STRUCTURE OF AN ATOM

A brief review of the structure of atoms

HISTORY OF ATOMIC THEORY See the Powerpoint on Atomic Theory Scientists for more

information and pictures/models. Review/Summary:

Democritus, 460 BC – proposes particles so small they can not be destroyed or divided, and describes them as “atomos” (uncuttable)

John Dalton, early 1800’s - first to use “atom”; proposes that atoms of the same element are identical, and atoms of different elements have different weights/masses; Solid Sphere Model

JJ Thomson, ~1897 – discovers the first subatomic particle, electrons; Plum Pudding Model

Ernest Rutherford, ~1912 – discovers the proton, and nucleus; Nuclear Model

Niels Bohr, ~1915 – discovers energy levels for the electrons; Planetary Model

Erwin Schrodinger, ~1926 – developed the Electron Cloud Model James Chadwick, ~1932 – discovers the neutron in the nucleus

Most Modern Model – The electron cloud model with all three subatomic particles

DEVELOPMENT OF ATOMIC THEORY

A more extensive review of Atomic Theory Development: http://

www.abcte.org/files/previews/chemistry/s1_p1.html

Use the “next” button at the bottom of the webpage above to cycle through the different scientists and their theories/models.

WHAT IS AN ATOM? Smallest particle of an element (pure substance)

that still has the properties of that element. Most of the atom is made of EMPTY SPACE

Example: an atom of gold is the smallest particle of gold (an element or pure substance) that still has the properties of gold.

Video: http://www.youtube.com/watch?v=o-3I1JGW-Ck

Brainpop (username: sclee password: cougars): Atom:

http://www.brainpop.com/science/matterandchemistry/atoms/

Atomic Model: http://www.brainpop.com/science/matterandchemistry/atomicmodel/

TWO MAIN REGIONS OF THE ATOM

Nucleus Positive charge Almost all of the mass of an atom Tiny, dense center of the atom Can be broken apart in chain reactions to produce

HUGE amounts of energy for use in electricity, medicine, weapons, etc (nuclear energy)

Electron cloud Negative charge Almost 0 mass Energy levels/shells

Max # electrons – 2,8,8* Valence level – outermost energy level

THE NUCLEUS OF AN ATOM Tiny and dense Center of the atom Contains protons and neutrons Positive charge (positive protons plus neutral neutrons) Very little of the volume (space) in an atom, but almost all

of the mass Mass = protons + neutrons Units for mass are amu (atomic mass unit)

Held together by a strong nuclear force Can be split apart in controlled chain reactions to release

nuclear energy: http://www.youtube.com/watch?v=ufEAg9h9wU8 http://www.youtube.com/watch?v=mBdVK4cqiFs Fermi is the first scientist to conduct controlled chain

reactions Nuclear energy in weapons:

http://www.brainpop.com/science/energy/radioactivity/

Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI

ELECTRON CLOUD

Most of the volume in the atom, but almost 0 mass

Contains only electrons Negative charge Energy levels

Closest to the nucleus is the lowest level Outermost level is the valence level

SUBATOMIC PARTICLES

Protons Neutrons Electrons

Video tutorial: http://www.youtube.com/watch?v=FSyAehMdpyI

ISOTOPES Atoms of the same element can have different

numbers of neutrons. This means their mass is also different (mass =

protons + neutrons)

Naming isotopes: use the name of the element, followed by the mass number of that atom Ex: Carbon-12, Carbon-13

Video Brainpop: Isotopes: http

://www.brainpop.com/science/matterandchemistry/isotopes/

Radioactivity: http://www.brainpop.com/science/matterandchemistry/periodictableofelements/

IONS In a neutral atom, the number of protons equals the

number of electrons. Neutral atoms are often unstable, because they do not have a

full valence level. Unstable atoms will gain or lose electrons to become

stable.

Atoms which have gained electrons (gained negative particles) are negative ions. They will have more electrons than protons.

Atoms which have lost electrons (lost negative particles) are positive ions. They will have fewer electrons than protons.

To see if it is an ion, compare protons and electrons.

Video Tutorial Brainpop: Ions:

http://www.brainpop.com/science/matterandchemistry/ions/

PERIODIC TABLE ARRANGEMENT

Dimitri Mendeleev developed the first (near) modern Periodic Table of Elements Page 71 in your book Based on physical properties, especially atomic

mass (later rearranged by atomic number)

Periods are rows, and tell how many energy levels the neutral atom has; elements increase left to right across the periods and are very different in properties/reactivity;

Groups or families are columns; atoms in the same group have the same number of valence electrons, and similar chemical reactivity.

CHEMICAL REACTIVITY ON THE PERIODIC TABLE

Metals on the left (2/3 of the table), metalloids on the break, metals on the right (except hydrogen). Most reactive metals – group 1, with 1 valence electron; Most reactive nonmetals – group 17, with 7 valence electrons; Nonreactive (inert) elements – group 18, with full valence level

METALS, NONMETALS, METALLOIDS ON THE PERIODIC TABLE

Property Metals Metalloids Nonmetals

Luster (shine) Yes No No

Malleable Yes No (brittle) No (brittle)

Ductile (wires) Yes No No

Conductivity Yes Semi- No

State at rom temp.

Solid (except mercury)

Solid Solid, liquid, or gas

PERIODIC TABLE TRENDS

Atomic number increases

Ato

mic n

um

ber in

crease

s

Atomic Mass Increases

Ato

mic M

ass In

crease

s

Metallic Properties Increase