Download The Periodic Table

Reviewing the Periodic Table
and other “Bohring” stuff from
Grade Nine
Atomic Mass
• Definition: Atomic mass is the mass of an
average atom of an element.
• Also equals the # of protons and neutrons
in an atom.
Atomic number
• Definition: An atomic number is the
number of protons in the nucleus of an
atom.
• Atoms are neutral (no charge). So atomic
number is also the number of electrons
around an atom.
Setting the table
Period: a horizontal row of
elements on the periodic table.
Group: (or “chemical
family”) is a column of
elements on the periodic
table.
The Main Groups
• We will focus on five groups of elements:
– IA (1) – The Alkali metals
– IIA (2) – The Alkaline earth metals
– VIA (16) – The Chalcogens
– VIIA (17) – The Halogens
– VIIIA (18) – The Noble gases
Periodic Patterns
• There are some important patterns on the
periodic table.
• These patterns involve atomic structure.
• The period number tells us __________
• The group number tells us __________
Patterns
Periodic Patterns
• The period number tells us how many
electron shells an atom has.
• The group number tells
us how many valence
(outer) electrons the
element has.
Periodic Patterns
• Metals, non-metals, and metalloids (semimetals) show up in predictable places.
Metals, Non-metals, Metalloids
Atomic Structure
• We use the Bohr-Rutherford model.
• This model says atoms have:
• Dense, heavy nucleus of protons and
neutrons.
• Spread-out, light electron cloud arranged
into shells.
Bohr-Rutherford Model
Bohr Diagrams
• These show the
number of protons
and neutrons in the
nucleus, and
arranges the
electrons into their
shells.
Bohr Diagrams - Guidelines
• 1) Put the number of protons and neutrons
in the middle (inside the nucleus)
• 2) The first electron shell can hold no more
than two electrons. Fill it first.
• 3) Put electrons in the second shell. It can
hold up to eight.
• 4) Put electrons in the third shell. It can
also hold up to eight.
Patterns: Atomic Radius
• Atomic radius: the distance from the
nucleus to the valence shell of an atom.
• Increases down a group.
• Decreases going right in a period.
Patterns: Atomic Radius
Patterns: Reactivity
• Metals can lose valence electrons.
– Doesn’t take a lot of energy.
• This makes the atom a cation – a
positively-charged ion.
• The bigger the atomic radius, the easier
this happens.
– “Bigger” metal atoms are MORE reactive!
Patterns: Reactivity
Patterns: Reactivity
• Non-metals can gain valence electrons.
– Causes a release of energy.
• This makes an atom an anion – a
negatively-charged ion.
• The smaller the atom, the easier this is.
– “Smaller” non-metals are MORE reactive!
Patterns: Reactivity
Patterns: Reactivity
• Elements in the same group share
chemical properties.
• This is due to having the same number of
valence electrons.
Determining Atomic Makeup
• The periodic table can tell us what the
atoms of any known element are made up
of.
• This is determined from the atomic
number and atomic mass.
Determining Atomic Makeup
• We know the total number of protons and
neutrons. How can we figure out the
number of neutrons, alone, that are in the
atoms of a given element?
• We can subtract the number of protons
(atomic number) from the number of
protons and neutrons (atomic mass).
Determining Atomic Makeup
• Ex: Hydrogen
• Step 1: Look up the element on the
periodic table.
• Step 2: Write down the equation
– # of neutrons = atomic mass – atomic number
• Step 3: Write in the atomic mass (rounded
to the nearest whole number) and atomic
number for the element and solve.
– # of neutrons for hydrogen = 1 – 1 = 0
Determining Atomic Makeup
• Ex: Hydrogen
– Hydrogen has: 1 proton, 1 electron, and 0 neutrons.
•
•
•
•
Ex: Aluminum
Atomic number: 13 ( # of protons and electrons)
Atomic mass: 26.9815… ≈ 27
# of neutrons = atomic mass – atomic number
= 27 – 13 = 14 neutrons
• Aluminum has 13 protons, 13 electrons, and 14
neutrons.
Lewis Dot Diagrams
• We can draw elements in a way that puts
the focus on valence electrons – Lewis dot
diagrams.
Lewis Dot Diagrams
Method:
1. Write the symbol of the element (like Li, or
B, or Ar).
2. Look up its group number on the periodic
table. Determine how many valence
electrons it has.
3. Starting on one side, draw dots
representing valence electrons around the
symbol.
N
4. Add a dot to each side of the symbol, one
at a time, going in order.
5. Stop adding dots once there are as many
dots as there are valence electrons.
Ions:
• Metals lose valence electrons.
– Forms a cation.
• To draw this:
1. Put the symbol in [brackets]
2. Write a number to show how many
valence electrons were lost.
3. Place a + next to that number.
Example:
Magnesium (normal)
Magnesium cation
2+
[Mg]
• Non-metals gain valence electrons.
– Forms anions.
• To draw this:
1. Surround the symbol with eight dots.
– Non-metals want a full valence shell.
2. Surround everything in [brackets].
3. Write a number to show how many
valence electrons were gained.
4. Place a – next to that number.
Example:
Phosphorus (normal)
Phosphorus anion