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