Unit 2 Chemistry
Atomic Mass and Isotopes While most atoms have the same number of protons and
neutrons, some don’t. Some atoms have more or less neutrons than protons.
These are called isotopes. An atomic mass number with a decimal is the total of the
number of protons plus the average number of neutrons. We write isotopes like this: Uranium has 2 isotopes: Uranium – 238 & Uranium - 239
U238
92
Mass #
Atomic # U239
92
Isotope ExamplesList the protons, neutrons, electrons and the symbol Carbon – 12 Carbon – 13 Carbon – 14 Note:
The # of neutrons may vary. Isotopes have different mass numbers. Isotopes of the same element are still chemically alike
because they have the same number of protons and electrons.
Properties of Metals Metals are good conductors
of heat and electricity. Metals are shiny. Metals are ductile (can be
stretched). Metals are malleable (can be
pounded into thin sheets). A chemical property of metal
is its reaction with water which results in corrosion.
Properties of Non-Metals
Non-metals are poor conductors of heat and electricity.
Non-metals are not ductile or malleable.
Solid non-metals are brittle and break easily.
They are dull (not shiny).
Many non-metals are gases.
Sulfur
Properties of Metalloids
Metalloids (metal-like) have properties of both metals and non-metals.
They are solids that can be shiny or dull.
They conduct heat and electricity better than non-metals but not as well as metals.
They are brittle and not ductile
Silicon
A Family is also called a Group.
based on their atomic numbers.
Groups or Families
Columns of elements are called groups or families.
Elements in each family have similar but not identical properties.
All elements in a family have the same number of valence electrons.
Each horizontal row of elements is called a period.
The elements in a period are not alike in properties.
In fact, the properties change greatly across even given row.
The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.
The period tells us how many orbitals the element has.
Periods
Groups of the Periodic Table
Alkali Metals: Group 1 Soft, shiny metals Good conducters Very reactive Will produce a coloured flame when heated
Excluding H – a diatomic molecule Li - lithium Rb - rubidium Na – sodium Cs - caesium K - potassium Fr – francium
Groups
Alkaline Earth Metals – group 2 Have 2 valence electrons Most are white in colour
Be – beryllium Mg – magnesium Ca – calcium Sr – strontium Ba – barium Ra – radium (not always considered an alkaline earth due to its
radioactivity)
Groups
Group 3 - 12: Transition Elements Elements that have an incomplete subshell
Group 13: Boron Group These elements are characterized by having 3 electrons
in the outer energy level (valence)
Group 14: Carbon Group These elements are characterized by having 4 electrons
in the outer energy level these elements share their electrons, the tendency to
lose electrons increases as the size of the atom increases, as it does with increasing atomic number
groups
Group 15 Nitrogen group These elements are characterized by having 5 electrons
in the outer energy level (valence)
Group 16 Oxygen group) These elements are characterized by having 6 electrons
in the outer energy level (valence)
Group 17 Halogens The term halogen was coined to mean elements which
produce a salt in union with a metal The elements are characterized by having 7 electrons in
the outer energy level (require 1 more electron)
Noble Gases
Noble Gases are colorless gases that are extremely un-reactive. One important property of the noble gases is their inactivity. They are
inactive because their outermost energy level is full. Because they do not readily combine with other elements to form
compounds, the noble gases are called inert. The family of noble gases includes helium, neon, argon, krypton,
xenon, and radon. All the noble gases are found in small amounts in the earth's
atmosphere.
Assignment
Families of the Periodic Table worksheetIn computer lab