# The Atom.

## Presentation on theme: "The Atom."— Presentation transcript:

The Atom

Two major parts of an atom
Nucleus (not to scale) Electron Cloud

Three Major Sub-Atomic Particles
Protons Neutrons Electrons

THE PROTON p+ Heavy = 1 amu Positive + 1 charge Location: Nucleus

THE NEUTRON Heavy = 1 amu No charge, neutral Location: Nucleus

e- THE ELECTRON Very light = 1/2000 amu Negative  -1 charge
Location: electron cloud

Nucleus: Protons and Neutrons Electron Cloud: Only Electrons
Where are they located? Nucleus: Protons and Neutrons Electron Cloud: Only Electrons

ATOMIC NUMBER (Z) The # of protons in an atom
Can not change for an element All atoms are neutral, so Z equals the # of electrons For an ion – the number of electrons may differ

Example: Sodium Atomic # = # of protons 11 Na

MASS NUMBER (A) The mass of an atom A = protons + neutrons
To determine # of neutrons Neutrons = A - Z

Example An atom of sodium has a mass of 24 amu, how many protons, electrons and neutrons does it have? 11 p+ 11 e- = 13 N° 11 Na

ISOTOPES Atoms of the same element that differ in mass. (They have the same # of p+, but different # of N°)

Isotope Notation Mass # Atomic #

Isotope Notation Can also be written as ELEMENT – MASS #
Example: Carbon - 12

So, why do the elements on the PT have masses with decimals???

AVERAGE ATOMIC MASS The weighted average mass of all naturally occurring isotopes of an element.

Example using exam scores!
Exam Scores can be weighted higher than homework or quiz grades: What if… And you received: Exam 50% Exam 93 Quizzes 20% Quizzes 82.5 Homework 30% Homework 85 Your grade = (93 x .5) + (82.5 x .2) + (85 x .3) = 88.5

Example Example: The element hydrogen has three isotopes. It exists in nature 99.41% of the time as Hydrogen-1, 0.4% of the time as Hydrogen-2 and 0.19% of the time as Hydrogen – 3. What is the average atomic mass of hydrogen? 0.9995* * *3 = u

Famous Scientists in Atomic Theory

Democritus (400 B.C.) First to develop the idea of an atom.

DALTON Dalton created an atomic theory that stated:
All elements are composed of tiny indivisible particles called atoms Atoms of the same element are identical. The atoms of any one element are different from those of any other element

J.J. Thomson “Plum Pudding Model” Solid positively charged sphere
Electrons embedded within

Rutherford’s Gold Foil Experiment

Rutherford Proved the existence of a tiny, dense, positively charged nucleus. The rest of the atom is mostly empty space.