Atoms and Elements
Chapter 1
How do we draw atoms?
1. Look at the Atomic number
2. Atomic number = # protons in the atom
3. # protons = # electrons in orbit
(we are assuming that the atom is overall neutral, meaning there are the same
number of positive charges [protons] as negative charges [electrons])
Example: Carbon
Atomic number: 6
6 protons in the nucleus
6 electrons in orbit
Orbit/Energy Level Rules
We will learn how to draw atoms of the first 20 elements in the
periodic table.
For the purposes of this course, when drawing Bohr-Rutherford
diagrams, use the following as a guide:
1st orbit/energy level : can hold up to 2 electrons
2nd orbit/energy level : can hold up to 8 electrons
3rd orbit/energy level: can hold up to 8 electrons (18 in reality)
4th orbit/energy level: in our class, the max it will ever have is 2
 You must fill in the lower levels before you start filling in higher
levels
 Protons go in the nucleus!!!!
Example: Nitrogen (N)
Atomic Number:
# Protons:
# Electrons:
Example: Calcium (Ca)
Atomic Number:
# Protons:
# Electrons:
Drawing Atoms- The Simplified Model
The simplified model includes neutrons
Flash Back:
• Chadwick discovered the Neutron
• It is in the nucleus
• It holds protons together
• It is neutral
The number of Neutrons is determined by:
Atomic Mass – Atomic # = # neutrons
Careful!
Atoms can be identified in 2 formulations:
Example Magnesium (Mg)
Atomic number: 12
Atomic Mass: 24 atomic mass units (u)
# Protons: 12
# Electrons: 12
# Neutrons: Atomic mass – Atomic number =
24 – 12 = 12
Example Aluminum (Al)
Atomic number:
Atomic Mass:
# Protons:
# Electrons:
# Neutrons: Atomic mass – Atomic number =
Isotopes
• Atoms of the same element always have the same number of protons
but may contain different numbers of neutrons.
NOTE: Isotopes have the same number of electrons!
Isotope: atoms of the same element that have different numbers of
neutrons
Example: Carbon
Most carbon nuclei have 6 neutrons (same # as the # of protons).
Some carbon nuclei have 7 or 8 neutrons (not the same # as protons).
In order to distinguish between isotopes, scientists refer to them by
stating the combined total or protons and neutrons in the nucleus (mass
number).
Ex: Carbon-12 (has 6 protons, 6 neutrons)
Carbon-13 (has 6 protons, 7 neutrons)
Carbon-14 (has 6 protons, 8 neutrons)
Isotopes
Because Isotopes have the same number of protons, but
have different amounts of neutrons, their masses are
not the same.
Reminder: Atomic mass = # protons + # neutrons
Isotopes have the same chemical properties but different
physical properties.
The atomic masses that appear on the periodic table are
the average of the masses of isotopes found in nature.
The Periodic Table of Elements
• Visual representation of the elements in groups according to
their properties
• Metals are on the left hand side of the staircase, non-metals to
the right of the staircase and metalloids are found around the
staircase.
Metals
• On the left side of the staircase (except hydrogen)
• Conduct heat and electricity
• Ductile (shaped into wires)
• Malleable (bendable)
• Shiny
• Solid at room temperature (except Mercury)
• React with acid (produces Hydrogen gas)
Non-Metals
• On the right side of the staircase (except Hydrogen
is a non-metal)
• Do not conduct heat or electricity
• Many are gases at room temperature (the few
that are solids are easily reduced to powder)
Metalloids
• Found touching the staircase
• Have properties of both metals and non-metals
• Semiconductors
Ex. B, C (sometimes), Si Ge, As, Sb, Te, Po (sometimes) and At
Families/Groups of the Periodic Table
• They are the columns of the periodic table
• ***Hydrogen is not in any group***
• Elements in the same family/group have similar chemical
properties
 Elements in the same family have the same # of valence
electrons!!!!!!
Valence Electrons: The electrons in the outer most Energy
level (orbit)
Family/Group # = # of valence electrons
Try This!
Draw the Bohr-Rutherford atomic models for
the first 20 elements in the periodic table.
Group IA Alkali Metals (except hydrogen)
• 1 valence electron
• Soft
• React with air and water (Stored in oil)
• NEVER found as an element in nature. Always
found as compound (attached to another
element) in nature.
• They get MORE reactive as you go DOWN the
column
Group IIA Alkaline Earth Metals
• 2 valence electrons
• Highly malleable
• Burn easily
• Can be exposed to air
• Never found as an element in nature
• Get MORE reactive as you go DOWN the column
Group VIIA Halogens
• 7 valence electrons
• Form salts when combined with alkali metal
(ex. NaCl)
• Form acids when combined with H (ex. HCl)
• Disinfectants (Chlorine cleans swimming pools)
• Get more reactive as you go UP the column
Group VIIIA Noble Gases (Inert Gases)
•
Stable (react minimally)
• CAN be found in nature as an element
Periods of the Periodic Table
• Period = Horizontal Row of the periodic table
• The period # is equal to the # of Energy Levels
(Orbits or Shells) of an atom
Periodicity of Properties
• Several patterns exist in the periodic table according to
periods (horizontal rows):
 boiling point, density, atomic radius, electrical conductivity, etc.
• Peaks and troughs characterize these patterns as they
occur over and over as you move to the next period
• Trends can be explained by the number of particles in the nucleus
Atomic Radius
• As # protons and electrons increases power of
attraction between them increases, which shrinks
the atom in size.
• Atomic radius INCREASES as you go across a period
to the LEFT
• Atomic radius INCREASES toward the BOTTOM
Chemical Reactivity
In metals:
• Metals give up electrons in chemical reactions
• Reactivity increases as you move to left in period and down in
periodic table (this is caused by increase in atomic radius)
Larger atomic radius means less attraction between protons and
electrons
 As electrons are more easily removed reactivity increases
In non-metals:
• Non-metals accept electrons in chemical reactions
 Reactivity increases as atomic radius gets smaller as positive
nucleus attracts electrons more strongly
• Reactivity increases toward top of periodic table and toward
right in period
Ionization Energy
Is the energy required to remove a
valence electron from its shell.
• Energy increases to the right and toward the
top of the periodic table (due to atomic
radius)
• The smaller the atom, the more energy will
be required to strip away an electron
(attraction to nucleus)
Electronegativity
Is the force with which an atom holds on
to its electrons
• Electronegativity increases as atomic
radius decreases (smaller atom means
greater attraction between protons and
electrons)
• Electronegativity increases toward right in
a period and toward top of periodic table
Summary of All Trends
Lewis Dot Diagram
 Is a simplified representation of the atom, in which only
Valence Electrons are drawn represented using dots.
The group # = # valence electrons = # of dots
***Exception: Helium in group VIIIA only has 2 dots***
Try This!
Draw the Lewis Diagrams for the
following elements:
Na
Mg
Al
C
P
O
Cl
Ne
Ball and Stick Diagram
Atoms are represented with circles and they are attached to
one another with sticks.
Examples:
H2O
CH4
 Atoms of different elements have different
sized/coloured circles