Everything is made of Atoms -Richard Feynman Review of scientific notation A brief history of the atom Composition of Earth’s crust Avagadro’s Number How

Everything is made of Atoms

-Richard Feynman

• Review of scientific notation

• A brief history of the atom

• Composition of Earth’s crust

• Avagadro’s Number

• How many atoms are in your body?

How many seconds are in a year?

606024365 = 31536000

= 3.1536107

• 3.15107 (to 3 significant digits)

Review: Scientific Notation

How many years are in a second?

1/3.1536 x 107 = 0.0000000317098

= 3.1709810-8

• 3.1710-8 (to 3 significant digits)


How many atoms are in my body?


?

A brief history of the atom

In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles in constant motion.

Aristotle, however, did not accept the theory, and it was ignored for centuries.

http://www.neutron.anl.gov/hyper-physics/histatom.html

atoma= non-divisible


Modern atomic theory began with the publication in 1808 by British chemist and physicist John Dalton of his experimental conclusions that:

1. all atoms of an element have the same size and weight, and

2. atoms of elements unite chemically in simple numerical ratios to form compounds.


Definition: Element

A single or isolated group of particles composed of only one species of atoms.

sulfur


In 1897, British physicist J.J. Thomson discovered the electron, a subatomic particle (i.e., a particle smaller than the atom). For this work, he was awarded a Nobel prize in 1906.

His discovery of the electron led to Thomson’s proposed plum-pudding model for the atom.


In 1911, New Zealander Ernest Rutherford explained an atom's structure in terms of a positively charged nucleus surrounded by negatively charged electrons orbiting around it.


His famous gold foil experiment showed that atoms are mostly empty space.

Perspective on the atom: If the nucleus could be enlarged to the size of a pea and placed at the centre of a football stadium, the electrons would be like flies buzzing around the cheap seats.

http://www.mgreen.com/stadpages/stad10.html


In 1913 Danish physicist Neils Bohr used quantum theory to explain why electrons could remain in certain allowed orbits without radiating energy.


Bohr model for the atom.

Modern view of the atom

Atom (definition): The smallest unit of matter that possesses the properties of an element.

Nucleus (not to scale)

Electrons (clouds)

Modern view of the atom

• Atoms are composed of subatomic particles: protons, neutrons and electrons.

• Protons and neutrons reside in the nucleus of the atom - the central core where virtually all of the mass of the atom is located.

• Electrons exist outside the atomic nucleus in a cloud of orbitals.

Nucleus (not to scale)

Electrons (clouds)

Important characteristics of the electron

• they orbit the nucleus in a cloud (or shell)

• they are bound to atoms because their negative charge is attracted to the positive charge in the nucleus

• the chemical behaviour of atoms and elements is largely controlled by the number and configuration of electrons

Physical facts of subatomic particles*

Proton Neutron ElectronMass (kg) 1.7×10-27 1.7×10-27 9×10-31

Charge + none -Location I nside

nucleusI nsidenucleus

Outsidenucleus

* There are actually a lot more known subatomic particles than those listed here

How many elements are there in the world?

•At this time, scientists know of 116 different elements, of which 92 occur in nature (the rest are man-made).

• The naming convention for new elements is to name them after people or places (e.g., Einsteinium or Gallium).

How many elements are there in the world?

“The first full-scale hydrogen bomb explosion in the Pacific in late 1952 produced two new chemical elements, atomic scientists disclosed today. The researchers recommend that the new elements be named after Dr. Albert Einstein and Dr. Enrico Fermi, who played major roles in the birth of the atomic age”

(New York Times, August 1955)

Composition of Earth’s crust(8 Major Elements)Element (Symbol) Percent by weightOxygen (O) 46.6Silicon (Si) 27.7Aluminum (Al) 8.1I ron (Fe) 5.0Calcium (Ca) 3.6Sodium (Na) 2.9Potassium (K) 2.6Magnesium (Mg) 2.1

Periodic Table of the Elements

PERIODIC TABLE OF ELEMENTS• Ordered by increasing atomic weight and atomic number (Z = number of protons in the nucleus of one atom).

• Atomic weight (grams/mol) is given below the element symbol.

Atomic Number (Z )

Atomic Symbol

Atomic Weight

Avogadro’s Number

• Avogadro’s number was determined experimentally in the 20th century, but was named in honour of 19th century Italian chemist LORENZO ROMANO AMEDEO CARLO AVOGADRO

• The 2002 CODATA recommended value for Avogadro's number is

6.0221415 x 1023 mol-1

Avogadro’s Number

• Avogadro’s number (N ) gives the number of atoms in 1 mole of an element

• Magnitude of N: If the Earth was covered by N peas, the peas would be piled to a height of 0.5 km!

How many atoms are in my body?• Suppose that I am made entirely of carbon

• Suppose that I weigh … 72.0 kg

•Number of moles (mol) of carbon

• Number of carbon atoms • 6.00 ×103 mol

× 6.022 × 1023 atoms/mol • 3.61 × 1027 atoms


12.01 g 7.20×104 g

1 mol X mol=

X = 7.2x104/12.01

= 6.00x103 mol

Documents

Everything is made of Atoms -Richard Feynman Review of scientific notation A brief history of the atom Composition of Earth’s crust Avagadro’s Number How