Welcome to the
ionic speed dating
tutorial
Where we teach you how to be a good ion and find your perfect life mate!
Lesson 2 Learning Target
1.
Explain, using the periodic table, how and why elements
combine to form compounds in specific ratios
Patterns in the periodic table
• Left of the staircase line are metals
• To the right are non-metals
•
Surrounding the staircase line are the
metalloids: these elements display both
metal and non-metal properties.
Patterns in the periodic table
The elements are numbered from 1 to 118 by MASS
Lightest
Heaviest
Patterns in the periodic table
The Lanthanoids and Actinoids slot into periods 6 & 7
Patterns in the periodic table
Elements are positioned horizontally (left to right) in PERIODS
• Properties change in 2 ways as you
move from left to right across a
period:
1. The elements change from
metal to non-metal
2. The elements become less
reactive.
Patterns in the periodic table
Elements are positioned vertically (up and down) in GROUPS
Elements in the same group have similar
properties
Patterns in the periodic table
Elements are positioned vertically (up and down) in GROUPS
Elements in the same group have similar
properties
• Group 1 – hydrogen and the alkali
metals.
• They are the most reactive metals and
react violently in air or water.
• Reactivity increases as you move
down the group
Patterns in the periodic table
Elements are positioned vertically (up and down) in GROUPS
Elements in the same group have similar
properties
• Group 2 –the alkaline-earth metals.
• Very reactive with oxygen, but less
reactive than the alkali metals.
Patterns in the periodic table
Elements are positioned vertically (up and down) in GROUPS
Elements in the same group have similar
properties
• Group 17 –the halogens
• The most reactive of the non-metals.
They tend to combine with other
elements to make compounds.
Patterns in the periodic table
Elements are positioned vertically (up and down) in GROUPS
Elements in the same group have similar
properties
• Group 18 – the noble gases
• The most stable and unreactive of the
elements.
Patterns in the periodic table
• Why do elements in the same group have
similar properties?
1
2
14 16
13 15 17
18
• How can you predict the kinds of compounds
elements are likely to form?
• How can you predict the ratios in which they
will combine?
Valence electrons!
Valence electrons
1
2
14 16
13 15 17
18
For the elements in the colored groups:
You can quickly and easily tell how many
valence electrons an element has by
looking at its group number
Example: Carbon is in group 14 so it has 4 valence
electrons
Example: Magnesium is in group 2 so it has 2 valence
electrons
Electron dot diagrams (a.k.a. Lewis diagrams)
An electron dot diagram is a useful way to
represent an atom’s valence electrons. It
has the element symbol in the middle with
the valence electrons shown as dots
around the symbol.
These will come in handy when we start
talking about how different atoms combine
Electron dot diagrams (a.k.a. Lewis diagrams)
Steps to drawing electron dot diagrams:
1. write the element’s chemical symbol
2. surround it by dots that represent the atom’s
valence electrons (use the group number to
determine the number of valence electrons)
3. if an atom has more than 4 valence electrons, the
additional electrons are paired
4. elements in the same group will have identical
dot diagrams since they have the same number of
valence electrons
Electron dot diagrams (a.k.a. Lewis diagrams)
Steps to drawing electron dot diagrams:
1. write the element’s chemical symbol
2. surround it by dots that represent the atom’s valence
electrons (use the group number to determine the
number of valence electrons)
3. if an atom has more than 4 valence electrons, the
additional electrons are paired
4. elements in the same group will have identical dot
diagrams since they have the same number of valence
electrons
Try these:
• Strontium (atomic number 38)
• Germanium (atomic number 32)
• Iodine (atomic number 53)
• Krypton (atomic number 36)
Break…
Formation of ions
• A neutral atom has the same number of
protons and electrons, so it has no net
(overall) charge
• Atoms may gain or lose electrons which
results in a net negative or positive charge,
respectively.
• Atoms, or groups of atoms, that have a net
positive or negative charge are called ions.
• A cation is positively charged and has fewer
electrons than protons
• An anion is negatively charged and has more
electrons than protons
Representation of ions
• Chemists represent ions using their charge and the symbol of the
element
Elements in the same group form ions with
the same charge
Forming Ionic Compounds
Why do ions form compounds?
 To be like
the cool kids
The formation of Ionic Compounds
• Compounds composed of ions are
called ionic compounds
• Ionic compounds formed from only
two elements are called binary ionic
compounds. These are formed when a
metal reacts with a non-metal.
• Metal atoms transfer valence electrons
to non-metal atoms. The oppositely
charged ions attract each other and
form an ionic bond
• Example: sodium ion reacts with a
chlorine ion to form sodium chloride
Opposite charges must balance in any chemical compound
• NaCl combines in a 1:1
ratio because the 1+
charge on sodium is
balanced out by the 1charge on chlorine
Elements combine in ratios that balance their overall charges
• Elements will combine in whatever ratio
balances their charges
Example:
• Lithium has a 1⁺ charge (it has lost
one electron)
• Oxygen has a 2⁻ charge (it has gained
two electrons)
• We can balance the charges by
using a 2:1 ratio of lithium to
oxygen
Li ⁺ O2⁻
Li ⁺
Elements combine in ratios that balance their overall charges
In what ratio would calcium and
chlorine combine? (Use your periodic
table to determine the charges of each
element)
We can balance the
charges by using a 2:1
ratio of chlorine to
calcium
Ca2⁺
Cl⁻
Cl⁻
Elements combine in ratios that balance their overall charges
In what ratio would sodium and
phosphorus combine? (Use your
periodic table to determine the charges
of each element)
We can balance the
charges by using a 3:1
ratio of sodium to
phosphorus
Na⁺
Na⁺ P3⁻
Na⁺
Elements combine in ratios that balance their overall charges
• What about an element with a 3⁺ charge
combining with an element with a 2⁻
charge?
• Is there a ratio that would balance the
charges?
Example:
3⁺
2⁻
2⁻
3⁺
2⁻
Atomic Speed Dating