# Chapter 5- Section 1 Arranging the Elements

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Chapter 5- Section 1 Arranging the Elements

A Russian chemist named Dmitri Mendeleev was the first person to determine a pattern for the elements.

Mendeleev

Mendeleev noted that there was a pattern within the properties of elements. He could then organize the elements depending on their atomic mass.

What is the atomic mass of
an element?

Atomic mass is the weighted average of the masses of all of the naturally occurring isotopes of an element. It is measured in atomic mass units.

To calculate the atomic mass:
Multiply the mass# of each isotope (P+N) by its % amount in decimal form. Add the two numbers together = atomic mass. EXAMPLE: Chlorine Cl-35 (76% of chlorine in nature) Cl-37 (24% of chlorine in nature) (35x0.76)=26.6 (37x0.24)= 8.9 =35.5amu

Properties of Elements

The properties of elements change in a periodic way, which means in a regular, repeating pattern. This is how the periodic table got its name.

Can you think of something in your life that has a periodic pattern?

Some physical properties of elements include: color, density,atomic mass and luster

Some chemical properties of elements include:conductivity, flammability, and reactivity.

Periodic Law

The periodic law states that the chemical
and physical properties of elements are periodic functions of their atomic number.

In other words….. The # of protons or electrons in an atom will help determine its characteristics.

Understanding the Periodic Table

The periodic table may look confusing, but if you understand its pattern it will make more sense.

There are 3 main categories that elements are divided into metals, nonmetals and metalloids

What are some characteristics of each category?

Elements are placed into a specific groups based on their properties.

Location and Description of Elements

A zig zag line can be drawn on the periodic table to help remind you of the location of each type of element.

Border of line = Metalloids
Right of line=Nonmetals Left of line = Metals Border of line = Metalloids

Metals usually solid at room temp Shiny malleable (flattened)
ductile (made into wire) good conductor of heat

Lithium

Sodium

Non Metals usually gas at room temp. non shiny
not malleable or ductile poor conductor brittle (can shatter)

Nitrogen

Metalloids share properties of both metals and nonmetals

Silicon

Boron