Quarter 1 Unit 2“Atomic Structure”

Defining The Atom

Early Models of the Atom

Atom: the smallest particle of an element

The Greek philosopher Democritus (460 B.C. – 370 B.C.) was the first to suggest the existence of atomsHe believed that atoms were indivisible and indestructible

His ideas were not based on experiments, just philosophy

Lavoisier: The Law of Conservation of Mass

Changed chemistry to a quantitative science

Measured the mass of a system before and after a reaction in a closed system▪ Stoichiometry

Isolated and named hydrogen and oxygen

Discovered how respiration and combustion are related

Major experiment involved cinnabar: red mercury oxide

Lavoisier’s Cinnabar Experiment

Proust: The Law of Definite Proportions

Copper carbonate from a variety of sources Lab-made was 57.48% Cu, 5.43% C, 0.91% H, and 36.18% O Natural was 57.48% Cu, 5.43% C, 0.91% H, and 36.18% O

Definite Proportions A compound always contains the same

elements in certain, definite proportions Also known as the law of constant composition

Dalton’s Atomic Theory~2000 years pass before more was known about the atom

John Dalton; English Chemist & School teacher; 1803

Thought the atom looked like a marble.(Round, solid sphere)

His findings were based on scientific experiments, not philosophy

Dalton Dalton (1803) Known as the FOUNDER of the atomic theory Dalton invented the word ATOM as the basic

unit of matter Dalton also claimed that all atoms of a given

element are IDENTICAL He also discovered that atoms of different

elements have different PROPERTIES AND MASSES

Found that combining atoms of different elements formed COMPOUNDS

Dalton’s Postulates

1. Compounds are composed of elements

2. Atoms of the same elements are identical and differ from other elements.

3. Atoms chemically combine in whole-number ratios

4. Atoms cannot be created or destroyed

Sizing up the Atom

Atoms are extremely small A penny containing pure copper

contains 2,400,000,000,000,000,000,000,000 atoms

Population of our planet: ~6,000,000,000

If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long

Can only be observed using a scanning tunneling (electron) microscope

SEM Microscope

Dmitri Mendeleev1869

Arranged elements into 7 groups with similar properties.  He discovered that the properties of elements  "were periodic functions of their atomic weights".  This became known as the Periodic Law.

Crookes Tube (CRT)

A magnet will deflect the cathode ray

Particles in the cathode ray are negatively charged

Drag picture to placeholder or click icon to addhttp://www.youtube.com/watch?v=IdTxGJjA4Jw

J.J. Thomsom 1897

• While using a CATHODE RAY TUBE he discovered that the ray was deflected (due to a magnetic/electrical field

• From this discovery he concluded that atoms contain small negatively charges particles called ELECTRONS

• Theory famously referred to as the PLUM PUDDING model because he visualized the ELECTRONS being EMBEDDED within the structure of the atom (just like raisin bread)

• The MASS of the rest of the atom (besides the electrons) was thought to be EVENLY DISTRIBUTED and POSITIVELY CHARGED

Thomson’s Atomic Model

“Plum Pudding” model: the electrons were like plums embedded in a positively charged “pudding,”

J. J. Thomson

The philosopher who first suggested the existence of atoms was ____________.

A. John DaltonB. DemocritusC. Ernest Rutherford

The three subatomic particles that make up an atom are

.

A. proton, neutron, electronB. nucleus, proton, electronC. cathode rays, canal rays,

neutrons

True or False? A Scanning Tunneling Electron Microscope is the only device we can use to see atoms.

A. TrueB. False

John Dalton’s model of the atom looked like a ___________

A. soccer ballB. marbleC. football

Democritus believe that atoms were _____

A. Indivisible & InvisibleB. Indestructive & InvisibleC. Indivisible & Indestructive

True or False? There were only ~200 years between Democritus’ theory and John Dalton’s work with the atom.

A. TrueB. False

The scientist who discovered the electron was _____________

A. JJ ThomsonB. Robert MillikanC. Ernest Rutherford

Mass of the Electron

1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a proton

Mass of the electron is 9.11 x 10-28 g

The oil drop apparatus

Goldstein (1886) Discovered the

“Proton” Goldstein proved

that when negative particles are formed, so are positive

These positive particles were found to have a mass 1837x that of an electron

932 – James Chadwick (1932)

discovered the “neutron”a particle with no charge, but a mass equal to a proton

Ernest Rutherford

In 1911, Designed the Gold Foil Experiment

Aimed a beam of alpha (α) particles at a thin piece of gold foil (only a few atoms thick.)

Most α particles passed through the foil…

A small amount of the α particleswere deflected

To their surprise, some α particlesbounced straight back.

1 in ~8000 did not go through the foil

Alpha Particle Experiment

Actual Results Most went straight through

Mostly empty space

Some were deflected at huge angles Positive charge in center of atom

Others bounced straight backwards!! Small, dense solid area in center of atom

Nuclear Model

A Visual Example

Rutherford’s Atomic Model

Conclusions:There is a nucleus in the center of the atom where most of its mass is.

The nucleus is positiveAtoms are mostly empty space

Disproved J.J. Thomson’s Plum Pudding Model

If an atom is the size of a football stadium, the nucleus is the size of a marble

Niels Bohr1885-1962 Planetary Model 1913

Nucleus surrounded by orbiting electrons at different energy levels

Electrons have definite orbits

Utilized Planck’s Quantum Energy theory

Worked on the Manhattan Project (US atomic bomb)

Bohr Model for Nitrogen

Change to Dalton’s atomic theory: atoms are divisible into subatomic particles:

Electrons, protons, and neutrons

Subatomic Particles

Particle Charge Mass Location

Electron(e-) -1 virtually

nothingElectron

cloud

Proton +1 1 Nucleus

Neutron 0 1 Nucleus

Atomic Number

Elements are different because they contain different numbers of PROTONS

atomic number = the number of protons in the nucleus

# protons in an atom = # electrons

Mass Number

Mass number = number of protons and neutrons in the nucleus

Mass # = p + nElement p n e Mass #

Oxygen - 8

- 33 42

- 31 15

8 8 1616

Arsenic 75 33 75

Phosphorus 15 3116

Nuclide SymbolsContain the symbol of the element, the

mass number and the atomic number.

X Massnumber

Atomicnumber

Subscript →

Superscript →

Symbols Find each of these:

a) number of protonsb) number of neutronsc) number of electronsd) Atomic numbere) Mass Number

Br80

35

Symbols If an element has an atomic number

of 34 and a mass number of 78, what is the: a) number of protonsb) number of neutronsc) number of electronsd) complete symbol

Symbols If an element has 91 protons and

140 neutrons what is the a) Atomic numberb) Mass numberc) number of electronsd) complete symbol

Symbols If an element has 78 electrons

and 117 neutrons what is the a) Atomic numberb) Mass numberc) number of protonsd) complete symbol

IsotopesAtoms of the same element can

have different numbers of neutrons.

Thus, different mass numbers.Isotopes change the number of

neutrons & the mass number for an atom

Frederick Soddy proposed the idea of isotopes in 1912

Isotopes: atoms of the same element having different masses, due to varying numbers of neutrons.

Elements occur in nature as mixtures of isotopes.

Naming IsotopesElement name – mass number:carbon-12carbon-14uranium-235

Isotope Protons Electrons Neutrons NucleusHydrogen–1 (protium)

1 1 0

Hydrogen-2(deuterium)

1 1 1

Hydrogen-3(tritium)

1 1 2

Atomic Mass The Gold number on the P.T. is the

Average Atomic Mass of the element This is based on the abundance of each

variety of that element in nature.Instead of grams, the unit we use is the

Atomic Mass Unit (amu)It is defined as one-twelfth the mass of a

carbon-12 atom.

The Periodic Table: A Preview

Each horizontal row is called a periodEach vertical column is called a group, or familyElements in a group have similar chemical and physical properties