The Structure of an Atom

Atomic Structure Atoms are composed of 2 regions: Nucleus: center of atom that contains mass of atom Electron cloud: region that surrounds nucleus that contains most of space in atom Nucleus Electron Cloud

What’s in the Nucleus? Nucleus contains 2 of 3 subatomic particles: Protons: subatomic particle w/ 1+ charge (p+) Rutherford - 1911 Neutrons: subatomic particle w/ no charge (no) James Chadwick - 1932

What’s in the Electron Cloud? The 3rd subatomic particle resides outside nucleus in electron cloud Electron: subatomic particle w/ 1- charge (e-) and virtually no mass JJ Thomson - 1897

How do these particles interact? Protons and neutrons live compacted in tiny nucleus most atom’s mass electrons small and reside outside nucleus small mass (2000 e- = 1 p+ or no) occupy large volume of space outside nucleus Atoms

How do the subatomic particles balance each other? In atoms: protons = electrons If 20 protons are present in atom then 20 electrons balance overall charge of atom—atoms are neutral The neutrons have no charge; therefore they do not need to (and often times don’t) equal protons or electrons

How do we know the number of subatomic particles in an atom? Atomic #: indicates # of protons in atom Ex: Hydrogen’s atomic # is 1 hydrogen has 1 proton Ex: Carbon’s atomic # is 6 carbon has 6 protons **Number of protons identifies element similar to how your fingerprint ID’s you. Ex. 2 protons = He, 29 protons = Cu ALWAYS!!

How do we know the number of subatomic particles in an atom? Mass number: number of protons and neutrons in nucleus (p+ + no) Ex: hydrogen can have a mass # of 3. Since it has 1 proton it must have 2 neutrons # of neutrons = mass # - atomic #

What are Isotopes? Atoms of same element with different # of neutrons Same atomic # Different mass # (b/c neutrons are different) Ex. Carbon 12, Carbon 13, and Carbon 14 all naturally occurring isotopes of Carbon. Each has 6 p+ and 6 e-, but each has different # of neutrons (therefore, different mass#)

Determining the number of protons and neutrons Li has mass # of 7 and atomic # of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic #) Ne has a mass # of 20 and an atomic # of 10 Protons = 10 Neutrons = 20 - 10= 10

What about the electrons? electrons are equal to protons So e- = p+ = atomic # Ex: He has mass # of 4 and atomic # of 2 p+ = 2 no = 2 e- = 2 Basic Atomic Structure 1:57

Determine the number of subatomic particles in the following: Chlorine has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17 Potassium has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19

Candy Atoms Atom #1 - mass # of 5 and an atomic # of 3. Atom #2 – 5 protons and 7 neutrons. Atom #3 – Atomic # of 7 and 8 neutrons.

Candy Atoms Atom #4 – mass # 18 and 9 electrons Atom #5 – build your own candy atom using the candies that you have. You should be able to accurately determine: Atomic # Mass # # of protons, neutrons, and electrons

Modern Atomic Theory

Electron Cloud Model Electrons travel around nucleus in random orbits. cannot predict location at any given moment. fast, appear to form “cloud” around nucleus. Ex. - Airplane propeller