Models of the AtomSection 13.1

The story of how the atomic

theory has evolved over time….

John Dalton

The atom is a solid indivisible mass. He had 4 key ideas: Page 107

All elements are composed of tiny indivisibleparticles called the atom.

Atoms of the same element are identical. Atoms of different elements are different. Atoms combine chemically with one another in

simple whole-number ratios. During chemical reactions, atoms are separated,

joined, or rearranged. Atoms are never creatednor destroyed.

JJ Thomson

Plum-pudding model. Sometimes called the Chocolate Chip Cookie

Model The atoms has negatively charged

electrons stuck into a lump of positively

charged material, like chocolate chips

stuck in a cookie dough. Did not address protons and neutrons.

Ernest Rutherford

Discovered the nucleus. Showed that most of an atom’s mass is

concentrated in a small, positively

charged region called the nucleus. Electrons resided on the outside. Did not address how electrons were

arranged.

Neils Bohr

Electrons are arranged on concentric

circular paths, or orbits around the

nucleus. Solar system model or planetary model. Gave us the idea of definite energy

levels.

Quantum Mechanical Model –Our Currently Accepted Model Erwin Schrodinger

Primarily a mathematical model using quantum

mechanics It addresses “probabilities” of finding an electron

at any instant in an area called “electron clouds”. Introduced the ideas of Principal Energy Levels

and Sublevels of energies. The electron clouds take certain shapes,

represented by the s,p,d,f subatomic orbitals.

Principal Energy Levels

Just like the Bohr model, the QuantumMechanical Model designates energy levelsof electrons by means of principalquantum numbers called (n).

Principal Energy Levels refers to amajor region where electrons are mostlikely to be found.

They are assigned values in order ofincreasing energy: n=1, n=2, n=3, etc.

Sublevels

Within each principal energy level, theelectrons occupy energy sublevels.

The number of sublevels within eachprincipal energy level is the same as

the principal quantum number. How many sublevels does the 4th

principal energy level have?

Atomic Orbitals

The regions in which electrons are likely

to be found are called atomic orbitals. Letters denote the atomic orbitals

S-shape orbitals are spherical P-shape orbitals are hour-glass shapes D-shape orbitals have clover-leaf shapes

Draw an example of each into yournotes.

Exploring further…

The lowest principal energy level (n=1)

has only one sublevel, called 1s. The second principal energy level (n=2)

has 2 sublevels, the 2s and 2p. The 2p is

higher in energy and consists of 3 p

orbitals. Let’s show an easy way to remember this

order of filling electrons…

The Electron Pyramid

The s orbitals have 1 spatial orientation,

therefore can hold 2 electrons The p orbitals have 3 spatial orientations,

therefore can hold 6 electrons The d orbitals have 5 spatial orientations,

therefore can hold 10 electrons The f orbitals have 7 spatial orientations,

therefore can hold 14 electrons.

Electrons Fill following 3 simplerules Aufbau principle: Electrons enter the

lowest energy level first. Pauli Exclusion Principle: An atomic

orbital may describe at most 2 electrons,both spinning in opposite directions.

Hund’s Rule: When electrons occupyorbitals of equal energy, one electronenters each orbital until all the orbitalscontain one electron with parallel spins.

Classifying Elements by Electron Configuration

Of the three major subatomic particles, the electron plays the most significant role in determining the physical and chemical properties of an element

The arrangement of elements in the periodic table depends on these properties

Elements can be classified into four categories according to their electron configurations

1. The noble gases2. The representative elements3. The transition metals4. The inner transition metals

The Noble Gases

These are elements in which the outermost s and p sublevels are filled

Belong to Group 0 (Group 8A)

Configurations

Helium 1s2

Neon 1s22s22p6

Argon 1s22s22p63s23p6

Krypton 1s22s22p63s23p64s23d104p6

The Representative Elements

In these elements, the outermost s or p sublevel is only partially filled

Usually called the Group A elements and include the noble gases in some definitions

ConfigurationsLithium 1s22s1

Sodium 1s22s22p63s1

Potassium1s22s22p63s23p64s1

Carbon 1s22s22p2

Silicon 1s22s22p63s23p2

Germanium 1s22s22p63s23p64s23d104p2

The Transition Metals

These are metallic elements in which the outermost s sublevel and nearby d levels contain electrons

Called the Group B elements

ConfigurationsZinc1s22s22p63s23p64s23d10

Tungsten1s22s22p63s23p64s23d104p65s24d105p66s24f145d4

Lead1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2

The Inner Transition Metals

These are metallic elements in which the outermost s sublevel and nearby f sublevel generally contain electrons

Characterized by the filling of f orbitals

ConfigurationsUranium1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f4

Curium1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f8

S1 S2

S2 p1 p2 p3 p4 p5 p6

d1 d2 d3 d4 d5 d6 d7 d8 d9 d1

0

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14

“D” Block

“F” Block

“P” Block

“S” B

lock

Period

1

2

3

4

5

6

7

6

7Period

Practice

Write the electron configurations for the following elements:

Nitrogen1s22s22p3

Nickel1s22s22p63s23p64s23d8

Vanadium1s22s22p63s23p64s23d3

Practice

What are the symbols for all the elements that have the following outer configurations?

S2 S2P5 S2D2

Helium (He) Fluorine (F) Titanium (Ti)Beryllium (Be) Chlorine (Cl) Zirconium (Zr)Magnesium (Mg) Bromine (Br) Hafnium (Hf)Calcium (Ca) Iodine (I) Rutherfordium (Rf)Strontium (Sr) Astatine (At)Barium (Ba)Radium (Ra)

Exceptional ElectronConfigurations Chromium and Copper have exceptional

electron configurations. They fill their d sublevel completely,

leaving their 4s partially filled. Much more stable this way! Write them correctly into your

notepacks…Cr: 1s22s22p63s23p63d54s1

Cu: 1s22s22p63s23p63d104s1

Physics and the QuantumMechanical Model This section studies the electron as a

property of light. Electrons travel as waves and are made

of particles of light called photons According to the wave model, light

consists of ELECTROMAGNETIC

RADIATION.

Electromagnetic Spectrum

This form of energy includes Gamma rays X-rays Ultraviolet rays Visible light Infrared rays Radar FM TV Shortwave AM

Electromagnetic Spectrum

Every element emits light when it isexcited by the passage of electric

discharge through its gas or vapor. The atoms first absorb energy, then

lose the energy as they emit light.

Electromagnetic Spectrum

Electrons are said to move from theirGROUND STATE (lowest energy level)

to and EXCITED STATE (higher energy

level). When the electron falls back to its lower

energy, it emits a PHOTON of energy,

and can be seen in the visible spectrum.

Electromagnetic Spectrum

Passing the light emitted by an elementthrough a prism gives the ATOMIC

EMISSION SPECTRUM of the element. Because each atom has a unique

electron arrangement, each atom emits

a unique wavelength during this

process. This wavelength falls within

the visible spectrum.

Kernel Structures

The kernel is a structure used toshorten an electron configuration.

A kernel is an inert gas symbol inbrackets that stands in place of all of

the filled orbitals contained in the inert

gas. Examples

Section 14.1

Classification of theElements By Electron Configuration

Classifying Elements byElectron Configuration Of the three major subatomic particles,

the ELECTRON plays the most

significant role in determining the

properties of an element. The arrangement of elements in the

PERIODIC TABLE depends on these

properties.

Elements can be classified into 4categories: The Noble Gases :

These are elements in which the

outermost s and p sublevels are filled.

Write for Helium, Neon, Argon, Krypton The representative elements:

In these elements, the outermost s

and p sublevel is only partially filled.

Write for Lithium, Sodium, Potassium,

Carbon, Silicon, Germanium

Elements can be classified into 4categories: The transition metals:

These are metallic elements in whichthe outermost s sublevel and nearby d

sublevel contain electrons.

Write for Zinc and Zirconium. The inner transition metals:

These are metallic elements in which

the outermost s sublevel and nearby f

sublevel generally contain electrons.

14.2 Periodic Trends

Atomic radius – ½the distance

between the nuclei

of two like atoms in

a diatomic molecule.

GroupTrends

Atomic size generally increases asyou go down a group on the

periodic table. Adding additional energy levels!

PeriodicTrends

Atomic size generally decrease as youmove from left to right across a period.

Same energy level -increasing nuclear charge pulls electronscloser to nucleus.

Ionization Energy

An ion – a charged atom that resultsfrom either losing or gaining an

electron. Ionization Energy – The energy

required to overcome the attraction of

the nuclear charge and remove an

electron from a gaseous atom. (The ease of losing an electron and

forming a +1 charge)

Ionization Energy

First ionization energy – the energyneeded to remove the first electron

from an atom. Second ionization energy – the energy

needed to remove the second electron

from an atom, etc.

Ionization Energy

Group Trends: The first ionizationenergy generally decreases as you

move down a group on the periodic

table. The size of the atoms increases, so the

outermost electron is farther from the

nucleus and will be more easily

removed.

Ionization Energy

Periodic Trends – For the representativeelements, the first ionization energy

generally increases as you move from

left to right across a period. Increasing nuclear charge makes it

more difficult to remove an electron.

Ionic Size

The atoms of METALLIC elements havelow ionization energies. They form

POSITIVE ions easily. By contrast, the atoms of

NONMETALLIC elements readily form

NEGATIVE ions.

Trends in Ionic Size

Positive ions are always smaller thanthe neutral atoms from which theyform. They lose their outer shell electrons

Negative ions are always larger thanthe neutral atoms from which theyform. This is because the effective nuclear

attraction is less for an increased numberof electrons.

Trends in Electronegativity

Electronegativity – the tendency for theatoms of the element to attract electrons

when they are chemically combined with

atoms of another element. Electronegativity generally DECREASES as

you go down a group. As you go across a period from left to right,

the electronegativity of the representative

elements INCREASES.

Electronegativity

The electronegativity of cesium, theleast electronegative element is 0.7

The electronegativity of fluorine, themost electronegative element, is 4.0

Electronegativity values help predict thetype of bonding that can exist between

atoms in compounds, either IONIC OR

COVALENT bonds.

Summary of Periodic Trends

Using page 406, create a summary ofperiodic trends into your notes.