Atomic Structure

What do you know about atoms?

Sticky note activity

Sizing up the atom activity1. Take your strip of

paper and cut it into equal halves.

2. Cut one of the remaining pieces of paper into equal halves.

3. Continue to cut the strip into equal halves as many times as you can.

4. Make all cuts parallel to the first one. When the width gets longer than the length, you may cut off the excess, but that does not count as a cut.

How far did you get? Here are some comparisons to think about!

Cut 1 14.0 cm 5.5" Child's hand, pockets

Cut 2 7.0 cm 2.75" Fingers, ears, toes

Cut 3 3.5 cm 1.38" Watch, mushroom, eye

Cut 4 1.75 cm .69" Keyboard keys, rings, insects

Cut 6 .44 cm .17" Poppy seeds

Cut 8 1 mm .04" Thread. Congratulations if your still in!

Cut 10 .25 mm .01"Still cutting? Most have quit by now

Cut 12 .06 mm .002" Microscopic range, human hair

Cut 14 .015 mm .006" Width of paper, microchip components

Cut 18 1 micron .0004"Water purification openings, bacteria

Cut 19 .5 micron .000018" Visible light waves

Cut 24 .015 micron .0000006"Electron microscope range, membranes

Cut 31.0001 micron

.0000000045" The size of an Atom!

http://www.miamisci.org/af/sln/phantom/papercutting.html

Notes• As we discuss the early models of the atom, draw

them on the provided worksheet• Write everything in RED on a piece of paper

Which is the correct model of an atom?

Defining the Atom

• The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”)o He believed that atoms were

indivisible and indestructibleo His ideas did agree with later

scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy

o To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes. Atoms were infinite in number, always moving and capable of joining together.

Dalton’s Atomic Theory (experiment based!)

3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds

4) In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.

1) All elements are composed of tiny indivisible particles called atoms

2) Atoms of the same element are identical. Atoms of any one element are different from those of any other element.

John Dalton(1766 – 1844)

Pictured atom as sphere with no internal structure

Sizing up the Atom Elements are able to be subdivided into smaller and smaller particles – these are the atoms, and they still have properties of that elementAtoms-the smallest particle of an element that retains its identity in a chemical reaction. If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long

Not all atoms are created equal!

Structure of the Nuclear Atom

• Atoms are divisible into subatomic particles: Electrons, protons, and neutrons

• Electrons- negatively charged subatomic particles that surround the nucleus

• Protons-positively charged particles found in the nucleus of an atom

• Neutrons-subatomic particles with no charge and a mass nearly equal to that of a proton. Found in nucleus

• Nucleus-tiny central core of an atom and is composed of protons an neutrons.

The Rutherford Atomic Model

• Based on his experimental evidence:o The atom is mostly empty spaceo All the positive charge, and almost all

the mass is concentrated in a small area in the center. He called this a “nucleus”

o The nucleus is composed of protons and neutrons (they make up the nucleus!)

o The electrons distributed around the nucleus, and occupy most of the volume

o His model was called a “nuclear model”

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Review• http://www.youtube.com/watch?v=lP57gEWcisY

Distinguishing among atoms-Elements are different because they contain different numbers of

protons.

Atomic Number- # protons in atom. This identifies the element. Remember, atoms are neutral, so # positive particles (protons) must equal negative particle (electrons)

Therefore, # protons = # electrons

Mass Number- # protons + # neutrons.

How to Find:

# Electrons: Atomic #

# Protons: Atomic #

# Neutrons: Mass # - Atomic #

Practice

• Carbon

• Sodium

• Nitrogen

Practice in Pairs!• Element Profile!

Distinguishing Among Atoms

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Isotopes

• Isotopes- Atoms that have the same number of protons but different number of neutrons.o They also have different atomic masses/mass numbers

• However, isotopes are chemically alike because they have identical numbers of protons and electrons (which are the particles responsible for chemical behavior)

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Atomic Mass• In nature, most elements occur as a mixture of two or

more isotopes. • Each isotope has a fixed mass and natural abundance

(the percentage that isotope is found in nature)• Atomic mass- weighted average mass of atoms in a

naturally occurring sample of the element. o This reflects the mass and the relative abundance of the isotopes as they occur in

nature.

• Atomic mass is expressed in amu or atomic mass units• 1 atomic mass unit = 1.66053886 × 10-27 kilograms

• Video on isotopes• Element exploration

Review

• Rutheford’s model could not explain why metals or compounds of metals give off characteristic colors when heated with a flame.

Bohr’s Model• Niels Bohr (1885-1962)-

Danish physicist and a student of Rutheford’s.

• 1913- changed Rutheford’s model to include new discoveries about how the energy of an atom changes when it absorbs and omits light.

• Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.

Bohr’s Model• Each possible electron

orbit in Bohr’s model has a fixed energy

• Energy Levels: fixed energy of an electron.o Like rungs of a laddero The lowest rung = lowest

energy level, which is closest to the nucleus.

o To move from one energy level to another (up or down the ladder), an electron must gain or lose just the right amount of energy.

Bohr’s Model• Quantum: amount of

energy is the amount of energy required to move an electron from one energy level to another.

• As you get farther away from the nucleus, it takes less energy to move from one energy level to the next.

http://science.sbcc.edu/physics/solar/sciencesegment/bohratom.swf

• The energy levels of electrons are labeled by principal quantum numbers (n).

• n= 1, 2, 3, 4…Always fill the energy levels with

electrons starting closest to the nucleus.

1 2

2 8

3 18

4 32

Energy Level (n)

Maximum # electrons

Let’s Try One!

He (2) N (7) Ne (10)

Electron Placement Activity!

• Periodic Table• Packet• Pen/pencil• Partner

Where Bohr was wrong…

• This model could explain Hydrogen (1 electron) but failed to explain the energies absorbed and emitted by atoms with more than one electron.

Quantum Mechanical Model

• In 1926 Erwin Schrodinger used a mathematical equation to describe the behavior of the electron in a hydrogen atom.

• Quantum mechanical model: describes electrons in atoms based on Schrodinger’s equation.

Quantum Mechanical Model

• Like the Bohr model, the quantum mechanical model restricts the energy of electrons to certain values.

• However, it does not involve an exact path that an electron takes around a nucleus.

• The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.

Electrons and Probability

• How likely it is to find the electron in a particular location is described by probability.

• Simile: Blades on a plane• The probability of finding

an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud.

Review

Atomic Orbitals• For each principal energy

level, there are many sublevels.

• Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

• 2 electrons can occupy each type of orbital.

• Quantum Mechanics• http://www.teachersdomain.org/asset/phy03_vid_

quantum/

• http://www.teachersdomain.org/asset/phy03_vid_atoms/

Electron Configurations!• Aufbau Principle- electrons occupy the orbitals of lowest energy first

(closest to nucleus)• Pauli Exclusion Principle- each orbital may hold up to 2 electrons, with

opposite spins. • Hund’s Rule- electrons occupy orbitals of the same energy in a way that

makes the number of electrons with the same spin direction as large as possible.

• Hydrogen• Lithium• Boron

• Beryllium

• Nitrogen

• Fluorine

• Aluminum

• Argon

• Calcium

• Chromium

Aufbau Principle- electrons occupy the orbitals of lowest energy first (closest to nucleus)Pauli Exclusion Principle- each orbital may hold up top 2 electrons, with opposite spins. Hund’s Rule- electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.

BINGO!• Li • Na• Be• He• B• O• N• F• Mg• Al

• Si• P• S• Cl• H• Sc• Ti

Valence configuration for NaValence configuration for SrValence configuration for LiValence configuration for NValence configuration for BeValence configuration for NeValence configuration for FValence configuration for ArValence configuration for CValence configuration for CsValence configuration for MgValence configuration for AlValence configuration for SiValence configuration for PValence configuration for SValence configuration for ClValence configuration for KValence configuration for RbValence configuration for BrValence configuration for Ga