Arranging the Elements, Chapter 12, Section 1

All of the more than 30 elements discovered since

1914 follow the periodic law.

Dmitri Mendeleev

a Russian chemist; he discovered a pattern to the elements in 1869.

group or family

a column of elements

period

a row of elements

Lanthanides and Actinides are placed below the table to

allow the table to be narrower.

group

also called a family; a vertical column of elements in the periodic table; elements in a group share chemical properties.

The chemical symbols are the same worldwide. For most elements, the chemical symbol has one or two letters. The first letter is

always capitalized. Any other letter is always lowercase. The newest elements have temporary three letter symbols.

Elements at the far-right end of a period, such as bromine,

are nonmetallic.

Mendeleev saw that when the elements were arranged in order of increasing

atomic mass, those that had similar properties occurred in a repeating pattern.

Nonmetals are not malleable or ductile. In fact, solid nonmetals, such as carbon in graphite of a pencil head, are

brittle and will break or shatter when hit with a hammer.

Boron is almost as hard as a diamond, but it is also very

brittle. At high temperatures, it is a good conductor of electric current.

ductile

can be drawn into thin wires.

malleable

can be flattened with a hammer and will not shatter.

Elements in the same group often have similar

chemical and physical properties. For this reason, a group is also called a family.

Dmitri wrote the names and properties of the elements on the cards. Then, he arranged his cards by different properties, such as

density, appearance, and melting point. After much thought, he arranged the elements in order of increasing atomic mass. A pattern appeared.

Periodic

describes something that occurs or repeats at regular intervals; "happening at regular intervals"

Most metals are ductile. All metals are good conductors of

electric current. The wires in electric devices in your home are made of copper.

Elements are classified as metals, nonmetals, and metalloids according to their properties. The number of

electrons in the outer energy level of an atom is one characteristic that helps determine which category the element belongs in.

Atoms of metalloids have about half of a complete set of

electrons in their outer energy level. Metalloids have some properties of nonmetals.

Atoms of most nonmetals have an almost complete set of

electrons in their outer level.

Atoms of the elements in group 18, the noble gases, have a complete set of

electrons.

The background color indicates the type of

element. (metals, nonmetals, metalloids)

The names and three-letter symbols of elements are temporary. They are based on the atomic numbers of the

element. Official names and symbols will be approved by an international committee of scientists.

The days of the week are periodic. They repeat in order every 7 days. Similarly, Mendeleev found that

elements properties followed a pattern that repeated every seven elements.

Properties such as conductivity and reactivity change

gradually from left to right in each period.

In 1914, Henry Moseley determined the number of protons- the atomic number- in an atom. All elements fit the pattern

in Mendeleev's periodic table when they were arranged by atomic number.

period

in chemistry, a horizontal row of elements in the periodic table.

Metals are found

left of the zigzag line on the periodic table.

Elements farther to the right, such as germanium, are

less metallic.

Mercury, however, is a

liquid at room temperature.

Mendeleev thought that more-accurate atomic

masses would fix these flaws in his table.

The zigzag line reminds you where the

metals, nonmetals, and metalloids are.

The zigzag line on the periodic table can help you recognize which elements are

metals, which are nonmetals, and which are metalloids.

Most elements are

metals.

Each square on the periodic table includes an element's

name, chemical symbol, atomic number, and atomic mass.

Scientists in the early 1860s had a problem with

organizing the elements.

With the man made elements, the atomic mass in

parenthesizes is also the mass number.

Mendeleev's table became known as the

periodic table of the elements.

The color of the chemical symbol indicates the

physical state at room temperature.

Mendeleev predicted that elements yet to be found would fill in the gaps that were blank. He used the pattern he found to

predict their properties. By 1886, all of the gaps had been filled. Mendeleev's predictions were right.

The physical and chemical properties of elements in a row follow a

repeating, or periodic pattern, as you move across the period.

Nonmetals are found to the

right of the zigzag line on the periodic table.

Atoms of most metals have few electrons in their outer energy level. Most metals are solid at

room temperature.

More than half of the nonmetals are gases at

room temperature. Many properties of nonmetals are the opposite of the properties of metals.

The names of elements come from many sources. Elements are named after

scientists, places, and the country it was first discovered in.

Most metals are malleable. Aluminum is flattened into

sheets to make cans and foil.

Sulfur, like most nonmetals, is not

shiny.

Metals tend to be

shiny. You can see a reflection in a mirror because light reflects off the shiny surface of a thin layer of silver behind the glass.

Tellurium is shiny, but it is brittle and can easily be

smashed into powder.

Values in parentheses are the mass numbers of those radioactive elements' most

stable or most common isotope.

periodic law

the law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements.

Nonmetals are poor conductors of thermal energy and electric current. If the gap in a spark plug is too wide,

the nonmetals nitrogen and oxygen in the air will stop the spark and a car's engine will not run.

Each vertical column of elements (from top to bottom) on

the periodic table is called a group.

Most metals are good conductors of

thermal energy. An iron griddle conducts thermal energy from a stove top to cook food.

The four properties of metals:

they are shiny, ductile, malleable, and good conductors of thermal heat and electric current.

Elements at the left end of a period, such as titanium, are

very metallic.

Metalloids, also called semiconductors, are the elements that border the

zigzag line on the periodic table.