Structure of Structure of MatterMatter

The branch of science that The branch of science that explains how matter is put explains how matter is put

together is known as together is known as chemistrychemistry..

Historical View of MatterHistorical View of Matter Democritus (in the 4Democritus (in the 4thth

century B.C.) realized century B.C.) realized if one could continue if one could continue to slice a piece of to slice a piece of bread into smaller bread into smaller pieces until it could pieces until it could be sliced no more.be sliced no more.

Atom originates from Atom originates from the Greek word the Greek word atomosatomos, which means , which means “cannot be cut”.“cannot be cut”.

The Atomic The Atomic TheoryTheory

An English An English scientist named scientist named John Dalton (1766-John Dalton (1766-1844) realized that 1844) realized that different types of different types of atoms existed from atoms existed from experimentation.experimentation.

John Dalton’s Atomic John Dalton’s Atomic TheoryTheory

1.1. All matter is made of All matter is made of atoms.atoms.

2.2. All atoms of an element All atoms of an element are identical in mass are identical in mass and properties and properties

3.3. Compounds are formed Compounds are formed by two or more different by two or more different kinds of atoms. kinds of atoms.

4.4. A chemical reaction is a A chemical reaction is a rearrangementrearrangement of of atoms. atoms.

J.J. Thomson (1897)J.J. Thomson (1897)

Performed the Cathode Performed the Cathode Ray Tube ExperimentRay Tube Experiment

He discovered He discovered electrons, which electrons, which are negatively are negatively charged charged particles within particles within the atomthe atom

JJ Thomson’s ExperimentJJ Thomson’s Experiment

Thomson concluded the cathode ray consists of a beam of negatively

charged particles (electrons) and that electrons are constituents of matter.

Ernest Rutherford’s Ernest Rutherford’s ExperimentExperiment Early 1900’s, proved the existence of the atomic nucleus.Early 1900’s, proved the existence of the atomic nucleus.

Shot particles of matter at a piece of gold foil.Shot particles of matter at a piece of gold foil. Most particles continued on a straight line, a few Most particles continued on a straight line, a few

deflected.deflected.

Why the Atomic Theory?Why the Atomic Theory?

Humans have never seen an Humans have never seen an atom directly because they atom directly because they

are so small!are so small!

How Small Are Atoms?How Small Are Atoms? If all humans on Earth were shrunk If all humans on Earth were shrunk

to the size of an atom, we could fit to the size of an atom, we could fit easily on the head of a pin!easily on the head of a pin!

The most powerful microscopes The most powerful microscopes cannot see atoms because they are cannot see atoms because they are too small!too small!

In 12 grams of Carbon, there are 6 In 12 grams of Carbon, there are 6 x 10x 102323 atoms! atoms!

The Emptiness of MatterThe Emptiness of Matter The space between an The space between an

atom’s center and its atom’s center and its edge is enormous.edge is enormous.

If an atom’s nucleus If an atom’s nucleus was expanded to the was expanded to the size of a penny and size of a penny and placed on the placed on the pitcher’s mound at pitcher’s mound at Fenway Park, then the Fenway Park, then the closest electron would closest electron would be somewhere along be somewhere along the Green Monster!the Green Monster!

Basic Structure of Basic Structure of MatterMatter

ElementsElements are are the simplest form the simplest form of matter and of matter and cannot be broken cannot be broken down any further down any further by chemical by chemical changes.changes.

Elements are Elements are made of made of atomsatoms..

Sub-Atomic ParticlesSub-Atomic Particles Atoms are not Atoms are not

indestructible, indestructible, they are made of they are made of smaller pieces of smaller pieces of matter. matter.

These These subatomic subatomic particlesparticles are are protons, neutrons, protons, neutrons, and electrons. and electrons.

The NucleusThe Nucleus Where the protons Where the protons

and neutrons exist.and neutrons exist. Over 99% of an Over 99% of an

atom’s mass is atom’s mass is found within the found within the nucleus. nucleus.

Each particle in Each particle in nucleus has a mass nucleus has a mass of 1 AMU (of 1 AMU (AAtomic tomic MMass ass UUnit)nit)

ProtonsProtons The number of The number of

protons in an atom protons in an atom determine the determine the identity of an identity of an element. element.

Atomic numberAtomic number – – Number of protons in Number of protons in nucleus. nucleus.

Protons carry a Protons carry a positive electrical positive electrical charge. charge.

NeutronsNeutronsFound in Found in

nucleusnucleusSame mass as Same mass as

a proton with a proton with no charge no charge (neutral)(neutral)

Mass number = Atomic number + # of Neutrons.

ElectronsElectrons Electrons orbit the Electrons orbit the

nucleus of an atom nucleus of an atom in what is called an in what is called an electron cloud. electron cloud.

Electrons have a Electrons have a negative electrical negative electrical charge.charge.

Electrons are Electrons are attracted to the attracted to the positively charged positively charged nucleus (from the nucleus (from the protons) of an atom.protons) of an atom.

IsotopesIsotopes Isotopes – two atoms of same element Isotopes – two atoms of same element

(same atomic number) with different (same atomic number) with different numbers of neutrons in the nucleus. numbers of neutrons in the nucleus.

Reading the Periodic Reading the Periodic TableTable

Chemical SymbolChemical Symbol Atomic Number (# Atomic Number (#

of protons)of protons) Average atomic Average atomic

mass (rounded to mass (rounded to the nearest whole = the nearest whole = mass number)mass number)

Number of Neutrons Number of Neutrons is determined by is determined by subtracting atomic subtracting atomic number from mass number from mass numbernumber

1.00197 (rounded to 1) – 1 = 0 neutrons

Apply what you just Apply what you just learnedlearned

How many How many protons in an iron protons in an iron atom?atom?

How many How many neutrons in an neutrons in an iron atom?iron atom?

Why do you Why do you suppose iron’s suppose iron’s chemical symbol chemical symbol is Fe and not is Fe and not something like Ir?something like Ir?

How Electrons are How Electrons are ArrangedArranged Atoms will usually have the same number of electrons Atoms will usually have the same number of electrons

as they do protons to balance the overall electrical as they do protons to balance the overall electrical charge.charge.

Electrons are arranged in energy levels. Each energy Electrons are arranged in energy levels. Each energy level can only hold a certain number of electrons.level can only hold a certain number of electrons.

Energy LevelEnergy Level Number of Number of ElectronsElectrons

11 2222 8833 8844 181855 1818

Bohr Model – Helium AtomBohr Model – Helium Atom

Valence Electrons- Amount of electrons in the outermost energy level; i.e Helium has two valence electrons. Carbon has 4 valence electrons (See next Slide)

Bohr Model - CarbonBohr Model - Carbon