Transcript period
Patterns and the Periodic Table
Featuring the Return of Bohr-Rutherford Diagrams and the Periodic Table SNC2D
The Periodic Table
• Designed by Mendeleev in 1869 • Organizes matter based on its properties and atomic number • Allowed for the prediction of then unknown elements
Periods and Families
• The rows in the periodic table are known as periods.
• The columns in the periodic table are known as groups.
• Groups tend to have similar properties.
• Major groups (multiple columns): – Metals – Non metals – Metalloids • Single column groups: – Alkali metals – Alkali earth metals – Halogens – Noble gases
Properties Compared
• Metals – Nickel (Ni) – Solid – Shiny – Malleable – Conductor • Non-Metals – Sulphur (S) – Solid, liquid, or gas – Dull – Brittle – Insulator
Atomic Theory of Matter
• Dalton brings back Democritus’ idea of the atom as an indivisible particle.
• Dalton gives us the “billiard ball” model.
Subatomic Particles
• Atomic theory is revised as subatomic particles are discovered.
– Electrons and Protons • “Raisin Bun” model • Saturn/solar system model – Neutrons • Bohr – Rutherford model
Modern View of the Atom
• Protons, neutrons, electrons • Mass measured in atomic mass units (amu) which is equal to 1.66 x 10 -24 g
Subatomic Particle Charge
Electron 1-
Symbol
e Proton 1+ p +
Mass (amu)
1/2000 1 Neutron 0 n 0 1
The Bohr-Rutherford Model
-used to show the arrangement of electrons in the atom Helium Atom • 2 positive protons in nucleus • 2 neutral neutrons in nucleus • 2 negatively charged electrons in the first energy level – 2-8-8-2 are the number of electrons in each energy level for the first 20 elements
How to Draw a Bohr Diagram Si
Element 14 has the symbol Si and 14 electrons • Find your element on the periodic table.
• Determine number of
electrons
, which for a neutral atom is equal to the number of _________, which is equal to the ________________
Si
• Place the element
symbol
middle.
in the • Draw in the
energy levels
– (determine which
period
(row) your element is in) • Add electrons following the 2-8-8-2 pattern for the first 20 elements
Check your work: Count your electrons per shell and your total electrons!
Standard Atomic Notation (for a neutral atom)
Atomic symbol Mass number Atomic number 14 28 Si Number of protons Atomic number (14) 14 p + Number of electrons (for neutral atom) Number of neutrons Atomic number (14) Mass number – Atomic number (28-14=14) 14 e 14 n 0
How to Draw a Bohr-Rutherford Diagram
• Determine the number of protons, neutrons, and electrons Element 14 has 14 electrons, 14 protons, and 14 neutrons • Place the number of protons and neutrons for the element in the middle • Draw in the energy levels • Add electrons following the 2-8-8-2 pattern for the first 20 elements
14 p + 14 n 0
Homework
1.
Refer to the periodic table to name and write the symbols for the following elements: [K] a.
b.
c.
d.
A halogen of the second period The alkaline earth metal in the fifth period The noble gas with the smallest atomic number The non-metal in the fifth period with seven outermost electrons e.
f.
The alkali metal of the fourth period The metal of the third period with three outermost electrons g.
The unreactive gas of the second period .
2.
Try drawing Bohr-Rutherford diagrams for each of the following elements: [C] [I] a) O b) Al c) Ne d) K 3. Imagine that a chemist discovers a new element with atomic number 119. [I] a) b) c) Use the periodic table to predict what chemical family this element would belong to.
How many outer electrons would an atom of this element have?
Predict one physical property and one chemical property of this element.
4. Why are atoms electrically neutral? [K]
Lewis Dot Diagrams
The electrons in the outermost shell are called ?
Lewis Dot Diagrams
The electrons in the outermost shell are called
valence electrons
.
Lewis Dot Diagrams
The electrons in the outermost shell are called
valence electrons
.
Lewis Dot Diagrams are abbreviated Bohr Diagrams that show just these outermost electrons, e.g.:
Valence Electrons and Families
Note that both hydrogen (H) and potassium (K) have just
?
electron in their outermost shell.
Note also that these elements are both found in the
?
column
of the periodic table.
This is not a coincidence!
Valence Electrons and Families
Note that both hydrogen (H) and potassium (K) have just
1
electron in their outermost shell.
Note also that these elements are both found in the
?
column
of the periodic table.
This is not a coincidence!
Valence Electrons and Families
Note that both hydrogen (H) and potassium (K) have just
1
electron in their outermost shell.
Note also that these elements are both found in the
1 st column
of the periodic table.
This is not a coincidence!
Valence Electrons and Groups
All elements in the same group (column) have the same number of electrons in their outermost shell (ref. p. 150) It is these electrons that determine the behavior of the element (chemical properties), including how it reacts with other elements – and how it forms ions.
Homework
1.
For each of the elements that you drew a Bohr-Rutherford diagram in question 2, draw its Lewis Structure. [C] [I] a) O b) Al c) Ne d) K 1.
Which of the above elements would you expect to be the most reactive and why? [K] 1.
Which of the above elements would you expect to be the least reactive and why? [K]
Credits
• • • • • • • • http://commons.wikimedia.org/wiki/File:IUPAC_Periodic_Table.PNG
http://commons.wikimedia.org/wiki/File:Atomic_size_periodic_table.svg
http://commons.wikimedia.org/wiki/File:Periodic_table_fluorine.svg
http://commons.wikimedia.org/wiki/File:Nickel_kugeln.jpg
http://commons.wikimedia.org/wiki/File:Sulphur2.jpg
http://commons.wikimedia.org/wiki/File:Radiosity.png?uselang=en-gb http://commons.wikimedia.org/wiki/File:Bohr_model.jpg
http://commons.wikimedia.org/wiki/File:Helium-Bohr.svg