4.1 & 4.3 Organizing the Elements

• People often organize things to make them more useful.– Cupboards– Closets– Study notes for tests

• Up to the mid-1800s, scientists were busy discovering new elements.

• Then they tried to organize the elements alphabetically. But every time a new element was discovered, the whole list had to be changed.

Organizing the Elements• Other methods of organization were considered

but later discarded.– State (gas, solid, liquid)– Color– Taste

• John Dalton then found a quantity that could be measured for an element - its atomic mass.

• Several scientists then tried to arrange the known elements by their atomic masses.

• The best arrangement was produced by a Russian scientist, Dmitri Mendeleev.

Organizing the Elements• Mendeleev began arranging the elements in

order of increasing atomic mass and noticed that many elements shared common properties. These elements typically belonged to the same vertical column of his table.

• Mendeleev’s arrangement showed a regular pattern. Mendeleev’s periodic law states:

If the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly.

Organizing the Elements• Mendeleev’s periodic table was a major

breakthrough in the understanding of the elements. However, it was discovered later on that using the atomic mass was not the proper way to organize the elements.

• The key was to use the atomic number or the number of protons.

• Therefore, a new law was born.• The modern periodic law states :

If the elements are arranged according to their atomic number, a pattern can be seen in which similar properties occur regularly.

Homework

• Activity Questions 1, 2, 3, 4, 5 on page 108.

• Understanding Concepts Questions 1,2,3,4 page 109.

4.4 Groups of ElementsThe periodic table groups elements

with similar properties. You can quickly identify an element as a metal if it is on the left or in the centre of the table.

Non-metals are generally found on the right side.

Chemical Groups

The set of elements in the same column in the table is called a chemical group (having similar chemical and physical properties).

These properties, however, vary from element to element in a column.

Periods

The horizontal rows of elements are called periods. The first period contains two elements: hydrogen and helium.

As you go from left to right within a row, the atomic number increases and the elements gradually change from metallic (lithium) to non-metallic (flourine), and then finally to noble gases (neon) at the far right.

http://www.chemicalelements.com/

1

AssignmentRefer to your periodic table as the class

reads pages 110-113 in the text.Use a colour code and colour in the

following sections on your periodic table:

1. Noble gases2. Alkali Metals3. Halogens4. Group of One5. Metalloids 6. Metals

Group of OneHydrogen is a unique element (yellow). It’s most common isotope has only a

single proton and no neutron in its nucleus.

Hydrogen doesn’t have much in common with the alkali metals. It’s a colourless, odourless, tasteless, highly flammable gas.

Almost all of Earth’s hydrogen exists in combination with other elements. Its reactivity is too great for it to exist in the atmosphere as a free element.

Alkali MetalsOccupy the far left column of the

periodic table (green).Extremely reactive.Found in nature only as compounds,

and are found everywhere on Earth.Most common are sodium

compounds, which occur in plants, animals, soil and sea water.

Lithium, sodium, patassuim, etc…shiny, silvery.

Metalloids

Elements that possess both metallic and non-metallic properties. Found on both sides of the zigzag line that divides the metals from the non-metals. (purple)

Ex. silicon, boron, germanium, arsenic, selenium, antimony, tellurium, polonium, and astatine.

HalogensOccupy the 17th column of the periodic

table (fluorine, chlorine, bromine…)Most reactive non-metals. (red)Because of their reactivity, they almost

always appear naturally as compounds, not as elements.

Most common halogen compounds are chlorine compounds found in living things, ocean water and rocks.

Noble GasesOccupy the far right column of the

periodic table (blue).All gases at room temperature, the

noble gases are often called inert gases because they are so unreactive, almost never forming chemical compounds with other elements.

Argon makes up 1% of every breath you inhale.

Very useful elements. Ex.: neon, helium

Homework

• Questions 1, 3, 4, 5 and 9 page 113

Chapter 4 Review

• Questions p. 126-127

–#2,4,5,10 & 11