History of the Atom & the Periodic Table. Parts of the Atom Protons = positive charge Neutrons = no...
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Transcript of History of the Atom & the Periodic Table. Parts of the Atom Protons = positive charge Neutrons = no...
History of the Atom & the Periodic Table
Parts of the Atom
Protons = positive charge
Neutrons = no charge
Electrons = negative charge
Nucleus = both protons and neutrons with positive charge
The Nucleus
Nucleus = protons + neutrons The nucleus occupies only a small
fraction of the atom However, it contains almost all the
mass of the atom One proton or neutron is almost
2000 times greater than the mass of an electron
Is There Anything Smaller than an Atom?
YES!! It is called a quark
How Atomic Models have Changed
Model of the atom has changed over the years 6 very important changes have taken
place! 1. Democritus 2. John Dalton 3. J.J. Thompson 4. Ernest Rutherford 5. Niels Bohr 6. Electron Cloud Model
Democritus
400 B.C. Idea proposed that atoms make up all
objects Aristotle disagreed with Democritus'
theory Aristotle’s theory that matter was the
same throughout was accepted
Thought atoms looks like a solid sphere
John Dalton
1800s Proved atoms existed Proposed:
1. All substances are made of atoms and cannot be destroyed
2. Atoms of the same element are exactly alike
3. Atoms join other atoms to make substances (like water)
Proved atoms existed by using a cathode tube
*****Not in notes!
*****Not in notes!
*****Not in notes!
Joseph John “JJ” Thompson 1904 Thompson did not know how
electrons were arranged He thought they were mixed
throughout atom Thought it was a positive sphere with
negative electrons on sphere, scattered around
He thought it looked like a ball of chocolate chip cookies!
Ernest Rutherford
1911 A student of JJ Thompson! Created the Gold Foil Experiment From the experiment, he learned:
1. The atom is mostly empty space 2. The nucleus is very densely packed 3. The nucleus is positively charged
Niels Bohr
Hypothesized that electrons travel in levels around the nucleus
Levels are called orbitals
Modern Electron Model
Known as the electron cloud model Electrons travel in “areas” instead of
levels Areas are called clouds
Match the Model with the Correct Theory…
1. Modern Theory
2. Rutherford Model
3. Thompson Model
The Periodic Table
I. 1st Periodic Table was developed by Dmitri Mendeleev
II. Elements are organized by increasing atomic number (in other words, increase number of protons in the nucleus)
III. Properties in lighter elements could be shown to repeat in heavier elements
Organization of Periodic TableI. Groups (also known as families)
A. Vertical columnsB. Organized by similar propertiesC. Have same # of electrons in outer energy levelsD. Each level can have a maximum # of electronsE. Each row ends when an outer energy level is filledF. You can use electron dot diagrams to represent
outer energy level electrons (known as valance electrons)
II. Periods A. Horizontal rowsB. Organized by increasing # of protons and neutronsC. Classified as metals, nonmetals, and metalloids
Periods…Vertical or horizontal?
HORIZONTAL!!
Groups…Vertical or horizontal?
VERTICAL!!
Valance Electrons (outer electrons) Valance electrons are electrons in the outer
most layer In general, the number of valance electrons
of an element is equal to the group number *Groups 3-12 are
skipped and do not follow the same
pattern Group 18 (Noble Gases)
Stable because outer electron level is full
Atomic Number vs. Mass NumberI. Each element has same number of
protons, but different number of neutrons
II. In a neutral atom, protons (+) and electrons (-) are equal… so they balance out to zero
I. Atomic # – number of protons in an atom (also identifies the element)
II. Mass # – sum of protons and neutrons in the nucleus (identifies mass of the nucleus)
Using Periodic Table, Complete this chart:
Element Atomic # # of Protons / Electrons
# of Neutrons
Mass #
Helium – 4 2 2 2 4
Carbon – 12
Carbon – 14
Oxygen – 16
Isotopes
I. Isotopes – atoms of the same element with different numbers of neutrons
A. Different isotopes have different properties
B. Name of the element, followed by mass # identifies the isotope
1. Ex) Uranium-235 and Uranium-238