag
Au
Na
Fe
Sn
Pb
H
C
B
O
P
S
N
He
Cl
Be
Os
Pt
Se
Ni
Where do the names come from?
Pu
U
Hg
Np
Es
Fm
Md
Bh
Cl Tc Ne He Te -
Am
Fr
Eu
Cf
light green
artificial
new
sun
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
NUCLEUS - fixed central
part of atom
- contains:
+ proton
positive charge
+
strong nuclear force
++
neutron
+
no charge
same mass as proton
does not affect
chemical identity
these are also called
nucleons-reside in nucleus
- 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)
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
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All matter = indivisible atoms
An element is made up of identical atoms
Different elements have atoms with different
masses
Chemical compounds are made of atoms in
specific integer ratios
Atoms are neither created nor destroyed in
chemical reactions
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 model
Electrons 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 nucleus
indicates mass since the electrons are negligible
new mass scale – STANDARDIZE
atomic 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 amu
ATOMIC MASS STANDARD
But mass number does not define element
can have different numbers of neutrons
For example: Lithium
Li
+
+ +
+
+ +
+
+ +
ATOMIC NUMBER:
3
3
3
MASS NUMBER:
3 amu
4 amu
5 amu
Isotope: elements with the same number of protons,
but different numbers of neutron – different mass numbers
How do we study isotopes?
Mass Spectrometer
Curve of ions depends on the
charge-to-mass ratio
-isotopes have different masses
N
S
Ions accelerated
in electric field
Each isotope will form a spot
At different places on the screen
oven
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 isotope
number of protons, neutrons and electrons
mass number
112
78Pt
atomic number
Example:
35
17Cl
Means atomic number=78
and mass number =112 amu
Atomic structureprotons: 78
electrons: 78 neutral
neutrons: 112-78=34
An important isotope : H
H
hydrogen
1 H
1
normal
hydrogen
hydrogen-1
lightest element
D
deuterium
2 H
1
heavy
hydrogen
hydrogen-2
T
tritium
3 H
1
radioactive
hydrogen-3
Natural
99.98%
0.015%
Abundance
atomic weight: 1.008 amu
< 0.005%
Remember atomic model: SOLAR SYSTEM MODEL
massive nucleus surrounded by electrons
problem: electron circles atom centripetal acceleration
classical charge radiates if accelerated
loses energy
e- falls into nucleus
New Theory needed -- F=ma didn’t work
Planck & Einstein :
matter absorbs discrete amounts of energy
QUANTA
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
n=1
n=2
2. Electrons in allowed orbits
do not radiate energy
-contrary to classical theory
n=3
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”
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 waves
electrons travel like waves
-normal objects have very small wavelength
-electron motion governed by wave properties
STANDING WAVE
SOLUTION
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
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
PROBABILITY DENSITY - probality at a
particular position
Cannot isolate position of an electron
HEISENBERG UNCERTAINTY PRINCIPLE
cannot measure momentum (motion)
and position of electron exactly
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,s
describe 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 0
n=1,2,3,4,…
closest
n=1
n=2
n=3
furthest
Angular Momentum Quantum Number ( l )
shape of electron orbit
-how spread out the orbital is
-restriction: l= 0 to (n-1)
l=0
sphere
l=1
hourglass
Magnetic Quantum Number ( m )
orientation of electron orbital
-the way the electrons are oriented about nucleus
-restriction: -l > m > +l
Example : n=2 electrons
l=0 electrons have possible m=0
only one way
to 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 electron
how 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 charge
spin clockwise
spin counterclockwise
S
N
-- N
S
spin up
spin down
electron magnets interact with magnetic field
split 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)
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 eonly 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 ELEMENTS
First note:
for the spatial orbital
n, l, m describe position in space
two values of s for each
nlm combination
Start building - add electrons successively to
each lowest energy orbital
H : atomic number = 1
one electron
put 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 lowest
n=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=1/2
n=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 Table
Note:
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
2
p orbital
l =1
6
electrons
d orbital
l =2
10
allowed in the
f orbital
l =3
14
orbital
Example : 3d2
n=3, l =2, 2 e- in orbital
Rewrite electron configuration in new notation
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc next: things are different, but first
Periodic (Moseley’s) Law - electron configurations repeat
properties of elements repeat when
ordered by increasing atomic number
periodic function of atomic number
similar outer shell, similar properties
First column : Alkali metals
s1 orbital
very 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
s 2 p1
Group IVA
s 2p 2
explains
Group VA
s 2p 3
Periodic Law
Group VIA
s 2p 4
Group VIIA –Halogens (salt former w/metal) s2p5
Group VIIIA - Noble (Rare)Gasses s2p6
{
never bond with others
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:
1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p6f7d
increasing energy
can write any electron configuration
Example 1. Write configuration for:
Zr
V
Example 2. Identify element electron configuration
1s22s22p63s23p64s23d7
1s22s22p63s23p4
Periods – row groupings of the Periodic Table
properties repeat as you go from one period to the next
-periods begin reactive (IA) and end stable (VIIIA)
Note: Period and Group of element identified properties
Historically: some elements undiscoveredchemists knew properties before
it even existed
How to read Periodic Table
Magnesium
12
Mg
24.31
Name
Atomic number
Symbol
Atomic weight
Group II (family): 2 egroup: # of outer ePeriod 4
Electron dot notation
KERNEL – nucleus and inner electrons
-dots represent the outermost electrons
-shows what’s available for the other
atoms to interact with
C 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 electrons
X1  Li+ stable [He] config
Li 1s22s
Mg 1s22s22p63s
X 2  Mg+2 stable [Ne] octet
NONMETALS- insulators
- dull appearance
- brittle
- form negative ions to complete octet
Cl 1s22s22p63s23p5+1  Cl- stable [Ar] config